Heatwaves driven by human-caused climate change have cost the global economy at least $16 trillion since the 1990s, according to a new study. The huge costs came because of the effects of high temperatures on human health, productivity, and agricultural output, the researchers said — a burden that has been especially severe on the world’s poorest.

Researchers at Dartmouth College combined economic data with the average temperature for the hottest five-day period for each global region. They found that from 1992 to 2013 heatwaves coincided with changes in economic growth, which differ in high- and low-income regions.

Losses averaged a whopping $16 trillion, they found.

Heatwaves and economic costs

Heatwaves aren’t just annoying but can also be dangerous, leading to illness and even death, especially among the most vulnerable (like the very young). Because of climate change, heat waves are happening more often, getting more intense and lasting longer. The global average temperature has raised 1.1 degrees Celsius since the industrial era.

“Increased extreme heat intensity significantly decreases economic growth in relatively warm tropical regions,” the researchers wrote. “This has amplified underlying inequality, disproportionately harming low-income, low-emitting regions, with major emitters shouldering primary responsibility for billions of dollars of losses.”

The researchers described their study as the first one to quantify the economic costs of extreme heat driven by climate change. They didn’t analyze data beyond 2013, which means their estimate would likely grow significantly if expanded to the present day. This year broke several records in temperature, including in the UK, Europe, and China.

While the richest countries have lost about 1.5% of their annual per capita GDPs because of heatwaves, poorer countries have lost about 6.7% of their annual per capita GDPs. The reason for that disparity is simple. Poor countries are located closer to the tropics, where temperatures are warmer. During heatwaves, they get hotter, which causes more problems.

In some very rare cases, some rich countries could even benefit from the extreme heat caused by climate change, the researchers said. The study showed that some regions in Europe and North America could theoretically benefit from having warmer spells. These regions are some of the wealthiest and biggest contributors to climate change.

As it highlights the differences between rich countries contributing the most to climate change and the poorest ones coping with its effects, the study is likely to fuel debate among countries over who should pay the costs to prevent or repair the damage. These discussions will become visible next week at the upcoming UN climate summit COP27.

“That warming has already increased the frequency and intensity of heat extremes is well known, but our results demonstrate the economic costs of these events and their unequal global distribution,” the researchers wrote. “Our work therefore increases the urgency of both climate mitigation efforts and investments focused on adaptation.”

The study was published in the journal Science Advances.