The Washington state Capitol is seen through tulips on a sunny day in Olympia, Wash., on Thursday, May 1, 2014. Temperatures in the state were expected to be in the 80s again during a week where records were already set in some cities.
April 2014 tied with the same month in 2010 for the distinction of being the warmest April on record globally, with an average global temperature 1.39 degrees Fahrenheit above the 20th century average, the National Oceanic and Atmospheric Administration (NOAA) said Tuesday. The month also extended the unbroken string of months with global average temperatures at or above the 20th century average to 350 straight months, or more than 29 years. This was the 38th straight April that had a global temperature at or above the 20th century average as well.
The last cooler-than-average April was in 1976, and the last average or below-average temperature for any month was February 1985, when the movie Back to the Future was first released.
Using different data processing techniques, NASA had previously found April to be the second-warmest such month on record. The two agencies' data closely match, but their rankings often differ slightly.
According to NOAA, the year-to-date is the sixth-warmest such period on record since data began in 1880.
NOAA said that much of the globe was "much warmer than average" during April, particularly in central Siberia, where temperatures were more than 9 degrees Fahrenheit above the 1981-2010 average. "This region, along with parts of eastern Australia and scattered regions in every major ocean basin, were record warm," NOAA said in a press release.
The warmth in Siberia was partly a result of a pullback in the polar jet stream, which transports cold air to that region. This pullback led to a record low snow cover extent in that area.
"As the snow has been melting you're going to get more heating on the surface," Jessica Blunden, a scientist at NOAA's National Climatic Data Center in Asheville, North Carolina, told Mashable.
On the other hand, parts of southern and eastern Canada, the northern U.S., and Eurasia were cooler than average. No land areas, though, were record cold.
For the contiguous U.S., April was not a particularly hot month.For the contiguous U.S., April was not a particularly hot month. The lower 48 states had its 46th warmest April on record, which demonstrates how different the global picture can be from the local situation.
Sea surface temperatures in the equatorial tropical Pacific Ocean have been increasing as a likely El Niño event develops. According to NOAA's Climate Prediction Center in Maryland, the odds of an El Niño increase for the rest of the year, exceeding 65% percent during the upcoming summer. El Niño events, which are characterized by unusually mild ocean temperatures in that region, can shift global weather patterns and add heat to the ocean and atmosphere, thereby raising global average temperatures even further.
"Ocean temperatures are continuing to warm," Blunden said. Blunden added that there is typically a three to four month lag between when El Niño events form and when they show up in global average temperature trends. Most of the 21st century has seen the opposite of El Niño, which is known as La Niña conditions. This has acted to dampen global average temperatures slightly.
Scientists expect that if an El Niño event does materialize as forecasts show is likely, then global average temperatures in 2015 are going to be even higher than they would be due to manmade global warming alone. "I think that if we move into El Niño, you're going to see the temperatures start to increase," Blunden said.