Arizona is heating up faster than any other state in the lower 48, federal records show.

Alaska and Hawaii weren't in that federal database analyzed by the Arizona Daily Star.

Arizona's statewide average temperature was about two degrees higher from 2000 to 2010 than during the 20th century.

In the same decade, Arizona was among the top 20 states nationally in racking up extremely high temperatures, according to separate new research by the environmentalist Natural Resources Defense Council.

No one knows why Arizona's temperatures are rising faster than those in other states. One possible explanation is the patterns of ocean warming and atmospheric circulation patterns induced by the jet stream, said Jonathan Overpeck, director of the University of Arizona's Institute of the Environment.

Another reason may be the state's dry weather - rainfall statewide averaged about an inch less in 2001-10 than a century earlier. When there's less moisture to evaporate, more of the sun's heat goes into making the land and air hotter, said Stephen Saunders, president of the Rocky Mountain Climate Organization.

This state's continued warming gives ammunition to experts including UA climatologist Overpeck, who has said Arizona is "ground zero" for the impacts of climate change.

The details:

• Numbers. Arizona's average temperature from 2001 to 2010 was about 61.5 degrees, compared with 59.45 degrees from 1901 to 2000, say data from the website of the Western Regional Climate Center, a federally financed program.

The global average increase for 2001 to 2010 was one degree, says the Rocky Mountain Climate Organization, a Colorado-based research/advocacy group.

Of Arizona's two-degree increase, "It is a lot. Plants will definitely notice a change like that, even if we don't," said Kelly Redmond, a regional climatologist for the Western Regional Climate Center of the National Oceanic and Atmospheric Administration.

All of Arizona's warming has occurred since 1980, after average temperatures declined 0.7 of a degree in the 1960s and '70s, climate center records show. The temperature changes were most acute in May and July.

As for extreme temperatures, the northern three-fourths of Arizona had at least two weeks worth of high temperatures yearly during 2000-09 that were warmer than 90 percent of the high temperatures for the year, according to data from the Natural Resources Defense Council. Southern Arizona including Tucson had 9 to 13 days where temperature averages exceeded that 90th percentile. Nine is the average number of days in a year when temperatures topped the 90 percent ranking from 1961 to 1990.

• Significance: These numbers put Arizona among the places in this hemisphere with the most obvious impacts of climate change, said four researchers: Overpeck, Saunders and Redmond, and Overpeck's UA colleague Zack Guido.

"In recent years, temperatures have been increasing while precipitation has been decreasing. People are in tune to that here," Guido said. "The Southwest is relatively poor compared to other regions, and our harsher climate causes increased burdens on the poor" who may lack air conditioning, for example, he said.

Other places with clear-cut impacts include the Pacific Coast and the Caribbean, where sea levels are rising; the Arctic, where sea ice is melting; and Alaska, where permafrost is melting, these experts said.

• Implications: The Natural Resources Defense Council and Arizona State University Professor Sharon Harlan said these higher temperatures mean officials need to pay more attention to heat-induced illness and death.

A Centers for Disease Control study using 2002 data - the most recent available - found that Arizona had the largest number of heat-related deaths of any state.

An Arizona Department of Health Services report last year found that 1,485 people died of heat-related illness in the state in 1992-2009. Nearly 45 percent of those deaths befell illegal immigrants crossing the desert, and 43.5 percent of the victims were Arizona residents; the rest were visitors from other states and countries. Assuming temperatures keep warming, other sectors of the population could be in danger, Harlan said.

Arizona, unlike California, has no action plan aimed at preparing people for heat-related health problems due to climate change. But the Arizona Department of Health Services has an emergency response plan for extreme heat episodes. It also has started work on a three-year project, financed by the CDC, to assess vulnerability and educate people about extreme heat. It will target vulnerable groups such as the homeless, athletes, outdoor workers and the elderly.


Contact reporter Tony Davis at or 806-7746.