State of the Climate 2015: global warming and El Niño sent records tumbling
The State of the Climate in 2015 report, led by the US National Oceanic and Atmospheric Administration, was released yesterday. Unfortunately, it paints a grim picture, write Andrew King and Sarah Perkins-Kirkpatrick.
Published on the 04 Aug 2016 by Andrew King and Sarah Perkins-Kirkpatrick
For a second consecutive year the globe experienced its hottest year on record, beating the 2014 record by more than 0.1℃. From May 2015 onwards, each month set a temperature record for that particular month, a pattern that has yet to end.
In all three global temperature series, 2015 stands out as the hottest year. UK Met Office, Author provided
The record-breaking temperature anomaly in 2015 (around 1℃ higher, on average, than what would be expected in a world without humans) was in large part due to human-caused climate change. A small fraction of the heat was because of a major El Niño event, which developed midway through 2015 and ran into this year.
During El Niño events we see warmer sea surface temperatures in the central and eastern Pacific Ocean. A resulting transfer of heat from the ocean into the lower atmosphere causes a temporary warming effect. In La Niña seasons, the opposite happens.
At regional scales we also saw many extreme events last year. The downward trend in Arctic sea ice continued, with the lowest annual maximum extent on record. Alaska’s winter was almost non-existent, with many Arctic mammals and fish being forced to change their behaviour and shift their habitats.
Many extreme heatwaves occurred in 2015. These included a deadly hot spell in India and Pakistan and severe heat events in Europe and North America. Combined, these events killed thousands of people.
Seasonal-scale extreme heat occurred over many parts of the globe. There were many more warm days and nights than normal over much of Europe in summer, and in Russia and North America in spring.
Extreme events occurred around the world in 2015. NOAA NCEI
Across the world there were more tropical cyclones than normal, mainly due to increased cyclone activity across the Pacific basin, and many significant flood events. On the other hand, large areas suffered severe drought (14% of the land surface, up from 8% in 2014).
The Ethiopian drought devastated crops and affected millions of people. Parts of South America experienced the worst drought in 80 years. The western US drought continued, despite the fact that El Niño events usually bring this region some reprieve.
…including in Australia
In Australia, probably the most significant climate extreme we had was the record heat in October.
The country experienced its biggest monthly temperature anomaly on record – almost 3℃ above the historical national average. The frequency of very warm days was also well above average. This unusual early heat triggered bushfires across the southeast.
Even given the El Niño event (which normally warms up Australia in spring and summer), the maximum temperature records that were set were, for example, at least six times more likely in Melbourne than they would have been in the absence of human-caused climate change.
Australia experienced its hottest October on record in 2015. Bureau of Meteorology, Author provided
For 2015 as a whole, Australia experienced its fifth-warmest year on record. Nine out of 12 months were warmer than average.
A continuation of climate change trends
Besides the record heat, the world saw many other unwanted records tumble in 2015, providing ever more extensive evidence for the effect that humans are having on the climate. Greenhouse gas concentrations (the primary cause of our changing climate) rose to record high levels, with carbon dioxide concentrations passing the 400 parts per million mark at many sites. The year’s margin of increase in atmospheric carbon dioxide concentrations was also the largest on record.
Unfortunately, in many ways, the climate of 2015 is not likely to stand out as especially unusual in a few years’ time. More record hot years are likely, with associated extreme weather events, as greenhouse gas concentrations continue to climb.
Only with rapid and substantial cuts to these emissions will it be possible to limit global warming to well below 2℃, a key aim of the Paris climate agreement, and reduce the likelihood of yet more climate records tumbling.