Near-term regional climate: the range of possibilities

What are the possible regional temperature trends over the coming few decades? Globally, on average, there is expected to be a long-term warming, but this is not necessarily true for any particular location or period. What are the probabilities of a local warming or cooling?

The temperature over the next few decades depends on any forced response to greenhouse gases etc, but also on the particular chaotic variability experienced. To quantify the range of possibilities Deser et al. ran a large ensemble of GCM simulations for the next 50 years, with only small changes to the atmospheric initial conditions. The range of outcomes for North America and Europe was perhaps surprisingly large, with most locations having the possibility of little warming (and sometimes cooling) and also very rapid warming.

Similar simulations have now been done with the FAMOUS GCM, using a 1%/year increase in CO2 concentrations for the next 90 years. Two parallel ensembles have been performed: MICRO — 96 ensemble members with only a tiny random initial perturbation to a single grid point, and MACRO — 30 ensemble members with varying ocean & atmospheric initial conditions. As an example of what can be done with such simulations, there is a global cooling trend of 24 years in one of these ensemble members.

The regional results can be explored in the applet linked to below, for different seasons, regions and trend lengths (N). The maps show mean trends for the first N years for the two ensembles (top row), and also the extreme possibilities for each grid point separately (middle and bottom rows). The right column shows the regional average properties using time-series (with red & blue lines showing the maximum & minimum trends) and histograms. To be clear – the only difference between the individual ensemble members is the initial conditions.


[Note that the variability in FAMOUS is probably too large, so the ranges are likely to be too broad if considering what this means for the real world.]

About Ed Hawkins

Climate scientist in the National Centre for Atmospheric Science (NCAS) at the University of Reading. IPCC AR5 Contributing Author. Can be found on twitter too: @ed_hawkins

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