Things Going Fast
Some revisions here 25 Dec. 2012
If you are here looking for Mahlman memory piece, it is here
An old Christmas Piece: Christmas at the Seven ElevenThis entry has been updated with a paragraph on the paper about West Antarctica released after the blog was first published.
In 2007 I started this blog with the release of the Intergovernmental Panel on Climate Change Fourth Assessment Report
. At the time of that report, the evolving scientific understanding made it clear that the melting of sea ice and ice sheets had been underestimated in the papers that were used in the 2007 report. A major reason for that underestimation was due to the simplicity of the way the freezing and thawing of large masses of ice were represented in the climate models. Freezing and thawing of large masses of ice on Earth is not like an ice cube melting away on the kitchen counter at normal room temperature. Rather, it is a far more dynamic process, with, for example, water from the ice melt collecting on top of an ice sheet, then flowing through the ice in a way that accelerates melting. In the ocean, the seawater accelerates sea ice melting through essentially stirring the ice in warmer water. If you go back to the ice sitting on the kitchen counter, you can speed up its melting by fanning it with warm air or by placing it in a glass of water and stirring it. In all of these cases heat is being carried to the ice more effectively than in the case of the static cube sitting on the counter.
Of course this stirring process melts ice if the temperature of the environment is warmer than the freezing point of water. If it were getting colder, then stirring could cause accelerated freezing – ice growth. That could be thought of as removing heat from the water and allowing it to freeze. We are set up here with a situation that in a warming environment, ice melts, and if we stir it up, we bring more heat to the ice and it melts faster. This is an example of a positive feedback, it gets hot and causes melting, and the response of the Earth is such that it accelerates melting. The opposite of a positive feedback is a negative feedback, if it gets warmer, then the systems reacts by cooling faster to bring it back to its original temperature.
There was a paper
by Gerard Roe
and Marcia Baker
in 2007 that made a convincing argument that when taken as whole, the current state of the Earth’s climate was that if it got warmer, then the response of the Earth would be to accelerate that warming. When I have been asked over the past five years about my opinion whether the models are right, then my answer has been that most of the evidence suggests to me that we have underestimated the rate of warming.
At the top of my list of observational evidence is what’s happening in the Arctic. There was a recent paper in Science Magazine
by Andrew Shepherd
and coauthors entitled A Reconciled Estimate of Ice-Sheet Mass Balance
. They looked at the mass budget of Greenland ice sheets and concluded 1) there was a lot of consistency between different measurements, and 2) the rate of melt was speeding up. (NBC News
and news summary by Kerr in Science
) The 2012 Arctic Report Card
documents numerous records in the melting of ice and snow as well as odd changes in ecosystems. This melting in the Arctic is a signal of accumulating heat. It is simply a fact of physics, that all of the heating of the Earth does not have to go into heating the surface air temperature. As we learn more, it goes more effectively into melting ice than we perhaps modeled 10 years ago. It goes into the ocean. These large changes in the Arctic are stunning evidence of a warming planet. (see this recent video, Glaciers and Global Warming
by my faculty colleague Jeremy Bassis
There is increasing evidence of warming in the Antarctic as well. Because of the geography and the details of heat transported by the ocean, the Antarctic and the Arctic behave quite differently. However, we expect the southern polar regions, also, to have amplified warming compared with the tropics and middle latitudes. We do not have as many measurements in Antarctica as in the Arctic. Since this blog was first published, David Bromwich
and colleagues published the paper, Central West Antarctica among the most rapidly warming regions on Earth
, in Nature Geoscience
. This paper is a complex study, which uses models to reconstruct and complete the temperature record in West Antarctica since the 1950s. They explain in detail their evaluation techniques and search for cause and effect of the regional warming that they find. Their ultimate conclusion is that West Antarctica is warming rapidly, especially in summer. They point to the summer of 2005, which saw significant surface ice melting, and warn that the temperature is getting to the point that melting might accelerate. This is especially significant in West Antarctica because the base of the ice sheets there are below sea level and especially vulnerable.
Feedbacks – it would be nice to hope that just as we underestimated the melting of ice in the period up to the 2007 IPCC Fourth Assessment Report – it would be nice to hope that we had somehow neglected or misrepresented some form of negative feedback in some fundamental way. The Roe and Baker paper referenced above, for example, suggests that such a misrepresentation of a negative feedback is unlikely.
Our most effective negative feedback mechanism is associated with cooling by clouds. At the risk of piling on, John Fasullo
and Kevin Trenberth
did an elegant analysis
where they used present-day observation of clouds to determine that many climate models are biased in a way that would ultimately underestimate the warming as carbon dioxide doubles. (see Shell’s Perspective
) The accumulation of evidence is, therefore, not only is the Earth warming, it is warming more rapidly that we expected in 2007.
This conclusion of rapid warming in concert with The Carbon Projects
statement, “These (2012) emissions (of carbon dioxide) were the highest in human history and 54% higher than in 1990 (the Kyoto Protocol reference year),” paints an Earth heading rapidly to twice the carbon dioxide of the mid 1800s. This is a warming Earth, and there is little evidence that we will meet that goal of limiting warming to a global average surface air temperature of two degrees Celsius. And … it’s pretty obvious with that melting ice and warming seas that that surface temperature goal might not be a complete enough goal.
rGlaciers and Global Warming
by Jeremy Bassis
. Give it some hits!