More on Climate Change from Mark Cochrane….
There, a title that should be red meat to those who want this issue of AGW to be minimized. What does it mean though?
In the last few years we have been treated to a series of alarming findings that basically indicate that the entire Western Antarctic ice sheet is now doomed to fall into the ocean and melt (Rignot et al. 2014, Joughlin et al. 2014). A recipe for 4.8m of sea level rise or so. The big question is, just how fast will this process occur, decades, centuries, millennia?
Scientists gravitate to such questions quickly and try to answer them. So, this month we get Ritz et al 2015 trying to do just that. To do so they basically took ice flow simulation models, running them many times and in many ways, to test the sensitivity of various parameters. In this case, they compiled 3,000 model simulations. That gave them a distribution of possible ice outflow rates. What they then did that was clever; they used 20 years of satellite data to try to constrain the model simulations to weight the ones that performed most realistically more highly than the ones that performed poorly. Models meet reality. The paper was in Nature so it got a lot of press and we got stories like this:
Scientists say the contribution of a melting Antarctica to sea-level rise this century will be significant and challenging, but that some nightmare scenarios are just not realistic.
Their new study models how the polar south will react if greenhouse gases rise at a medium to high rate.
The most likely outcome is an input of about 10cm to global waters by 2100.
But the prospect of a 30cm-or-more contribution – claimed by some previous research – has just a one-in-20 chance.
Ok, what most of the public sees is, ‘sea level rise of 10 cm by 2100’ and they infer that more than that is not likely to happen. Almost no one who reads the BBC article will ever bother to dig up and read Ritz et al 2015 (conveniently linked here for the second time…). Alas, many of those who do try to read it will either give up in frustration or misinterpret it. From the quote above, we see that the 30cm or more amount of potential sea level rise still has a 1 in 20 (aka 5%) chance of occurring. Not exactly trivial. Do you feel lucky? From figure 2 in the actual Nature paper you can learn that although 10cm is the most likely amount of sea level rise that there is a 50+% chance it will be exceeded. There is also a 20% chance that 20cm will be exceeded. Again I ask, do you feel lucky?
I don’t say these things to belittle what looks to be a nice piece of scientific work. I am simply showing you that science is a process in work and that it doesn’t lend itself to simple conclusions. From the BBC article above “The most likely outcome is an input of about 10cm to global waters by 2100” what they don’t provide is the qualifier that this is true only — IF(!) the last 20 years of observations are a good proxy for what the next 85 years of ice sheet movement are going to be like. Who is it that says that the next 20 years are not going to be like the last 20? [in case any DTM reader doesn’t know, it’s Chris Martenson] It is also dependent on the models getting the physics and processes right. There is also this little detail.
There would of course be separate and additional inputs from Greenland and other ice stores, and from the general expansion of waters in the warming oceans.
That is a BIG caveat. All of that additional melting will act to lift the ice sheets of Antarctica where they pour into the ocean, speeding up the decay process further. So ultimately that statement “The most likely outcome is an input of about 10cm to global waters by 2100” should probably be understood as saying ‘The most likely outcome is an input ofat least 10cm to global waters by 2100′. Please note that in the actual scientific paper that the authors do not try to spin their findings as being conclusive. In the conclusion of the Nature paper they say “But, given current understanding, our results indicate that plausible predictions of Antarctic ice-sheet instability leading to greater than around half a meter of sea level rise by 2100 or twice that by 2200 would require new physical mechanisms” Note the parts I emphasized.
In any case, you can rest assured that several other scientists are even now working up ways to test these findings. In science, publishing is only the start of the process. Your work has to stand up to every criticism and test that other scientists can devise. Only when exhaustion takes over will your ideas be accepted. It took about 100 years of this for Anthropogenic Global Warming (AGW aka Global Climate Change) to be accepted by just about every scientist in the field. The last serious attempt to test it was by Berkeley Earth (link) who despite great hopes and funding from Koch brothers and their ‘skeptical’ company ended up proving AGW to be all too real, yet again…