As 2023 draws to a close, it's going out on top.
"It's looking virtually certain at this point that 2023 will be the hottest year on record," says Zeke Hausfather, climate scientist at Berkeley Earth, a non-profit that analyzes climate trends.
Though temperature records from December have yet to be finalized, climate scientists at the National Oceanic and Atmospheric Administration have found there's a more than 99% chance that 2023 will have the hottest recorded global average temperature, beating out 2016, the previous leader.
The record-breaking year helped fuel climate-driven disasters around the globe – from extreme heat that plagued Arizona for weeks, to devastating floods in Libya, to record-hot oceans that caused corals to bleach off Florida. Scientists say the extreme temperatures are in line with forecasts for how the planet will continue to warm.
"If we don't change things, if we keep going on the trajectory that we're going, we will look back at 2023 and think of it as: remember that year that wasn't so bad?" says Tessa Hill, marine scientist at the University of California Davis.
Many months during 2023 topped the charts
2023's record-breaking status was largely fueled by extremely hot temperatures during the second half of the year. Every month from June to November was the hottest ever recorded globally.
The year will be the hottest in 174 years of record-keeping where humans have directly measured the temperature of the planet. It's also likely to be the hottest in the last 125,000 years, which scientists measure by reconstructing temperature records from physical evidence like tree rings and layers of polar ice that have grown over time.
The biggest driver of the heat is the buildup of greenhouse gasses in the atmosphere from burning fossil fuels.
"We know why this is happening," Hausfather says. "A year like this would not have occurred without the trillion tons of carbon we've put into the atmosphere over the last century."
The past eight years are already the hottest eight on record. Some scientists see evidence that the pace of climate change is accelerating, though others say not enough years have passed to confidently show that trend.
2024 could vie for the top spot
The hotter climate drove extremes around the world in 2023. Over the summer, Phoenix, Arizona baked for weeks, spending 31 days above 110 degrees. More than 500 people died in the area from heat-related causes. But it wasn't alone – China, southern Europe and Mexico also saw intense heat.
"The major lesson is how unprepared we are," says Kristie Ebi, who studies the effects of heat at the University of Washington. "There are places with heat wave early warning and response systems. They certainly saved lives. They didn't save enough."
Heat waves hit the ocean as well. Off the coast of Florida, the water temperature reached 100 degrees Fahrenheit, the same conditions as a hot tub. Heat-sensitive corals can't survive prolonged heat, with many bleaching, turning a ghostly white color, or dying outright.
Even with the chart-topping heat this year, next year could be equally as hot. A strong El Niño has already begun, where ocean temperatures warm up in the eastern Pacific. El Niño years are typically hotter, because a large amount of heat that's stored in the ocean is released to the atmosphere.
Even if 2024 doesn't take the top spot, climate scientists say the years ahead will continue to rank highly, if humans keep burning fossil fuels at the current rate.
"There's absolutely still time to act," Hill says. "Everything we do to change course today will make things better in the future."
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