Bright_sunBy Bill Dawson
Texas Climate News

What will the ongoing, planet-wide warming of the atmosphere mean for Texans’ day-to-day lives?

It will bring a lot more days with dangerous heat-illness risks, according to one new analysis. And a lot more days when Texans want to crank up the A.C., other researchers recently calculated.

Neither finding is very surprising, perhaps, but it can be hard to imagine such spin-off particulars of what scientists’ projected temperature increases will actually entail.

Some Texans might shrug: This is a warm place already. What’s an extra degree or two (or three or four)? The two recent statistical appraisals, however, may help explain temperature projections’ impacts more forcefully and comprehensibly.

One analysis, by a nonprofit research and reporting organization called Climate Central, focused on “danger days” when the heat index reaches or exceeds 105. By mid-century, several Texas cities now averaging just a few of these days each year (or none at all) could annually experience dozens – more than 100 “danger days” per year in five cities, the researchers calculated.

The other analysis, by Stanford University researchers, examined energy consumption in terms of heating days and cooling days – when the temperature typically means a furnace or air-conditioner is switched on. For all Texas cities studied but one, they projected big increases in total days with one or the other in use – a 33 percent increase in Houston, for instance.

Both assessed “business as usual” scenarios regarding emissions of greenhouse gases – that is, with no new limits on the heat-trapping pollution, which mainly comes from the use of fossil fuels and scientists say is causing an average warming of the earth.

“Danger days”

The heat index, a familiar mainstay of broadcast weather reports, is the combined heat-and-humidity number that conveys how hot a certain temperature feels at a certain humidity reading.

The level labeled “danger” by the National Weather Service – indicating the “likelihood of heat disorders with prolonged exposure or strenuous activity” – varies from a heat index of 103 to 106, depending on the particular temperature-humidity combination.

Climate Central’s report defined “danger days” as those with a heat index of 105 or higher. It  noted that of the 144 U.S. cities that were assessed, “only 12 of them averaged more than one danger day per year since 1950.”

Houston, for example, which qualifies as a hot and humid place by just about anyone’s standards, averages just one “danger day” per year now (in statistics from 2010-14), according to Climate Central. Besides Houston, it reported four other Texas cities are now averaging one or more such day annually – Austin (3.7 days), Corpus Christi (1.3), Fort Worth (3), Wichita Falls (12).

With global warming due to “business-as-usual” emissions, however, Climate Central projected that 12 Texas cities among the 144 it studied nationwide will average between 14 and 140 “danger days” annually in the 2045-54 period:

  • Amarillo – 50 days
  • Austin – 72
  • Brownville – 105
  • Corpus Christi – 140
  • El Paso – 17
  • Fort Worth – 139
  • Houston – 102
  • Lubbock – 14
  • Port Arthur – 124
  • San Antonio – 109
  • Waco – 77
  • Wichita Falls – 68

Corpus Christi’s and Fort Worth’s numbers meant they ranked fifth and sixth nationally on Climate Central’s list of cities projected to have the most “danger days” around the middle of the century.

Among other impacts such as reduced productivity among outdoor workers and the need to adjust sports practices, Climate Central noted that a rise in “danger days” and “extreme caution days” (those with a heat index of 90 or higher) “will also drive up how much people spend on energy as air conditioning goes from being handy to being a necessity.”

Heating and cooling days

“Handy” and “necessity” are relative terms, of course – some Texans, even in the hottest parts of the state – can’t afford air conditioning or at least to use it as much as they’d like.

To standardize their calculations, the Stanford researchers based their assessment on an assumption that temperatures on either side of 65 degrees are likely to prompt air-conditioning or heating use. What they called a degree day was a day with a temperature of 66 or 64.

Researcher Ken Caldeira explained to the Washington Post: “Ten heating degree days could be one day when it’s 55 degrees outside. Or it could be 10 days when it’s 64 degrees.”

The same yardstick defined a “cooling degree day.” The Post noted: “Fewer degree days means less combined heating and cooling, suggesting a more comfortable climate that requires less energy use.”

Seven Texas cities were among the 50 around the country for which the researchers combined historical climate data and computer projections of warming conditions to forecast changes in their heating and cooling days. The seven in Texas were Arlington, Austin, Dallas, El Paso, Fort Worth, Houston and San Antonio.

If “comfortable” indeed means fewer degree days, Houston was the most temperate of those cities in the 1981-2010 period that was assessed, with 4228 “degree days.” Fort Worth and Dallas had the most, with 5,041 each.

Looking ahead to 2080-99, all seven cities but El Paso were projected to have major overall increases, balancing the likelihood of heating and air-conditioning demand, in their degree days – and therefore, their likely energy use to warm or cool building interiors.

In El Paso’s case, a projected 55 percent drop in heating degree days was essentially offset by a 54 percent increase in cooling degree days, yielding an overall decline of 2 percent in all degree days. In all the other Texas cities, however, projected increases in air-conditioning demand greatly exceeded reductions in heating demand.

Houston’s increase was biggest at 33 percent, reflecting a 43 percent drop in heating degree days overshadowed by a 66 percent increase in cooling degree days.

San Antonio’s overall increase in degree days was next largest at 26 percent, Austin’s was 23 percent, and the jumps of the three North Texas cities in the same metro area were about the same – Arlington at 16 percent, Dallas at 15 percent and Fort Worth at 14 percent.


Bill Dawson is the founder and editor of Texas Climate News.

Image credit: Jalal Hameed Bhatti / Cropped photo used under a Creative Commons license.