The Earth Day Network supplies a "Climate Change Fact Sheet" on its Web page. One of its statements declares: "Much of the United States has already warmed, by as much as 4 degrees Fahrenheit."
According to Michael Crimmins, assistant specialist in climate science at the UA, we haven't seen that type of dramatic increase around here--yet.
"In the Tucson area," Crimmins says of the last 10 years, "the temperature has risen a half to 1 degree Fahrenheit on average, especially in the summertime. That is certainly a significant trend."
Despite this relatively tiny increase in average temperature, Crimmins points out two noticeable impacts brought about by climate change so far.
"We're certainly seeing (its effects) across Arizona in the last 10 years, with the most warm years ever, even at rural weather stations," he says. "With precipitation, we're seeing a lot of variability. In the last 10 years, there have been many dry winters and less summer rains."
The effects of these climatic changes--even if not generally perceived by the average person--are potentially significant for the gardeners, growers and farmers of Southern Arizona, says Eddie McPheeters of Catalina Heights Nursery.
"In the early days, near Tucson Country Club (located next to the confluence of the Pantano Wash and Tanque Verde Creek in northeast Tucson), you really couldn't grow some plants, because it would freeze," he says.
But today, McPheeters says, plants like citrus trees and Mexican honeysuckle do pretty well there. Whether that's because of warmer temperatures or because of increased protection from the elements caused by development, he doesn't know.
Since 1947, when his family moved to Tucson, McPheeters says he recalls both dry and wet periods, and both cold and warm winters.
McPheeters has noticed another thing about Tucson's warmer summers, aside from the heat's effects on his plants: "I've seen some insects hanging out longer in the fall."
Last year, McPheeters adds, there was another sign of warm temperatures sticking around later into the year: "We grow a lot of pansies, but in late October, we couldn't make them bloom. They reacted like, 'It's too hot for us.' But then with a break in the temperature, they did fantastic."
From another perspective, UA extension agent John J. Kelly says of Tucson's warming temperatures: "We haven't seen any difference in home gardens, because they're irrigated."
As for the many pine trees around town displaying brown tips on their needles, which some people associate with climate change, Kelly explains: "No one irrigates in the winter here. The trees need one or two real good irrigations in the winter."
Down Interstate 19 in Sahuarita sit the orchards of the Green Valley Pecan Company. Roger Hooper is the farm manager of the business, which has more than 100,000 trees on about 6,000 acres of scenic land.
Pecans can't be harvested until after the first freeze, and that didn't occur until almost Christmas last year. As a result, the process began about a month late. Hooper, however, doesn't think that's a sign of anything unusual.
"It will happen cyclically," he says, "and one year, a trend does not make." But Hooper also observes: "Summer storms seem a little stronger, possibly because of climate change."
Cochise County extension agent Rob Call has also seen some minor variations in the weather. "Temperatures are rising a little bit," he says, "but we have erratic springs, anyway.
"I haven't heard anyone complain about (global warming), but farmers and growers usually don't complain about the weather, because they can't do anything about it," Call says. "Warmer weather in February this year pushed trees along a little bit, but on the other hand, an early frost a couple of years ago killed buds. It's spring frosts that are problems here."
Jeffrey Silvertooth, head of the UA's Soil, Water and Environmental Science Department, points out the difference between people noticing something happening with the weather, and a real, significant climatic trend. He says there is a lot of conversation about some weather variables among the Yuma farmers he deals with.
"It's kind of a mixed bag," Silvertooth says about the weather along the Colorado River. "We've had extended warm seasons for (summer) crops."
Silvertooth estimates that 90 to 95 percent of the nation's winter vegetables, such as lettuce and cauliflower, are grown in the Yuma area. He says that warming conditions may reduce the winter-growing season window.
Except for with uncertain water supplies, climate unknowns might be the greatest challenge facing farmers and growers on this year's Earth Day, which will be celebrated in Tucson on April 19 at Reid Park. (See www.tucsonearthday.org for more information.)
Despite all our modern technology, weather forecasting may be best left to animals.
McPheeters' late father, Ralph, had a friend who lived along the Tanque Verde Wash and owned a burro.
"If the burro had a thick winter coat," McPheeters remembers with a smile, "it meant it would be a cold one. But if it was thin, then the winter would be mild."