Changing the climate: The real punchline is in June 2023, not July 2023 when global temperature reached 1.55 CeV

“When it started getting weird was around June and July of the summer,” says Zeke Hausfather, a climate scientist with the organization Berkeley Earth. July 2023 crushed all previous heat records from that month. Then August beat records by even more. “Then September was gobsmacking bananas, nearly a full degree above previous records, an enormous margin,” I said at the time.

Several international organizations that independently track the global temperature made the announcement. Although each group calculated a slightly different figure, averaged together the data indicate a consensus that, last year, Earth’s temperature hit 1.55 °C above the average for 1850–1900 — considered to be a ‘pre-industrial’ period before humans began pouring large amounts of greenhouse gases into the atmosphere. Unexpectedly, the 2024 figure also shows a statistically significant increase over that for 2023, when heat records were set. Climate scientists are looking at whether the two-year temperature surge is just a blip or a sign of change in Earth’s climate system that will cause global warming to accelerate.

There is no magic about the 1.5 C threshold according to scientists. It is a political target that was included in the Paris agreement in acknowledgement of concerns that an earlier goal of limiting warming to 2 C might not be strong enough to protect the most vulnerable countries. If the world were to fall apart, it wouldn’t happen if it was not breached, because the world is not below 1.5 C. It’s a spectrum, Hayhoe says, “and every bit of warming matters”.

“The real punchline is, it was another really warm year,” says Russell Vose, a climate scientist at NOAA’s National Center for Environmental Information, the group that produces the temperature estimates.

The Nature of the Warming Effect on Climate Change: The Hunga Tonga-Hunga Ha’apai Equation of State

El Niño and La Niña events are part of a natural climate cycle that can influence weather across a broad swath of the planet. During El Nio phases, global temperatures tend to be higher, while cooler global temperatures prevail during La Nia phases.

In eruptions gases and particles are usually shot into the air as a reflection of sunlight back into space. But the Hunga Tonga-Hunga Ha’apai volcano, which erupted in 2022, was underwater. It shot water high into the air, which can be used to trap heat.

Some scientists hypothesized that the warming effect could have contributed to some of the mystery heat. But after close study, scientists realized the impact was probably minimal.

“People talked about that a lot but our best guess is that it had an impact of zero,” says Andrew Dessler, a climate scientist at Texas A&M University.

A December study in Science took an even wider look at clouds. Cloud cover and the bright white reflectivity they bring has dropped in several key parts of the globe over the past ten years. The authors calculated that the effect could add up to 0.2 C of extra warming, which is about the size of the difference between climate models and actual global temperatures.

In 2020, international rules governing the fuels for the shipping industry changed. The sulfur in the old fuel caused sulfate pollution to cause water droplets to fall behind a ship in the ocean.

The newer, cleaner fuel produces less sulfate pollution—and fewer, smaller cloud plumes. The ship trails are reflective enough to be seen on the planet. Because the climate system doesn’t respond instantaneously, the reductions in pollution set in motion in 2020 could have started having an impact in 2023—to the tune of roughly 0.1 C, or about half the total mystery heat.

The scale isn’t enormous, compared to the overall impact of human-driven global warming, says Andrew Gettleman, a scientist at the Pacific Northwest National Laboratory. But it’s not nothing. “It is likely to be roughly 10% of the global warming we would expect in the next decade,” Gettleman says.

Helge Goesseling is the lead author of a new study, and he claims that the clouds are the main players.

Some researchers are looking at pollution-focused possibilities. China has a new air pollution policy that has caused sulfate pollution levels to plummet. Researchers theorize that with less pollution, there are more water droplets in the air and less in the ocean to form clouds.

If the cloud changes are part of natural variation, like the El Nio effect, or a deeper, fundamental change brought on by climate change, it’s important to understand.

Gail Whiteman is a social scientist who studies climate risks and she says it is both aphysical reality and a symbolic shock. “We are reaching the end of what we thought was a safe zone for humanity.”

“Individual years pushing past the 1.5-degree limit do not mean the long-term goal is shot,” said UN secretary-general António Guterres in a prepared statement. We need to fight harder to get on track. Leaders must act — now.”