Matt McGrath BBC News 15 Jan 13;
US scientists say that 2012 was among the 10 warmest years the world has experienced since 1880.
Nasa researchers said it was the ninth warmest year while experts from another American agency said it was the tenth.
Both teams said that temperatures would have been higher if it hadn't been for the La Nina weather pattern that brought cooling to some regions.
They were equally certain carbon dioxide had been the principal driver of the rise over the past 50 years.
The National Oceanic and Atmospheric Administration (Noaa) said that their analysis of temperature data from a global network of weather stations indicated that the average temperature for 2012 was 0.57C above the 20th century average.
The agency stated that all 12 years of the 21st Century rank among the 14 warmest in the 133-year period of record keeping.
"This past year, unlike the US they were not a record globally but they certainly were warm," said Thomas Karl, director of NOAA's National Climatic Data Centre.
"In fact it marks a persistent above average - every year has been above average since 1976."
Using the same data but carrying out a slightly different analysis, Nasa said it was the 9th warmest year with temperatures 0.6C warmer than the mid 20th century baseline.
Dr James Hansen, from Nasa's Goddard Institute for Space Studies acknowledged that even in a period of global warming some seasons will be cooler than the long term average.
"The perceptive person should notice that the frequency of unusually warm extremes is increasing. It is the extremes that have the most impact on people and other life on the planet," he said.
According to both groups of researchers most areas of the world had higher than average temperatures in 2012 while the Arctic experienced a record breaking ice melt.
NASA: 2012 Was 9th Hottest Year on Record Worldwide
Tia Ghose LiveScience.com Yahoo News 15 Jan 13;
Last year was the ninth hottest year for the globe since 1880, according to new data released by NASA and the National Oceanic and Atmospheric Association (NOAA) today (Jan. 15).
Of the nine hottest years on record, eight have come since the year 2000, with 2005 and 2010 sharing the dubious title of hottest year on record. The new data reveal the alarming, long-term trend of global warming caused by human emissions of carbon dioxide and other greenhouse gases, climate scientists said.
"The planet is out of balance, there's more energy coming in than going out," said James Hansen, director of NASA's Goddard Institute for Space Studies, during the press conference. "So therefore we can predict with confidence that the next decade is going to be warmer than the last one."
To calculate the global surface temperature, scientists at the NASA's Goddard Institute for Space Studies in New York collect temperature data from 1,000 weather stations around the world and combine that with sea-surface temperatures derived from satellite imagery and data from Antarctic research stations. The global surface temperature last year was about 58.3 degrees Fahrenheit (14.6 Celsius), about 1 degree Fahrenheit (0.6 Celsius) above the average from 1951 to 1980.
While the planet overall experienced a warm year, the continental United States faced a particularly hot year that blew all previous records away. The average temperature, about 55.3 degrees Fahrenheit (12.9 Celsius) was 3.25 degrees Fahrenheight (1.8 degrees Celsius) higher than the average from 1951 to 1980. [The 7 Hottest Climate Change Stories of 2012]
"We've broken the record by more than one degree, that is quite impressive," said Thomas R. Karl, director, NOAA's National Climatic Data Center, Asheville, N.C., during a press briefing today. "It literally smashed the record."
The incredibly warm spring and summer in the United States led to early greening of vegetation, followed by extreme drought conditions that are still going on, Karl said in the press conference.
The findings emphasize that skyrocketing emissions of greenhouse gases such as carbon dioxide and methane are warming the planet. These gases trap heat in the atmosphere rather than letting it escape back into space.
The amount of carbon dioxide in the atmosphere has risen precipitously since the advent of the industrial revolution: In 1880, the atmospheric carbon dioxide concentration was about 285 parts per million, while today, it is more than 385 parts per million, according to NOAA's data. Though that carbon dioxide can come from natural sources, most of it comes from the burning of fossil fuels to power modern society.
Natural variations in weather mean the spike in atmospheric carbon dioxide may not translate into a year-over-year, consistent increase in the planet's temperature, but each successive decade will probably be warmer.
But one trend that will most probably occur next year is 2012's stunning loss of sea ice in the Arctic this summer and fall, Karl said. That can have global implications because the Arctic can affect weather patterns across the planet.
