2012 was one of the 10 warmest years since 1880, according to US scientists. NASA researchers said it was the ninth warmest year while experts from another American agency said it was the 10th.
Both teams said that temperatures would have been higher if it had not been for the ‘La Nina’ weather pattern that managed to cool some regions. They were equally certain that 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 since records began.
The average temperature in 2012 was around 58.3 degrees Fahrenheit (14.6 Celsius), which is 1.0 F (0.6 C) warmer than the mid-20th century baseline. The average global temperature has risen about 1.4 degrees F (0.8 C) since 1880, according to the new analysis.
Scientists emphasize that weather patterns will always cause fluctuations in average temperature from year to year, but the continued increase in greenhouse gas levels in the Earth’s atmosphere assures a long-term rise in global temperatures. Each successive year will not necessarily be warmer than the year before, but on the current course of greenhouse gas increases, scientists expect each successive decade to be warmer than the previous decade.
“One more year of numbers isn’t in itself significant,” says Gavin Schmidt, a climatologist at NASA’s Goddard Institute for Space Studies (GISS). “What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming. The reason it’s warming is because we are pumping increasing amounts of carbon dioxide into the atmosphere.”
Carbon dioxide is a greenhouse gas that traps heat and largely controls the Earth’s climate. It occurs naturally and is also emitted by the burning of fossil fuels for energy. Driven by increasing man-made emissions, the level of carbon dioxide in Earth’s atmosphere has been rising consistently for decades.
The carbon dioxide level in the atmosphere was about 285 parts per million in 1880, the first year in the GISS temperature record. By 1960, the atmospheric carbon dioxide concentration, measured at NOAA’s Mauna Loa Observatory, was about 315 parts per million. Today, that measurement exceeds 390 parts per million.
Dr James Hansen of GIFF 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.