Sunday, October 25, 2015

Dyson's Sphere of Influence, Part 2

(This is part 2 in a series of posts. Part 1, Part 2,  Part 3)

I've been looking at climate modelling studies with a renewed vigor since reading Dyson's statement that projections of global warming are based on flawed climate models. It's not only Dyson's comment that provokes me. The climate models fallacy is promoted by many private interest groups trying to influence the COP21 climate talks in November. For example, the Cornwall Alliance is a group of faith-based, pro-fossil fuel, evangelicals:
Many fear that carbon dioxide emissions from fossil fuel use endanger humanity and the environment because they lead to historically unprecedented, dangerous global warming....
Computer climate models of the warming effect of enhanced atmospheric carbon dioxide are the basis for that fear. -- An Open Letter on Climate Change to the People, their Local Representatives, the State Legislatures and Governors, the Congress, and the President of the United States of America. Cornwall Alliance, 2015. 
This letter also cites a lot of inaccurate and outdated information on the instrumental record, and credits the Judeo-Christian Heritage with the rise of the modern scientific method and dismisses computer modelling as not a reliable avenue of research.

So, I want to share what fictions climate models help us to maintain, and I didn't have to dig deep for good example, rather, just open my mailbox. My most recent issue of Nature (15 Oct. 2015) reports on modelling the loss of continental ice from Antarctica:



The article cites four paleoclimate studies that connect global warming in the past with the loss of Antarctic ice (three of which I've read). One of these articles is open access, so I'll use it to discuss underlying assumptions driving our computer modelling study:
 Levermann's paper cites the following sea level rises based on paleoclimate studies:
For the Eemian Interglacial (115,000 years ago): "We thus assign a possible sea-level range of 5–9 m higher than present...."
For Marine Isotope Stage 11 (a time 400,000 years ago when orbital configurations most resembled those of our current Holocene): "We thus assign a possible sea-level range of 6–13 m higher than present...."
For the Pliocene (over 1 million years ago): "We thus conclude that sea level was at least 7 m above present during mid-Pliocene warm periods"
These estimates converge around 7 meters, or 21 feet. This is big. It requires relocating hundreds of millions of coastal inhabitants, including the evacuation of some nations. Therefore, it's important to know the following:
  • How fast can the sea level rise occur?
  • What global temperature makes the outcome unstoppable?
  • What pathway is there to preventing a return of some or all of this paleo-historical sea level rise. (I say "paleo-historical" to emphasize that paleoclimates are history, though not recorded by humans.) 
To answer these questions, we can take what we know about the physics of ice sheets and try to model the behavior of the ice sheet to various levels of warming.  I created a diagram to summarize the many of the factors to include in an ice sheet model:


Golledge et al. put special emphasis on understanding how the topology of the shoreline maintains ice shelves that in turn slow the flow of ice sheets into the ocean. Golledge et al. clearly acknowledge that their resolution on topography is coarser than what would be ideal, due to limits on computer processing power. According to a reviewer of the article, their results represent a best case scenario:
...Golledge and collegue's simulations might represent a best-case scenario for future sea-level rise. (The long future of Antarctic melting, Robel, Nature 15 Oct. 2015)
A best case for what? Best case means minimum rise of sea level, the best that we can hope for. This study describes what rate Antarctica will contribute to sea level rise under emissions scenarios that stabilize global temperatures from 2.6 to 8 degrees C above pre-industrial. The paleoclimate background makes a strong case that at least 7 meters of sea level rise should be expected. But by modelling the mechanics of ice loss, we can get some useful information on the following:
  1. We are probably committed to a rise of 0.5-3 meters by 2300 CE. 
  2. If we do not reduce emissions according to the 2.6 degree scenario, the ice shelves currently trapped in Antarctica will collapse and allow a steady flow of ice loss to the ocean till at least 3000 CE. This is a lot of coastal adaption to push onto nearly a thousand years of future generations. 
  3. The 2.6 scenario requires cutting our emissions by 2050 to half our emissions level in 1990. No doubt these are big cuts, but without them, we are committing future generations to nearly a thousand years of moving coastlines.
So, my big point is that climate models are the only way we have of knowing how big our window of opportunity is to avert costly and dangerous climate change. One may believe climate models are responsible for the fiction that global warming is dangerous, but this is backwards. That we can escape the consequences of spiking the atmosphere with CO2 is the fiction, and modelling gives us a working plan.

My opening may have criticized the evangelical community. Many conservative Christians side with the policies of the Cornwall Alliance. But I know enough evangelicals to know that many of them are present where natural disasters strike, e.g., rebuilding homes in poor nations and helping relocate refugees (something our nations don't have the best track record at). Christian charity is great and noble, but my instincts tell me that it's not as noble if you use ignorance and confusion to make the work necessary.

2 comments:

Cajundaddydave said...

I think we can all agree that the earth is warming and if we understand radiative physics, we also agree that man made CO2 plays a role in that warming. The $10 questions yet to be answered are: how much warming are we in for? And will that bring positive or negative consequences. The true, unbiased, scientific answer is, we don't really know.

We have a lot of speculation but very little consistent verifiable data to narrow our error bars which are currently about as wide as the Pacific Ocean. If climate sensitivity is on the lower end of estimates, we will see warming similar to the Climate Optimum Period 3000BC when plants, animals, and man thrived. This is consistent with experimental data on CO2 and our temp data. All other estimates require highly speculative feed backs which are not consistent with the last 30 years of temp data. Our models have a problem. Feed backs and changes in the water cycle are still well beyond our understanding. When in doubt, trust hard data over speculative estimates every time.

This characterizes my difficulty with the doom and gloom predictions. They require far too many speculative leaps and ignore empirical data suggesting a different outcome.

jg said...

Thanks, Cajundaddydave, for your well-reasoned comment. I agree that doom and gloom may not be helpful framing. I'd replace it with stress, strife, and costs. Humanity's population is the big problem, and though we have the resources to adapt, I fear it won't play out well when there are 9+ billion people.

I also agree with the uncertainties you cite. If climate sensitivity is low, we may just get an intensified hydrological cycle. If high, I don't have a good idea of what to expect.

In part 3 I'm dabbling with Dyson's second heresy, the wet Sahara.
jg