“2024: Unprecedented Heat Waves and Record-Breaking Temperatures Transform Our Planet”

2024 has officially been recognized as the hottest year ever documented on Earth, at least since humans have been present, based on counts from meteorological institutions across the globe.

The National Oceanic and Atmospheric Administration (NOAA), NASA, and Copernicus—the EU’s meteorological institution—published their yearly assessments of global temperatures [Friday]. They all found that the Earth has warmed approximately 1.5 degrees Celsius (2.7 Fahrenheit) above the levels observed in the 1800s, prior to humanity commencing the burning of extensive fossil fuel reserves.

The reported figures differ slightly. NOAA indicates 1.46 degrees C of warming, NASA reports 1.47; and the EU’s Copernicus, 1.6.

“The true punchline is that it was yet another exceptionally warm year,” remarks Russell Vose, a climate researcher at NOAA’s National Center for Environmental Information, the organization responsible for generating the temperature estimates.

The 1.5C figure gained significance a decade prior. Within the 2015 Paris Climate Agreement, the majority of nations committed to endeavor to restrict global warming to below 2 Celsius, and ideally no higher than 1.5. Then, in 2018, scientists issued a substantial report cautioning that exceeding the 1.5 C threshold of warming would considerably amplify the risks of prolonged and more intense heat waves, more catastrophic hurricanes, and severe biodiversity losses.

Researchers utilize a long-term average to assess overall warming, thus this isolated year beyond the 1.5 level does not indicate that the Paris Agreement targets have been violated—but they express it’s a distressing signal. Projections suggest the planet will warm by approximately 3 degrees Celsius (5.4 Fahrenheit) above pre-industrial levels by the century’s end without significant, additional efforts to mitigate planet-warming emissions, according to a recent global report on climate change.

“This isn’t even the new usual—this is halfway to the new usual,” asserts Clair Barnes, a climate scientist at Imperial College London.

The 2024 record is built upon the foundation of 2023, which itself shattered prior records.

In certain respects, the extreme high temperatures of the last two years come as no surprise, states Gavin Schmidt, a climate scientist at NASA’s Goddard Institute for Space Studies: an increasingly warmer planet is the anticipated consequence of burning large quantities of fossil fuels.

However, in other aspects, the heat was unexpected, as it exceeded the levels that he and numerous other scientists had anticipated and that models had foreseen.

A dual impact of warming and an emerging enigma

It was midway through 2023 when scientists began examining temperature statistics with growing concern.

“Things started to get peculiar around June and July of that summer,” notes Zeke Hausfather, a climate scientist associated with Berkeley Earth. July 2023 demolished all previous heat records for that month. August then surpassed records by an even greater amount. “And then September was, as I remarked at the time, utterly astonishing—” nearly a full degree Fahrenheit above prior records, an astounding margin.

Ultimately, 2023 concluded at least nearly 1.5 C (2.7 F) degrees above pre-industrial levels.

“Not only was that a record, but it was a record by a record-setting margin,” Schmidt states.

Climate models indicate the Earth should have warmed about 1.3 C by this time, due to fossil fuel combustion and other human-induced changes to the environment. This leaves roughly 0.2 degrees of warming, beyond the models’ expectations, unexplained.

This figure may seem minor, according to Hausfather. But “that’s the amount the world typically warms in around a decade,” he states—far from trivial.

El Niño cycles

Consequently, researchers explored answers to the enigma of rising heat, considering factors from volcanoes to solar activity and clouds above.

The initial theory? Perhaps the heat was due to El Niño.

El Niño and La Niña occurrences are components of a natural climate cycle that can affect weather in a wide area of the globe. During an El Niño phase, which typically occurs every few years, global temperatures usually trend higher overall, while La Niña phases generally result in cooler global temperatures.

The Earth transitioned into an El Niño state in mid-2023 and remained there until spring 2024. Thus, Schmidt suggests, it likely played a part in the record-setting heat of 2023. However, it cannot account for all of it: the timing was misaligned. 2023 commenced in a La Niña state and persisted in that cooler phase when the heat began to break records in June of that year.

“Therefore, it’s challenging to attribute the El Niño to events that unfolded before the El Niño truly began,” Schmidt explains.

It likely did have a role in the heat of 2024, even as the El Niño influence waned later in the year, Schmidt notes.

Volcanoes?

An additional theory pertained to a volcanic explosion.

Usually, eruptions expel gases and particles into the atmosphere that reflect sunlight back into space and assist in cooling the planet. However, the Hunga Tonga-Hunga Ha’apai volcano, which erupted in 2022, was submerged. This resulted in the release of vast quantities of water vapor high into the sky, which has the ability to retain heat.

A few researchers speculated that this warming effect might have played a part in the enigma of the heat. Yet, upon further examination, scientists determined the effect was likely negligible.

“Many people discussed that extensively, but our best estimation is that it had an impact of none,” states Andrew Dessler, a climate researcher at Texas A&M University.

Vessels—and clouds

The subsequent theories concentrated on what exists in the atmosphere: clouds. They can have a significant influence on global temperatures.

Bright clouds reflect incoming sunlight away, leading to a cooler planet. However, cooler clouds also function as a blanket, retaining heat close to the Earth’s surface. Hence, alterations in cloud types, behaviors, or presence can affect temperatures on Earth.

In 2020, international regulations regarding the fuels of the shipping sector underwent changes. The previous fuel was rich in sulfur; when released into the atmosphere, sulfate pollution attracted water droplets, resulting in visible cloud trails following a vessel moving through the ocean.

The newer, more environmentally friendly fuel produces less sulfate pollution—and subsequently fewer, smaller cloud trails. Upon performing the calculations, scientists recognized that those ship trails had been prevalent and reflective enough to contribute to cooling the planet. Because the climate system does not react immediately, the pollution reductions initiated in 2020 might have begun affecting climate in 2023—to the tune of around 0.1 C, which is roughly half of the total unexplained heat.

The magnitude isn’t substantial, especially relative to the overall extent of human-induced global warming, remarks Andrew Gettleman, a scientist at the Pacific Northwest National Laboratory. Nonetheless, it is not insignificant. “It likely accounts for about 10% of the global warming we would expect to see over the forthcoming decade,” Gettleman states.

A study published in December in Science examined clouds on a broader scale. It concluded that, overall, cloud cover—and their characteristic bright white reflectivity—has decreased in several crucial regions of the planet over the last ten years, particularly in 2023. The collective effect, the authors estimated, could equate to approximately 0.2 C of additional warming—almost precisely the magnitude of the disparity between climate models and actual average global temperatures.

“It is evident that clouds, particularly low-level clouds, are playing the predominant role,” states Helge Goesseling, a climate scientist at the Alfred Wegener Institute in Germany and the primary author of the new investigation.

It remains unclear what might be driving the alteration in cloud behavior, Goessling mentions. The alterations in shipping-related clouds are likely a contributing factor.

However, some other researchers are exploring another pollution-related hypothesis. Sulfate pollution levels in China have dropped sharply since 2013, due to recent air pollution regulations in the nation. With reduced pollution, there are fewer nuclei for water droplets to cluster and form clouds—and thus fewer clouds, both above land and over the ocean downstream, researchers speculate.

The essential inquiry, Schmidt posits, is to ascertain if the changes in cloud behavior are a product of natural variation—something akin to El Niño, an effect that will revert on its own—or a more profound, fundamental transformation triggered by human-induced climate change.

Nevertheless, the warming impacts, although significant, pale in comparison to the climatic harm caused by the combustion of fossil fuels, asserts Dessler.

“Don’t let year-to-year fluctuations distract you,” he advises. “As long as we continue emitting greenhouse gases into the atmosphere, the climate will keep warming. And that will have enormous consequences for people’s lives.”