The climate crisis is often discussed as though it were an imminent event, a disaster on the environmental horizon, heading straight for us at increasing speed.

In reality, though, it's more like the rising sun, and while we haven't yet reached noon, the heat of the day is already upon us.

Between 1991 and 2018, new models estimate more than one-third of all heat-related deaths in summertime were caused by recent rising temperatures.

In other words, in a world without human-induced climate change and the temperature increases it brings, far less people would be dying, the results suggest.

In some regions, like Southern Europe, Central and South America, and South-East Asia, the risk of heat-related death is particularly high.

In Ecuador and Columbia, for instance, up to three-quarters of all heat-related deaths have been linked to rising temperatures from human emissions.

"[I]n many locations, the attributable mortality is already on the order of dozens to hundreds of deaths each year," researchers warn.

"This has occurred with average global temperature increase of only ~1 °C, which is lower than even the strictest climate targets outlined in the Paris Agreement (1.5-2 °C) and a fraction of what may occur if emissions are left unchecked."

The results come from comparing two different worlds: one, in which humans hadn't emitted any fossil fuels, and the other, which reflects our current reality. Researchers then ran simulations on both, using health and climate data from 732 locations in 43 countries.

In every single location, the annual average temperature in summer was found to increase under the climate change scenario.

Under 'normal' conditions, without human emissions, the annual average temperature in summer was around 21.5 °C. Under 'real conditions' in the 2010s, on the other hand, the average reached almost 23 °C .

While that increase might sound small, overall it has deadly consequences. On every continent, the authors found human-induced climate change coincided with a spike in heat-related deaths, although low- and middle-income countries were most affected.

Regions with more than a 50 percent increase in heat-related deaths include southeast Asia, Central and South America, and southern and western Asia, like Kuwait and Iran.

On a smaller scale, some cities were also more vulnerable than others. In New York City, for instance, 141 more people die each year from heat-related causes than if global temperatures were only subject to natural forces. That's 44 percent of the total heat-related deaths in the city.

Meanwhile, half a world away in Bangkok, over 50 percent of the city's heat-related deaths are due to climate change.

Unfortunately, there aren't many models to compare these results to, and empirical data on heat-related deaths are missing for a lot of countries in Africa, Asia, and the tropics.

Research so far has mostly focused on what will happen to heat-related deaths in the future, and not on what is occurring right now.

In some areas around the equator, for instance, initial predictions suggest future tropical heat waves could increase mortality by as much as 2,000 percent.

By 2080, those same studies estimate at least four times as many people will die in Australian and American cities from increasing temperatures. Already, research suggests Australia's mortality records are underreporting heat-related deaths by at least 50-fold.

"This is the largest detection and attribution study on current health risks of climate change," says statistician Antonio Gasparrini from the London School of Hygiene & Tropical Medicine.

"The message is clear: climate change will not just have devastating impacts in the future, but every continent is already experiencing the dire consequences of human activities on our planet. We must act now."

The study was published in Nature Climate Change.