Last year was one of the warmest ever recorded on Earth since scientists began keeping global average temperature stats 134 years ago, climate experts from two U.S. agencies revealed today.
The U.S. National Oceanic and Atmospheric Administration (NOAA) ranked 2013 as being the fourth-warmest year ever, tied with 2003. NASA, which conducted its own report and processed the data sets differently, declared 2013 to be the seventh warmest year since 1880.
What is a temperature anomaly?
According to the U.S. National Oceanic and Atmospheric Administration, the term "temperature anomaly" refers to a temperature that is different from long-term average temperatures, also known as reference values. Temperature anomaly is used by climate scientists to get a big-picture overview of average global temperatures compared to a reference value.
Despite the difference in rankings between the two agencies, the data "clearly makes this decade the warmest in historical period," Gavin Schmidt, deputy director of NASA's Goddard Institute for Space Studies, told reporters in a teleconference.
Schmidt noted that both analyses are actually very similar.
"The difference between the joint fourth place and the joint seventh place is within 0.02 C of a degree," he said, adding that NASA processes its data differently than NOAA.
NASA and NOAA are the keepers of the world's climate data. Each year, both agencies produce independent reports charting the planet's temperature changes, matched against historical data.
The annual reports are considered to be state of the climate addresses and help to give scientists a big-picture overview of the effects of global warming.
9 out of 10 warmest years were in 2000s
In NOAA's annual global analyses, researchers put the average world temperature (combined land and ocean surface temperatures) last year at 14.52 C.
That was 0.62 C above the 20th-century average of 13.9 C, making 2013 the 37th consecutive year that the yearly global temperature exceeded the average.
The global land temperature was just shy of 1 C (0.99 C) above the 20th-century average, according to NOAA.
Both NOAA and NASA said that nine out of 10 of the warmest years ever recorded between 1880 and 2013 were within the last 13 years. Only one entry prior to the 2000s, the year 1998, cracked the top 10.
The hottest recorded year so far was in 2010, when a temperature anomaly of 0.66 C was recorded above the 20th-century average. It topped both NOAA and NASA's lists.
Tom Karl, director of NOAA's National Climatic Data Center, told reporters that as the world continues to warm, high latitudes generally get wetter and the subtropics get drier.
"We saw, for example, in Brazil they had severe droughts for the second consecutive year, in many ways it was probably the worst in the past 50 years. We had an early onset to the southwest Indian monsoon, some of the worst flooding in the past half century," he said.
Warmer winter, spring in Canada
"Even though we had, on balance, a rather average-looking precipitation year, certainly in some parts we had far too much rain and in other parts far too little."
NOAA's analysis said Canada experienced a warmer-than-average winter and spring, as well as the eighth-warmest summer on record.
North America as a whole was hotter than normal in 2013, with Alaska having its second-warmest winter on record.
However, Karl said that some parts of the U.S. experienced cooler-than-average temperatures, due to the cooling effects of La Nina in the eastern Pacific and significant rainfall during the warmer months of the year.
A NOAA map showing global precipitation trends showed that a section of southern and central Canada was the wettest on record in 2013, while a region of coastal western Canada was the driest.
In recent years, parts of Asia, Africa, Australia and the Arctic in particular have undergone dramatic warming.