February 2013

It's Time to Bury the "Two Degrees Celsius Temperature Rise is Safe" Meme

The journal Science has just published a paper by Anton Vaks, O. S. Gutareva, S. F. M. Breitenbach, E. Avirmed, A. J. Mason, A. L. Thomas, A. V. Osinzev, A. M. Kononov, and G. M. Henderson about historical periods of Siberian permafrost melt, entitled Speleothems Reveal 500,000-Year History of Siberian Permafrost.

Unfortunately it's behind a paywall (grumble, grumble), but the abstract and reports give us enough information to be very concerned. From the paper's abstract:

Growth at that time indicates that global climates only slightly warmer than today are sufficient to thaw significant regions of permafrost

Siberian permafrost thaw warning sparked by cave data, reports the Beeb, who mention temperatures 1.5ºC above the present, without qualifying 'the present'. Such lack of rigour is a godsend to the climate change deniers, who doubtless will be equally sloppy. But read on.

Scientific American elaborates:

The details of the study reveal that conditions were warm enough even in Siberia for these mineral deposits to form roughly 400,000 years ago, when the global average temperature was 1.5 degrees Celsius higher than present. It also suggests that there was no permafrost in the Lena River region at that time, because enough water seeped into the northernmost cave to enable roughly eight centimeters of growth in the formations.

That was, in fact, the last time the formations in the Ledyanaya Lenskaya Cave grew, although other caves further south showed multiple periods of growth coinciding with other warmer periods. "That boundary area of continuous permafrost starts to degrade when the mean global temperature is 1.5 degrees C higher than present," Vaks explains. "Such a warming is a threshold after which continuous permafrost zone starts to be vulnerable to global warming."

Since Vaks's present is the "preindustrial late Holocene," that means the planet is already more than halfway there, having experienced 0.8 degree C warming to date. Such a thaw is no small matter, given that permafrost covers nearly a quarter of the land in the Northern Hemisphere and holds roughly 1,700 gigatonnes of carbon—or roughly twice as much carbon as is currently trapping heat in the atmosphere. Much of that carbon would end up in the atmosphere if the permafrost was to thaw further.

...

"The potential impact of these results extends to global policy: these results indicate the potential release of large amounts of carbon from thawed permafrost even if we attain the 2 degree [C] warming target under negotiation," says Kevin Schaefer, a scientist at the U.S. National Snow and Ice Data Center, who has also studied permafrost but was not involved in this, in his words, "great science" effort. "Permafrost thaws slowly and the carbon will be released into the atmosphere over two to three centuries."

Read that again. An average global temperature rise of 1.5ºC above pre-industrial levels would be enough to cause significant permafrost melt.

Time to stop talking that "2ºC rise is safe" nonsense, a myth I debunked over six years ago.

Postscript, March 22nd, 2013

Dr Chris Shaw, aka @kalahar1, has an interesting post today on Talking Climate, "Time to ask the public: Why 2 degrees?"

The most important determinants of the two degree limit are the social settings in which the deliberations are conducted. Under conditions of empirical uncertainty, such as those characterising climate change projections, institutional setting alongside social and political values come to play a determining role in defining what is considered ‘true’.

Achieving group uniformity becomes an increasingly important determinant of decision making the greater the level of uncertainty. The groups that have defined the two degree dangerous limit are powerful political and technical actors. The idea of a limit has been defined according to the interests of those groups making the decisions.

What does climate change look like if the available information is interpreted by the values of citizens? The purpose of such an exercise would not be to agree a new ‘dangerous’ limit. Rather, it would be to allow publics to better understand the decision making process and see how uncertainty - rather than offering a reason for doing nothing - actually shows that there is not a single dangerous limit, the avoidance of which means safety from harmful climate impacts.

Postscript, December 2nd, 2013

Also read this summary from David Spratt - Is climate change already dangerous (5): Climate safety and an unavoidably radical future (and the rest of the series).

And today's hot story: 2C rise will be a disaster say leading scientists

Postscript, October 1st, 2014

Controversy erupted today when David Victor and Charles Kennel, writing in Nature, suggested that we should ditch the 2°C warming goal.

Climate Controversy: Does the 2 Degree Goal Need to Go? asks Stephanie Pappas at Livescience.

Limiting global warming to 2°C – why Victor and Kennel are wrong argues Stephan Rahmstorf over at RealClimate.

Victor and Kennel: re-arrange the deckchairs, says William M. Connolley.

I hadn't seen this one before, but it's worth a read: Defining dangerous anthropogenic interference. A handy background by Dr Michael E. Mann to the whole two degrees thing.

Joe Romm nails it in 2°C Or Not 2°C: Why We Must Not Ditch Scientific Reality In Climate Policy.

My own view, for what it's worth, is that it's hard to avoid the conclusion that 2°C is way too high, and that 1°C is the better, more cautious target.