by Professor James Renwick
Is climate change going to wipe out humanity over the next 10 years? Prof Jim Renwick doesn’t think so…
Ecologist Guy McPherson has been touring New Zealand for the past couple of weeks, explaining why humanity has only 10 years to live (a kind-of Ziggy message that has immediate appeal to me). After his appearance on the Paul Henry breakfast show, I was called by TV3/Newshub for comment. Based on my understanding of climate change science I said that though the situation is very serious — dire even — extinction in 10 years is not going to happen. When I gave my remarks to Newshub, I knew little about McPherson but I understood that he is a very knowledgeable biologist who should not be dismissed lightly.
So, what’s the story? Is McPherson right? Is the IPCC woefully conservative and keeping the truth from us all? I had the opportunity to hear Prof McPherson speak in Paraparaumu on Saturday (Dec 10th) to get more insight into what his views really are. It was a very interesting presentation, and a very interesting discussion with the audience of 50-odd Kāpiti coasters who showed up to hear him. As the old saying goes, extraordinary claims require extraordinary evidence. What we heard was extraordinary for sure, but was not too convincing in terms of evidence.
Extinct in 10 years?
McPherson’s presentation was as much philosophy as science. Much of his message is built around the undeniable truth that we are all, one day, going to die. Hence, we would do well to live in and for the present, express our love to those close to us, and act rightly according to our own beliefs and principles. Excellent advice, and a great philosophy for living well, what you would be told in any number of “life-coaching” books. Where he differs from most is in saying that all of us, i.e. all of humanity, and most other species, will be extinct in 10 years or so. Why is that, you might ask?
The detail on his view of the climate system can be gained by reading his “monster climate change essay”. A briefer overview, and what he bases much of the scientific side of his presentation on, comes from a blog post at the Arctic-News blogspot site, written by “Sam Carana” (not his or her real name – you know why). This piece suggests that the globe will warm around 10°C in the next decade, and since such warming was associated with mass extinctions in past epochs, humanity and most vertebrates etc will be toast very soon.
The blog post starts by assuming the February 2016 global mean temperature represents the current average temperature of the earth, then throws in another 0.8°C for pre-1900 (0.3°C) and unavoidable future (0.5°C) warming. This is pushing it, as February was the warmest single month on record (in difference from normal terms), several tenths of a degree above the annual mean for 2016, and the amount of unavoidable future warming is small (maybe 0.1°C?), should greenhouse gas emissions stop now.
Shaky grasp of science
However, the next steps are where McPherson’s grasp of the science seems shakiest. Cutting aerosol pollution to zero (as would happen when and if industrial society falls over) will unmask another 2.5°C of warming. This is a factor of ten too large, as the actual amount would be around 0.25°C by current best estimates (see figure 10.5). Reduced planetary reflectivity (albedo) from loss of Arctic ice will add another 1.6°C (perhaps in the Arctic, but not in the global mean), plus the water vapour feedback, seafloor methane release etc will add an extra 3.5°C. So that’s another 7.5°C on top of essentially where we are at now, giving a total of about 10°C warming compared to pre-industrial, assumed to happen in the next 10 years. Then, all the world’s nuclear reactors melt down, and we are all extinct.
The way Guy McPherson talks about water vapour shows his sketchy grasp of atmospheric physics. He states that most of the water vapour in the atmosphere is above 6km altitude, where it “acts like a lens” to heat the earth. Most of the water vapour is actually in the lowest few kilometres of the atmosphere, as the upper troposphere is too cold to support much water vapour. Perhaps he’s thinking of the release of latent heat in the tropics, which does occur mostly in the upper troposphere, leading to a warming “hot spot” in the tropical upper troposphere as greenhouse gas concentrations rise (See AR5 WG1, figure 12.12).
Water vapour is of course a critically important part of the climate change story and is the main amplifying feedback of greenhouse gas increase. McPherson is trained as an ecologist, so it’s no surprise that he isn’t totally on top of the vertical profile of water vapour in the atmosphere. But, if your public profile depends on your image as an authority on “global warming”, you would do well to be clear on the science.
Now, the potential consequences of climate change, and the lurking feedbacks such as Arctic methane release and other carbon cycle changes, are an extremely serious concern, one that I think the governments of the world have yet to really take on board. The risks of severe food and water shortages, population displacements and conflict over resources, already has the potential to endanger hundreds of millions of lives – even with another degree or two of warming (as outlined in the last IPCC report). But truly catastrophic and extremely rapid climate changes do not look to be on the cards, at all.
Bad but not that bad!
Earth’s climate is not poised for “runaway” change (as per Venus), nor is there any clear indication from the geological record that the climate system is so sensitive to greenhouse gas increase that 10°C of warming in 10 years is imminent, or even possible. The climate community of course does not know everything about past climate change nor about what the climate system is capable of if pushed hard. But, the extinction in 10 years scenario is really at the outer edge of speculation about the future.
Even without imminent extinction, the consequences of climate change are more than dire enough to galvanise us into action. My perception is that concerted global action within the next decade can avoid the worst consequences. The flip side is that business as usual, even for another ten years, could lock in changes that do indeed put global society at risk and threaten possibly hundreds of millions to billions of lives. Not instant death but a very unpleasant future for a very long time. I find that prospect plenty scary enough, and it leaves room for us to take action. Let’s take it.
Gareth adds: McPherson’s views are a good example of real climate “alarmism”. Deniers love to paint the IPCC or consensus position on climate change as alarmist, thereby implying that their rejection of that consensus is somehow sensible or moderate. McPherson’s stance shows that to be a mere debating trick. The truth, of course, is that by rejecting the consensus view on what we can expect, deniers are as extreme as McPherson — polar opposites, but just as guilty of exaggeration.
James Renwick is a climate science and Professor of physical geography at Victoria University, Wellington.