With just a few exceptions, observed climate data only goes back to around the 1880s. That’s roughly when scientists more or less agreed on how to measure the large elements of climate (temperature, weather conditions, humidity, wind strength, and so forth) and how to record it. But there are plenty of ways to look back farther—much farther—and gather ancient climate data, too.

Early in 2020, a team of 93 scientists scoured existing research for climate data from the last 12,000 years. They pulled more than 1,300 data points from concrete sources like lake-bottom deposits, marine sediment, ancient peat bogs, animal middens, subfossilized pollens and insect larvae, cave and coral deposits, and glacier ice cores, gathered from almost 700 sites around the world. On all of these, the climate at the time they were laid down left an indelible record that science can read.

From these data points, the research team was about to create a map of the surface air temperatures around the world over the past 12,000 years, or from the last major ice age to today. What the climate data shows for the first half of that 12 millennia is what everyone knows: the world was gradually warming out of the Ice Age, by approximately half a degree to three degrees every thousand years. But that trend only lasted until 6,500 years ago. From then until the mid-1800s, the earth was cooling again. Not as much and not as swiftly as it had warmed, but there was a distinct downward trend to the temperature data.

Then came the 1800s, and that downward trend halted. As the Industrial Revolution dawned in waves around the world, the temperatures of the planet ceased falling. For a few decades, they held steady, and then an inexorable and sudden rise, far, far faster than the previous one of twelve to six thousand years ago. Since the dawn of the internal combustion engine, average global temperatures have risen back to their 6,500-years-ago high, with no indication of another cooling period to come.

Even though this ancient climate data comes from a series of reconstructions based on fossilized evidence, ice cores, and more, it shows a clear “macro” pattern of subtle warming and subtle cooling, followed by a sharp upward trend over the past 200 years.

Photo: A peat bog in Ireland. Credit: Shutterstock