These extreme weather events have correlated with monsoons in Bangladesh, India, and Pakistan; decreases in Arctic sea ice; high ocean temperatures; and flooding in New York, Libya, Hong Kong, and Brazil. When Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, saw the data, he was shocked. 

“[My] scientist brain is like, ‘What's going on?’ And then there's the… ‘Oh, shit’ part of my brain,” he said, “We predicted this.” NASA reported in 2020 that Geophysical Research Letters has evaluated its climate-change projections and found them to be accurate. 

“The long-term trends here are all due to human-caused climate change,” he said. “All of the record-breakingness of this is really due to those long-term trends which are all our fault.” Data from NASA and World Weather Attribution supports this conclusion. 

The heatwave enraged the public, creating debate on its causes. Some researchers have been looking for explanations that do not involve climate change. There are three causes that scientists are seeing as potentially contributing to the heatwave, Schmidt said, but they each would cause only hundredths of a degree of warming. The global mean temperature this summer went up by around 0.2°F. 

(This August, according to a graphic from the National Oceanic and Atmospheric Administration (NOAA), temperatures on land frequently hovered between 2°F and 3°F above the average between 1991 and 2020. In some locations, they were between 3°F and 4°F above the average. Greenland had a higher temperature rise than other land masses — largely between 4°F and 6°F.)   

First, NOAA reports the sun has been ramping up to a solar maximum, a high level of irradiance that increases the global mean temperature several years afterward. This, Schmidt said, should not yet be creating a significant impact. 

Second, water vapor was ejected from the Hunga Tonga-Hunga Ha’apai volcanic eruption which led to an explosion in January 2022. Schmidt said this emitted 10% of the water vapor that is currently in the stratosphere. (Geophysical Research Letters also estimates that it is 10%.) A study in Nature Climate Change said that this could warm the planet by 0.06°F.   

Third, he said ships using cleaner fuel reduced the amount of sulfur dioxide in the atmosphere, which might change the level of aerosols in the sky and alter the level of cloud cover. This could potentially warm the globe. However, this effect, according to a NASA model, would only be a few hundredths of a degree Fahrenheit.

These three effects would only add up to around 0.1°F, which is not enough to explain the heatwave, he said. 

“There's a lot of kind of unbridled speculation about tipping points and things like that, which really isn't justified,” Schmidt said. “And then there's a whole bunch of ‘Oh! Blame the volcano! Blame everybody except us!’ from the people who don't want to pay attention to the long-term trend [of climate change since the beginning of the Industrial Revolution].”

This year, according to NOAA, June through August were the warmest recorded in 174 years of NOAA data. The average temperature of the land and oceans in August was 2.25°F greater than the average in the 20th century. Between June and August, the global surface temperature was 2.07°F above the 20th-century average. The last 10 years of this season have been the warmest on record.   

“We've been effectively monitoring the climate… for over 40 years now,” Schmidt said.  “You'd think nothing would surprise us, but no. This summer really has been something very special — and not in a good way.” NASA is very active in climate research. It provides extensive information about climate change on its website, where it reports long-term trends affecting the globe. 

Partly, the unseasonable heat has been due to an El Niño — an event in which the sea surface warms occasionally in the tropical Pacific, causing global temperatures to shift upward, he said. This event will peak in December through February and will affect global temperatures mainly during the next three to six months.

The consequences of heating up the globe can create catastrophic events such as torrential rain, tropical storms, intense wildfires, and extensive droughts. For example, this year, Storm Daniel caused the death of over 10,000 people in Libya, according to NOAA. In August, Hurricane Dora exacerbated a wildfire on the island of Maui in Hawaii, which then became the deadliest wildfire in U.S. history. During the same month, monsoon flooding in Pakistan and India caused the evacuation of over 100,000 people. New York City declared an emergency due to flash flooding at the end of September.  

“Every degree you warm the oceans, you add 7% to the amount of water vapor in the atmosphere that's available for big rain events,” Schmidt said. “We saw these 40°C days in the United Kingdom [that] never happened before. We saw new records being broken with temperature in North Africa and in Europe.”

NASA bases its data summaries on information from buoys, weather stations, ships, and satellites, he said. The agency also looks at data from a few separate predictive systems and uses a Monte Carlo simulation method that uses random sampling to predict uncertainty in its datasets. 

“Ocean data is now based on a network of ocean buoys which have temperature sensors embedded within them,” he said. “They go up and down through the ocean column. When they come up, they relay the information back to headquarters, and then it gets collated. So you've got these ocean buoys, you've got ocean ship measurements, you've got weather station data. We have instruments onboard some NASA satellites. We can check what we're doing by comparing [it] to the satellite measurements.”

NASA’s Jet Propulsion Laboratory is monitoring this El Niño from space using the satellite Sentinel-6. Its website says, “El Niños are characterized by higher-than-normal sea levels and warmer-than-average ocean temperatures along the equatorial Pacific. These conditions can then propagate poleward along the western coasts of the Americas. El Niños can bring wetter conditions to the U.S. Southwest and drought to regions in the western Pacific, including Indonesia.“  

“Even small differences from seasonal average temperatures are associated with increased illness and death,” the World Health Organization website says. “Some populations are more exposed to or more physiologically or socio-economically vulnerable to physiological stress, exacerbated illness, and an increased risk of death from exposure to excess heat.

These include the elderly, infants and children, pregnant women, outdoor and manual workers, athletes, and the poor.”