Global Surface Temperatures Highest on Record in April

NASA's Goddard Institute for Space Studies (GISS) and the National Oceanic and Atmospheric Administration (NOAA) have just released data showing that global surface temperatures in April were the warmest on record. Indications of the warmth include record low snow cover in North America, a precipitous decline in the extent of Arctic sea ice, and record high sea surface temperatures in the region of the tropical Atlantic where most hurricanes originate.

Data released by NASA on Friday (14 May 2010) show that globally, the combined land-surface air and sea-surface water temperature anomaly was 0.73°C above the 1951-1980 mean, shattering the previous record of 0.66oC set in April 2007. The records go back to 1880. For the Northern Hemisphere alone, it also was a record breaking month, with surface temperatures 1.32°C above the long term mean, slightly above the previous record of 1.29°C set just two years ago in 2007.

The National Oceanic and Atmospheric Administration also just released (on 15 May 2010) its April surface temperature data, showing a combined land and sea surface temperature anomaly of 0.7590°C above the 20th century average (1901-2000). Like NASA's data, the NOAA data ranks April 2010 as the warmest April on record. NOAA's data places April 1998 as the second warmest, with an anomaly of 0.7107°C above the long term average.

The last decade (2000-2009) was the warmest on record; and the data for January through April 2010 suggest that this year ultimately may be the warmest year yet. According to NOAA, January-April 2010 was the warmest January-April on record. As the figure below indicates, it is part of a long term warming trend for the period. (see State of the Climate > Global Analysis > April 2010, from the National Climatic Data Center).

Above: Jan-Apr Land & Ocean Surface Mean Temp Anomalies. Source: National Climatic Data Center.

Above: Global surface temperature anomalies, April 2010. Source: NASA GISS.

As the figure above indicates, the largest temperature anomalies were concentrated in the northern latitudes, particularly in the Arctic. In the United States, the northeast portions of the country were the warmest. According to NOAA, "[r]ecord warmth prevailed throughout the Northeast as Maine, Connecticut, Rhode Island, and New Jersey each had their warmest April on record. Illinois also had its warmest such period. In total, 31 states had above-normal temperatures." (see NOAA: Above-Normal Temperatures and Below-Normal Precipitation in April, press release [7 May 2010] from NOAA; and NOAA's State of the Climate > National Overview > April 2010).

NOAA's data also show that global sea surface temperatures (SSTs) were the highest on record for April, with a temperature anomaly of 0.5706°C above the 20th century average. Now in second place is 1998, with sea surface temperatures of 0.5570°C above the 20th century average.

Source: National Oceanic and Atmospheric Administration, National Climatic Data Center.

The figure above shows that one sea surface area where the temperature anomaly is particularly large is the tropical Atlantic Ocean, especially in what is called the hurricane "Main Developement Region" (MDR) off the African coast. Atmospheric disturbances called African waves form in this area and Jeff Masters of the Weather Underground explains that "[t]hese African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) "

In Record Atlantic SSTs continue in the hurricane Main Development Region (15 May 2010), Masters reports:

"SSTs in the Main Development Region (10°N to 20°N and 20°W to 85°W) were an eye-opening 1.46°C above average during April. This is the third straight record warm month, and the warmest anomaly measured for any month--by a remarkable 0.2°C. The previous record warmest anomalies for the Atlantic MDR were set in June 2005 and March 2010, at 1.26°C....The high April SST anomaly does not bode well for the coming hurricane season. The three past seasons with record warm April SST anomalies all had abnormally high numbers of intense hurricanes."

These circumstances would be worrisome in any year. But tropical storms entering the Gulf of Mexico this year will repeatedly disrupt efforts to stop the oil leaking into the water and to contain the growing oil slick -- and strong storms will add additional devastation, including possible damage to both offshore and coastal oil and gas facilities.

For a short backgrounder on trends in the intensity of tropical storms in the Atlantic, and on the relationship between SSTs and storm intensities, see Tropical Cyclone Intensity [PDF], a two-page excerpt from Climate Change Indicators in the U.S, a report from the U.S. Environmental Protection Agency (dated 27 April 2010)

Another indication of the record high temperatures (and in many areas low winter snowpacks) in the Northern Hemisphere was the April snow cover for North America which not only the lowest on record for April, but was the single largest monthly negative anomaly on record (i.e. since 1966) for any month. See the figures below.

North American (excepte Greeland) Snow Cover Anomalies, April, 1966-2010. Source: Rutgers University Global Snow Lab.

Above: North American (except Greeland) Snow Cover Anomalies, April, 1966-2010. Source: Rutgers University Global Snow Lab

Above: Northern Hemisphere Snow Cover, April 2010, Departure from Normal. Source: Rutgers University Global Snow Lab. Areas shaded brown have below normal snow cover, whereas blue area have above normal snow cover.

Meanwhile, another reflection of warmth in northern latitudes is the sea ice in the Arctic. The extent of Arctic sea ice is declining with unusual rapidity right now – faster than average and faster than in 2007, the year when Arctic sea ice plunged to a record minimum extent. See the figure below and our earlier posting, Thinner than Normal Arctic Sea Ice Poised for a Rapid Decline in 2010 (6 April 2010).