Regarding the May 11 editorial on the "costs of climate's impact on future Arizonans": Although I believe human activity has a significant effect on climate, I also believe it's a mistake to assume a scary report with John Holdren's name on it is an accurate assessment of either future climate or the cause of its changes.
As regards Arizona, I decided to do my own assessment.
I analyzed temperature data from four stations based on population density: Phoenix airport, Prescott, Tuzigoot, and Walnut Creek (west of Chino Valley). Temperature data (in degrees Fahrenheit) was available from 1933, 1898, 1977, and 1951, respectively.
Dates of record high temperatures at Phoenix (122° in 1990), Prescott (105° in 1925), Tuzigoot (118° in 1994), and Walnut Creek (114° in 1969) suggest an inconsistent upward trend, but that's not the case. Overall, average temperatures show a rise until about 1996, after which differences become more interesting.
Phoenix average temperature remains elevated--in 2013 it was a whopping 3.36° above its 66-year mean. At Prescott, Tuzigoot, and Walnut Creek, however, average temperatures have been declining. Prescott's average temperature dropped from 56.87° in 2001 to 54.44°in 2013--1.2° above its 94-year mean. Tuzigoot's dropped from 65.26° in 1996 to 62.64° in 2013--just 0.44° above its 34-year mean. And Walnut Creek's dropped from 55.34° in 2000 to 53.02° in 2013--just 0.7° above its 55-year mean.
Daily temperature records set last year show similar trends. Phoenix had 10 days with record high temperatures and 2 days with record lows. Prescott had 7 record highs and 5 record lows. Tuzigoot, with a much shorter history than the other stations, had 5 record highs and 19 record lows, while Walnut Creek had 2 of each.
If rising carbon dioxide levels were really the primary driver of rising temperatures, it seems logical that all four stations would show similar trends. What could explain the differences?
Answer: Population, development, and groundwater depletion. These, along with agriculture and sprawling 'green energy' farms, are known as 'land use changes'--something carbon-as-pollutant promoters don't want to consider.
Phoenix, with over 4 million people and growing, is a 16,000 sq. mi. blanket of heat-soaking concrete, asphalt, and steel. With all inflow intercepted and precipitation diverted, groundwater mining has dropped water levels 300-500 feet, and resulting subsidence has lowered some areas of the valley more than 18 feet since 1900. The effect on local climate is not trivial.
Greater Prescott is minuscule compared to Phoenix, but it still has more concentrated development than the areas around Tuzigoot and Walnut Creek, where natural climate variation is clearly taking precedence over CO2's greenhouse effect.
But then, CO2 alone never posed a threat of catastrophic warming. Climate modelers assumed that a small amount of warming from CO2 would force an increase in atmospheric water vapor (a much stronger greenhouse gas), accelerating the warming. That hasn't happened.
In Arizona, our contributions to climate change are primarily groundwater depletion and over-development.