Extended forecast: Unbearable heat, diminishing water supply, more frequent and devastating wildfires, eradication of indigenous plants and animals. It’s not an absolute certainty, but it’s not science fiction, either, say scientists studying the impact of global warming on the Valley.
Sophisticated computer models designed to predict climate change over the coming decades show average temperatures in the Valley could increase anywhere from 4 degrees to 13 degrees before the century’s end.
“By 2080, a new extreme might well be 130 degrees Fahrenheit,” said Alan Thorpe, a leading British atmospheric scientist who visited Arizona State University this month to discuss the latest global warming predictions.
Thorpe, who heads the National Environment Research Council — the British counterpart to America’s National Science Foundation — has been studying the effects of industrialized society on the Earth’s climate for about 10 years.
Despite continued debate about global warming in the political arena, most experts studying the phenomenon no longer harbor any doubt that the recent surge in average global temperature “is entirely from human activity,” Thorpe said.
The reason for the recent surge is that recorded temperatures and atmospheric concentrations of carbon dioxide — which is produced by fossil fuel combustion and traps heat beneath the atmosphere — have increased far more rapidly in recent years than can be accounted for by natural climate cycles.
Joseph Zehnder, director of the Southwest Consortium for Environmental Research and Policy, describes himself as a reformed skeptic of man-made global warming.
“Now, every credible person in the business believes there is something going on,” the ASU geography and meteorology professor said.
Zehnder is pioneering research into another local phenomenon that already has made the Valley hotter. His team is looking for ways to reduce the heating effects of air conditioners, roads, block walls and other artificial surfaces, also known as the “urban heat island.”
There is solid evidence to suggest the Valley will continue to get hotter, he said, but questions remain about how drastically the local climate will change.
“Do you nudge up the temperature 2 or 3 degrees, or do you expect an increase in extreme events?” Zehnder said.
‘FRINGE OF HABITABILITY’
A confluence of environmental factors contributes to the Arizona desert’s extreme summer heat, including low elevation, latitude, moisture and wind.
The atmosphere’s weight presses down on the air at low altitudes, packing its free-floating molecules more tightly together and creating heat as they collide.
At relatively low latitudes, the sun’s rays shine down more directly through the atmosphere, reducing the extent to which they are deflected back into space by the atmosphere itself before striking the Earth’s surface.
Evaporation has a cooling effect on the air, but the Valley’s dryness doesn’t allow for much relief. Wind turbulence also tends to reduce temperatures, which is of little help in the still, desert air.
Those factors often push conditions in the Valley to the limits of human tolerance, and significant changes due to global warming could pose serious health risks.
“We’re sort of on the fringe of habitability,” Zehnder said. “I mean, people aren’t supposed to live in deserts.”
The full effect of those changes is still unknown, but evidence already shows slight increases in temperature tend to cause a chain reaction of warming events in what scientists call a “positive feedback loop.”
Since the Valley’s environment lacks significant forces to negate a warming trend, such a loop could have far-reaching effects.
Another, more immediate concern to Zehnder and his colleagues is the warming of Valley cities caused by man-made surfaces and technology.
In what is known as the urban heat island effect, asphalt and concrete absorb the sun’s rays during the day and radiate heat at night. In addition, vertical surfaces such as buildings and walls delay the escape of heat back into the atmosphere by deflecting it sideways.
Even air-conditioning units contribute to the effect, by displacing heat from inside buildings out into the air. A trend toward placing those units on the ground rather than on rooftops exacerbates the problem, Zehnder said.
The heat island effect has raised summer low temperatures by about 10 degrees, he added.
HOT TIMES AHEAD?
Valley temperatures have reached or exceeded 120 degrees three times in recorded history — twice in June 1990, and again in July 1995. The hottest day on record was June 26, 1990, when the temperature hit 122 degrees.
On that day, extreme heat was blamed for at least three deaths, and several passenger jets were grounded at Phoenix Sky Harbor International Airport because they had not been tested for the ability to generate adequate thrust for a safe liftoff at temperatures above 120 degrees.
National Weather Service officials in 1990 were quick to point out that a high-pressure weather system caused the extreme heat, not global warming or the urban heat island effect.
Weather and climate are caused by a variety of environmental factors that are often interconnected, making it difficult to predict how altering one variable will affect the others. Most are naturally occurring events that have nothing to do with human activity, such as the ebb and flow of ocean currents.
For example, Arizona’s monsoon season is influenced in part by the surface temperature of equatorial waters hundreds of miles away off the coast of Peru.
Warmer surface temperatures, known as El Niño, tend to cause more precipitation, while cooler temperatures — La Niña — lead to drier weather.
Likewise, regular shifts in the Earth’s rotation and orbit have been responsible for climate changes since long before man burned his first lump of coal.
“There is a strong natural variation of climate — nothing to do with human input,” said the British atmospheric scientist Alan Thorpe.
Still, he said global warming could increase the frequency of record-high temperatures and turn weather that once seemed extreme into the norm.
The temperature boost is likely to bring about a series of related environmental changes, according to a recent report by the Intergovernmental Panel on Climate Change, a multinational group of climatology experts.
A report called “The Regional Impacts of Climate Change” on the group’s Web site — www.ipcc.ch — contains a section on North America that describes how global warming could affect life in Arizona.
In addition to thermal extremes, the report lists likely effects such as extended drought, longer and more active forest fire seasons, decreases in water supply due to evaporation, shrinking forests and disrupted wildlife habitat as heat drives out water and food sources.
Other possible effects include the proliferation of diseases carried by insects and rodents, and an increase in heatrelated illness and deaths, the report said.
“Climate change is likely to have wideranging and mostly adverse impacts on human health,” it says.
LATE IN THE GAME
Despite repeated warnings from the scientific community, state and local policymakers in Arizona have been slow to respond.
However, one adviser to Gov. Janet Napolitano said she has been working on a policy plan that could make Arizona a front-runner in the race to reduce greenhouse gas emissions.
Diane Brown, who heads the Governor’s Climate Change Advisory Group, said the group will release a report Monday called “A Blueprint for Action: Policy Options to Reduce Arizona’s Contribution to Global Warming.”
The report outlines 14 strategies that would benefit the state both environmentally and economically, she said.
“There are steps that can be taken today, and there are steps that need to be taken today,” said Brown, who is also executive director of the Arizona PIRG Education Fund, an environmental and public advocacy group.
The strategies include a “clean cars program” that would create incentives for purchasing hybrid-electric cars while imposing limits on vehicle carbon dioxide emissions.
The report also proposes requiring insurance companies to offer “pay-as-you-drive automobile insurance,” in which insurance rates would be calculated based on the number of miles driven.
Other suggestions include reducing urban sprawl, requiring more renewable fuels and energy, and encouraging the use of public transit.
“These global warming strategies are in the best interest of Arizona for our economy and for public health,” Brown said.
While Zehnder said he applauds consumers who conserve energy and minimize their own fuel emissions, it will take policy changes at the national and international levels to make a real difference.
“Just because you went out and bought a hybrid car, it’s not going to keep the north pole from melting,” he said.