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Certainty and uncertainty in climate change predictions: What use are climate models?

TitleCertainty and uncertainty in climate change predictions: What use are climate models?
Publication TypeManual Entry
Year of Publication2008
AuthorsWatson, A. J.
Environmental & Resource Economics

Despite great advances in understanding of the earth's climate, our estimate of the global temperature rise due to a doubling of atmospheric CO2 has not greatly changed in a hundred years, and the estimate of the uncertainty on that number has actually increased. This is because while the basic mechanism of greenhouse-gas forcing of climate is well understood, the multiple, mostly positive, feedback loops that amplify this effect are not. The combined effect of many of these feedbacks can be seen in the record of past climate, and analysis of these suggests that our present models tend to under-predict the eventual, equilibrium climate change due to a given increase in atmospheric CO2. In the foreseeable future (next 20 years) climate modelling research will probably not materially decrease the uncertainty on predictions for the climate of 2100. The uncertainty will only start to decrease as we actually observe what happens to the climate. The best use of climate models at present is via ensembles of predictions that give a probabilistic description of the range of uncertainty involved in future climate. Recent studies suggest a skewed probability distribution, with a tail stretching out to high climate sensitivities. Combined with estimates of the likely economic impact of climate change, this strongly suggests that research should be concentrated on trying to reduce the uncertainty represented by this tail of low probability, but high impact, scenarios.

Citation Key123
Community Notes

This reference outlines the change of thought from uncertainty in knowing if the climate is changing and why it is changing to how it will continue to change.  The perception of uncertainty in non-scientists is often tainted by politics and ideology, though.  Watson outlines the range of expected global temperature increase from sources back to 1896 to demonstrate that the uncertainty in it has not changed over time.  He also does not expect a radical improvement in decreasing uncertainty in the near future since the uncertainty has many sources.  Improvements may occur as we observe climate change and can incorporate those observations into our climate modeling.  Although there is currently high uncertainty in climate projections for the next century, it is also realized that the climate’s response to forcing is delayed roughly 50 years so if we wait to see if climate change is going to be an issue, it will be too late to take corrective action.  Watson believes although the probability of a very damaging change is low, it is still significant and should be taken seriously.  This article is useful for laying out the changes in perspectives of climate change and the dynamic of mitigation versus adaptation perspectives.