NASA Goddard Institute for Space Studies
This map represents global temperature anomalies averaged from 2008 through 2012. NASA ranked 2012 as the ninth warmest on record in a new analysis released Tuesday.
By John Roach, NBC News
Government scientists said Tuesday that 2012 was among the top ten warmest on record globally and continues a trend of rising temperatures due to increasing emissions of the greenhouse gas carbon dioxide.
“The 'climate dice' are now sufficiently loaded,” James Hansen, director of NASA’s Goddard Institute for Space Studies, wrote in a note explaining the findings.
Loaded dice mean that temperature extremes such as the heat and drought in the central Rockies and Great Plains in 2012; and Oklahoma, Texas and Northern Mexico in 2011 are becoming more common than they were several decades ago.
"The observant person who is willing to look at the past over several seasons and several years, should notice that the frequency of unusual warm anomalies has increased and the extreme anomalies," Hansen said in telephone conference with reporters.
The average temperature in 2012 was about 58.3 degrees Fahrenheit (14.6 Celsius), which is 1.0 F (0.6 C) warmer than the mid-20th century baseline, NASA reported.
The average global temperature has risen about 1.4 degrees F (0.8 C) since 1880, according to the new analysis.
Ranking the warmth
NASA ranked 2012 as the ninth warmest since record keeping began in 1880. A separate analysis from NOAA said 2012 was the 10th warmest since that time and the warmest La Nina year on record.
La Nina is the cold phase of El Nino phenomenon characterized by cooler than average temperatures in the eastern Pacific.
The difference between the two reports hinges on the different methods the agencies use to collect and interpret data. One biggie is that NASA extrapolates observational data into regions without meteorological stations, including the polar regions, whereas NOAA does not.
Some of the fastest warming is occurring in the Arctic, which hit a new low for summer sea ice extent in 2012.
NASA noted that with the exception of 1998, which had an exceptionally strong el Nino and thus warm temperatures, the nine warmest years in its 132 year record have all occurred since 2000, with 2010 and 2005 ranking as the hottest on record.
NOAA reported that 2012 marks the 36th consecutive year with a global temperature above the 20th century average. The last below average year was 1976.
The mean pace of warming over the past five years has been flat, Hansen noted, a phenomenon he explained as likely due to several recently strong la Nina years, which lead to a cooling in the tropical eastern Pacific Ocean, and the effect of aerosols, or airborne particles that reflect sunlight.
"We are very suspicious that global aerosols have increased," Hansen said. "We know from anecdotal evidence that China and some developing countries their air pollution has gotten worse."
What’s more, the sun’s irradiance has decreased over the last solar cycle, which has a slight effect on temperatures as well.
Nevertheless, Hansen noted, the long term trend is warming.
"Each decade has been significantly warmer than the prior decade since the mid 1970s and that warming trend has been conclusively linked to the effect of increasing greenhouse gases, particularly carbon dioxide," he said.
Hot in the US
The new reports on global temperatures fall on the heels of a NOAA report released earlier this month that found 2012 was the warmest ever on record in the US and a draft assessment from the federal government that found global warming is already impacting American life.
A new report from the Natural Resources Defense Council released Tuesday found that said 2012 saw 3,527 monthly weather records broken for heat, rain, and snow in the US.
"The evidence is undeniable: extreme weather events are pounding our communities and if we don't curb climate change, many will grow more severe," Frances Beinecke, the environmental group's president, wrote in a blog post about the new report.
The record warmth in the continental U.S. was offset by notably cooler than average temperatures in Alaska, far western Canada, central Asia, parts of the eastern and equatorial Pacific and parts of the Southern Ocean.
In addition to the warmth in the US, above average temperatures were felt in South America, most of Europe and Africa, and western, southern, and far northeastern Asia, the NOAA report said.
Temperatures this "past year, unlike the US temperature, were not a record globally, but they certainly were warm," Thomas Karl, director of NOAA’s National Climatic Data Center, said in the call with reporters.
"In fact it marks a consistent above average global temperature. Every year has been above average since 1976."
John Roach is a contributing writer for NBC News. To learn more about him, check out his website.