Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

Climate sensitivity uncertainty and the need for energy without CO2 emission

Ken Caldeira, Atul K. Jain, & Martin I. Hoffert

It has generally been called a necessity for humans to stabilize greenhouse gas emissions to prevent radically large interference in the climate. However, exactly how sensitive the climate is to certain amounts of greenhouse gasses is uncertain. Here it is displayed how this uncertainty makes it very difficult to predict what amounts of CO2 would be safe to emit.

Caldeira, K., A.K. Jain, and M.I. Hoffert, Climate sensitivity uncertainty and the need for energy without CO2 emission, Science 299, 2052-2054, 2003.

Percentage of primary power that must be carbon free to stabilize the climate: the required percentage of power that must be carbon free to maintain a stable climate graphed as a function of time for various climate sensitivities. The results differ greatly depending on sensitivity - it is impossible to tell what our stabilization requirements will be without better knowledge of exactly how our climate reacts to increased CO2.

Acceptable carbon emissions: the amount of carbon emissions that will be safe over time shown for different climate sensitivities. The wide variety of "acceptable" values again implies that we will not be able to determine what is safe until we know more about the sensitivity of our climate.


The UN Framework Convention on Climate Change calls for “stabilization of greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system.”Even if we could determine a “safe” level of interference in the climate system, the sensitivity of global mean temperature to increasing atmospheric CO2 is known perhaps only to a factor of three or less. Here we show how a factor of three uncertainty in climate sensitivity introduces even greater uncertainty in allowable increases in atmospheric CO2 concentration and allowable CO2 emissions. Nevertheless, unless climate sensitivity is low and acceptable amounts of climate change are high, climate stabilization will require a massive transition to CO2 emission–free energy technologies.