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Posts Tagged rain

Lost in the flood Gareth Renowden Mar 09

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CantyfloodsNASAEO

This morning’s NASA Earth Observatory image of the day shows the impact of last week’s heavy rain in Christchurch and Banks Peninsula on the sea around. The light blue colours show sediment washed off the land. If you visit the EO page, they provide a helpful reference image: the region snapped from space in late February, when there’s no sign of any sediment at all.

The heavy rain brought flooding to many parts of Christchurch, as NASA notes:

Christchurch’s flood control infrastructure has been under increasing pressure in recent years because a series of earthquakes struck the area in 2010 and 2011. According to University of Canterbury researchers, the quakes caused land in some areas to drop, while narrowing and uplifting certain river channels. The result is an increased risk of flooding.

This rainfall map from NIWA shows rainfall over the last 15 days (right) compared with the average for the same period (left) and the anomaly (centre). The rain event is immediately obvious as the blue thumb sticking out of the South Island east coast:

CantyfloodsNIWA15day

The Weather Underground’s Christopher Burt provides numbers for the storm:

The powerful storm pounded the Christchurch area between March 3-5 with wind gusts up to 119 km/h (74 mph) and rainfall of 151.6 mm (5.97”) as officially measured at Christchurch’s weather station. Of this amount 100 mm (3.94”) fell in just a single 24-hour period on March 4-5. The suburb of Lyttelton received 160 mm (6.30”) in 24 hours and other suburbs reported storm totals of 170 mm (6.70”). The normal monthly rainfall for Christchurch in March is just 45 mm (1.77”).

For a selection of pictures, see these galleries at Stuff.co.nz: Christchurch, Lyttleton and Banks Peninsula.

The severe flooding in parts of Christchurch – notably the “Flockton Basin” – was caused or made worse by a number of factors. The earthquake sequence caused ground levels to fall by up to half a metre in parts of the eastern suburbs and along the Avon River (see map here), raised and narrowed river and stream beds and damaged or destroyed storm water infrastructure. Add to that a heavy rainfall event that would have taxed the drainage system in pre-quake times, not to mention the tail end of a sequence of high spring tides causing water to back up in the estuary, and you have all the makings of a historic flood event.

Local and national politicians have rushed to promise action to address the flooding, but Christchurch’s problems will not be solved by a crash programme to defend homes that now flood every time there’s a rainstorm. Continuing sea level rise and increasing rainfall intensities — both already observed and projected to get much worse — suggest that serious consideration should be given to managed retreat in some areas, rather than rebuild and defend. How high should you make a stop bank when you expect sea level in a hundred years time to be a metre higher than now?

Christchurch is facing the sort of problems that all coastal cities are going to have to confront over coming decades, brought forward by the earthquake sequence that caused so much death and destruction. Unfortunately for the citizens of the city, the earthquake recovery programme is being overseen by Gerry Brownlee, a cabinet minister who is on the record as a climate sceptic. If he fails to consider the big picture, and neglects to plan for a future when the waters have risen far above today’s levels, then Christchurch will be even deeper trouble every time it rains old women and sticks1.

[Brooce, at his best.]

  1. Mae hi’n bwrw hen wragedd a ffyn – It’s raining old ladies and sticks: Welsh idiom.

Where the wind blows, it rains: Arctic warming and wacky jetstream ruins European summers Gareth Renowden Oct 31

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The dramatic loss of summer sea ice in the Arctic has prompted a lot of research interest in the way that this is affecting weather patterns around the northern hemisphere. The latest contribution is Influence of Arctic sea ice on European summer precipitation, by Dr James Screen of the University of Exeter [PhysOrg]. In this “video abstract”, he explains how reductions in Arctic sea ice affect the position of jetstream — the ribbon of winds winding around the planet that guides weather systems — bringing more summer storms to Western Europe, and a recent run of record-setting wet summers to the UK. But as he points out, the effects are planet-wide:

The impacts are not just over northwest Europe. Actually in the model, what we find is that whilst the sea ice loss increases rainfall over northwest Europe, we actually find drier conditions over Mediterranean Europe. Also the jet steam shifts over North America, which can have implications for the weather there too.

Dr Screen’s study underlines a point that I have been making for some time: rapid climate change is not something theoretical that will happen in the future — it’s happening now and we’re feeling the effects. Warming in the Arctic is driving sea ice loss, and the atmospheric consequences are changing the shape of the weather right round the northern half of the planet.

Also interesting, and also looking at jetstream patterns is Probability of US heat waves affected by a subseasonal planetary wave pattern, in which the authors find that US heatwaves might be predictable 15-20 days earlier than at present by monitoring a particular jetstream wave pattern. [Science Daily]

It’s worth noting that an especially vigorous jetstream directed and helped to intensify the recent huge European storm that hammered the UK, Germany and Denmark, killing 16 people and causing huge amounts of damage. Christopher Burt at WeatherUnderground provides a handy overview of the storm that has four names — St Jude, Christian, Simone and Carmen. The storm centre moved 2,000 km in 26 hours, a remarkable pace of 77 kph.

I think it’s going to rain today (when it’s wet, it’s very very wet) Gareth Renowden Jun 23

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I took Rosie the truffle machine for a walk around the farm just before dark yesterday. We were both a bit stir-crazy after four days of cold, cold rain and a couple of days of screaming southerlies that brought snow to our hills. The ground passed field capacity at the beginning of last week, when an atmospheric river brought torrential downpours and flooding to much of the South Island. Now the soil is sodden, quivering with water and oozing mud at every footstep. Every drop of extra rain is taking that mud and sluicing it down to the river. A stream runs through my black truffle plantation. I spent this afternoon digging a drainage trench. Truffles don’t enjoy sitting in water. My crop might rot. The Waipara is roaring along at the bottom of our cliff at about 50 cumecs1, an impressive sight for a river that normally dribbles down to the sea at under a cumec. It peaked last week at about 110 cumecs. The riverbed will have been reshaped. But we got off lightly.

Over the last couple of days the New Zealand news has been dominated by extreme weather. The southerly storm that soaked us also battered Wellington and brought deep snow2 to much of the South Island. It made for compelling pictures. But what’s going on elsewhere in the world is even more dramatic:

The early arrival of particularly intense monsoon rain has brought flooding and chaos to northern India. At the time of writing, it is estimated that 600 people have died and 40,000 are stranded by rivers and landslides [BBC, NASA Earth Observatory, Jeff Masters.]. In The Times of India, government earth sciences secretary Shailesh Nayak was reported as saying that climate change played a role in the flooding:

The catastrophic rainfall in Uttarakhand was most likely a climate change event as it is in keeping with a pattern of increasing incidents of extreme weather events that often cause phenomenal damage as was seen in the hill state…

In Alberta, Calgary — Canada’s fourth largest city — has been flooded by torrential rains in the catchments of the Elbow and Bow rivers. Three people have died and 100,000 have been displaced. [Christopher Burt at Weather Underground, Calgary Herald, National Post, podcast: interview with Robert Sandford, ]

The central European flooding that I wrote about a couple of weeks ago at The Daily Blog is now estimated to have cost the regional economy US$22 billion. Germany is now “enjoying” a heatwave.

Meanwhile, Alaska has been experiencing a heatwave of record proportions as a slow moving giant loop in the jet stream has allowed a dome of high pressure to linger over the state.

New Zealand’s recent extreme weather was also down to a large excursion the in the southern hemisphere jet stream, as Jim Renwick told the Science Media Centre:

To get an event like this, which is pretty extreme, we need the westerly wind that normally blow across New Zealand and the southern oceans to slow down and to buckle into a series of big meanders, north-south waves around the hemisphere. […] Right now we have a series of large-scale waves around the southern hemisphere, with big southerlies near New Zealand, over the central Pacific, off the eastern South American coast, over the eastern South Atlantic, and over the central Indian Ocean. The southerly flow over/near New Zealand is the most impressive, as it reaches all the way south to south of 60S […] which is almost down to the edge of the sea ice at this time of year.

So where’s the climate change in all this? In India, Canada, Alaska and Europe we have extreme weather events happening more or less simultaneously, with a common factor — jet stream meanders — playing a significant role. Those meanders are most likely a symptom of a reduced equator to Arctic temperature differential, as Jennifer Francis and Stu Ostro explain in this recent Climate Desk event. We also have to consider the fact that the climate system is now operating at higher energy levels than before — a warmer atmosphere can carry more water vapour, and water vapour is the fuel for weather systems. More water vapour, more rain — and more intense rainfall.

Weather extremes are where the climate change rubber hits the road3. We might think that our future is described by the smoothly rising curves we see in multi-model means of global temperature projections over the next 100 years, but we don’t live in a multi-model world. We only have the one climate system, and we all live in regions, not in a notional global average.

We have to live through the noise — the bumps, the lumps, and the jumps that go with energy accumulating in the planet’s climate system. There will be more floods, more lives lost to climate instability. It’s happening now, and it’s going to get worse.

[Peter Gabriel, Dusty Springfield, Nora Jones or the original?]

  1. Cubic metres per second.
  2. The Mt Hutt ski field got 2.8 meters of snow — just over 9 feet in the old money — a record start to the season. Take a look at the green line on their snow graph to get some sense of the context.
  3. And sometimes the road explodes, as happened in the recent German heatwave.

The Climate Show #33: Salinger, carbon carnage and recursive fury Gareth Renowden Feb 08

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In this week’s news-packed edition of The Climate Show we have an exclusive interview with Jim Salinger, probably New Zealand’s highest profile climate scientist, talking about extremes and the shape of things to come. John Cook discusses his new paper with Stephan Lewandowsky, Recursive fury: Conspiracist ideation in the blogosphere in response to research on conspiracist ideation, which is already upsetting climate cranks around the world, plus we look at carbon bubbles, renewable energy beating coal on price, and a simply superb iPad app.

Watch The Climate Show on our Youtube channel, subscribe to the podcast via iTunes, listen to us via Stitcher on your smartphone or listen direct/download from the link below the fold.

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

The Climate Show

Story references

News

Carbon bubble begins to bite: Hot Topic.

Increases in extreme rainfall linked to global warming: Science Daily.

New Mexico Utility Agrees To Purchase Solar Power At A Lower Price Than Coal: Climate Progress.

Renewables now cheaper than coal and gas in Australia: REneweconomy.

Interview

[13:15] Jim Salinger, NZ’s best-known climate scientist.

Debunking the sceptic

[31:30] John Cook of Skeptical Science discusses Recursive fury: Conspiracist ideation in the blogosphere in response to research on conspiracist ideation. Shaping Tomorrow’s World blog post here.

Solutions

EarthViewer app for iPad: Howard Hughes Medical Institute, and at the iTunes app store.

We have an email!

Thanks to our media partners: Idealog Sustain, Sciblogs, and Scoop .

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

The Climate Show #29: if the sun don’t come, you get a tan from standing in the English rain Gareth Renowden Oct 11

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This week The Climate Show brings you an all news special. We have wet summers for Europe, permafrost warming delivering a methane kick, La Niña driving floods that make sea level fall, a glacier calving in Antarctica, mammoths and sabre tooth tigers — all delivered with Glenn and Gareth’s inimitable panache (!).

Watch The Climate Show on our Youtube channel, subscribe to the podcast via iTunes, listen to us via Stitcher on your smartphone or listen direct/download from the link below the fold.

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

The Climate Show

Story references

Wet British summers: Guardian, Nature.

Permafrost & methane: Skeptical Science.

US swing voter survey: China Daily(!)

La Niña driving sea level fall: Geophysical Research Letters.

SE Australia drying: eScience News

Thwaites Glacier calving: From a Glaciers Perspective.

Mammoths

Thanks to our media partners: Idealog Sustain, Sciblogs, and Scoop .

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

Title reference: Gareth’s favourite Beatles track…

The Climate Show #23: Durban and the return of the electric car Gareth Renowden Dec 21

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Grab some holly, deck your halls, heat up some mince pies, and then settle down to the last Climate Show of 2011. We look at the outcome of the Durban conference, discuss heavy rain in New Zealand and record-breaking weather extremes in the USA, and ponder the implications of news of more methane erupting from the seabed off Siberia. Glenn interviews Chris Paine, director of EV documentary Revenge of the Electric Car, and we round off the show with some optimistic news on possible energy solutions.

Watch The Climate Show on our Youtube channel, subscribe to the podcast via iTunes, listen to us via Stitcher on your smartphone or listen direct/download from the link below the fold…

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

The Climate Show

News & commentary: [0:02:00]

Durban – the deal, and what it means

Mark Lynas at Hot Topic: http://hot-topic.co.nz/the-verdict-on-durban/

Gareth’s take: http://hot-topic.co.nz/a-mad-deal-in-durban/

Climate Action Tracker

Flooding in Nelson: Stuff.co.nz

Philippines: 400+ killed in flash floods yesterday: BBC

Record year for extremes in US: NOAA, Jeff Masters.

WMO on 2011: world’s 10th warmest year, warmest year with La Niña on record, second-lowest Arctic sea ice extent: release.

Methane in the Arctic: Independent.

[Background] http://hot-topic.co.nz/siberian-seabed-methane-first-numbers/ and the links therein.

Interview [0:34:30]

Chris Paine: Revenge of the Electric Car

Solutions [0:54:00]

Game Changing Technologies Promise Climate Change Optimism: Celsias NZ

U.S. Geothermal Resources Could Replace Coal 10 Times Over: Ecogeek

Solar Power Much Cheaper to Produce Than Most Analysts Realize, Study Finds: Science Daily

Solution Fail: Congress spared the 100-watt incandescent light bulb from a government-enforced phaseout in a win for Tea Party activists over manufacturers who said they are already switching to more energy-efficient products: Business Week

Thanks to our media partners: Idealog Sustain, SciblogsScoop and KiwiFM.

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

Wake of the flood (first reprise) Gareth Renowden Oct 26

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EOBangkok20111025

Thailand is experiencing its worst monsoon flooding for at least 50 years. The NASA Earth Observatory image above shows the waters piling up to the North of the capital Bangkok, which is already beginning to experience flooding (visit the EO page to see a comparison with earlier floods, and The Guardian for a striking set of flood pictures). The Thai government yesterday declared a five day weekend to allow the city’s inhabitants to make preparations. The intense monsoon season has also brought extensive flooding to Cambodia and northeastern India over the last couple of months, and destroyed a significant part of SE Asia’s rice crop. On the other side of the planet, heavy rain and flooding has been affecting Mexico, El Salvador, Costa Rica, Honduras, Guatemala, and Nicaragua. Jeff Masters reported that in the ten days up to October 20th, Huizucar in El Salvador received an astonishing 1.513 metres of rain.

At first glance, it looks like a continuation of the remarkable series of extreme weather events — especially heavy rainfall and flooding — that we’ve seen over the last few years. But apart from the human suffering and economic dislocation being experienced around the world, it appears there’s another interesting consequence of all this precipitation — it’s causing global sea level to fall.

I stumbled across this idea in a NASA news item released back in August, and referred to it in the last edition of The Climate Show, but I think it’s worth developing the idea a little further. Here’s what NASA had to say:

[Josh] Willis said that while 2010 began with a sizable El Niño, by year’s end, it was replaced by one of the strongest La Niñas in recent memory. This sudden shift in the Pacific changed rainfall patterns all across the globe, bringing massive floods to places like Australia and the Amazon basin, and drought to the southern United States.

Data from the NASA/German Aerospace Center’s twin Gravity Recovery and Climate Experiment (Grace) spacecraft provide a clear picture of how this extra rain piled onto the continents in the early parts of 2011. “By detecting where water is on the continents, Grace shows us how water moves around the planet,” says Steve Nerem, a sea level scientist at the University of Colorado in Boulder.

So where does all that extra water in Brazil and Australia come from? You guessed it–the ocean. Each year, huge amounts of water are evaporated from the ocean. While most of it falls right back into the ocean as rain, some of it falls over land. “This year, the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year,” says Carmen Boening, a JPL oceanographer and climate scientist. Boening and colleagues presented these results recently at the annual Grace Science Team Meeting in Austin, Texas.

The story included a couple of graphs to illustrate the point. Here’s the drop in sea level, as recorded by satellite:

NASAsldrops

And here’s where the GRACE satellites showed it ended up.

NASAGRACEwater

When I first read the NASA article, I was amazed. Perhaps I shouldn’t have been. After all, lots of things can cause sea level to rise and fall — thermal expansion, ice melt (or freeze), and so on. During ice ages lots of ocean ends up on land in the form of the great ice sheets that are built by accumulating snowfall. But this is, to coin a phrase, a really neat demonstration of an interesting effect — one that we can only begin to appreciate because of the application of truly remarkable technology.

So what’s happening now? Here’s the latest sea level chart from the University of Colorado (data to Sept 19th):

CUSLR

There’s been a slight upwards tick over the last few months, but no dramatic surge back towards to the trend line. That suggests to me that the processes that caused the drop in the first place are still operating. The population of Thailand might agree…

Eventually, as Josh Willis says at the conclusion of the NASA article, the floodwaters will run off the land and return to the ocean, La Niña will swing back to El Niño, and sea level rise will resume its upwards trajectory. With La Niña likely to stay in place through the southern summer, it will be some time before El Niño returns and imposes its own pattern on the world’s weather. But when it does we could be in for a wild ride as sea level surges and global temperatures reach new peaks. We live in interesting times.

[Update 27/10] Flash flooding has ripped through Liguria and Tuscany in Italy. Both the Guardian and BBC videos open with water roaring down the streets of (I think) Monterosso — a place I visited in September. Dublin has also experienced torrential rain and flash flooding in the last few days: video here. Intensification of the hydrological cycle anyone?

[Grateful Dead]

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]

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):

extreme_events_mid.gif

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...]

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