Earth’s climate has built-in natural brakes that operated at full force for hundreds of millions of years, preventing the planet’s temperature from fluctuating as sharply as scientists had previously believed. However, a new study shows that during those ancient hot periods, the planet’s temperature was actually significantly lower than previously thought, Earth.com writes.

The results look especially alarming because they mean that unchecked human-caused warming could push Earth toward fluctuations never seen before. The study was conducted by a team from the University of Leeds — the scientists used a new measurement method to reconstruct Earth’s temperature over the Phanerozoic period, spanning roughly from 540 million years ago to the present day.

Previous studies estimated the planet’s temperature to be 20°C above pre-industrial levels during some geological periods, Focus reports. Moreover, it was believed that in some early eras, when the first animals were evolving, temperatures may have reached 30°C above. According to the scientists, these figures painted a picture of a planet capable of withstanding extreme heat.

But now the new study shows a completely different picture: the data point to natural stabilizing processes that kept the planet’s temperature within narrower limits over geological time.

According to the scientists, such processes gave Earth’s biosphere the opportunity for further evolution rather than repeatedly being driven to catastrophic extremes. Thus, the scientists concluded that in the past our planet experienced extreme temperatures that were at most 10°C above pre-industrial temperatures. This is still hotter than today, but a full 10–20°C cooler than previously assumed.

According to the study’s lead author, Dongyu Zheng of Chengdu University of Technology, the results recreate a much more detailed picture of past global temperatures than earlier methods allowed.

The study also suggests that Earth’s long-term climate sensitivity may probably be lower than some recent estimates. The results show that Earth’s temperature in the past was tightly regulated; however, human-caused warming of the planet by 10°C could potentially lead humanity into conditions our planet has never seen before.