Simultaneous heat waves scorched land areas all over the Northern Hemisphere last summer, killing hundreds and hospitalizing thousands while intensifying destructive and deadly wildfires.

A study published this week in the journal Earth’s Future concludes that this heat-wave epidemic “would not have occurred without human-induced climate change.”

The alarming part? There are signs record-setting heat waves are beginning anew this summer — signaling, perhaps, that these exceptional and widespread heat spells are now the norm.

Just in the past few days, blistering, abnormal heat has afflicted several parts of the Northern Hemisphere, including major population centers.

New Delhi, India’s capital, soared to 118.4 degrees Monday, its highest temperature ever recorded in June. Some parts of India have seen the mercury eclipse 122 degrees in recent days, not far off the country’s all-time high.

On the other side of the hemisphere, the temperature in San Francisco shot up to 100 degrees Monday, its highest temperatures ever recorded in the months of June, July or August, or this early in the calendar year.


About 45 million people were under a heat advisory or excessive heat warning for a third straight day Tuesday because of an unusually strong area of high pressure lodged over the region.

The core of the heat shifts northward as it eases through midweek. By Wednesday, the hottest weather relative to normal should be focused in the Pacific Northwest, where record highs are possible in Oregon while temperatures are expected to hit the mid-80s in Seattle.

June is often a month where the wind blows off the cool ocean into coastal areas while scorching heat is confined to the interior valleys. But, at the moment, a strong high-pressure system is keeping the clammy maritime air out to sea while the scorching sun bakes land areas, even along the coast.

Globally, heat spread unusually far north, even up into the northern reaches of Scandinavia. Mika Rantanen, a meteorologist at the University of Helsinki, tweeted last Friday that “[t]here are no known cases in Finland’s climate history when it has been hotter than now so early in the summer.” Temperatures above 86 degrees penetrated inside the Arctic Circle, he noted.

A heat wave in Japan at the end of the May set scores of records, including the country’s highest temperature ever recorded in the month (103.1 degrees). The oppressive conditions were blamed for five deaths and nearly 600 hospitalizations.

While some scientists hesitate to attribute individual heat spells to climate change, Daniel Swain, a climate scientist at the University of California Los Angeles, tweeted that his research suggests that we’ve “reached the point where a majority (perhaps a vast majority) of unprecedented extreme heat events globally have a detectable human influence.”


Last summer, exceptional heat affected 22% of the populated and agricultural areas of the Northern Hemisphere between the months of May and July, the Earth’s Future study said. The contiguous U.S. witnessed its hottest May on record, California endured its hottest July and numerous European cities notched their highest temperatures ever recorded, while cities in Asia, the Middle East and Africa also established new heat milestones.

It remains to be seen whether heat waves this summer become as pervasive and intense as last summer. That said, the Earth’s Future study concluded we’ve entered “a new climate regime,” featuring heat waves on a scale and ferocity not seen before.

The study’s modeling analysis, conducted by researchers in Switzerland and the United Kingdom, found heat events like last summer’s do “not occur in historical simulations” and “were unprecedented prior to 2010.”

As the climate warms, the study projects that the area affected by heat waves like last summer will increase 16% for every 1.8 degrees of warming.

“Heat waves will likely reach highly dangerous levels for ecosystems and societies over the coming decades,” the study said.

Heat events like last summer are predicted to occur two every three years for global warming of 2.7 degrees and every year for warming of 3.6 degrees.

So far, the Earth has warmed by approximately 1.9 degrees since 1880. The goal of the Paris agreement on climate change is keep the global temperature rise to 3.6 degrees or less.

Just last week, a study in the journal Science Advances found keeping warming to 2.7 degrees compared to 5.4 degrees could avoid between 110 and 2,720 heat-related deaths annually in 15 different U.S. cities.

“A strong reduction in fossil fuel emissions is paramount to reduce the risks of unprecedented global-scale heat-wave impacts,” the Earth’s Future study concluded.