There is no shortage of debate over whether the recent storms and floods can be blamed on climate change. In reality any answer will involve probabilities rather than a simple ‘yes’ or ‘no’. So what do we know, what are the uncertainties, and can we say whether or not there is a clear link?
It is very hard to make precise calculations of the amount by which individual weather events have been influenced by our warming of the global climate. Scientists have carried out these calculations for some other weather extremes in the past and found a human contribution, but they are not routine and they require a lot of time and computing resources.
Despite the current lack of a precise answer, the recent heavy rainfall and coastal inundation is consistent with some basic physics of a warming world:
- Firstly, sea levels are rising. During the last century the sea level in the English Channel has risen by around 12 cm and is continuing to rise at a rate of 1.3cm per decade. This is because land-based snow and ice is melting into the sea and because seawater expands as it warms. Higher seas mean a greater chance of storm surges breaching coastal defences.
- Secondly, warmer air can hold more moisture. So, in a warmer world, a given storm has the capacity to drop more rain. While rainfall in the UK varies a lot from year to year there is some evidence to suggest that extreme rainfall is becoming more common – what was a 1-in-125 day event seems to be occurring on average every 85 days now.
So we can expect heavier storms when they do come, and climate models suggest that the UK will get warmer and wetter winters on average. Less certain however is how often these sorts of storms will cross our path in future.
What has made this winter unusual is that we have had not one storm, but a sequence of storms leading to continued heavy rain. The storms have been fed to us by a complex weather pattern involving the jet stream, which is interlinked with weather across the globe. Understanding how this pattern might change as different parts of the world warm at different rates is a key challenge that scientists are working on.
Regardless of the causes of the recent flooding, its effects are devastating for many. Reducing global emissions of greenhouse gases will help to limit long-term increases in risk. And as the weather continues to throw up surprises from time to time against a backdrop of climate change, it’s clear we need to invest adequately to ensure protection against future flooding and other extremes.