Weather Forecasts Are Connecting Hot Days to Climate Change

HTexas’s Ouston is currently experiencing the hottest summer ever recorded. There are sizzling hot stretches with triple-digit temperatures and blackouts due to extreme power demands. Lena Arango is a FOX26 meteorologist and wanted to explain why. “The temperatures we’re experiencing today are five times more likely [because of] climate change,” she said on a TV forecast earlier this month. “I thought that was pretty interesting.”

In the past, television meteorologists have been cautious in discussing daily weather and climate change on TV. They want to keep their scientific bases solid. Long term trends are clear in many areas—milder winters and more scorching days during the summer—but no one was necessarily running the calculations to show how the rising concentrations of CO2 in the atmosphere may be affecting the weather on any given day. American weather forecasts often feel like they have been silenced about climate change. Meteorologists are able to talk only about the extreme, record-breaking temperature, but not mention long-term trends.

This may be changing. Arango’s forecast made use of a new data tool called the Climate Shift Index, which shows the extent to which extreme heat is caused by rising levels of greenhouse gases in the atmosphere. Climate Central is a non-profit organisation that focuses on communicating climate change. They developed this tool earlier this summer.

“What we want to be able to do is help close this gap between the weather that people experience every day and this big nebulous slow moving climate change problem,” says Andrew Pershing, director of climate science at Climate Central. “No one experiences global mean temperature; we experience the weather. We’re trying to make that connection really clear.”

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For years, politicians have underplayed climate change and put off making the investments we need to decarbonize society—most recently in the slow death of President Joe Biden’s climate change agenda at the hands of West Virginia Senator Joe Manchin. Climate change is urgently needed. It takes many years for climate change to be implemented, and even longer for warming to slow down. Despite increasing emissions year on year, we are still not in a position to achieve the Paris Climate Accords’ goals. That would have disastrous and possibly irreversible consequences.

It is hoped that people will see the impact of climate change on weather and be able to push leaders for the necessary action to ensure that we have livable temperatures over the next decade. The first efforts towards that aim began back in 2003, when scientists started looking into how they could show if climate change caused a deadly heatwave in Europe that year—but it took a full year before the results were published. Scientists improved their methods and found faster ways to do the same. The goal was to show how climate change makes weather more probable before it is too late. Although such analysis of extreme precipitation can be quite time-consuming, scientists are now able to perform the simple calculations necessary to find a climate signature for extreme heat events within days.

These efforts, so far, have focused on trying prove the relationship between climate change and extreme weather. For example, the Pacific Northwest’s blistering heat dome last year was impossible to explain without human-caused global warming. Climate Central’s effort is a bit different, though. Pershing is the leader of their research. Pershing’s work focuses on showing if climate change affects everyday weather in the U.S. Each day an automated system compares weather data from the past and 24 climate models. The result shows if climate change made the day’s weather in different regions more likely, and by how much. For instance, models showed that atmospheric CO2 made Houston’s 105°F heat five times more likely on July 10, the day of Arango’s forecast, the most extreme metric on the Climate Shift Index. A model also shows if climate change has made an event less probable, such as unusually cold temperatures in the middle summer. “These are the conditions that your kids or your grandkids might not experience,” says Pershing.

Some unusual weather can be made more likely by climate change than ever before. The Climate Shift Index doesn’t show if climate had any impact on extreme weather events, but it does illustrate the whole picture. It’s a more straightforward job, mathematically speaking, than trying to illustrate something like the “virtually impossible” conclusion from the Pacific Northwest heat dome last year, which is what lets the Climate Shift Team run the analysis across the entire continental U.S. every day.

When scientists retrospectively looked at weather data in recent months, the new system produced some surprising results. December 2021, for instance, was “remarkably weird,” according to Pershing, with a clear climate change fingerprint on balmy temperatures across much of the upper midwest. But even though climate change can have a sizable effect on winter temperatures, people are less likely to associate that knowledge with the need for urgent climate action—namely, because while warm winter days can feel strange, a lot of people don’t necessarily mind a break from freezing temperatures.

The heat waves of summer are the time when many people start to notice the dangers of climate changes. This is why Climate Central raced to complete the Climate Shift Index work before the scorching days of summer arrived. They hit a snag over Christmas break last year—their calculations were running too slowly, and it looked like they might not have the system ready by summer. However, clever software engineering was able to accelerate the entire process.

With a few forecasters now starting to include maps and Climate Central information into their forecasts, there is hope that the Climate Shift Index will become another standard piece of data that people are looking for in weather reports like chance of rain and humidity.

“It’s not like you’re going to take your climate change umbrella out,” says Pershing. “It’s telling you that these are the conditions that are going to be more common in your future. These are the ones that we need to prepare for.”

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