Texas heat wave has two connections to the warming climate

Everything is bigger in Texas, including the heat. But the recent heat wave there was big even by Texas standards, rewriting local weather records.

The anchor of the heat was in southwest Texas, which is already hot to begin with. In Del Rio, on the east side of the Rio Grande, an all-time high of 113 degrees was set on June 20. The next day, it was even hotter, reaching 115 degrees.

<p>Sweat rolls off the lip of Robert Harris as he digs fence post holes Tuesday in Houston. Scorching temperatures taxed the Texas power grid and brought record highs to the state.</p>

David J. Phillip, Associated Press

Sweat rolls off the lip of Robert Harris as he digs fence post holes Tuesday in Houston. Scorching temperatures taxed the Texas power grid and brought record highs to the state.

San Angelo reached 114 degrees on back-to-back days on the 20th and 21st. Laredo tied its all-time record of 115 degrees on the 19th.

Richard Berler, a veteran broadcast meteorologist for KGNS in Laredo since 1980, has kept meticulous weather records and was amazed at the consistency of the heat.

“This was the hottest 16-day period in the Laredo record (June 13-28), with records going back to 1895. Sporadic records which go back to 1849 at old Fort McIntosh show no heat episode that equals what we have just experienced.”

And there was not much cooling at night, making it even more difficult for the body to recover from the intense heat of the day.

“We just recorded 14 consecutive midnights at or above 90 degrees,” Berler said, adding that some years have none. “We had 102 degrees at 10 p.m. on 2 nights. Tragically, eight people in our county lost their lives due to heat illness last week, nine across the river in Nuevo Laredo.”

<p>Nationally averaged summer low temperature since 1970 have been climbing.</p>

CLIMATE CENTRAL

Nationally averaged summer low temperature since 1970 have been climbing.

The intensity of heat is one of the most direct connections to the warming climate. As the planet has warmed over the past century, the hottest weather is getting hotter, and the coldest weather is not as cold.

<p>Ed Newby, owner of All Star A/C and Heating, fields calls during a heat wave Monday in Houston.</p>

Raquel Natalicchio, Associated Press

Ed Newby, owner of All Star A/C and Heating, fields calls during a heat wave Monday in Houston.

Carbon dioxide in the atmosphere, a greenhouse gas emitted from the burning of coal, oil and natural gas, has increased more than 30 percent since 1958, and it is the primary reason the climate is warming. It may not cause the heat on any one day, but it drives the weather patterns that lead to the extreme heat.

Like stacking a deck of cards or loading a pair of dice, it makes extreme heat on any given day more likely than a century ago. More troubling, there is growing evidence that such extremes are now lasting longer.

Weather patterns in the middle latitudes — that area between the Arctic and the tropics — are largely governed by how the winds move several miles up in the atmosphere. The strongest part of those winds are known as the jet stream.

In general, those winds travel from west to east across North America, moving weather systems along at a reasonable pace. However, they rarely travel in a straight line. When swings in those winds to the north or to the south become large, weather patterns become stagnant, whether they are wet patterns, cold spells or, in the case of Texas recently, heat waves.

The speed and direction of the jet stream winds are largely governed by the temperature difference between the poles and the tropics. A bigger difference in that temperature leads to a faster jet stream, but also one that tends to move in a more direct west to east fashion. And this is where the warming climate may be playing a secondary role.

Over the last half-century, the Arctic has warmed about three to four times more than the rest of the world, so the temperature difference from the poles to the tropics is decreasing, weakening those winds. And like water moving through a stream, as the wind slows down, it starts to meander — less likely to continue in a straight line.

The result, in work pioneered by Jennifer Francis at the Woodwell Climate Research Center in Massachusetts, is a jet stream flow that may tend to become much more wavy.

<p>Tubers float the Comal River on Thursday in New Braunfels, Texas, to try to beat the heat.</p>

Eric Gay, Associated Press

Tubers float the Comal River on Thursday in New Braunfels, Texas, to try to beat the heat.

This leads to larger bulges both north and south, slowing down the progression of weather systems across the continent like cars in a traffic jam. Consequently, the weather over any one point becomes stagnant. During this time of the year in Texas, that means heat.

The pattern has broken down for now, so the worst of the heat has migrated into the mid-South, giving Texas a break. But July is climatologically the hottest month of the year nationally, and there are signs of another surge of intense heat across the Plains later in the month.

This year is on pace to be one of the 10 hottest on record globally, so expect heat waves like these to gradually become more common as the climate warms. How much more common will depend on how quickly we can reduce emissions of greenhouse gases — like carbon dioxide.

Sean Sublette is the chief meteorologist for the Richmond Times-Dispatch in Virginia.

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