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Study: Warming Not Natural

In case you were thinking, or hoping, that global warming isn't such a big problem after all, consider a study appearing in Friday's issue of the journal Science.

It says that an area of sea ice larger than the state of Texas has melted over the past 19 years.

Researchers using complex computer programs that mimic the climate system concluded that there is only about a two percent chance that so much melting is a result of natural climate changes. The team was led by Konstantin Vinnikov of the University of Maryland.

In recent years scientists have become increasingly concerned about the possibility that chemicals released into the atmosphere by industry are causing the climate to warm, though some contend that the changes are part of natural variability.

Vinnikov's team concentrated on satellite measurements of arctic sea ice taken since 1978, showing an overall decline in ice area larger than the state of Texas.

The result, the team reports, "strongly suggests that the observed decrease in northern hemisphere sea ice extent is related to (human caused) global warming."

Claire Parkinson, a climatologist at NASA's Goddard Space Flight Center and one of the study's co-authors, said, "We have to be careful how much we're affecting the atmosphere and the ocean, especially as we're really not fully aware yet what the consequences might be."

Parkinson points out that observation records are very short - only a few decades.

"We have a lot of uncertainties left," she said. "But we should try to be conscious that the human population is great enough now that it is indeed causing effects on the Earth's system. The important thing is that humans be cautious."

In addition to the University of Maryland and NASA, participating in the study were researchers at Rutgers University, the National Oceanic and Atmospheric Administration, the University of Illinois, and the Hadley Center in Britain and the Arctic and Antarctic Research Institute in Russia.

Since the ice is floating, the melting does not affect sea levels.

The researchers used computers in Princeton, N.J., and at the Hadley Center in Britain to calculate the probable normal changes in the Earth's atmosphere over long periods.

They then studied computer simulations that include greenhouse gas increases, tending to warm the atmosphere, and aerosol increases, tending to cool the atmosphere.

The model results with these human-induced changes included were a much better match with the observed sea ice decreases than the model results simulating natural variability.