Thousands more Arizonans will likely die. Farmers’ crop yields will drop. Electricity bills will rise sharply, along with the use of air conditioning.

These forecasts for Arizona by the end of the 21st century come from a new report that for the first time tries to project specific impacts of a hotter climate in each U.S. state.

“Risky Business,” a national report prepared for a group of blue-ribbon business leaders, is targeted at the business community. With two former Treasury secretaries, former New York City Mayor Michael Bloomberg and former Secretary of State George Shultz leading the study effort, the report seeks to show that climate change will have severe economic costs.

Arizona’s impacts are expected to be among the most severe among the 50 states, the report says. But that’s not because our temperatures will rise faster than other states, says Trevor Houser, project manager for the Risky Business project.

In fact, the report — prepared by New York City economic research firm the Rhodium Group — predicts that northern states’ temperatures will rise faster than those in the Southwest. Arizona’s impacts will be more severe than most because the state’s temperatures are already among the country’s hottest, Houser says.

“A lot of change in temperatures in northern states will be delivering benefits — less heating demand, less cold-related mortality, improved agricultural production and the growing season becoming better,” Houser says. “The southern states will see less of the benefit of warmer winters and a greater share of overall impacts.”

Western experts on energy, heat-related mortality and agriculture say the report’s research methods were generally credible. Two leading University of Arizona climate researchers say that, if anything, the report understated climate change impacts here because of what it didn’t study.

But one of the UA researchers Kathy Jacobs offers a cautionary note. While Jacobs agreed that the research methods were credible, she added that there are limits to how much one can “downscale” national forecasts of climate change impacts to individual states. In general, neither climate nor relevant economic data for these impacts exist on these scales for the whole country, she says.

“What you have here is a very challenging project. This is being done at a scale that is probably unprecedented in the U.S.,” says Jacobs, who directed the recent, federally financed National Climate Assessment from Washington, D.C., and now runs a UA climate adaptation research center.

Stressing she’s not being critical of the report, she says, “Getting to specific numbers of deaths or dollars of agricultural impacts in particular places is likely challengeable.” But many of these trends are well understood and have been clearly documented on a national level by the climate assessment, she says.

Also, while this report had a 12-member outside expert review panel, that wasn’t nearly as detailed or rigorous a review as the National Climate Assessment got, Jacobs says. The reviews of the two reports don’t need to be the same or even comparable because the climate assessment is a government report, she says. At the same time, “This opens up many avenues for potential criticism,” she says.

“But overall, it seems like a useful effort to help the business community understand why climate impacts — and opportunities — are important,” Jacobs says. “Maybe more important than the absolute numbers are the relative impacts between different regions of the country.”


Look for a huge increase in the number of Arizona days with high temperatures that exceed 95 Fahrenheit, the report says.

Average daily temperatures in Maricopa, Yuma, Mohave, Pima and Pinal counties by 2100 will be about 6 to 10 degrees higher than today, maps from the report show.

This will likely push Arizona’s above-95-degree days from 116 today to as many as 205 by 2099, the report says. Nationally, the average U.S. resident will likely see an average of 46 to 96 days annually over 95, compared with 15 such days between 1981 and 2010, the report says.

Three prominent UA climate researchers – Jacobs, Jonathan Overpeck and Gregg Garfin – say the projections are in line with those in other reports, including the National Climate Assessment.

“The results appear to have been generated by a credible team, at least with respect to the climate science,” says Overpeck, director of UA’s Institute for the Environment. The numbers “highlight how Arizona will get hit hard by climate change unless the climate change is slowed significantly.”

If you add the report’s projected temperature increase by midcentury of about 4 degrees, plus additional nighttime warming from the urban heat-island effect, Tucson’s temperatures would match those of Phoenix today, says Garfin, a deputy director for the institute. Go to the end of the century and, “now we in Tucson are exceeding current temperatures in Yuma and Phoenix,” Garfin says.

“There’s going to be a price to pay for that kind of increase, and that price will be the cost of water and energy if we continue with business as usual,” Garfin says. “I don’t see this becoming a ghost town. But given those kinds of scenarios it will be more challenging to live here and we’ll see changes in the environment.”

But Tucson isn’t doomed to go down this path, since the report doesn’t consider the possibility of local measures to buffer the impacts, Garfin says. They could include planting trees for more shade and using new forms of road building materials that would absorb less heat, reducing the pain of the heat-island effect.


The report forecasts a seemingly modest increase of 2 to 6.4 percent in deaths related directly or indirectly to heat in various parts of Arizona by the end of the 21st century.

But numerically, that amounts from 924 to more than 2,800 additional deaths in Arizona each year, assuming the current population. Overall, the study projects increases in temperature-related deaths of 14 to 43 per 100,000 Arizonans annually by 2099.

Last year, the Arizona Department of Health Services reported 139 deaths from heat-induced illness. But that number typically includes only those linked to heat stroke and related symptoms caused directly by high temperatures, says Sharon Harlan, a senior sustainability scientist at Arizona State University’s Global Institute of Sustainability.

The Risky Business estimates include all deaths directly or indirectly related to temperature — cardiovascular and respiratory diseases, and other underlying medical conditions. “There are many more deaths that are indirectly related to high temperatures than those caused by heat stroke,” she says.

By contrast, the northern U.S. will experience declining temperature-related death rates by 2100, the report says. Temperatures will rise enough in those areas to reduce cold-related deaths, but not enough to significantly boost hot weather deaths.

ASU’s Harlan says she believes the report is backed by high-quality research and should be taken seriously. The authors have thoroughly reviewed literature on temperature-mortality relationships and selected the best national long-term studies to estimate deaths in individual states, she says.


Too hot? Flip on the air conditioner. That’s what the Risky Business report predicts will happen more and more in Arizona and the Southwest over the next century.

That should raise Arizona’s energy demand by 12 to 22.5 percent and energy costs by 23.8 to 44.2 percent by 2099, the study says. The national average increase is expected to be 6.2 to 14 percent by 2099.

People living in the cooler New England and Pacific Northwest will likely have energy demand increase by percentages in the low single digits by the end of this century, the report says.

Generally, studies have found that temperature increases cause electricity use to rise more rapidly than when the temperature drops, the report says. When areas switch from needing more heat to needing more cooling, total energy costs rise.

Also, climate-driven increases in cooling demand boost electricity consumption during hot times and seasons when demand is already peaking, the report says. Higher peak demand typically requires utilities to build more power plants or other power generation capacity to satisfy it. That raises costs more.

Experts at the California Energy Commission in Sacramento and Sandia National Laboratories in Albuquerque agreed that these findings are credible.

The commission pointed out that the study based its predictions on a model of the country’s energy system developed by the U.S. government. The main authors include lead economist professor Solomon Hsiang from the University of California-Berkeley, whose work has been published several times in major scientific journals such as Science and Nature.

Since computer models used by the report generally meet industry standards, and its predicted national average electricity use increase matches the forecast by the federal National Climate Assessment, “I don’t see any red flags in their analysis,” says Sandia’s Vince Tidwell.


Crop yields for staples such as wheat, cotton, soybeans and corn could take a big hit in Arizona by 2099, dropping by 25.9 to 51 percent from current levels, the report says.

Such declines would place Arizona at or near the bottom of the heap among states, although broader regions such as the Upper Midwest or the Deep South will experience crop yield declines over a broader area than what’s forecast for the Southwest. In the Pacific Northwest and Northern Rockies, on the other hand, crop yields are generally expected to rise by 2099. Overall nationally, yields are projected to decline sharply by the end of this century.

The reasons for such a wide range of possible outcomes for Arizona crop yields include the uncertainty of climate computer models, since researchers used 40 different ones to make these predictions. There’s also statistical uncertainty in the relationship between temperatures and crop yields.

In general, warming weather at first tends to improve growing conditions because the growing seasons typically last longer. As temperatures rise over time, however, the benefits from longer growing seasons are overwhelmed by the negatives caused by hotter, drier weather, the report finds.

George Frisvold, a leading UA agricultural economist, says the research methods used to predict crop yields are valid. But Arizona farmers likely will be able to adapt to higher temperatures and offset many expected declines in crop yields, says Frisvold, a professor and extension specialist in UA’s College of Agriculture and Life Sciences. The Risky Business report doesn’t try to predict how much adaptation is possible.

“It’s like you’re trying to predict the outcome of the Super Bowl and you ask what would have happened if the Seattle Seahawks had run a draw play every single play?” Frisvold says. “They wouldn’t do that, but what if they did that?”


What the report doesn’t study is how a broiling climate will affect the state’s well-loved but fragile natural environment and its water supply – and on the broader economic impacts of those environmental impacts.

Because of that, UA’s Overpeck and Jacobs and Risky Business project manager Houser agree the report probably or definitely understates the Arizona impacts. The report also doesn’t examine climate change impacts on quality of life, on communities that must be relocated and on valued cultural practices, Jacobs says.

The study takes a decidedly conservative approach, by limiting its analyses to impacts where there’s strong enough research or mature enough private sector-based computer models to make researchers confident of their projections, Houser says.

Impacts to water and ecosystem services “are fairly challenging to quantify” he says, “though in many parts of the country — including Arizona — they will likely be substantial.”

Contact reporter Tony Davis at or 806-7746. Follow Davis on Twitter @tonydavis987, and his Desert Blog at