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Caldeira Lab

Maximum warming occurs about one decade after carbon dioxide emission, Katharine L. Ricke

[Environmental Research Letters]

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A lot of climate scientists have intuition about how long it takes to feel the warming from a particular emission of carbon dioxide, but that intuition might be a little bit out of sync with our best estimates from today's climate and carbon cycle models. For example, my co-author for this study has also publicly stated in the past that “it takes several decades for the climate system to fully respond" to an emission. 

In this study we combined results from two recent state-of-the-art model intercomparison projects to find a best estimate of the time to maximum warming effect of an emission of CO2 today. The results yield a central estimate of 10.1 years after a CO2 emission until maximum warming, with a 90% probability range of 6.6 to 30.7 years.  We also quantify uncertainty in the amount of warming from an individual CO2 emission.  

We look at the time in the context of a few categories of uncertainty:

  • carbon-cycle uncertainties associated with the magnitude and timescales of changes in uptake and release of CO2 by the ocean and biosphere 
  • uncertainties of climate sensitivity associated with the radiative forcing of the emission and feedbacks of the climate system to that forcing that determine the resulting equilibrium global mean temperature change  
  • and uncertainties of thermal inertia in the climate system associated with the exchange of heat between the atmosphere and the surface and deep oceans which influences the timing of climate change 

We take 15 models of carbon cycle response to an emission, 20 models of climate sensitivity and 20 models of thermal inertia and combine them for 6000 possible combinations representing the response of the climate to an emission.

Global temperature rises in response to the CO2 forcing, but with a lag of about a decade. The warming then persists for a long time. The shape of this of the curve is governed by all three factors:  carbon cycle, climate sensitivity, and the thermal inertia of the oceans.

We find the median time between an emission and maximum warming is 10.1 years, with a 90% probability range of 6.6 to 30.7 years. 

We also found that if uncertainty in any one factor is reduced to zero without reducing uncertainty in the other factors, the majority of overall uncertainty remains. So, narrowing uncertainty in century-scale warming depends on narrowing uncertainty in all contributing factors. 

Our paper corrects a potential misconception that the largest effects of today’s emissions will be felt only by future generations. Benefit from avoided CO2 emissions will most likely be manifested within the lifetimes of the people who act to avoid that emission.

 


Ricke, K. L., and K. Caldeira, 2014: Maximum warming occurs about one decade after a carbon dioxide emission. Environ. Res. Lett., 9, 124002, doi:10.1088/1748-9326/9/12/124002.


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