Climate watch: What climate models can teach us about heat

It has been hot in Texas this summer. A long-lived heat dome centered over northern Mexico brought high temperatures to Texas and expanded to include nearby states.

The heat dome is a region of high pressure associated with a kink in the jet stream that extends further south than usual. Maximum daytime temperatures in Austin and San Antonio in June were consistently over 100 degrees Fahrenheit. The heat index, which is measured in the shade, but accounts for relative humidity, reached 109 F in both cities.

High humidity slows the evaporation of sweat, making it more difficult to cool one’s body. In Houston, the temperature was slightly lower, but the relative humidity was higher, so the heat index went as high as 111 F. Two hikers died on June 24 in Big Bend National Park in south Texas on a day during which the temperature reached 119 F. Exposure to direct sunlight makes the danger from overheating much worse.

How much of this extraordinary heat is normal, and how much is associated with our warming climate? Any good meteorologist will tell you that it is difficult to blame global warming for any particular weather event. Nevertheless, temperature records were already broken in multiple cities in Texas in June. So, climate change may be partly responsible for this Texas heat wave.

Here is where climate models can help us. Climate models predict that severe heat waves should become more common as the climate warms and that the most severe of them will become even more deadly. The physics behind this prediction is straightforward: If greenhouse gas concentrations continue to increase, global average temperatures and maximum regional heat indices will go up along with them, as the Earth will be unable to cool itself as efficiently.

How worrisome is the predicted increase in future heat waves? In my view, this is the scariest, and most imminent, change associated with global warming — more dangerous, even, than sea level rise.

Few Americans die in heat waves today because most homes in warmer parts of the country are equipped with air conditioning. The same is not true elsewhere. In northern India, one of the hottest places on Earth, hundreds of people die of heat stroke almost every year, including 44 or more who passed away in a heat wave last month. Fewer than 15% of homes in India are air conditioned, and some households still lack access to electricity, so they cannot even run fans. By 2050, heat waves in India are expected to produce heat index temperatures that are lethal to even young, healthy humans lying in the shade. So, future generations of Indians will need to rely heavily on air conditioning, as we do here in the U.S. But if that air conditioning is powered by fossil-fuel-generated electricity, the problem will only continue to compound.

The problem of extreme heat may seem remote to many Americans, although it must be becoming more apparent to those living in Texas! But it could eventually become a huge issue, as people from tropical regions that are already uncomfortably warm seek shelter at higher latitudes. Legal and illegal immigration of people from countries to our south is already a hot-button issue in many border states. This problem could be greatly exacerbated if the global climate continues to warm.