Bloomberg: Scientists bracing for record-breaking heat in 2024

This year will be hot. Very hot. So hot that some experts are already predicting it may beat 2023 as the hottest year in recorded history.

Climate change is, of course, primarily responsible. Burning fossil fuels is increasing the amount of greenhouse gases in the atmosphere, causing the global average temperature to rise. In 2023, the average was about 1.4C higher than the pre-industrial era; early estimates suggest this year will be up 1.3C to 1.6C, Bloomberg reports.

But what makes scientists even more secure in their 2024 predictions is El Niño, one of three phases of a multi-year climate cycle known as the El Niño-Southern Oscillation. El Niño is defined by hotter waters in the tropical Pacific, while La Niña is its cooler counterpart. (There’s also a neutral phase.) When sea surface temperatures heat up during El Niño, so does the air above the water due to changes in ocean circulation and weather patterns.

Picture a pot of water heating up on a stove, says Ulla Heede, a scientist who works on ocean modeling at the nonprofit [C]Worthy. If you pour cold water into the pot, “you will only feel a slight change in temperature in the pot,” she says. That’s effectively what happens during La Niña, when cold water rises from deep in the ocean to the surface.

Now stop pouring the cold water. Suddenly, the water in the pot is warming up much faster. This is the impact of El Niño, Heede says, and the longer it lasts, the warmer the Pacific and the air above it get. Since El Niños usually take months to peak, there’s also a “lag or delay between heating of the tropical Pacific and the rise in global surface temperatures,” says Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration.

In other words, the second year of an El Niño is often warmer than the first.

Over the past few decades, the climate change-El Niño double whammy has produced a string of record hot years. According to one study, extremes between El Niños and La Niñas have intensified roughly 30% since 1960 compared to the six decades prior, with global warming likely contributing a third of that. It may not sound like much, but means “the stronger events are getting even stronger,” says McPhaden. “Those are the most damaging.”

Still, last year’s heat was particularly shocking. Practically every month in 2023 was warmer than the 1991-2020 average, and the latter part of the year, after El Niño started, shattered records: June, July, August, September, October and November were all the hottest of their respective months in recorded history. July was the warmest month ever observed and July 6 was the hottest day. September was so anomalously hot that Berkeley Earth climate scientist Zeke Hausfather called the record “gobsmackingly bananas.”

Some of that heat fell outside the typical patterns of El Niño. Temperatures in the Atlantic Ocean set a record in late July, for example, something not usually caused by El Niño.

The anomalies in 2023 make 2024 temperatures all the more important to study. And there are already some good guesses as to what this year’s heat will bring, since El Niño tends to increase the odds for certain types of weather in certain regions.

Drought and flooding

As the warmest part of the Pacific Ocean shifts eastward, we can expect a “reorganization” of winds, ocean convection and rainfall across the planet, says Heede. That’s likely to mean a drying trend in places accustomed to more rainfall, and vice versa. Both of those shifts have implications for agriculture: The United Nations’ Food and Agriculture Organization is particularly concerned about food insecurity this year due to drought in East Asia, southern Africa and Central America.

El Niño also brings dry weather to the Amazon — which is already experiencing severe drought — and could trigger more rainfall in southeastern Brazil and neighboring Uruguay, McPhaden says. Meanwhile, he expects the southern US to be “wetter and cooler than normal” this year.

Wildfire

El Niño’s shifting of warmer water and rainfall across the Pacific leaves clearer skies over southeast Asia, particularly where it borders the ocean. That means more sun getting through to dry out the land and vegetation, which increases the risk of wildfire. Indonesia has already been battling some of its worst forest fires since 2019, says Thomas Smith, associate professor of environmental geography at the London School of Economics. The first few months of this year are likely to bring more fire risk to these areas, as well as eastern Australia.

In the US and Canada, El Niño is expected to bring heat to the northwest Pacific coast come spring, meaning those regions could see a severe summer fire season. Smith says there’s a particularly high risk of “extreme fire behavior” in Alaska.

Stronger storms

Last year’s record low sea ice and high sea surface temperatures could also lead to unexpected impacts in Europe, says Vikki Thompson, a climate scientist at the Royal Netherlands Meteorological Institute. “The change in the sea ice is likely to impact the jet stream across the North Atlantic, maybe changing its location more, which could lead to stronger storms across Europe,” she says. “Or the storms could track differently and impact a different area to what’s been the most likely regions in the past.”

Coral reef bleaching

In December, a paper in the journal Science warned about the possibility of a mass coral bleaching and mortality event caused by warming oceans. Adam Scaife, head of long-range prediction at the UK’s Met Office, says he has “no doubt at all that there will be unprecedented coral bleaching in the Pacific in the coming months.” In 2016, the second year of another strong El Niño event, the Great Barrier Reef suffered its worst bleaching ever.

If conventional wisdom holds that the second year of an El Niño is hotter than the first, it also suggests that this El Niño will tucker itself out by mid-2024. At that point, temperatures should return to “normal” — i.e. still rising, but not so wildly out of trend.

But the way in which 2023 was hot raises the specter of weather-climate dynamics we don’t fully understand. And that means no conventional wisdom is foolproof.

“We don't know whether something else has happened in the climate system and we may have passed some tipping point,” says Carlo Buontempo, director of the Copernicus Climate Change Service at the European Centre for Medium-Range Weather Forecasts. “We don't have evidence of it, but we don't have evidence of the contrary either.”