Earth Has Warmed 0.4 C in 30 Years

Half of the globe has warmed at least one half of one degree Fahrenheit (0.3 C) in the past 30 years, while half of that -- a full quarter of the globe -- warmed at least one full degree Fahrenheit (0.6 C), according to John Christy, Ph.D., a professor of atmospheric science and director of the Earth System Science Center (ESSC) at The University of Alabama in Huntsville.

Globally, Earth's atmosphere warmed an average of about 0.4 C (or about 0.72 degrees Fahrenheit) in 30 years, according to data collected by sensors aboard NOAA and NASA satellites. More than 80 percent of the globe warmed by some amount.

A map of Earth's climate changes since Dec. 1, 1978, (when satellite sensors started tracking the climate) doesn't show a uniform global warming. It looks more like a thermometer: Hot at the top, cold at the bottom and varying degrees of warm in the middle.

This is a pattern of warming not forecast by any of the major global climate models. The area of fastest warming is clustered around the Northern Atlantic and Arctic oceans, stretching from Arctic Canada across Greenland to Scandinavia. The greatest warming has been on opposite ends of Greenland, where temperatures have jumped as much as 2.5 C (about 4.6 degrees F) in 30 years.

During the same time, however, much of the Antarctic has cooled, with parts of the continent cooling as much as Greenland has warmed. But areas of cooling were isolated: Only four percent of the globe cooled by at least half of one degree Fahrenheit.

"If you look at the 30-year graph of month-to-month temperature anomalies, the most obvious feature is the series of warmer than normal months that followed the major El Nino Pacific Ocean warming event of 1997-1998," said Christy. "Right now we are coming out of one La Nina Pacific Ocean cooling event and we might be heading into another. It should be interesting over the next several years to see whether the post La Nina climate 're-sets' to the cooler seasonal norms we saw before 1997 or the warmer levels seen since then."

Virtually all of the warming found in the satellite temperature record has taken place since the onset of the 1997-1998 El Nino. Earth's average temperature showed no detectable warming from December 1978 until the 1997 El Nino.

As part of an ongoing joint project between The University of Alabama in Huntsville, NOAA and NASA, Christy and Roy Spencer, Ph.D., a principal research scientist in the ESSC, use data gathered by microwave sounding units on NOAA and NASA satellites to get accurate temperature readings for almost all regions of the Earth. This includes remote desert, ocean, and rain forest areas for which reliable climate data are not otherwise available.

The satellite-based instruments measure the temperature of the atmosphere from the surface up to an altitude of about eight kilometers above sea level.

Once the monthly temperature data is collected and processed, it is placed in a "public" computer file for immediate access by atmospheric scientists in the U.S. and abroad.

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