Department of Climate and Space Sciences and Engineering in the College of Engineering at the University of Michigan


Professor Andronova’s paper in the The Economist

Posted: April 5, 2013

Professor Andronova’s paper in the The Economist

The Economist magazine references a paper written by Professor Natalia Andronova in a recent climate science article. The paper, written when she was at the University of Illinois, used temperature data to estimate the sensitivity of the climate system.

Climate sensitivity describes the way the climate reacts to changes in carbon-dioxide levels. The world has added about 100 billion tonnes of carbon to the atmosphere between 2000 and 2010, yet the five-year mean global temperature has been flat for a decade. Climate scientists are trying to solve this mismatch between rising greenhouse-gas emissions and not-rising temperatures.

The article states that conventional wisdom predicts that global temperatures could rise by 3 degrees Celsius or more in response to a doubling of greenhouse-gas emissions. The 3 degrees Celsius prediction is based party on general-circulation models, or GCMs. These models divide the Earth and its atmosphere into a grid which generates an enormous number of calculations in order to imitate the climate system and the multiple influences upon it. These models simulate the way the climate works over the long run, without taking account of what current observations are.

Some studies, such as Andronova’s, use energy-balance models instead of GCMs. These models are top-down, treating the Earth as a single unit or as two hemispheres and representing the whole climate with a few equations reflecting things such as changes in greenhouse gases, volcanic aerosols and global temperatures. These models explicitly use temperature data to estimate the sensitivity of the climate system, so they respond to actual climate observations. The studies that use this model predict a warmth of about 2 degrees Celsius, give or take, instead of 3 degrees Celsius.

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