Were I come from, we measure ice by mass (for which volume is a decent proxy). Methinks your title is a bit of an understatement.
Yep, three-quarters of the volume gone. Yet the surface area is what we can track day-to-day, and that matters too.
I've got an acronym; FUBAR.
Nothing to panic about, Chris, it's not like the melting Arctic is unlocking vast reserves of permafrost carbon that are already contributing a chunk of CO2 emissions the size of Pakistan.http://www.bitsofscience.org/siberian-arctic-yedoma-permafrost-carbon-release-6213/
Yep, it's the land permafrost.I'm working on a blog post to outline why I've moved forward my assessment of when we'll see the first sea ice free summer. I've gone from 'late 2020s at earliest, but more likely after 2030', to 'almost certainly this decade, and could be a virtually sea ice free state (<1M km^2 CT area) within 3 years'.That's not changed my opinion on marine clathrates, I still think it's a problem that will turn out to be chronic, not catastrophic. But land permafrost is a whole different issue. With an early transition we can expect massive land warming and consequent melt of permafrost. Temperatures will rise higher and faster than ocean temperatures.What's worrying is that the main paper in this respect shows that modelled early melt of pre-warmed permafrost brings the whole schedule significantly forward in time.Lawrence et al 2008, Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss.
"That's not changed my opinion on marine clathrates, I still think it's a problem that will turn out to be chronic, not catastrophic."I don't disagree at all. The question becomes, with so many large carbon feedbacks on the table, how many rounds of Russian roulette are we going to play? At last count, you had the methyl hydrates of the ESAS, the land permafrost of the Arctic, the deeper methyl hydrates in the Arctic, the Amazon which must not die back, and lately more methane and CO2 under the WAIS and the EAIS both. All of which need to stay in their places and not misbehave for humans to have the honor of wrecking their own climate gradually over a few centuries.I think you're exactly right, that these various carbon-cycle feedbacks are shaping up to be a chronic, rather than a catastrophic problem. Let me tell you what frightens me about that. Absent carbon feedbacks, suppose we ignore mitigation or take halfhearted stabs at it until finally we suffer a global economic and social breakdown, in the course of which a couple of billion people die and anthropomorphic emissions fall by 80 or 90 percent.In the course of things as we have previously imagined it, that's the point at which atmospheric CO2 starts to fall, and although the consequence will be with us for a long time, there's little to prevent our civilization from rebuilding itself.But suppose by the time we have 3-4C of warming, we have 10-15 Gton/year of carbon seeping out of these various sinks, emissions that will continue for centuries. Atmospheric CO2 continues to rise. Global warming continues to get worse every after there is no longer a global civilization to cope with its impacts.Humanity is then on a downward trajectory from which we might not recover for a long time. Scary, no?