Newswise — With a global average temperature that was three-tenths of a degree Celsius (0.54° Fahrenheit) warmer than seasonal norms, 2005 tied with 2002 as the second warmest year in the past 27, according to data gathered by NOAA satellites and processed at The University of Alabama in Huntsville (UAH).
Temperatures in 2005 followed a general pattern seen over the past 27 years, with the most significant warming seen in the northernmost third of the planet — especially in the Arctic. Large regions of slightly warmer than normal temperatures covered much of the globe.
Since November 1978, the Arctic atmosphere has warmed at a rate that is more than seven times faster than the average warming trend over the southern two-thirds of the globe.
"It just doesn't look like global warming is very global," said Dr. John Christy, director of UAH's Earth System Science Center. "Obviously some part of the warming we've observed in the atmosphere over the past 27 years is due to enhanced greenhouse gases. Simple physics tells you that.
"But even if you acknowledge the effects of greenhouse gases, when you look at this pattern of warming you have to say there must also be something else at work here.
"The carbon dioxide from fossil fuels is distributed pretty evenly around the globe and not concentrated in the Arctic, so it doesn't look like we can blame greenhouse gases for the overwhelming bulk of the Northern Hemisphere warming over the past 27 years. The most likely suspect for that is a natural climate change or cycle that we didn't expect or just don't understand."
Averaged globally, the satellite data show a 27-year atmospheric warming of 0.35 C (about 0.63° Fahrenheit) since late November 1978, when the first temperature sensors were launched aboard a NOAA satellite.
Average temperatures over the Arctic have warmed by 1.16 C (about 2.1° F) in the past 27 years, according to the satellite temperature data, which is processed at UAH. During that same time, however, temperatures over the southern two-thirds of the globe warmed only 0.16 C (about 0.29° F).
Average atmospheric temperatures in the northern third of the globe, which includes the Arctic, have warmed by 0.7 C (about 1.26 degrees F) in that time. Atmospheric temperatures over the contiguous 48 U.S. states warmed an average of 0.73 C — about 1.31° F — during that time.
While computer models used to forecast climate change do predict regional differences in the effects of global warming, this warming pattern doesn't match the forecast.
"The computer models consistently predict that global warming due to increasing greenhouse gases should show up as strong warming in the tropics," Christy said.
Even with a recent data correction that added tropical warming to the dataset, however, the satellite data still shows that the tropical atmosphere has warmed by only 0.19 C — just over one-third of a degree Fahrenheit — in 27 years.
Recent research (Esper et al., 2005) that looked at temperature trends over similar periods of time going back more than 1,000 years found the probability that a few cases experienced that much warming in such a short time, Christy said. "It would be fairly rare to have this much warming all from natural causes, but it has happened. What we've seen isn't outside the realm of natural climate change."
The five years from 2001 through 2005 have been five of the six warmest years in the 27-year satellite global temperature record. The warmest year in the satellite climate record was 1998, during the "El Niño of the century." The global composite temperature that year was 0.5 C (about 0.9° Fahrenheit) warmer than seasonal norms.
2002, which tied 2005 as the second warmest year, was also an El Niño year. El Niño Pacific Ocean warming events are caused by vast regions of warmer than normal surface water in the tropical Eastern Pacific.
In addition to warming large parts of the globe, El Niño events can also change weather patterns from the Middle East across the Indian and Pacific Oceans to the Eastern Caribbean.
As part of an ongoing joint project between UAH and NOAA, Christy and Dr. Roy Spencer, an Earth System Science Center principal scientist, use data gathered by microwave sounding units on NOAA 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.
Neither Spencer nor Christy receives any research support or funding from oil, coal or industrial companies or organizations, or from any private or special interest groups. All of their climate research funding comes from state and federal grants or contracts.
High resolution color maps of regional temperature anomalies for both 2005 and December 2005, as well as a map of regional 27-year climate trends, are available.
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