Hotter weather the 'new normal'
LAST year was among the 10 hottest on record, with sea levels at record highs, Arctic ice at historic lows and extreme weather in various corners of the globe signalling a "new normal", scientists said on Tuesday in the 2012 State of the Climate report.
Meant as a guide for policymakers, the report did not attribute the changes in climate to any one factor, but noted continued increases in heat-trapping greenhouse gases, including carbon dioxide, methane and nitrous oxide.
"Our planet as a whole is becoming a warmer place," said Dr Kathryn Sullivan, acting administrator of the United States National Oceanic and Atmospheric Administration (NOAA). The report was edited by NOAA scientists and drew contributions from 384 scientists across 52 countries.
The report's data indicates "new normal" conditions that can inform planning decisions, instead of relying on models that "count on the future being statistically a lot like the past", Dr Sullivan said at a news briefing.
Global surface temperatures - land and water - were the eighth or ninth warmest, depending on which data set was used, since record keeping began in the late 1800s, the report found.
However, in the decade leading up to last year, global temperatures actually declined by 0.05 deg C, according to Mr Thomas Karl, director of NOAA's National Climatic Data Center.
He said the 50-year trend indicates that global temperatures have consistently increased about 0.15 deg C per decade.
The recent decrease in temperatures has been noted by climate-change sceptics, who question the impact of human activities - such as the burning of fossil fuels that emit carbon dioxide - on climate.
Other changes detailed in the report paint a more complex picture:
Sea levels reached a record high after a sharp decrease in 2011, possibly linked to the Pacific Ocean phenomenon La Nina, which can have a cooling effect;
Arctic sea ice shrank to its smallest summer minimum since satellite records began 34 years ago, while Antarctic sea ice reached a record high;
More than 97 per cent of the ice sheet covering Greenland melted at least a bit in the summer of last year, four times greater than the 1981-2010 average;
Average sea-surface temperatures rose, but not much;
Ocean heat was near record-high levels in the upper 800m of the water, and temperatures also increased in the deep ocean.
The State of the Climate report is being published as a supplement to this month's Bulletin Of The American Meteorological Society.