We know that more regular and more widespread periods of extreme heat are already having a significant impact on human life, but the problem is about to get much worse, according to a new study.

Researchers from the University of Pennsylvania dug into mortality and temperature data patterns from 2008 to 2019 for each county across the contiguous US, then modeled how those trends might evolve as the planet warms up.

The result: a potential 162 to 233 percent increase in cardiovascular-related deaths due to extreme heat by the middle of this century, depending on the path we take going forward.

According to records, high temperatures were responsible for an annual average of 1,651 excess cardiovascular deaths between 2008 and 2019, but in scenarios where we continue with current environmental policies, that average could jump up to 4,320 between 2036 to 2065.

"The magnitude of the percent increase was surprising," says cardiologist Sameed Khatana from the University of Pennsylvania.

"This increase accounts for not only the known association between cardiovascular deaths and extreme heat, but it is also impacted by the population getting older and the proportionate increases in the number of people from other races and/or ethnicities in the US."

Those figures are based on a relatively optimistic scenario, where currently proposed US policies to curb greenhouse gas emissions actually get implemented. The study also modeled the consequences of a scenario where emissions continue to rise.

That more pessimistic view of our future would lead to an average of 5,491 deaths per year, a 233 percent rise. It's another reminder of the serious challenge facing us – and the differences that varying emission levels will continue to make.

Black adults and elderly people are most at risk from these heat-related deaths, the team found, triggered by days with a maximum heat index of 32 degrees Celsius (90 degrees Fahrenheit) or higher.

"Previous studies have suggested Black residents may have less access to air conditioning, less tree cover, and a higher degree of the urban heat island effect," says Khatana.

"Living conditions may also have a role in terms of social isolation, which is experienced by some older adults and has previously been linked with a higher probability of death from extreme heat."

The cardiovascular system is crucial in regulating the body's temperature, which is why a hotter climate can cause major health problems in this area. Extra sweating can lead to dehydration, for example, lowering blood pressure and forcing the heart to work harder.

Despite the continuing warnings from scientists, though, the world continues to get hotter and hotter. We now know that's going to end up costing lives – but every step we can take to limit global warming will make a difference.

" Climate change and its many manifestations will play an increasingly important role on the health of communities around the world in the coming decades," says Khatana.

The research has been published in Circulation.