In Weather this month, a paper by Colin Clark discusses temperature data from two rural stations in Somerset (UK). These two stations show a cooling trend over the last two decades which Clark suggests is opposite to that expected. The associated editorial suggests that this is a controversial finding.
What are the implications of these temperature observations?
Maintaining long temperature records is an essential way to monitor our climate. And, as discussed in the previous post, local measurements can show the same signal as a global average, but only when averaged over long time periods. But, how long is needed?
Clark (2015) reports on temperatures in rural Somerset from 1985-2014 (figure below). The two stations show an increase until 1994, and a small decrease in temperature since 1994. During the same period global temperatures have risen – but how likely is it that local temperatures would show such a decline?
To briefly examine this, we use an example from a climate model simulation for the same period as the Clark observations. The simulated temperature at a single grid point (roughly representing central England) shows a cooling for the whole 1985-2014 period, but the same simulation shows a warming globally (left).
When looking at the longer-term (right), this local cooling is put into perspective: it is not unlikely that (simulated) temperatures at such small spatial scales will apparently move in the opposite direction to the longer term trends, both locally and globally. We see similar features in the observations also.
We must continue to improve our communication to highlight that our expectations are for greenhouse-gas induced warming over large spatial and temporal scales, and that we also expect that some locations will show a cooling over a couple of decades or more.
This should not be a surprise. One cooling location does not mean that the globe is cooling. But, we must, of course, keep monitoring to understand whether our expectations are consistent with what happens. Clark’s efforts in maintaining these stations are very welcome!