10000 Years

A paper by lead author Peter Clark argues that the impact of climate change will extend over ten thousand years. From Chris Mooney's article:

From 1750 to the present, human activities put about 580 billion metric tons, or gigatons, of carbon into the atmosphere ... . 

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. 

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 ... . 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 ... . 

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 [coauthor Raymond] 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.

Meanwhile, the sea ice extent in the Arctic Ocean was the lowest for any January in the satellite record.

Update (February 28):  A paper by lead author Joeri Rogelj published in Nature Climate Change concludes that the carbon budget for fossil fuel emissions has been overestimated by 50 to 200 percent. The most appropriate budget is 590 to 1240 gigatons carbon dioxide to remain under 2 degrees Celsius warming. (But this seems consistent with the figure cited by McKibben.)