Looking to beat temperatures that reached into the low 90s, swimmers gathered on July 4, 2019, on and around a ledge of exposed rock at high tide in the inner harbor of Blue Hill. Credit: Bill Trotter|BDN

The reasons for concern about climate change continue to grow. In Maine, the number of days when it feels like 90 degrees will grow 14-fold by mid-century. Nationally, as hurricane season begins, data show that these weather systems are becoming more intense — and most costly. Globally, scientists warn that we are quickly nearing a tipping point where these trends can’t be stopped.

All of this points to a need for sustained action to reduce emissions of heat-trapping greenhouse gases, especially from the burning of fossil fuels like oil, gas and coal to power our electrical grid and transportation sector. On the national level, the Trump administration continues to downplay climate change and to silence those calling for federal action.

This is a dangerous course that will continue to cost American lives and resources.

A report from the Union of Concerned Scientists, released this week, predicted that the number of days of dangerous heat in the United States will grow exponentially in coming years if significant steps are not taken to reduce carbon emissions. The group used the heat index — a measure of how hot it feels when air temperature and humidity are combined — in its assessment.

In extreme heat, it becomes increasingly difficult for human bodies to remain cool. At a heat index above 90 degrees, people working outside become susceptible to heat-related illnesses. Above 100 degrees, children, pregnant women, the elderly and people with underlying medical conditions are at heightened risk, and everyone is at risk when the heat index rises above 105 degrees.

In Maine, there has been one day per year on average with a heat index above 90 degrees from 1971 to 2000. This would increase to 14 days per year on average by midcentury and 36 by the end of the current century, according to the Union of Concerned Scientists projection.

Historically, there have been zero days per year on average with a heat index above 100 degrees in Maine. This would increase to two days per year on average by midcentury and 11 by the century’s end. Of Maine’s largest cities, Lewiston would experience the highest frequency of these days.

For much of the U.S., dangerous heat is already a problem and simply getting worse. More than half of continental U.S. states are predicted to have air temperatures in excess of 95 degrees in upcoming days, according to the National Weather Services. Eighty-five percent of the states will have temperatures above 90 degrees.

It is especially concerning that nighttime low temperatures will remain elevated. The most significant temperature increases in Maine has been in overnight low temperatures, especially in the summer and fall. This is because of melting sea ice in the Arctic, says state climatologist Sean Birkel, who is also a research professor at the Climate Change Center at the University of Maine. Since the 1980s, the amount of sea ice in the Arctic has dropped by half. Less ice means more open water, which translates to more moisture in the air. Wetter air holds the heat more than colder air.

As a result, Maine has broken five daytime record high temperatures for every record low temperature since 2010, according to an Associated Press data analysis earlier this year of temperature trends across the United States.

Against growing evidence that the Earth is warming because of human-produced pollutants, the Trump administration’s disregard for — and even hostility toward — climate change is disheartening and dangerous. By all means, our congressional delegation should continue to speak out and push for legislation to reduce emissions, but without a change in leadership — in both the U.S. Senate and White House — significant U.S. action is unlikely.