The past year was the sixth warmest year on record since temperature records began in 1850. Global average surface temperature in 2013 was 14.5–0.50 °C above the 1961–1990 average and 0.03 °C above the 2001–2010 average, the Geneva-based World Meteorological Organization (WMO) reports in its latest statement of the status of the global climate, released today.
For its annual assessment, the WMO, a United Nations agency, uses the average of three independent global temperature data sets maintained by the UK Met Office, the US National Oceanic and Atmospheric Administration and NASA’s Goddard Institute for Space Studies, based in Greenbelt, Maryland.
With 13 of the 14 warmest years on record having occurred in the 21st century, there is no indication that global warming has stopped, says the report. Although the rise in air temperatures has slowed in recent years, heat continues to be trapped in the oceans, which take up more than 90% of the excess energy that reflects back to the surface as greenhouse gases accumulate in the atmosphere, says the report. Atmospheric greenhouse-gas concentrations reached new record highs last year and are now more than 40% above pre-industrial levels, and carbon dioxide in particular is now crossing the symbolic threshold of 400 parts per million.
Temperatures last year were particularly high in parts of the southern hemisphere, the report says, with Australia having experienced its hottest and Argentina its second-hottest year on record. A comparison of climate-simulation runs with and without elevated greenhouse-gas concentrations — made by scientists at the University of Melbourne and included in the WMO report — suggests that the record-warm Australian summer was about five times as likely as it would have been in a climate unaltered by human activity.
In the northern hemisphere, the prevailing negative mode of the Arctic Oscillation, a large-scale mechanism of natural climate variability, brought lower-than-average spring temperatures to parts of the United States, western Europe, Russia and Japan.
Global precipitation during 2013 equalled the 1961–1990 average of 1,033 millimetres. Even so, severe drought conditions hit Australia, southern Africa and parts of South America and China.