Remo Casilli/Reuters
- Climate scientists officially named 2023 the hottest year on record dating back to 1850.
- Data from ancient ice cores and tree rings suggest the world hasn't been this warm in 100,000 years.
- Greenhouse gas pollution is the main cause of rising heat, but other factors are being investigated.
- This article is part of Business Insider's weekly newsletter on sustainability. Sign up here.
Anyone who made it through 2023's scorching summer won't be surprised to learn that last year was the hottest on record. But climate scientists who track these trends were still shocked by how high temperatures soared.
Europe's Copernicus Climate Change Service made the official call this week. The planet's average temperature was 1.48 degrees Celsius warmer than the preindustrial era was more than a century ago. The new average topped the record set in 2016. Most alarming, the year-over-year jump was the largest scientists have recorded.
Carlo Buontempo, the service's director, said evidence suggests the world hasn't been this warm in 100,000 years, meaning no cities, farms, or other parts of modern society have ever endured this heat.
"This calls for a fundamental rethink of the way in which we assess our environmental risk," Buontempo said during a press call Tuesday, "as our history is no longer a good proxy for the unprecedented climate we're already experiencing."
The scorching heat is exacerbating natural disasters, which the insurer Munich Re estimated cost the global economy $250 billion last year.
Copernicus scientists answered many burning questions from reporters. Here are my top three:
What made 2023 so hot?
The main cause was all the greenhouse-gas emissions entering the atmosphere from burning fossil fuels for energy, transportation, and other industries, Buontempo said. These emissions trap heat, the vast majority of which is absorbed by oceans.
Another contributor to the record heat was El Niño, a natural climate pattern that warms the Pacific Ocean. It began in early July, making July and August the hottest months of the year. El Niño is expected to peak this month or next. This is partly why scientists expect 2024 to be even hotter than 2023.
But the Copernicus climate scientists said that these weren't the only factors and that some required more research. They pointed to unusual marine heat waves beyond the Pacific; Antarctic sea ice that temporarily reached record lows; and an underwater volcano that erupted in 2022 near Tonga, an island in the Pacific, and spewed water vapor — a powerful greenhouse gas — into the atmosphere. They also said it was unclear whether the shipping industry's efforts to reduce emissions were having the counterintuitive effect of worsening the climate crisis.
How do scientists know what the climate was like 100,000 years ago?
Samantha Burgess, Copernicus' deputy director, said scientists at the organization look at recent data from satellites; global temperature records dating back to 1850; and archival "paleoclimate and proxy data" from deep-sea sediments, coral skeletons, tree rings, and ice cores around the world.
"The last time global temperatures were this high there were no satellites," Burgess said.
Scientists have measured the concentration of greenhouse gases like carbon dioxide and methane in ancient ice cores and other natural sources — those samples create a record of what the atmosphere was like tens of thousands of years ago.
Does this mean global climate goals are unreachable?
No. Countries are aiming to limit global warming to 1.5 degrees Celsius above preindustrial levels, as set out in the 2015 Paris Climate Agreement. While the average temperature in 2023 was dangerously close to that threshold, one year of data isn't enough to call the climate deal a failure. There would need to be a long-term trend.
Under the guidelines from the UN Intergovernmental Panel on Climate Change, if the global average temperature were to hold at more than 1.5 degrees above preindustrial levels for at least two decades, the signatory countries would have failed to uphold their promise.
"We are likely to overshoot 1.5 degrees," Burgess said. "That's basic physics of the system and the amount of warming that is locked into the system. However, the reality is that every single fraction of a degree matters."
However, some researchers say that if there isn't a steep drop in emissions this decade, that 1.5-degree goal will likely be a lost cause.