Disastrous sea level rise past 2100 removes the "uncertainty monster"

Further to my complaint about climate change policy considerations misleadingly concentrating on effects up to 2100, I see that last year Andy Revkin responded (in his overly mild way) to Bret Stephen's "let's just wait to see what is happening with more certainty" column in the NYT with a piece in ProPublica. 

The problem for Revkin is that his thing for criticising environment advocates for not being careful enough with details enabled him to be cast as a supporter of the Judith Curry style "do nothing, it's all too uncertain" crowd.   But, in the article linked above, he talks about the really big picture, going beyond 2100, to show that he's not really aligned with the "do-nothings":

Kenneth Caldeira, a much-published Carnegie Institution climate scientist, now divides his time between studying unfolding impacts of climate change, including on coral reefs, and research on possible clean-energy solutions — and occasionally fact-checking the internet with others. On Saturday, he posted a critique stressing the dangers in the Stephens interpretation of uncertainty and lack of attention to what is clearly known:

“Bret Stephens writes of ‘sophisticated but fallible models’ as if ‘sophisticated but fallible’ gives one license to ignore their predictions. A wide array of models of different types and levels of complexity predict substantial warming to be a consequence of continued dependence on using the sky as a waste dump for our CO2 pollution. It doesn’t take much scientific knowledge to understand that the end consequence of this process involves approximately 200 feet of sea-level rise. We already see the coral reefs disappearing — a predicted consequence of our CO2 emissions. How much more do we need to lose before recognizing that our ‘sophisticated but fallible models’ are the best basis for policy that we have?”

Caldeira is hardly alone in this view. There are entire issues of scientific journals devoted to understanding and responding to deep climate change uncertainty.

So those calling for nothing but delay and debate, as Environmental Protection Agency administrator Scott Pruitt did on MSNBC in March, have some explaining to do. What is it they are waiting for?

In fact, if anything, the core challenge of global warming is both clearer and vastly bigger than most of those debating it either understand or care to talk about. What is perhaps the most important scientific analysis pointing this out went largely uncovered early last year — a paper describing, with essentially no uncertainty, the enormous “consequences of twenty-first-century policy for multi-millennial climate and sea-level change.”

I hope Stephens will stay on this issue, but perhaps looking beyond the uncertainty red herring toward common-sense ways to build a durable relationship with energy and climate that any conservative can embrace.

So, lets go the 2017 paper in Nature Climate Change which is at that last link.  (I don't think I have posted about it before.)

Unfortunately, apart from the abstract and supplementary material, it's behind a paywall, and I have not yet been able to find a full free copy at anyone else's site. But, the key results were summarised in some reporting, Chris Mooney at the Washington Post being a decent example:

From 1750 to the present, human activities put about 580 billion metric tons, or gigatons, of carbon into the atmosphere — which converts into more than 2,000 gigatons of carbon dioxide (which has a larger molecular weight).

We’re currently emitting about 10 gigatons of carbon per year — a number that is still expected to rise further in the future. The study therefore considers whether we will emit somewhere around another 700 gigatons in this century (which, with 70 years at 10 gigatons per year, could happen easily), reaching a total cumulative emissions of 1,280 gigatons — or whether we will go much further than that, reaching total cumulative levels as high as 5,120 gigatons. (It also considered scenarios in between.)

In 10,000 years, if we totally let it rip, the planet could ultimately be an astonishing 7 degrees Celsius warmer on average and feature seas 52 meters (170 feet) higher than they are now, the paper suggests. There would be almost no mountain glaciers left in temperate latitudes, Greenland would give up all of its ice and Antarctica would give up almost 45 meters worth of sea level rise, the study suggests.

Still, anyone observing the world’s recent mobilization to address climate change in Paris in late 2015 would reasonably question whether humanity will indeed emit this much carbon. With the efforts now afoot to constrain emissions and develop clean energy worldwide, it stands to reason that we won’t go so far.

“With Paris, it does get us off the exponential growth, and we might level off at 2,000, 3,000 gigatons,” said Pierrehumbert.

Still, what’s striking is that when the paper outlines a much more modest 1,280-gigaton scenario — one that does not seem unreasonable, and that would only push the globe a little bit of the way beyond a rise of 2 degrees Celsius over pre-industrial temperature levels — the impacts over 10,000 years are still projected to be fairly dramatic.

In this scenario, we only lose 70 percent of glaciers outside of Greenland and Antarctica. Greenland gives up as much as four meters of sea level rise (out of a potential seven), while Antarctica could give up up to 24. Combined with thermal expansion of the oceans, this scenario could mean seas rise an estimated 25 meters (or 82 feet) higher in 10,000 years. There is, to be sure, “a big uncertainty range on that prediction,” Pierrehumbert said by email.

Once again, a key factor that could mitigate this dire forecast is the potential development of technologies that could remove carbon dioxide from the air and thus cool down the planet much faster than the Earth on its own can through natural processes. “If we want to have some backstop technology to avoid this, we really ought to be putting a lot more money into carbon dioxide removal,” Pierrehumbert said.

Pierrehumbert said he believes that we will manage to develop such a technology in coming centuries, so long as human societies remain wealthy enough — but he added that we don’t know yet about how affordable it will be.

The new study fits into a growing body of scientific analysis suggesting that human alteration of the planet has truly brought on a new geological epoch, which has been dubbed the “anthropocene.” Taking a 10,000-year perspective certainly reinforces the geological scale of what’s currently happening.

Interestingly, I note from the supplementary material that the modelling work which forms the basis of the paper did include using runs with a Equilibrium Climate Sensitivity of 1.5 degrees to see what difference that made - and that figure is below the recently revised Nic Lewis/Judith Curry median estimate discussed in my last post.  (It also references modelling at an assumed ECS of 3.5 degrees.)

As I cannot read the whole Nature Climate Change paper (jeeez, I ask again of philanthropists - if you want material widely read, make it free) I don't know for sure what difference the lower ECS may have made for their 10,000 year sea rise estimates.  But clearly, they did take some account of the possibility of a low end ECS.  One suspects that in the long run, it doesn't make that big a difference.

OK, I hear some reader, presumably Jason Soon, saying "if even the low end total emissions still gives rise to 25 m sea level rise, doesn't this support my argument that it's too late to do anything effective and we will just have to deal with this technologically?"

But there are two important points to make in response:

1.   Look at the graphed rate of sea level rise using the different scenarios, which I get from the supplementary material to the paper:

Even at this low resolution, it's clear that the rate of sea level rise in the first 1,000 years is sharply faster in the next higher carbon emission scenario they considered than in the lower, achievable, scenario they worked on.  (And I'm just guessing here, but I suspect that even on the most optimistic guess, the process of removing CO2 back to 20th century levels will be a project requiring centuries of effort.)

2.  Surely that means that that the work involved in a technological fix can be undertaken at slower rate, which also surely means at less cost and less risk of failure (given that there is more time to adjust, change and improve the technological fix.)   And this would apply regardless of  whether the fix be by CO2 extraction or the (much, much more potentially environmentally risky*) use of something like spraying sulphates into the upper atmosphere. 

The point is - even these long term dramatic sea level change predictions do not mean that defeatism is an appropriate response.   That actually seems to be the motivation of the authors of the paper, too.

It makes sense that taking steps now to ensure that total carbon emissions are limited gives more chance to reverse the millennia scale disastrous sea level rises that are bound to happen if you keep pumping carbon into the atmosphere. 

I know that there is a libertarian idea that (when they are not busy disgustingly actually promoting climate change denial, as is the wont of a large section of the movement) the right way to deal with climate change is to race ahead with economic growth, because riches can deal with all climate change problems.  (Air condition the Third World, develop fusion power, spray sulphates into the air.)

That idea is fanciful for many reasons (it is at heart, a statement of faith not dissimilar to Evangelicals who can't believe that God would let humans destroy the Earth, and deserves a post of its own); but for now, the point here is to make it clear that if ripping ahead with economic growth means releasing high end CO2 emissions, they are advocating for a dramatic long term problem that, if not addressed, will literally re-write the shape of the inhabitable globe and inundate scores of those things we currently consider cultural and economic centres of civilisation - cities.

They will also be kicking the economic can for any possible solution to that down to future generations.   The least you would think they could do is to agree to give their descendants more time to deal with it.  (No one has any reason to think that removal of CO2 is going to be easy.)



 

*  Apart from very uncertain regional effects, the biggest worry is that if the program is stopped, the planet would undergo rapid heat increase that species - including humans - would not have time to deal with.  Read this article at Science.