Climate change is setting new records all the time. According to a recent study which compiles information from 1,200 estimates of ancient temperatures and CO2 concentrations, if we don’t deal with greenhouse gases soon, by 2250 or so the world will have the highest concentrations of CO2 in 200 million years.The cause is twofold. For one, the sun has been steadily getting brighter, and therefore delivering more heat to the Earth, since the planet was first formed. That hasn’t had much of an impact on the Earth, at least not enough to really effect life, because the CO2 concentrations have general been between 200 and 400 parts per million. Concentrations have fluctuated, but are within the normal ranges for “icehouse” periods, which the Earth has been in until recently.

Before the industrial age, the atmosphere contained about 280 ppm of CO2. By 2016, that number had risen to 405 ppm. And that rise has happened far too fast. That much change would normally take millions of years, not a few centuries. At current rates and without replacing fossil fuels, CO2 concentration in the atmosphere could exceed 2,000 ppm by 2250.

“However, because the sun was dimmer back then, the net climate forcing 200 million years ago was lower than we would experience in such a high CO2 future,” says study lead author Gavin Foster, a professor of isotope geochemistry at the University of Southampton in England. “So not only will the resultant climate change be faster than anything the Earth has seen for millions of years, the climate that will exist is likely to have no natural counterpart, as far as we can tell, in at least the last 420 million years.”

There’s more to determining global climate than just sunlight and CO2, but there’s never such a large increase in CO2 concentrations this fast before. And CO2 isn’t the only greenhouse gas that exists in our atmosphere, or that human activity is introducing in increasing numbers. Methane, for example, is an even more powerful greenhouse gas, though it doesn’t stay in the atmosphere as long. But it does for long enough to do damage, and as the CO2 concentration continues to increase, along with other greenhouse gases, the sun is hotter than it was millions of years ago, meaning that the temperature will be rising even faster.