Baltimore might not be breaking any temperature records this weekend, but the extreme heat could likely be a harbinger of the future, experts say.

The city is under a “Code Red Extreme Heat Alert” from the Baltimore City Health Department. Temperatures through the weekend are expected to hit the mid-90’s or higher, with heat indexes of more than 101 possible.

“I’ll start by saying that heat is the leading weather killer in the U.S. The initial, immediate concern is overall safety, especially for the vulnerable populations,” said Baltimore City Health Commissioner Dr. Letitia Dzirasa.

The elderly, children and those who do not have a place to escape the heat are typically the most vulnerable during extreme heat events, she said.

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The city has opened cooling centers, including at library branches and senior centers, where residents can go for a safe place to wait out the heat.

But how did we get to the point where temperatures are so high it’s hard to be outside? And what does it mean for the future? We talked to experts to get some answers.

Why is it so hot?

Typically, a heat index of 105 is required for Baltimore to declare a code red, Dzirasa said, but because there are “successive days” of a high index, the extreme heat alert was warranted.

The simple explanation for why Baltimore is seeing successive days of extreme heat has to do with the jet stream, said Brendon Rubin-Oster, lead meteorologist with the National Weather Service in the Baltimore-Washington region.

The jet stream is a fast-flowing band of air in the upper atmosphere that moves weather systems. As the seasons change, the jet stream moves in latitude from north to south. This time of year, Rubin-Oster said, the jet stream is farther north, so weather systems in the United States can stagnate.

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It is not practical to attribute any one weather event to climate change. But it’s “obvious that the seasonal temperatures are going up,” he said.

Baltimore’s future

Other experts agreed that Baltimore will likely see hotter summers in the future. Matt Fitzpatrick, a professor at the University of Maryland Center for Environmental Science, said this heat wave is “absolutely” a preview of Baltimore’s future.

“The probability of having these higher-temperature events increases as we continue to pump greenhouse gases,” he said. “The probability of a week like this week will increase through time until it becomes the average, basically.”

Carbon dioxide, the most commonly discussed greenhouse gas, is a byproduct of the burning of fossil fuels. Transportation and power generation are the two most significant sources of carbon emissions in the U.S.

Greenhouse gases have their name for a reason: They warm the planet by trapping heat from the sun in the atmosphere. The more greenhouse gases there are in the atmosphere, the more heat gets trapped — just like in a greenhouse.

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In early 2019, Fitzpatrick was author of a study that analyzed how temperatures will change by 2080. The forecast compares Charm City in 2080 to present day northern Mississippi. That means Baltimore could see temperatures that are, on average, 9.1 degrees warmer than they are today.

“This might not be considered a heat wave in the future — it might just be July,” he said.

Matthew Baker a professor of geography and environmental systems at the University of Maryland, Baltimore County also said Baltimore “should expect to have more summers like this.”

Parts of the city and region will feel the heat differently, Baker said. Areas with impervious surfaces, like asphalt and concrete, hold — and then radiate — more heat than forested areas, for example.

“Any place that you are close to large patches of forest will experience a mitigation of heat. There are parts of the city that, by design, don’t have a lot of trees because they’re very urban,” Baker said. “The downtown, the east and west, don’t have a lot of trees. The outer parts of the city have more tree cover.”

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What can be done?

Despite the heat and the grim projections for the future, Baker and Fitzgerald both said there’s work that can be done to avoid worst-case scenarios. While planting trees is not a replacement for reducing planet-warming greenhouse gas emissions, Baker said, a bigger tree canopy can help.

“We don’t really want to be thinking about the heat wave we’re dealing with now, we want to think about the heat waves we’re going to have in the future, and whether our cities are prepared for those temperatures,” Baker said.

Trees cool areas through shade and through evapotranspiration, the process through which trees move water from the ground into the atmosphere. Planting trees in an area is a mitigation technique, Baker said, not a way to prevent warming temperatures.

Experts agree there’s only one way to prevent the worst outcomes from climate change, and that’s reducing greenhouse gas emissions. According to the United Nations Intergovernmental Panel on Climate Change, Earth is on a path toward significant negative impacts unless emissions are reduced.

It is likely that cutting emissions enough to avoid the worst effects of climate change will require switching to renewable energy for power generation, transportation and industrial use.

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Fitzpatrick’s model shows that if emissions are reduced, Baltimore (and other parts of the globe) can avoid the most extreme temperature increases. Instead of an average increase of 9 degrees, Baltimore could see an increase of 4.9 degrees.

“A large proportion of people might think it’s too late to do anything. But it’s not,” Fitzpatrick said. “We’re certainly at an inflection point where we need to do something soon to prevent any more severe impacts. But the cause is not lost.”

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