Excessive heat warning: Why are US states facing record-breaking heatwaves?

Excessive heat warnings issued for areas in Arizona, California, Texas and Utah

Louise Boyle
Senior Climate Correspondent, New York
Tuesday 15 June 2021 14:07 BST
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A triple-digit heatwave is rolling through the US Southwest with states on high alert over dangerous health conditions and fire risk.

A high-pressure ridge has built over deserts, with forecasters warning on Tuesday that the temperature in California will hit triple digits in the next 48 hours.

Excessive heat warnings were also issued for areas in southwest Arizona, including the city of Phoenix, along with parts of Texas and Utah.

“Dangerous heat will affect much of the western US for much of this week with temperatures up to 120 degrees. These temperatures make any outdoor activities dangerous so stay cool and hydrated,” the National Weather Service (NWS) tweeted.

Energy officials in Texas were urging residents to cut back on power usage over fears that demand will outpace supply amid the soaring temperatures.

The request came from the Electric Reliability Council of Texas, the private entity controlling much of the state’s power supply. ERCOT was the focus of intense criticism following the catastrophic failure of Texas’s power systems during Winter Storm Uri earlier in the year, leaving millions without power in below zero temperatures. The will last through to 18 June.

California’s grid reported no anticipated rotating outages on Monday but encouraged citizens to conserve power.

Meteorologists told Reuters that the heatwave, brought on by the early high-pressure system, could not be blamed directly on the climate crisis.

“It’s difficult to tie any one particular event to climate change,” said Eric Schoening, a NWS meteorologist in Salt Lake City. “But studies show that as the climate changes and it gets warmer, we will see more of these anomalous events over time.”

Overall, extreme heatwaves are becoming more frequent in the US and around the world as the planet heats up.

The latest climate averages from the US National Oceanic and Atmospheric Administration (NOAA) for the 1991-2020 period found that in the 48 contiguous states, the 30-year average temperature reached a record 11.8C (53.28 degrees Fahrenheit).

At the beginning of the 21st century, “normal” was 11.3C (52.3F), according to NOAA’s 1971-2000 data. The 20th century’s average US temperature was 11.1C (52F).

Since the first dataset was collected in the period 1901-1930, around 1C of warming has taken place in the contiguous US – excluding Alaska and Hawaii – a similar increase to the rest of the world.

Of the 10 decadal datasets produced by NOAA, the two most recent 30-year periods have seen the biggest rises in temperatures.

The US government’s National Climate Assessment projects that there will be 20-30 more days over 90F in most areas by 2050.

Extreme heat is a catalyst for a slew of disasters including greater risk of drought, and priming the hot, dry conditions that can lead to wildfires.

Heatwaves exacerbate the “heat island effect” in cities, leaving buildings and roads and infrastructure up to 90F hotter than the air temperature.

Dangerous heat is also a serious public health threat. US officials estimate that heatwaves kill more than 600 people annually, more than all other weather-related deaths, with the exception of hurricanes.

Heatwaves could be a factor in food insecurity in the future in the southwest region along with other conditions like drought, and fewer winter chill hours.

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