Posts Tagged Trenberth

Stormy weather: we’re making it worse, and there’s more on the way Gareth Renowden Nov 20

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The IPCC released the summary for policymakers of its Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) in Kampala, Uganda, on Friday (SPM, SREX site, launch presentation slides). The report concludes that globally there has been a significant decrease in cold days and nights and an overall increase in warm days and nights, that it’s likely that “anthropogenic influences” have led to warming of extreme daily minimum and maximum temperatures, and that heavy rainfall events are increasing in many areas. There has also been an increase in extreme coastal high water events.

The report also projects that it is “virtually certain” that increases in the frequency and magnitude of warm daily temperature extremes will continue through this century, and that there will be corresponding decreases in cold extremes. It’s also very likely that heat waves and warm spells will become more frequent and warmer. Heavy rainfall events are also expected to increase, and the proportion of rain falling in those events is likely to increase. There are also likely to be more problems from storm surges and sea level rises, an increase in droughts, and landslides in mountainous regions.

Much of the report’s content will come as little surprise to those who have been following the subject — in common with previous IPCC reports the conclusions are conservative, couched in laboriously exact language, and exclude the most recent work1 — and for me the most interesting parts are the discussions of how extreme weather events interact with human populations to create disasters. In this respect, arguing about whether an event was “caused by” or “made worse by” warming is largely irrelevant to trying to find ways to reduce the impact of current and future extremes.

See also: Jeff Masters has an interesting post going into more detail about the report’s findings, RealClimate considers the report’s discussion of tropical cyclones, plus news reporting from the BBC, Guardian, and Reuters.

Meanwhile, the usual suspects are scrabbling around looking for ways to misrepresent the report’s findings. The most egregious to date comes from Nigel Lawson’s secretly-funded “Global Warming Policy Foundation”, who pick a paragraph out of context and pretend that it shows that…

According to a preliminary report released by the IPCC, there will be no detectable influence of mankind’s influence on the Earth’s weather systems for at least thirty years, and possibly not until the end of this century.

… which is not what the report says at all!

Finally, Green.TV and WeatherUnderground have launched a new twice monthly video on current global extreme weather events. Here’s the first episode:

Definitely one to follow with interest…

  1. Unavoidable, given the way these things are put together.

Current extreme weather events part of climate change Bryan Walker Sep 20

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Al Gore didn’t hesitate to dwell on extreme weather events as evidence of the reality of climate change in his closing address for the 24-hour Climate Reality Project last week. There has certainly been no lack of them in the past year or so. Was he pushing the boundaries of the science? It wouldn’t worry me too much if he was because there’s plenty else in the scientific projections which is clearly under way, such as the melting polar ice or the acidification of the oceans. But Gore is a very intelligent and well-informed man and I don’t think he allowed himself to be carried away beyond the scientific mandate. Consider what is being said by some scientists right now.

Two recent papers have looked at extreme heat. A Stanford team paper (full text) was published in Climate Change Letters in June. The lead author Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford, had this to say:

“According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years.”

And the process is already under way:

“We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun. It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well.”

This supports the projections:

“The fact that we’re already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded.”

Boston University researchers have published a paper (full text) in the current issue of Climatic Change Research. The lead author is Bruce Anderson,  Associate Professor, Geography and Environment. The press release explains:

Anderson’s research indicates that if the 2°C increase [the current international target for limiting emissions] were to come to pass 70—80% of the land surface will experience summertime temperature values that exceed observed historical extremes (equivalent to the top 5% of summertime temperatures experienced during the second half of the 20th century) in at least half of all years. In other words, even if an increase in the global mean temperature is limited to 2°C, current historical extreme values will still effectively become the norm for 70-80% of the earth’s land surface.

Anderson comments:

’Many regions of the globe–including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon–are already committed to reaching this point, given current amounts of heat-trapping gases in the atmosphere.’

In the United States, the impacts are expected to be most severe over the western third of the country. ’In these regions, if the 2°C threshold is passed, it is more likely than not that every summer will be an extreme summer compared with today.’

’While previous work, including our own and that of researchers at Stanford, has highlighted that summertime temperature extremes, and how frequently they occur, will change significantly even in response to relatively small increases in global-mean temperatures, the extent and immediacy of the results really caught us off guard. Because these results are referenced to increases in global-mean temperatures, and not some particular time or change in amount of heat-trapping gases, they hold whether we reach this global-mean temperature increase in the next 40-50 years as currently projected, or the next century. They really are telling us that this is a temperature threshold that poses significant risks to our lives and livelihoods.’

Climate Communication is a new group set up to combine expertise in climate science with clear and accessible communication to the public. They have recently published an article setting out very clearly the connections scientists see between recent extreme weather events and climate change. The expert science reviewers are Kevin Trenberth and Jerry Meehl, National Centre for Atmospheric Research, Jeff Masters, Weather Underground and Richard Somerville, Scripps Institution of Oceanography, University of California, San Diego. Here are one or two extracts from the overview:

As the climate has warmed, some types of extreme weather have become more frequent and severe in recent decades, with increases in extreme heat, intense precipitation, and drought. Heat waves are longer and hotter. Heavy rains and flooding are more frequent. In a wide swing between extremes, drought, too, is more intense and more widespread…

Small changes in the averages of many key climate variables can correspond to large changes in weather. Substantial changes in the frequency and intensity of extreme events can result from a relatively small shift in the average of a distribution of temperatures, precipitation, or other climate variables…

Rigorous analyses have shown that natural variability alone cannot explain the observed long-term trends of changing extremes in temperature and precipitation.

In contrast, the observed trends fit well with our understanding of how climate change drives changes in weather. Computer models of the climate that include both natural forces as well as human influences are consistent with observed global trends in heat waves, warm days and nights, and frost days over the last four decades. Human influence has also been shown to have contributed to the increase of heavy precipitation over the Northern Hemisphere.

The article covers several aspects of the subject in the course of its 28 pages — precipitation patterns, floods, droughts, heat waves, hurricanes, winter storms and more.  All is unobtrusively but carefully referenced to scientific papers and reports. It is fully accessible reading for the non-scientist and betokens a valuable role for Climate Communication.

The conclusion of the article:

Human-induced climate change has contributed to changing patterns of extreme weather across the globe, from longer and hotter heat waves to heavier rains. From a broad perspective, all weather events are now connected to climate change. While natural variability continues to play a key role in extreme weather, climate change has shifted the odds and changed the natural limits, making certain types of extreme weather more frequent and more intense.

While our understanding of how climate change affects extreme weather is still developing, evidence suggests that extreme weather may be affected even more than anticipated. Extreme weather is on the rise, and the indications are that it will continue to increase, in both predictable and unpredictable ways.

So no, Al Gore did not overstep the mark. He simply expressed with urgency the reality that we are indeed causing more extreme weather events by continuing to increase the level of greenhouse gases in the atmosphere.

Here it is straight from the scientists in the Climate Communication article:

Things to do in Wellington and Dargaville Gareth Renowden Jul 13

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Late notice, for which I apologise, but climate scientist Kevin Trenberth is giving a public lecture in Wellington on Friday (July 15th) on The Russian heatwave and other recent climate extremes. Trenberth’s talk is being organised by the NZ Climate Change Research Institute and will be at the Old Government Buildings Lecture Theatre 2, from 12:30 — 1:30pm. If you can’t make it, you can get a good idea of what he will discuss from this guest article by KT posted at Skeptical Science this week. Well worth a read. Trenberth is also holding a media briefing for the Science Media Centre tomorrow afternoon, which I hope to report on in due course.

Also this week, the Saunders, Oram and Salinger road show has added an extra gig into their Northland tour — in Dargaville tomorrow at 1-30 pm at the Kaipara District Council, 42 Hokianga Road, Dargaville. Contact for more information. Jim S also asks me to note that the title of the urban talks ( in Timaru, Auckland and Dunedin) has changed to Preparing for White Swans: Climate change and opportunities for the economy. Full tour details here (pdf).

The CCRI has just released the July edition of their What’s Hot newsletter, full of recent climate related news, linked to the original articles. It’s a good digest of recent news, worth the download.

Riders on the storms Bryan Walker Mar 06

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I listened with interest to Kevin Trenberth on the latest Climate Show describing how the increased water vapour in the atmosphere resulting from human-caused global warming is leading to greater extremes in weather events. It sent me back to take another look at the section in James Hansen’s book Storms of My Grandchildren where he explains the greatly increased strength of storms we can expect as the century unfolds, unless we leave most fossil carbon in the ground. I reviewed the book a while back on Hot Topic and thought it worth outlining more closely here, as an extension of my review, Hansen’s argument in the ten pages where he specifically addresses the storms of which the book’s title speaks.

As ice sheet disintegration begins in earnest he writes of a chaotic transition period in which our grandchildren will live the rest of their lives. Ice sheet disintegration in Earth’s past needed millennia, but human forcing is so much more powerful than natural forcings that ice sheets will respond much more rapidly.  Currently most of the recent energy imbalance due to increased greenhouse gases in the atmosphere is warming the ocean and only a small fraction is being used to melt ice. This division of excess energy will shift more to ice melt as the ice sheets are softened up and begin to discharge ice to the ocean more rapidly.

Increased ice discharge in both West Antarctica and Greenland will cool the neighbouring ocean. Although Greenland is not as vulnerable to rapid collapse as West Antarctica is it can lose mass fast enough to influence North Atlantic Ocean surface temperature. This freshwater melt will also decrease the salinity and hence the density of the water, making it less able to sink to the ocean bottom as it currently does, where it feeds the ocean ’conveyor’ circulation and allows warmer water to move north to replace it. If that deepwater formation slows down the regional North Atlantic cooling from ice melt will be enhanced.

Meanwhile in low latitudes the atmosphere and the ocean surface will be getting warmer and warmer as the century proceeds. This will exacerbate trends already apparent such as mountain glacier melting, expansion of dry sub-tropical regions, more intense forest fires and competition for diminishing freshwater supplies. There will be increased desiccation but in other times and places heavier rain and increased floods.

The greatest impact warming will have on storms is through the increase in water vapour it causes. Atmospheric water vapour increases rapidly with only a small temperature rise. Latent heat is the energy acquired by water vapour when it evaporates. When it condenses that latent energy is released as heat that is potentially available to fuel a storm. The storm types driven by latent heat include thunderstorms, tornadoes, and tropical storms such as hurricanes and typhoons. The greater availability of this heat will mean that the strength of the strongest storms will increase as global warming increases. There will also be an expansion of the regions liable to severe storms.

This is just the beginning. There are three ratcheting effects in waiting. One is the development of more powerful and destructive mid-latitude or frontal cyclones. They depend on the temperature difference between the cold and warm air masses as well as on the amount of moisture in the atmosphere behind the warm front. The melting ice sheets will exacerbate this once they begin to disintegrate rapidly enough to keep regional ocean surface temperature from rising as fast as continental temperatures and temperatures at lower latitudes. Increased moisture content in lower- and mid-latitude warm air co-existing with ice-cooled polar air masses will increase the intensity of frontal cyclones.

The consequences of even a metre of sea level rise combined with increased storm strength are horrendous to contemplate.

The second ratcheting is far greater. It occurs when the ice sheets’ rapid disintegration causes a sea level rise measured in metres. Eventually ice sheets begin to disintegrate at rates of several metres of sea level rise per century. We could soon create conditions that guarantee this happening, but it is likely to be several decades before a rapid sea level rise begins. Hansen notes that we have been surprised by how fast some other climate changes have occurred, but for the moment offers his best estimate of when large sea level change will begin as during the lifetime of his grandchildren. The consequences of even a metre of sea level rise combined with increased storm strength are horrendous to contemplate. He offers a few examples of what it will mean for vulnerable places in various parts of the world.

The third ratcheting effect would be the melting of methane hydrates. Of greatest concern are those in sediments on the ocean floor, because of their great volume. Hansen relates the chance of their melting to possible ocean circulation changes because of the freshwater additions to both the North Atlantic and Antarctic Oceans through ice sheet disintegration. Global ocean circulation reorganised during the Paleocene-Eocene thermal maximum about 54 million years ago when a sudden large global warming occurred and deep water formation took place in the Pacific rather than the North Atlantic, flooding the ocean floor with warmer Pacific Ocean water. If that happens again, melting methane hydrates, there will be no plausible way for humans to reverse the change of ocean circulation. The released methane added to the high levels of carbon dioxide will result in a huge planetary energy imbalance and the remaining ice on the planet will disappear. That means a sea level rise of 75 metres.

Hansen, as usual, communicates the science to his readership with clarity and fully appropriate urgency.  These are not remote consequences he is exploring, but at least strong possibilities and in some cases inescapable certainties. No lay reader prepared to take a little time to come to terms with the concepts can fail to understand the serious risks we run if we carry on exploiting fossil fuels. No policy maker can claim not to have been made aware of the danger of continuing on our present course.

Hansen is not off on some flight of fancy of his own. He is interpreting solid mainstream science. It’s from that base that he says towards the end of the book that our planet is in imminent danger of crashing and that the fight for effective policies to prevent that is the most urgent fight of our lives.

[Blondie v. The Doors]

The Climate Show #8: Kevin Trenberth and our shaky future Gareth Renowden Mar 03

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The Climate Show returns with a packed show, featuring one of the world’s best known climate scientists, NZ-born, Colorado-based Dr Kevin Trenberth — star of the Climategate “where’s the missing heat” emails. He’s been in New Zealand to visit family (experiencing the Christchurch quake in the process) and to attend a conference, and his comments on the state of our understanding of climate change should not be missed. John Cook of Skeptical Science returns with his new short urls and an explanation of why declines have never been hidden, and Gareth and Glenn muse on Arnie “Governator” Schwarzenegger riding to the rescue of climate science, cryospheric forcing and carbon cycle feedbacks from melting permafrost, and a new paper that suggests that current policies are pointing us towards extremely dangerous climate change. All that and hyperbranched aminosilica too…

Watch The Climate Show on our Youtube channel, subscribe to the podcast via iTunes, or listen direct/download here:

The Climate Show

Follow The Climate Show at The Climate Show web site, on Facebook and Twitter.

Show notes below the fold.

News & commentary:

Christchurch earthquake, Feb 22 2011. At the time of writing the death toll was expected to rise to over 240. At least 100 of those who died were tourists or foreign students. If you would like to donate to support the recovery effort, please consider the Red Cross appeal.

Schwarzenegger: It’s Time to Terminate Skepticism on Climate Change

Good northern hemisphere cryosphere graphic from NASA, and bad news from the permafrost.

Models guiding climate policy are ‘dangerously optimistic’: Computer models predicting future climate change are underestimating emissions and overestimating technology, warns climate scientist Kevin Anderson. Guardian story here, and full paper [Anderson and Bows. Beyond 'dangerous' climate change: emission scenarios for a new world. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences (2011) vol. 369 (1934) pp. 20-44 -- PDF], and Bryan Walker’s discussion at Hot Topic.

Increased flood risk linked to global warming

Feature interview:: Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder Colorado. Born in NZ, worked at MetService, now based in Colorado, one of the highest profile climate scientists in the world, and a regular subject of attacks by denialists. The AMS paper referenced is available from KT’s web site linked above.

Debunking the skeptic with John Cook from Skeptical Science.
Skeptical Science Short URLs:

Clearing up misconceptions about ’Hide the Decline’

1. It’s not about ’global temperatures’ but a small number of high latitude tree rings:

2. ’Hide the decline’ has nothing to do with ’Mike’s trick’ which is the simple technique of plotting instrumental temperature and reconstructions on the same graph.

3. It’s not hidden at all but openly discussed in the peer-reviewed literature since 1995:


Green Machine: Sucking carbon dioxide out of the air.

Thanks to our media partners:, Scoop and KiwiFM.

Theme music: A Drop In The Ocean by The Bads.

Shaken and stirred: Christchurch earthquake Feb 2011 Gareth Renowden Feb 23

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It’s a grim day in Canterbury. 75 people are confirmed dead and 300 are missing following the magnitude 6.3 earthquake which struck at 12-51pm yesterday. As I write, teams of urban search and rescue specialists from NZ and Australia (soon to be joined by teams from all over the world) are crawling over collapsed buildings throughout the central city. The cathedral (above) has lost its spire, and there are bodies in the rubble around it. I am glad to report that my family and friends, and that of Climate Show co-host Glenn Williams are well, but no-one is untouched by this terrible disaster. Up here in Waipara the initial shaking was bad enough to make us run outdoors, but our relief at escaping damage was immediately tempered by the realisation that someone had just taken a hammering…

For an inkling of the scale of this tragedy and its impact on people who had already survived a magnitude 7.1, but much less damaging, quake last September, I commend author David Haywood’s eloquent description in the Guardian, and Press journalist Vicki Anderson’s heartfelt story of her escape from the Press building (under the cranes in the picture above). US-based NZ climate scientist Kevin Trenberth was also in town, holidaying with his family. This is his account:

Where we were [hillside suburb of Mt Pleasant] was actually the epicentre of the earthquake, which occurred at 9 minutes to 1p.m. We immediately got under the dining room table. The quake was very sharp and the whole ground bucked and heaved. It was very shallow and the devastation was immediate. Everything came off the walls, the china cabinet and all the crystal, nearby crashed around us. In the kitchen, 2m away, the cupboards emptied, the built-in wall oven crashed onto the floor followed by the built-in microwave. Then the big refrigerator with bottom freezer fell on top of all that. Broken glass everywhere. In the room we were in, there were 6 mm plate glass windows that were smashed, and likewise in the adjacent living room. But the house held in front. Not so in the back. The back wall was bricked and had a French door: the wall collapsed and the door jerked out and away from the house so it is wide open (and thus open to looters). The adjacent walls were half brick and they too were wiped out.

Banks of rocks and solid ground near the house collapsed and made it difficult to get out. The road outside had a big crack and the sidewalk dropped 20 cm relative to the road and a gap opened 8 cm wide. The water main broke just above there and water cascaded down past the front of the house, making it a wet experience getting to my rental car, which was OK.

Trenberth spent today in Christchurch helping the rescue effort, along with many, many others. You can get some idea of the size of this event by looking at aerial pictures taken by the NZ defence forces: aside from the building damage in the central city, extensive damage has occurred in many suburbs and soil liquefaction and flooding is affecting tens of thousands of homes. Power is out in 50 per cent of the city, and the mayor has described the water and sewer systems as “trashed”. Recovery is going to take a very long time, but recover and rebuild we will.

I would urge anyone with spare cash to make a donation to the various appeals that are running — there’s a full list here, and the NZ Red Cross is calling for donations (link was down at time of writing). [Update: see NZ based donation service at bottom of article -- 100% of monies will go to ChCh mayoral fund.]

Earth science geeks will want to check out the Christchurch Quake Map here (link takes you to last seven days — use the drop down to select Feb 22) for a remarkable visualisation of the earthquake sequence we’ve been experiencing, and the Highly Allochthonous blog has an excellent description of the tectonics of the quake here. It also worth noting that the quake caused a major calving event on the Tasman Glacier lake near Mt Cook. An estimated 30 million tons of ice broke off the glacier tongue when the quake hit.

I hope that Hot Topic readers will understand if my contributions to the site are somewhat disrupted over coming weeks. My focus will be elsewhere, and at the moment it’s very difficult to take the future for granted. A lesson for us all there, perhaps?

Update: this amazing picture of the clouds of dust rising from the city moments after the quake hit looks to have been taken from one of the hill suburbs. Hat tip to @georgedarroch on Twitter, photographer unknown*. Click for full size.

Dusttodust small

*[Edited incorrect photo attribution]

Fire and rain Gareth Renowden Aug 12

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The last few weeks have seen some extraordinary weather events around the world: relentless extreme heat in Russia, biblical flooding in Pakistan and devastating landslides in China. Tens of millions of people have had their lives disrupted and thousands have died, and — beyond reasonable doubt — global warming is playing a part in creating these extremes. But how much of a part? Michael Tobis asked this question in a recent post:

Are the current events in Russia “because of” “global warming”? To put the question in slightly more formal terms, are we now looking at something that is no longer a “loading the dice” situation but is a “this would, practically certainly, not have happened without human interference” situation?

The answer, at least in the case of the current extremes, would appear to be yes.

Jeff Masters at Weather Underground has (as usual) been providing exemplary coverage of the Russian heat wave, and in a post on August 6th he described it as “one of the most remarkable weather events of my lifetime”. Over the month of July, Moscow’s mean daily temperature was 7.8ºC above normal (the previous record, set in 1938, was 5.3ºC above normal), and since the beginning of August the daily maximum has been consistently 15ºC above average, which Masters describes as “a truly extraordinary anomaly”. At the time of writing, Moscow had experienced 29 successive days with temperatures over 30ºC, easily the longest and most intense heat wave since records began. Masters quotes Alexander Frolov, head of Russia’s weather service:

Our ancestors haven’t observed or registered a heat like that within 1,000 years. This phenomenon is absolutely unique.

What’s particularly striking about this event is the large margin by which previous long-standing records are being smashed. The Economist, in an excellent article on climate change and extreme weather, quotes Dutch meteorologist Geert Jan van Oldenborgh on the odds:

…a straightforward comparison of the temperatures seen this summer with those of the past 60 years suggests that a large patch of Russia is experiencing temperatures which might be expected only once every 400 years or so. Some places within that patch are hotter than might be expected over several millennia.

Those numbers assume the climate isn’t warming. When van Oldenburgh assumes warming:

…the heatwave starts to look less improbable–more like the sort of thing you might expect every century. As the warming trend continues in the future, the chances of such events being repeated more frequently will get higher.

Van Oldenborgh did a similar analysis of the heat and cold anomalies of last northern hemisphere winter, which I covered back in April. The key point is that if the climate were not changing, an event as dramatic as the Russian heatwave would be very, very unlikely. If we factor in the warming trend, it remains unusual, but less so. And if that warming trend continues (and it will), then we can expect more record-breaking heat waves around the world.

Global warming impacts the weather we experience in two ways: by increasing the probability of new records — when a heat wave happens, you are likely to get more warmth (see the graph in my post on rainfall). But there is a second impact: the potential for changes in the circulation of the atmosphere. The climate of any part of the planet depends on lots of factors, but the flow of weather systems is crucial. As an example, consider the South Island of New Zealand. The prevailing (or normal) wind is westerly, and when that wind bumps into the Southern Alps it drops rain, and lots of it. Hence rainforest, speedy glaciers and tourism. On the other side of the Alps, we get warm dry winds and little rain. Now imagine that the frequency of easterly winds increases and westerlies decrease. The east coast gets wetter, and the west coast dryer. Cue big change in climate, even if the temperature doesn’t warm. There’s actually a hint of this happening in the modelling toward the end of the century — though for the east coast of the north island, not down here.

So can we draw a line between Russian heat, flooding in Pakistan and China and changes in the pattern or shape of weather? Perhaps a combination of the after-effects of El Niño, record sea-surface temperatures in the tropical Atlantic and a reduction in Arctic sea ice are affecting the way the jet stream meanders around the northern hemisphere, creating a persistent ridge of high pressure over Russia — a blocking pattern that has flow on effects for Asia. Wired asked Kevin Trenberth if the heat and floods could be linked:

’The two things are connected on a very large scale, through what we call an overturning or monsoonal circulation,’ he said. ’There is a monsoon where upwards motion is being fed by the very moist air that’s going onshore, and there are exceptionally heavy rains. That drives rising air. That air has to come down somewhere. Some of it comes down over the north.’

Rob Carver at Weather Underground explains more here, New Scientist discusses the “frozen” jet stream here and UK Met Office scientist Peter Stott (who wrote the definitive paper on the record-breaking European heat wave of 2003) offers his thoughts at the Guardian.

What I find scary in all this is the multiple coincidence of record heat and catastrophic flooding in Pakistan and China — in a year where the first six months had already set a record for insurance losses on extreme events. The last 12 months have been the warmest in the global record. A modest El Niño event has boosted temperatures and affected weather patterns in an eery echo of events that followed the great El Niño of 1997-98. Back in 1999, Kevin Trenberth reviewed the extreme weather events of 1997-98. It was, as he suggests, a wild ride:

In early August, for example, major floods devastated parts of Korea, and in August and September 1998, extensive monsoon-related flooding struck heavily-populated eastern India and Bangladesh. Widespread heavy rains in China, at about the same time, released the mighty Yangtze River from its banks, with ensuing reports of more than 3,000 deaths, some 230 million people homeless, and over $30 billion in flood damage. In the summer of 1998 heat waves and air pollution episodes plagued many regions of the world, particularly in Egypt and other Mediterranean countries, and in southern Europe. In New Zealand, record floods in July and October 1998 were the worst in 100 years. But the costliest disaster of them all, in terms of human life, struck the Caribbean in late October. Hurricane Mitch caused the deaths of more than 11,000 people in Honduras, Nicaragua, Guatemala and El Salvador, primarily through the extensive flooding that followed prolonged and heavy rains.

This time round the floods are in Pakistan instead of India and Bangladesh, and the heat has moved north from the Mediterranean to Russia. The Atlantic hurricane season has not yet really got going, but we can only hope there won’t be another Mitch. In the 12 years since that El Niño, the climate system has continued to accumulate energy. When an ENSO event releases that energy it has to go somewhere, and that’s into heatwaves, floods, hurricanes and melting ice.

As the years go by and the warming continues, those extremes are only going to get worse. To me, it looks very much as though it won’t be a gradual warming that causes us the biggest problems, it’ll be the direct and indirect effects of increasing weather extremes. Hot years are going to be hard years for humanity.

[Update: The Wonk Room covers the same subject, but includes an interview with Rob Carver:

I agree with Michael Tobis’s take at Only In It For the Gold that something systematic has changed to alter the global circulation and you’ll need a coupled atmosphere/ocean global model to understand what’s going on. My hunch is that a warming Arctic combined with sea-surface-temperature teleconnections altered the global circulation such that a blocking ridge formed over western Russia leading to the unprecedented drought/heat wave conditions. Without contributions from anthropogenic climate change, I don’t think this event would have reached such extremes or even happened at all.


[Update 2 (in quick succession): Stu Ostro at The Weather Channel posts on Russian heat, extremes and 500mb anomalies:

The upshot: Whether with temperatures, precipitation, or storms (tropical or otherwise), and regardless of in which direction the extremes are, it's a case of Weather Gone Wiggy, and this is happening at the time when the Earth's climate is at an exceptionally warm level compared to that of at least the past century. There have been extremes for as long as there has been weather; it's their nature which is changing along with changing atmospheric moisture, stability, and circulation patterns.


[Update 3 (on a roll!): World Meteorological Organisation on recent extremes]

[Update 4: The Guardian expands on Weather Underground's list of new temperature records.]

[Update 5, 14/8/10: Jeff Masters posts on the jetstream and its influence on the heatwave: The Great Russian Heat Wave of 2010 is one of the most intense, widespread, and long-lasting heat waves in world history.]

[Sweet dreams and flying machines in pieces on the ground]

We call upon the author… Gareth Renowden Jun 29

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I must have been asleep last week when the IPCC announced its selection of authors for the Fifth Assessment Report (AR5), due in 2013/14. As usual, NZ scientists are making a significant contribution:

  • Tim Naish is a lead author for Working Group 1 (The Physical Science Basis) chapter 5, Information from Paleoclimate Archives.
  • Jim Renwick is a lead author for WG1 Chapter 14, Climate Phenomena and their Relevance for Future Regional Climate Change.
  • David Wratt is a review editor for Chapter 14 (as is Kevin Trenberth)
  • Phil Boyd (NIWA) is a lead author for WG2 (Impacts, Adaptation and Vulnerability), Chapter 6, Ocean Systems.
  • Alistair Woodward is one of the two Coordinating Lead Authors for WG2, Chapter 11, Human Health.
  • Andy Reisinger is a Coordinating Lead Author for Chapter 25, Australasia, Paul Newton (AgResearch) and Andrew Tait (NIWA) are lead authors, and Blair Fitzharris is a Review Editor.
  • Ralph Sims is a Coordinating Lead Author for Working Group 3 (Mitigation of Climate Change), Chapter 8, on Transport.
  • Harry Clark is a lead author for WG3, Chapter 11, Agriculture, Forestry and Other Land Uses (AFOLU).
  • Complete author lists: WG1, WG2, WG3.

Congratulations to all. Now the hard work starts…

And a plug: Jim Renwick is giving a talk on climate change at the Hurunui Library (yes, the one in the heat pump ads) in Amberley on Monday, July 5th at 7-30pm. All welcome. I’ll be heckling from the cheap seats…

[Thanks to Frogblog]

[Nick Cave]

When the rain comes… Gareth Renowden Jun 22

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The extreme weather flavour of the moment is without doubt heavy rain and flooding. As I write, severe flooding has caused 132 deaths in southern China and 19 in Burma. The Var region in southern France is recovering from spectacular flash flooding that killed 25 people (watch the BBC video), Tennessee’s recovering from a 1000 year flood in May, and NZ hasn’t escaped. The Metservice blog reports that the flooding in Whakatane a few weeks ago was caused by rainfall of 89.8mm in one hour (with more heavy rain either side of that hour). As the blog notes, that’s tropical rain happening well outside the tropics. But what struck me at the time was a comment from a Whakatane resident included in the TV3 News coverage of that flooding. I can’t remember his precise words, but it was something along the lines of “should be a wake-up call for anyone who doesn’t think global warming’s an issue, because this is what global warming delivers…” Perceptive, I thought, because one of the more robust predictions of climate science is sometimes described as an intensification of the hydrological cycle.

It works like this. Increasing CO2 in the atmosphere warms the planet. As the oceans warm up, more water vapour enters the atmosphere, and because it is itself a heat-trapping gas this adds to the warming. This positive feedback is important because it increases the amount of warming triggered by the CO2, but it’s also important because of impacts of the increase in water vapour itself. The increase has been measured: there’s about 4% more water vapour in the atmosphere now than there was 30 years ago, and I suspect that we’re now seeing the effects of that on our day to day weather.

Water vapour is sometimes described by meteorologists as the “fuel” that drives storms. As water evaporates from a warm ocean, it cools the surface and transfers energy into the atmosphere. As the water vapour condenses into clouds and rain, that energy is released, intensifying the storm. More water vapour, stronger storms, heavier rainfall.

4% extra water vapour doesn’t sound like a lot, does it? But it’s enough to change the probabilities of heavy rainfall events in two ways. Firstly, the frequency of heavy rainfall events will increase, and secondly the amount of rain that falls in the heaviest events will increase. Take a look at this graph (from NASA’s Earth Observatory feature on the costs of climate change):


The graph considers temperature extremes, but the same principle applies to rainfall (except that the probability distribution is pegged at zero — no rain). The top curve shows what happens if the climate warms but the variance — the size of the swings between warm and cold — remain the same. The middle curve shows a stationary climate (ie, not warming or cooling) but with a variance increase — more dramatic swings between hot and cold, but no new records. The effect is to squash the curve and create more warm and cold events. Combine the two, and you get increases in both the hot weather and in record heat. This is already being seen with heatwaves in Australia, for instance, and I suspect we’re now seeing the same effect happening with rainfall.

Joe Romm at Climate Progress has been diligently pursuing the issue of weather extremes as a symptom of climate change, and last week interviewed NZ scientist Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado, on the subject. It’s worth reading the full interview, and following the references, but here’s Trenberth making an important point. Romm asks about the best way to describe the increasing extremes:

I find it systematically tends to get underplayed and it often gets underplayed by my fellow scientists. Because one of the opening statements, which I’m sure you’ve probably heard is ’Well you can’t attribute a single event to climate change.’ But there is a systematic influence on all of these weather events nowadays because of the fact that there is this extra water vapour lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.

Earlier in Romm’s interview Trenberth had drawn attention to research that demonstrated that in the US, “the really heavy rainfall events – the top 1% and the top 0.3% – had gone up at even more alarming levels something like 27% as I recall over the last 30 or 40 years [actually 1967 to 2006].” Ring any bells? Jeff Masters comments and amplifies the point here. Then try a Google News search for the term “flood“, and see what pops up.

From my personal perspective, sitting in a farmhouse in North Canterbury on the east coast of the South Island of New Zealand, deep down in the South Pacific ocean, I think we’re seeing this effect quite clearly. I haven’t crunched the numbers for New Zealand, but I think they might show the same thing as the research Trenberth quotes. I’ve pondered the subject before, when considering the evidence of my rain gauge in 2008 and the climatic swings of 2009, but I can’t help but feel that as we head into the second half of a year that might set another global temperature record, we’re already seeing the concomitant impacts of increased water vapour in the atmosphere in the dramatic flood events happening around the world.

The lesson: climate change is not an abstract thing, a problem reserved for the future. It’s not only a slow but steady increase in long term averages, it’s also a change in the probability of extreme events, which are themselves becoming more extreme. The impact of climate change will be delivered by changes in the weather that we experience — and those changes are already happening. Worse, when the weather’s bad, it can and will be very bad indeed.

[Update 23/6: The Guardian reports on a new paper which suggests intensification of the hydrological cycle will persist, due to the thermal inertia of the global ocean, for a considerable period after CO2 levels have stabilised and been reduced. And Nature News discusses the terrifying power of flash flooding...]


Oops, he did it again Gareth Renowden Jan 08

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It pays to beware of leaving hostages to fortune: saying or doing something that might cause you some embarrassment in the future. There’s a very fine example in this recent blog post by Ian Wishart, titled “Top 10 global warming myths exposed“. It takes the form of a piece Wishart has submitted to the Coromandel Chronicle, taking exception to a column by Thomas Everth [PDF]. He begins:

In a blatant effort to mislead and scare your readers, Green blogger Thomas Everth makes more errors in the first 200 words of his recent global warming diatribe than I have made in my last three books totalling around 400,000 words.

As hostages go, that’s pretty impressive. Wishart proceeds to find fault with ten of Everth’s opening points, but does he make a few mistakes of his own in the process? I’m going to take a long, hard look: is that hostage feeling lucky?

Myth number one:

[quoting Everth]“One would think that in the face of: visibly vanishing Arctic ice Caps…”

[Wishart's response] In fact, after hitting a record low extent in 2007 caused mainly by wind patterns blowing ice into warmer waters, Arctic sea ice has grown significantly in coverage since 2007, even exceeding the 30 year average it is measured against. “Visibly vanishing”? I don’t think so.

That piqued my curiosity. Has sea ice “coverage” exceeded “the 30 year average” recently? I had a look at the (new, improved) graph at Cryosphere Today. Nope, the area anomaly has been below the long term average over the last two years. What about ice extent? The National Snow and Ice Data Centre in the US has just issued its 2009 year end summary, and helpfully provides this graph (Click the image for a bigger version):


As you can see, in early May 2009 the ice extent just bumped under the ‘79-2000 average (grey line), but certainly didn’t exceed it. Since then it’s been well below average, as it was prior to May. The NSIDC also provides an average line (the pale blue one) based on the full 79-09 data. It runs below the 79-2000 average because it includes the low ice levels of recent years, and May’s extent did bump slightly over that line. So: for a few days in May, Arctic ice extent was above the 30 year average. Wishart’s little factoid is technically correct, but it’s a prime example of cherry picking — choosing a fact that tells the story you want, rather than providing the full picture. And the big picture in this case is easy to see in the graph. After flirting with average in spring (thanks to a cold April), ice extent then dropped rapidly, and despite a cool summer reached the third lowest minimum in the record. It’s been bumping along the lowest recorded since — and might even have set new record negative anomalies in recent months. Here’s how the NSIDC sums up 2009:

Despite the cool summer, the ice remained thin and vulnerable at the sea ice minimum, with little of the older, thicker ice that used to characterize much of the Arctic. Recently published research by Barber and colleagues shows that the ice cover was even more fragile at the end of the melt season than satellite data indicated, with regions of the Beaufort and Chukchi Seas covered by small, rotten ice floes.

You can see David Barber talking about that rotten ice here. So: no new record lows, but no real recovery, and the trend in every month of the year remains strongly downwards.

Number two:

[Everth] “…the break up of huge Antarctic ice shelves,”

[Wishart] Actually, the “huge” ice shelves amount to less than a fraction of one percent of Antarctica’s area, and they’re in an area hit by warmer ocean currents than the rest of the ice continent. Furthermore, a string of recent scientific studies show the area has been even warmer in the past one thousand years than it currently is, naturally. Hardly the stuff of nightmares.

Actually, there are about 1.5 million km2 of ice shelves fringing Antarctica, and in the last 50 years the Antarctic Peninsula alone has lost over 40,000 km2 – a little more than 2.5% of the total for the continent. Antarctica’s a big place (14 million km2), so if you compare apples (ice shelves) with oranges (continental ice sheets) you can come up with a very small — and very meaningless — number. For a fuller perspective, the NSIDC has an excellent page on ice shelves here.

Wishart also claims that “a string of recent studies show the area has been even warmer in the past one thousand years than it currently is”. It appears likely that Ian’s “string” is one paper he’s quoted before, about possible elephant seal colonies in the Ross Sea (Hall et al, PNAS, 2006 [PDF]), and he was given the relevant context (that it doesn’t necessarily imply increased temperatures at the time) by Prof Tim Naish on his own blog last year. He seems to have forgotten that… The big picture? Take a read of Chapter 3, Antarctic climate and environment history in the pre-instrumental period from the SCAR report [PDF]. A lot more nuanced, a lot more interesting than Wishart’s cartoon portrayal, and not much sign of warmth in the last 1,000 years — until recently.

Number three:

[Everth] “…methane bubbling melting permafrost,”

[Wishart] This is one of the favourite scare stories of Everth and some others, particularly those who frequent the local Chicken Little website Hot Topic, run by a South Island truffle grower. I was therefore amused when NIWA recently rubbished the idea of a major threat from methane hydrates. They had to rubbish it, because scientific data suggests the methane stores are actually highly stable. The permafrost was 30% warmer in the 1930s than it is now (naturally, again), but we did not all vanish in a methane explosion.

Didn’t take him long to get to truffles… ;-) I am mystified by his comment about NIWA “rubbishing” the threat from methane hydrates. NIWA’s release of the latest methane data didn’t mention hydrates at all, just arctic warming as one potential source of the recent increase. To be fair to Wishart, many of the largest deposits of methane hydrates are thought unlikely to bubble up any time soon — they are on deeper continental shelves where the combination of high pressure and low temperature keeps them stable. It’s the Arctic sea floor methane hydrates that are causing concern. The shallow seas north of Siberia have enough methane beneath them to cause a lot of warming if rapidly released, and there’s plenty of evidence of large plumes of bubbles, as I noted in my last post. A scare story, or a genuinely scary prospect? The evidence is what the evidence is, not what Wishart might want it to be — you can make up your own mind.

Wishart’s claim that “the permafrost was 30% warmer in the 1930s” is also mystifying. What permafrost, where? Extensive monitoring of permafrost temperatures has really only been going on since the 1950s, though some Alaskan records stretch back to the 1920s. The section on permafrost in the IPCC’s 4th report (WG1, section 4.7, PDF) provides no support for his contention.

Number four:

[Everth] “…vanishing glaciers,”

[Wishart] As the US National Science Foundation and others have well documented, glaciers and ice sheets have much longer response times (thermal lag) to warming or cooling than you’d think. Big glaciers, for example, can take up to a thousand years to show serious effects from a warmer climate, and big ice sheets can take up to tens of thousands of years, according to the US NSF (details in the book Air Con). All of which means that the melting we are seeing now is a delayed reaction to warming that took place between a hundred and a thousand years ago. I would remind readers that the warming that took place back then was entirely natural, as the knights of old were not driving SUVs.

This is classic Wishart. Here he assumes that glacier response time is equivalent to “thermal lag” — a concept that pops up regularly in Air Con. His statement that “the melting we are seeing now is a delayed reaction to warming that took place between a hundred and a thousand years ago” is nonsense. Here’s a simple explanation of why…

The vital statistic for any glacier is its mass balance: the amount of ice it contains, and how that changes. The quantity of ice in a glacier is determined by the amount of ice that melts during the year (or for glaciers that terminate at sea or in lakes, lost as calving icebergs), balanced against the amount of new ice that forms at the source of the glacier — the névé or snow field at its highest point. If the amount of ice loss is smaller than the ice gain, then the mass balance is positive and the glacier grows. If melt exceeds replenishment, the glacier shrinks. A glacier’s mass can grow one year and shrink the next, based purely on the local weather it experiences (see NIWA’s graph for ice mass in the Southern Alps, to see how NZ’s total ice mass changes from year to year). No “thermal lag” involved…

A glacier has two kinds of “response time”. The first is the length of time it takes a glacier to respond to a change in climate — to achieve a new equilibrium with its local climate. If the local climate cools (or snowfall increases) then a glacier’s mass balance will be positive and the glacier will grow until the (lower) melting (or calving) zone is large enough to balance out the increased ice input from snowfall. When that happens, the glacier will stop growing and will stabilise. It will have responded to the change in climate. If the climate change — lets say warming, for the sake of argument — continues long enough, the glacier may never get back into equilibrium, and will disappear. This is true for the bulk of the Tasman Glacier: it’s already certain to retreat at least as far as the Ball Hut, leaving a new deep lake behind. Whether it can stabilise at a new much smaller size remains to be seen. The second kind of response time is the time it takes for changes at the snowfield at the top to work their way down to the terminus of the the glacier. For a small glacier, this response time can be short — 5-7 years for NZ’s Franz Josef and Fox glaciers for instance — but for large ice sheets, the time can be thousands of years or more.

Wishart’s error here is a big one — a very basic misunderstanding of the meaning of “response time”. He appears to think it means that the ice somehow has to wait for a period before it can start melting — he calls it “thermal lag”. This is, not to put too fine a point on it, complete rubbish. If the climate warms, ice starts melting straight away and the glacier starts losing mass. No lag. No heat mysteriously stored away for hundred or thousands of years before making itself felt. Current melting is not a “delayed reaction” to events a long time ago, it’s a direct response to current weather and climate change as it happens.

[For more detail on glaciers, check out this article at the NIWA web site. It has a great opening line... Then have a look at Mauri Pelto's From A Glaciers Perspective blog for examples, and check out this recent NZ report on the Tasman Glacier (discussed at Mauri's blog, too).]

Number five:

[Everth] “…heat waves,”

[Wishart] Everth conveniently forgets to include the balancing factor for heatwaves: cold spells. As many of your readers are now aware, the Northern Hemisphere has been hit by another brutal icy winter, even bigger than last year’s record breaker. In December alone nearly 900 snowfall records in US towns and cities were broken or tied, and temperatures were 15 degrees below average in some areas. As a matter of factual record, more people die from the cold than in heat waves.

Here’s a balancing picture of this northern hemisphere winter:


This is an NCEP/ESRL plot of temperature anomalies over the northern hemisphere for the first six days of January. Big blue blobs for cold weather in the eastern USA, northwestern Europe and central Russia (where Europe’s cold air is coming from). The yellow and red blobs are warm anomalies, and at a rough eyeball guess, I’d say they at least balance out the cold. We’ll know when the winter analysis is done… To give you some idea of the size of those warm anomalies, Goose Bay in Labrador is normally -25ºC at this time of year. A couple of days ago temperatures were hovering round 0ºC — a full 25 degrees warmer than normal!

As for temperature records in the US, here’s what a recent study at the National Center for Atmospheric Research in the US shows:


This graphic shows the ratio of of record daily highs and lows for about 1,800 US weather stations for each decade of the last 60 years. During the slight cooling of the 60s and 70s there were more new cold records than new hot ones, but in the last ten years there have been just over twice as many new hot records as cold ones — a clear signal of a warming climate.

[For a discussion of the atmospheric drivers of the current cold winter patterns up North, check out this post by Jeff Masters, and there's a beautiful image of a completely snow-covered British Isles at NASA's Earth Observatory.]

Number six:

[Everth] “…record bush fires”

[Wishart] Your correspondent refers to the Australian bush fires, but readers of Air Con who’ve seen the chapter on those fires will recall that Australian temperatures are not fuelled by CO2 but by hot seasonal winds blown in from the central desert. (same problem in California and vulnerable parts of the US) It is a matter of factual record, again, that last summer’s ‘record’ temperatures were no different to those measured in the great fire of 1851 — a blaze ten times larger than the 2009 killer fires in Victoria. The death toll in Victoria, incidentally, was far higher than 1851 because of a daft resource management bylaw introduced by Green councillors that prevented homeowners from cutting down vegetation close to their homes. Hence, when the blazes hit, houses burnt to the ground.

Australian temperatures have increased by 0.9ºC over the last 50 years. Heat extremes have increased while cold extremes have reduced, and there is little doubt that increasing heat has contributed to fire danger. Here’s what the latest CSIRO/BOM climate change update [PDF] has to say about bush fires:

The pattern of recent extreme fire danger is part of a broader shift towards more severe fire seasons in central Victoria. It is very likely that climate change has increased the likelihood of extreme fire danger in south-east Australia. The climatic conditions experienced in Victoria on February 7 2009 were unprecedented. The area north-east of Melbourne had experienced a 12-year drought before the fires, as well as record high temperatures, a record
heat wave two weeks earlier, record low rainfall and record low
humidity. The area was also experiencing an unprecedented sequence of days without rain.

The frequency of extreme heat waves has also markedly increased. You can read about that in the Aussie climate change update, or for more detail of the truly unprecedented sequence of extreme heat events in South Australia, read what Adelaide climate scientist Barry Brooke had to say last November:

Consider that in prior to 2008, the record length for an Adelaide heat wave in any month was 8 days (all occurring in summer). Now, in the space of less than 2 years, we’ve had a 15 day event in Mar 2008 (a 1 in 3000 year event), a 9 day sequence in Jan/Feb 2009 (which included 8 days above 40°C and 13 consecutive days above 33°C), and now, another 8 day event in Nov 2009. How unusual is this? There have been 6 previous heat waves that lasted 8 days, many more of 7 days, more still of 6, and so on – the return time is logarithmically related to it’s length. Given these data, and the fact that the latest spring event has equaled previous all-time summer records(!), and the alarm bells should rightly be ringing. Statistically speaking, it’s astronomically unlikely that such a sequence of rare heat waves would occur by chance, if the climate wasn’t warming. But of course, it is.

It’s also worth reading the Aussie BOM 2009 summary for more context.

Wishart wants us to believe that the bush fires were caused by weather (true), and that the weather wasn’t unprecedented (not true). Everth points to bush fires as symptoms of climate change, and the Aussie data supports that point.

Number seven:

[Everth] “…the last decade being the hottest on record ever,”

[Wishart] Sounds impressive, except that technically ‘ever’ means only in the past 30 years, which is how long we’ve had satellite coverage of the planet. So really what Thomas is saying is that the last decade was the hottest of the last three decades. But as he didn’t tell you, there’s been no statistically significant warming at all over the past ten years, which is why one of the world’s top climate scientists, Kevin Trenberth got so hot under the collar in the Climategate emails where he wrote:

“The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t”.

Green blogger and lobbyist Thomas Everth says one thing, climate scientist says, admittedly through gritted teeth, something quite different in implication.

Oh dear. The misconceptions and misdirections in this little section alone are enough to merit a whole post to themselves, but I’ll have a go at a precis.

Wishart makes the astonishing assertion that we can only rely on the temperature record since the advent of satellite measurements. This will be news to the meteorological community, who have been making direct measurements of temperature with very accurate thermometers for 150 years or more. Temperature measurements from satellites are anything but direct. Roy Spencer has recently blogged on the process, explaining how the satellite instruments work, and how the data has to be processed to extract a temperature signal. Fascinating, undoubtedly, but he also points out:

Because of various radiometer-related and antenna-related factors, the absolute accuracy of the calibrated Earth-viewing temperatures are probably not much better than 1 deg. C.

Direct thermometer measurements can do far better than that. Of course, absolute accuracy is not that important when you’re looking at trends over time, provided that the instruments are consistent (that is, always err by the same amount). When we compare the satellites with the ground-based thermometer record we find that they show the same picture — nobody would trust the satellites if the disparities were huge (that happened in the 90s, and a lot of effort went into correcting the satellite data) — so we can be confident that the pre-satellite record is at least as reliable as the satellite data. On that basis, Everth is correct, because the World Meteorological Organisation has already indicated that the last decade will be the warmest in the long term (150 year) record. Wishart’s attempt to limit the record to 30 years? Epic fail.

Next: no statistically significant warming for ten years? We already know that the average of the ten years 2000-09 was warmer than the 1990-99 average. Warming continues. The accuracy of Wishart’s claim rests on the definition of “statistical significance”. I make no claims to being a statistician (and neither does Wishart, as far as I know), so I defer to Tamino’s analysis at Open Mind, where a professional statistician and expert in time series analysis shows that you need 15 years of GISS temperature data to be confident that trend is greater than zero. Here’s Tamino’s conclusion:

That does not mean that there’s been no warming trend in those 15 years – or in the last 10, or 9, or 8, or 7, or 6 years, or three and a half days. It only means that the trend cannot be established with statistical signficance. Of course, it’s another common denialist theme that ’there’s been no warming.’ This too is a fool’s argument; any such claims are only statements about the noise, not about the trend. It’s the trend that matters, and is cause for great concern, and there’s no evidence at all that the trend has reversed, or even slowed.

The Trenberth quote? Taken out of context (explained here). Trenberth was not admitting anything through gritted teeth, he was bemoaning the lack of adequate data to fully account for all the elements in the planetary heat budget.

So: Everth’s statement is correct, and Wishart’s attempt to suggest otherwise is unconvincing.

Number eight:

[Everth]“…new records for ocean temperatures broken in 2009,”

[Wishart] Well, there have been big lows in the past 24 months compared with the past couple of decades as well, so on balance, not such a big deal. As Thomas would be the first to acknowledge, short term fluctuations are not hugely meaningful. The only reason ocean temperatures were higher this year was because of the naturally occurring El Nino. Much more detail on this topic can be found in Air Con.

Ah, so short term fluctuations are not meaningful here, but a cold snap in North America this winter is? Wishart suggests that this year’s record sea surface temperatures (see here for details) were caused by El Nino. In one sense, that’s true: El Nino always brings warm SSTs to the Pacific. However, El Nino alone can’t explain the record high temperatures. As with the Aussie heatwaves and US temperature records, it’s the underlying warming that tips the odds towards new record highs. For that reason, many people expect 2010 to set a new global temperature record — a warm event overlaid on the underlying warming trend makes the odds at least reasonable.

Number nine:

[Everth]“…ocean acidity increasing fast”

[Wishart] Not technically true either. The oceans are alkaline. What is happening is a tiny decline in alkalinity as the result of higher CO2 levels, but there is not actually enough surplus CO2 around at present to physically turn the oceans acid. What is probably much more significant, however, is a new peer reviewed study in the journal Science which shows overfishing could be a far bigger reason for declining alkalinity in the oceans.

Technically, what Everth says is exactly true. Ocean waters remain on the alkaline side of neutral, but their acidity is increasing rapidly. Wishart’s “tiny decline” – a 0.1 unit decrease in pH doesn’t sound like much, after all — is actually a 30% increase in hydrogen ion concentration, because pH is a logarithmic scale. That’s a huge change, happening fast in geological terms, and there’s more than enough CO2 in the atmosphere now, and expected to be emitted over the next few decades to cause huge problems for oceanic ecosystems. Here’s what a recent introductory guide for policy makers prepared by EPOCA (the European Project on Ocean Acidification) has to say [PDF here]:

Ocean acidity has increased by 30% since the beginning of the Industrial Revolution and the rate of acidification will accelerate in the coming decades. This rate of change, to the best of our knowledge, is many times faster than anything previously experienced over the last 55 million years.

The significance of overfishing… is much more complex than Wishart suggests. Check out the original press release and abstract to see why what he says is a remarkable overstatement.

Number ten:

[Everth] “With CO2 concentrations shooting up to pass 400ppm soon, we have entered a territory of Earth’s atmospheric composition not seen for millions of years — CO2 having stayed at or below 280 ppm during those millions of years.”

[Wishart] Er, not strictly true either. Recent studies have found global warming scientists ‘cherry picked’ only the CO2 readings from the past that suited their low 280ppm starting point. In fact, readings over the last 200 years suggest CO2 levels have averaged around 335ppm, and as high as 500ppm in some areas. Why is this significant? Because if you choose a low starting point, say 280, and you can show we’ve risen to 380 today, then that’s a big rise in CO2 levels. But if the starting point was really 335, then the increase is nowhere near as big, and that would be “inconvenient” for the human impact on global warming argument that Thomas is running.

Both Everth and Wishart are “strictly” wrong, but Everth’s mistake is the smaller. CO2 levels have exceeded 280ppm during recent interglacials – up to around 300ppm in the most recent, for instance. The rest of what he says is quite correct. On the other hand, Wishart wants us to believe, apparently on the basis of an infamous “paper” by EG Beck (so ludicrous that it’s been disowned by “serious” sceptics), that recent CO2 levels may be much more volatile than we think. Beck’s big mistake? To assume that all CO2 measurements were equally valid, wherever and whenever they were taken. Wishart’s? To swallow Beck whole, and regurgitate it in public.

For a man who claims to have made no mistakes in three books and 400,000 words, Wishart’s error rate in this latest piece is astounding. Perhaps his most telling mistake concerns the “thermal lag” he says operates in glacier response to warming. If he had troubled himself with a little study, perhaps spoken to a few glaciologists, he would have seen that his “lag” was a physical impossibility. Perhaps now that his mistake has been pointed out he’ll correct the pages in Air Con where he misconstrues glacier response times (pps 96/7/8) for the next edition. But I won’t hold my breath.

Thomas Everth’s presentation of the facts of climate change and its impacts is far less misleading than Wishart’s. In every one of the ten “myths” Wishart tries to expose, he gets something wrong — cherry picking facts to suit his argument, ignoring the balance of evidence, relying on “studies” that have long been shown to be rubbish. In one respect, however, Wishart has done me a service. In researching this examination of his arguments I’ve had to dig around in the literature, and exchange emails with a few experts to check my understanding. I’ve done some learning, and it’s been fun. It could also be a teaching moment, but I doubt the student it might help the most will be inclined to benefit.

And the hostage Wishart left dangling? On the evidence, it doesn’t look like he’s going to be rescued any time soon.

[Richard Thompson]