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Annual State of the Climate Report for 2013 published

BAMS State of the Climate in 2013 Report Front Cover

July 2014 - During 2013, signs of a warming planet continue to be reflected in climate data from the air, land, sea and ice.

The annual State of the Climate reports are lead by scientists from NOAA's National Climatic Data Center in Asheville (North Carolina, USA), with Met Office scientist Kate Willett leading the Global Climate chapter. The report is an international effort compiled by 425 scientists from 57 countries, including 9 Met Office scientists. It is published by the American Meteorological Society. It provides a detailed update on global and regional climate indicators and notable weather events using all available climate monitoring data for as many climate variables as possible. The key features of the year are discussed in context of the historical record and uncertainty across different observing systems.

A wide array of climate indicators averaged over the year 2013 continue to show that the earth has warmed. Ocean heat content, sea level, global surface and lower tropospheric temperature, surface specific humidity and total column water vapour are all above the long-term average. Lower stratospheric temperature, Arctic sea ice, glacier mass balance and surface relative humidity are all below the long-term average.

Alongside these we see CO2 levels peaking above 400ppm at Mauna Loa for the first time since records began in 1958, and most likely for the first time in over 800 000 years, with the annual global average reaching 395.3ppm. Methane and Nitrous Oxide levels are also higher than in 2012, continuing a long-term upwards trend. The combined radiative forcing from long-lived greenhouse gasses is now 34% above 1990 levels at 2.92 W m-2.

2013 was an ENSO neutral year, meaning that neither an El Niño (warm equatorial Pacific Ocean) nor La Niña (cooler equatorial Pacific Ocean) phase developed strongly nor dominated. Other modes of natural variability were more active such as the North Atlantic Oscillation (NAO). The Northern Hemisphere winter at the beginning of 2013 moved to negative NAO conditions, bringing colder, snowy weather to the UK. At the end of 2013 the NAO was strongly positive with strong westerly winds bring milder wet conditions across the UK. The summer NAO was strongly positive in 2013 resulting in relatively warm and dry conditions over the UK.

Global annual average temperatures were again among the top ten warmest years both at the surface (over land and ocean) and through the lower troposphere, according to a large range of estimates from different products.  The year 2013 ranked within the top ten years for the frequency of warm days and bottom ten years for the frequency of cool days. The global average maximum temperature index, which tracks extreme daytime heat, was also within the top ten highest years, largely driven by the record-warm summer in Australia.

This is the 24th State of the Climate report, All reports from 1991 onwards are freely available online.

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