Already roasting in extreme heat? 2024 could be even hotter, NASA scientists warn.

Unprecedented heat has cooked the U.S. Southwest to dangerous levels, stressed air-conditioning reliability and prompted water conservation in parts of Texas and elsewhere. In Arizona, the mercury at Phoenix Sky Harbor Airport again reached 110 Fahrenheit (43.3 Celsius) on July 18, breaking the previous record of 18 consecutive days at or above that temperature, set in 1974.

The story doesn’t stop there. Extreme temps have hit Europe, handing Greece its longest string of extreme-heat days on record. And if these conditions aren’t tough enough, extreme heat has been joined by dramatic floods in the U.S. Northeast, India, Japan and China.

Man-made climate change — caused by the greenhouse gas emissions put off by burning coal, oil
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and gas and blamed for accelerating historical climates shifts — has been warming the Earth’s temperature. And now there’s another factor at work, NASA-based researchers and scientists from around the globe stress. 

El Niño, the somewhat regular pattern in the tropical Pacific that brings warmer-than-average sea-surface temperatures and influences weather, has only just started in recent months. That means its full impact has yet to be felt, said Gavin Schmidt, a climatologist and director of the NASA Goddard Institute for Space Studies, talking to reporters this week.

“Its really only just emerged, and so what we’re seeing [with this summer’s extremes] is not really due to that El Niño,” Schmidt said.

For more: Cerberus heat wave: What’s the meaning behind the blistering weather system’s name? 

For nearly all of July, the world has been in uncharted hot territory, according to the University of Maine’s Climate Reanalyzer. And June was also the hottest June on record, according to several weather agencies.

Just a week ago, over 110 million people, or about a third of Americans, were under extreme heat advisories.

Even just past the halfway point, scientists say there is a strong chance that 2023 will go down as the hottest year on record, with measurements going back to the middle of the 19th century.

“What we’re seeing is the overall warmth pretty much everywhere — particularly in the oceans,” NASA’s Schmidt said. “The reason why we think that’s going to continue is because we continue to put greenhouse gases into the atmosphere. Until we stop doing that, temperatures will keep on rising.”

“We anticipate that 2024 is going to be an even warmer year because we’re going to be starting off with that El Niño event,” Schmidt said. “That will peak towards the end of this year, and how big that is is going to have a big impact on the following year’s statistics.”

Heat has also meant that North Atlantic Ocean temperatures have soared this summer. Roughly 40% of the world’s oceans are experiencing marine heat waves, the most since satellite tracking started in 1991, according to the National Oceanographic and Atmospheric Administration.

“The oceans are running a fever,” said Carlos Del Castillo, chief of NASA’s Ocean Ecology Laboratory. “This issue with ocean temperature is not a problem that stays in the ocean – it affects everything else.”

For instance, warmer oceans put key food ecosystems at risk and melt glaciers that raise the water level and lead to coastal flooding. What’s more, hurricanes tend to suck up greater amounts of water when that ocean water is warmer, leading to stronger flooding as the storm moves inland.

Some scientists have their eye on the bigger picture.

There’s a more than 60% chance that the Earth’s temperature will bump up against the warming level that has shaped global climate policy — 1.5 degrees Celsius, or 2.7 degrees Fahrenheit — within the next five years, the United Nations weather organization said earlier this year.

A flirtation with that increase in average temperature would likely be fleeting, driven by a temporary blast of heat from El Niño, the cyclical, naturally occurring weather phenomenon.

But the development is still one to watch, scientists say, because an increase in man-made global warming means that when El Niño layers on its temperature boost, the dangerous implications of potentially extreme heat on human health, agriculture, ocean bounty and more are made worse.

Read more from MarketWatch’s Living With Climate Change section.

The Associated Press contributed.