According tomedia New Atlas, without human intervention, what would the Earth’s climate be like? Researchers at the University of Northern Arizona have now analyzed more than 12,000 years of climate data and found that human-induced warming has disrupted and reversed long-term natural global cooling periods.
It is no secret that the Earth is warming at an alarming rate, breaking temperature records in recent months, years and decades. But this data dates back to the 1880s, when observations began to be routinely recorded. So, in the long run, what is the current trend?
To find out, researchers have been compiling data from a variety of sources dating back thousands of years. A few months ago, a team of 93 scientists published a particularly comprehensive record of paleoclimate data spanning the past 12,000 years. It includes 1,319 data records from lake sediments, marine sediments, peat, cave sediments, corals and glacier ice cores, collected from 679 sites worldwide.
As a result, researchers were able to map changes in surface air temperature over the past 12,000 years — the last ice age in the world. It then compares the average temperatures of the century between 1800 and 1900 to track the changes that the industrial revolution may have brought about.
As expected, temperatures were much lower than the 19th-century baseline at the beginning of the period. But over the next few years, temperatures rose steadily, eventually exceeding the baseline. Temperatures peaked 6,500 years ago, and the earth has been cooling slowly but surely ever since.
“The cooling rate after peak warmth is subtle, at only about 0.1degrees per 1000 years,” said Michael Erb, co-author of the study. “This cooling appears to be driven by a slow cycle in Earth’s orbit, which reduces the amount of summer sunlight in the northern hemisphere and eventually leads to nearly a century of ‘xiaobing periods’. “
Since the middle of the 19th century, however, human activity has increased the average temperature by as much as 1 degree Celsius. This is a huge peak in a relatively short period of time, higher than the peak of 6,500 years ago.
“The last time the average global sustained temperature was 1 degree Celsius above the 19th century, it was probably back about 125,000 years ago, when sea levels were about 20 feet higher than they are today,” said Darrell Kaufman, lead author of the study.
The study was published in the journal Scientific Data.