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The current global increase in temperature from human-caused greenhouse gas emissions is the fastest change to the planet’s climate since the peak of the last Ice Age 24,000 years ago. In a new data analysis, researchers reconstructed the variation in temperatures over the last 24 millennia and found current global temperatures are "unprecedented".
The new study, led by the University of Arizona and published in Nature, adds to evidence that human activity is the cause of the climate crisis. By reconstructing the Earth's climate since the last Ice Age, it highlights the main drivers of climate change and the speed this change is occurring.
It showed that over the 9,000 years between the early Holocene and the beginning of the Industrial Revolution, the global mean temperature increased by about 0.5°C ( 0.9°F). Over the last 150 years, however, the global mean temperature has increased by over 1.2°C ( 2.16°F). An incredible magnitude and speed of change compared to natural variation.
"This reconstruction suggests that current temperatures are unprecedented in 24,000 years, and also suggests that the speed of human-caused global warming is faster than anything we've seen in that same time," co-author Professor Jessica Tierney, who is a contributing author of the UN's IPCC report and briefs US Congress on climate issues, said in a statement.
"The fact that we're today so far out of bounds of what we might consider normal is cause for alarm and should be surprising to everybody," added lead study author Dr Matthew Osman.
To study the changes since the last glacial maximum, the team combined two independent methods. One is to use marine sediments. The shells of mollusks can be used as a temperature proxy as temperature changes over time affect the chemistry of their shells. This is not a perfect thermometer but it is a good starting point.
The other method is simulated climate models using humanity's best understanding of Earth's historic climate, which is also limited but by assimilating the data of the two, the team aimed to strengthen their findings. They created maps of the entire planet, where temperature changes can be tracked for the whole 24,000 years in intervals of 200 years.
"These maps are really powerful," Osman said. "With them, it's possible for anyone to explore how temperatures have changed across Earth, on a very personal level. For me, being able to visualize the 24,000-year evolution of temperatures at the exact location I'm sitting today, or where I grew up, really helped ingrain a sense of just how severe climate change is today."
The team is now using this method to look at climate changes that occurred even earlier, to better understand the evolution of the planet’s climate before we altered it so dramatically.
