Summertime heat is forecast to become even deadlier without action to drastically reduce the greenhouse gas emissions that cause climate change, according to a new study.

Under the Paris climate agreement, 195 countries pledged to cut their greenhouse gas in an effort to hold global warming to two degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels. They also promised efforts to limit the temperature increase even further, to 1.5 degrees Celsius.

The half-degree difference between 1.5 and two degrees may not seem like much, but, according to research published Wednesday in the journal Science Advances, it could mean saving or losing thousands of lives each year in the United States alone.

The researchers wanted to assess the benefits of the Paris Agreement “not in terms of the climate or the temperature, but in terms of how many human lives could be saved or how many heat-related deaths could be avoided by mitigating climate change,” said Eunice Lo , a research associate at the University of Bristol and lead author of the study.

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