For the most recent report of the Intergovernmental Panel on Climate Change (IPCC), fifteen climate modelling groups from around the world were asked to provide simulation outputs from their state-of-the-art carbon cycle models. The objective of these experiments was to provide up-to-date estimates of what happens to anthropogenic CO2 emissions, how they will be apportioned between atmosphere, ocean and vegetation, how long they will stay in the atmosphere and what are the long-term climate change implications.

Researchers in the Palaeoenvironmental Change group were one of the contributing groups, providing results from more than 50 different experiments using the Earth system model GENIE. Strict protocols were defined for all of these experiments that every group had to adhere to. These protocols defined precisely how the experiments should be set up, an important element of all model inter-comparison projects as comparing the results of “identical” simulations from many different models helps to identify and quantify areas of uncertainty in our understanding.

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The results of these experiments were an important component of the IPCC AR5 report. They were also published as three separate scientific papers, examining separately the recent historical period, projections into the future and a specific study to quantify the atmospheric lifetime of anthropogenic CO2 emissions.  Predictions from twelve of the participating models are illustrated above, comparing simulated global warming with observations since preindustrial times. One significant conclusion of this inter-comparison project was that the uptake of CO2 by vegetation appeared to be underestimated by all contributing models. This conclusion was subsequently examined in some detail by the Palaeoenvironmental Change group, producing a study which helped to better quantify the strength of this important global sink.

Read more about the inter-comparison project in our scientific papers:

Eby, M. et al: Historical and idealized climate model experiments: an EMIC intercomparison, Climate of the Past, 9, 1111-1140, 2013.

Joos, F. et al.: Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: a multi-model analysis, Atmospheric Chemistry and Physics, 13, 2793–2825, 2013.

Zickfeld, K. et al., Long-term climate change commitment and reversibility: an EMIC intercomparison, J. Climate, Vol. 26, pp. 5782–5809, 2013.

Posted by Phil Holden