Sudden carbon sequestration experiment

This experiment uses exactly the same setup as the Seasonal Attribution Experiment but instead looks at the effect of a sudden sequestration of greenhouse gases.

• Some simulations used in this experiment were run previously under the Seasonal Attribution Experiment.
• The first simulation dedicated to this experiment was started on 2 May 2008.
• The final simulation was started on 11 December 2008. Thanks to all who volunteered their computers!
• This experiment will enter the analysis phase when all simulations are completed.

On the one hand people are becoming increasingly concerned about climate change caused by human emissions of greenhouse gases, but on the other hand they are also realising both that a lot of greenhouse gases have already been emitted and that reducing future emissions substantially could be quite difficult. Therefore, an idea is gaining favour that we should actively extract greenhouse gases from the atmosphere and sequester them somewhere out of harm's way. This should preferably be done very soon, the faster the better.

But is faster really better? Consider the extreme case that we were suddenly able to extract the entire anthropogenic greenhouse gas contribution from the atmosphere, thus returning to a "natural" state. In this scenario, we would expect to find that the land would have cooled nicely (away from the coasts anyway), which seems ideal. But the ocean would have been much slower to cool, so we also think that the warm ocean/cool land contrast would have produced more severe storms and rainfall events for some time afterward, which is not so ideal. This experiment will examine this extreme case.

This new experiment consists of two components. The first is a set of simulations of the year 2000 (actually March 2000 to April 2001) using the actual conditions experienced in year 2000. These conditions include observed values of the atmospheric concentrations of greenhouse gases and other gases and aerosols, as well as observed ocean surface temperatures and sea ice coverage. Simulations differ in the initial weather state set for midnight on 1 March 2000, such that each simulation gives an example of what the weather could have been like in year 2000. Altogether, these simulations give an estimate of the climate for that year. These simulations were completed as part of the Seasonal Attribution Experiment.

The second component involves re-running these simulations, but with greenhouse gas concentrations reduced to 1900 levels. In effect, this supposes that in 1999 we had suddenly found a very, very cheap and fast way of removing all of the anthropogenic greenhouse gases from the atmosphere and that this method was adopted in early 2000. Because the ocean responds slowly, we can plausibly suppose that this did not affect the ocean over the 2000-2001 period of the simulations, so we will leave the ocean surface temperatures and sea ice coverage as observed in 2000 (and as in the first set of simulations).

Dáithí Stone (University of Oxford; University of Cape Town)
Tolu Aina, Milo Thurston (University of Oxford)
Pardeep Pall (ETH-Zürich)