Wettest December in over 100 years and the role of a changing climate
December 2015 has been one of the wettest and warmest on record (based on observations since 1853), and has also been marked as the wettest calendar month since 1910. Unsurprisingly, this has raised thoughts over what factors may have influenced this record-setting weather, assuming it has been anything out of the norm to begin with.
According to Professor Dame Julia Slingo, Chief Scientist at the Met Office, whom discusses this topic in a recent blog posted here, the unusual warmth of the North East Pacific Ocean over 2015 – which has been touted as a potential indication of a changing climate – may have been the culprit behind the moisture-laden air into the UK (as a side note, this was also associated with the conditions for the devastating tornadoes in the US).
In contrast, there has been much debate whether the El Nino phenomenon – an intermittent warming of the equatorial Pacific Ocean which has been very strong this year – was to blame. The result of the El Nino cycle has been to create large atmospheric waves which force particular air patterns over North Atlantic, although this is not unexpected.
Although a definitive answer currently eludes us, according to Professor Slingo, the excessive rainfalls observed recently may plausibly be related to the a warmer climate on the basis of climate physics. The moisture content in the atmosphere increases by around 6% for every 1°C warming in the oceans, and the added energy this provides for developing weather systems enables them to draw more moisture and hence produce more rainfall. Therefore, it can be said that both the unusual warmth observed in some ocean basins and the positive El Nino cycle were both important for the extreme rainfall observed during December 2015.