Extremely Hot Summers Will Soon Be the Norm, Scientists Say

By Alyson Kenward

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Anyone who’s been paying the slightest attention knows that extreme weather and climate have wreaked havoc in Texas and many other states this year. The worst one-year drought in Texas history and its hottest summer on record — which was the hottest summer ever recorded in any U.S. state — have left Texas short on water, coping with billions of dollars in crop damage, and fighting off record wildfires. The total area burned in Texas so far this year would cover the entire state of Connecticut, and officials says agricultural losses are the largest in state history.

“Our current estimate is that the drought in Texas has led to $5.2 billion in agricultural losses,” says Mark Waller, professor and agricultural economist with the Texas AgriLife Extension Service. Cash crops have been especially hard hit, like cotton, corn, and wheat, and ranchers are struggling to feed their cattle. And if the drought continues as recent projections show, says Waller, lost winter wheat crops could make the drought even more expensive.

Jerry Gannaway plows up a field where he had planted cotton July 27, 2011 near Hermleigh, Texas. Gannaway is among the majority of dry-land (non-irrigated fields) cotton growers in Texas whose crops have failed because of a severe drought in the region. The cotton in his field should have been about knee-high by now, yet most has not even broken through the soil. Credit: Scott Olson/Getty Images.

In short, this has been a highly unusual summer in Texas, and also in much of the U.S. east of the Rocky Mountains. In July alone, nearly 3,000 daily high temperature records were set or tied across the country, along with about 6,000 record warm nighttime low temperatures, according to Climate Central's record temperature tracker. 

But what’s unusual today will be typical in the future, climate scientists say. Due in large part to manmade global warming, summers like this one will happen so often, in fact, that they will be the new normal.

“If the planet hits the two degree [Celsius] warming threshold, 70-80 percent of the global land surface will be regions where historical extremes have become the norm,” says Boston University climate scientist Bruce Anderson.

In the Western third of the U.S., for example, odds are better than even that every summer will be what we now consider to be extreme, he says.

Global surface temperature departures from average, showing much warmer than average conditions across much of the US from June through August, 2011. Credit: NASA GISS.

What’s the magic about two degrees? Global leaders have agreed that in order to minimize the worst effects of climate change, average global temperatures shouldn’t rise more than 2°C, or 3.6°F, higher than they were before the Industrial Era began. In the past 60 years, temperatures have already climbed 0.8°C, or about 1.4°F, above that pre-Industrial benchmark, driven by increasing levels of heat-trapping gases in the atmosphere — put there by humans and natural sources.

According to his new analysis published in the journal Climatic Change, Anderson says that within the next decade or two, parts of the planet that only see extremely hot summers every so often will be more likely to see them every year because of the warming that has already occurred globally.

“Many regions of the globe — including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon — are already committed to reaching this point,” he says, “given today's concentrations of greenhouse gases.” As for the U.S., Anderson explains, “it is certainly on the brink.”

Researchers from Stanford University recently set out to learn at what point exceptionally hot summers will to become more commonplace around the world. Climate scientist Noah Diffenbaugh has studied how the warming to date has influenced the weather patterns that lead to unusually hot seasons. Projecting forward over the next few decades, he says the combination of warmer temperatures and changing weather patterns mean that the extremes will be changing quickly.

“According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years,” Diffenbaugh said when his study was published earlier this summer in the journal Climatic Change Letters. 

Scientists say the trend towards more hot extremes has already begun. In the U.S., for example, record breaking hot days have already become more common than they once were. According to climate scientist Jerry Meehl, recording breaking hot days used to be as common as cold ones. But in 2000, there were twice as many warm temperature records as cold records in the U.S., and he says that in 2011, so far there have been three times as many.

Over the past decade, a growing body of research has concluded that heat extremes are going to get worse later this century, and not just in the West. Heat waves that last a few days are likely to happen more frequently in the Midwest, too. In the Southeast, scientists predict that the number of days that climb above 90°F every year could triple towards the end of this century.

The new analyses from BU and Stanford look specifically at how extremes are going to change for entire seasons, which could have dramatic effects on agriculture, water availability and wildfire susceptibility. Texas’s hardships this summer are a reminder of how damaging prolonged heat and drought can be, says Anderson. “This summer has been an analogue for the summers to come.”