2015 has seen some significant climate events, both meteorological and political.
Overall, it has been the warmest year on record for the globe – a clear 0.1°C above all other years on record, meaning that 2015 will be the first year breaking the 1°C above pre-industrial threshold. The Met Office have predicted that 2016 will very likely break this new record. This extreme warmth is due to the large El Nino event occurring on top of the long-term warming trend. At the same time, levels of carbon dioxide in the atmosphere have passed 400 parts per million, probably for the forseeable future.
El Niño: (by Geert Jan in comments)
2015 saw one of the strongest El Niño’s on record, comparable in strength though different in some aspects from the 1997/98, 1982/83 and 1877/78 events. The Niño3.4 index was higher than those, but the coastal warming was much less. Effects were reasonably standard: big drought in Indonesia south of the equator July–October, a bit wetter short rains in East Africa October–November, lots of rain in Paraguay last month, drought in South Africa, more rain in the southern US, warm weather in Canada. It peaked late November and is forecast to disappear by next summer.
After a record warm 2014 for Central England (10.95°C), 2015 was always likely to be cooler. So it has turned out, with the annual temperature being 10.3°C, which is 0.8°C above the average of 1961-1990. However, December 2015 has been extraordinarily warm – more than 5°C above normal – the largest monthly anomaly in the entire Central England series (back to 1659). 2015 has been very wet also, with a series of December storms causing extreme floods in northern England, breaking many rainfall records. [UK summary]
The ice covered polar regions continue to show differing changes. The Arctic sea ice winter extent was the lowest in the satellite era, and 4th lowest in summer. CryoSat now monitors Arctic sea ice thickness in real-time from October until May which will help monitor ongoing changes. In the Antarctic, the sea ice extent was lower than some recent years, but still above average.
2015 was dominated by the Paris Conference of the Parties (COP21) which I was fortunate to attend for a couple of days. The eventual agreement signals a desire to keep global temperatures well below 2°C above pre-industrial. This is to be achieved by lowering greenhouse gas emissions until there is a balance of sources and sinks in the second half of the century. This signals the eventual target of net-zero emissions. The mention of a possible 1.5°C target was a surprise, and the COP21 agreement also invited the IPCC to investigate the plausible pathways to this aim.
Any forecasts for 2016?