An unprecedented type of computer simulation found shows that the levels of carbon dioxide have likely never been as high in the past 3 million years. During this time, global mean temperatures never exceeded preindustrial levels by more than 2 degrees Celsius.

Image credits: NOAA (not from this study).

Rising CO2

As climate science has continued to develop, researchers have found more and more pieces of data which can be included in models, finessing the results more and more. This latest computer simulation is the first to look at ocean floor sediment data of climate evolution over this period of time.

Essentially, researchers used a very efficient numerical model to reproduce the causes and features of climate variability over the past few million years. They tested the model results with known climate events, and the model successfully predicted these events — adding substantial confidence regarding its accuracy.

The study also shows that along with the Earth’s orbit, CO2 also plays a vital role in directing ice ages.

“We know from the analysis of sediments on the bottom of our seas about past ocean temperatures and ice volumes, but so far the role of CO2 changes in shaping the glacial cycles has not been fully understood,” says Matteo Willeit of the Potsdam Institute for Climate Impact Research, lead author of the study now published in Science Advances. “It is a breakthrough that we can now show in  that changes in CO2 levels were a main driver of the ice ages, together with variations of how the Earth’s orbits around the sun, the so-called Milankovitch cycles. These are actually not just simulations: we compared our results with the hard data from the deep sea, and they prove to be in good agreement. Our results imply a strong sensitivity of the Earth system to relatively small variations in atmospheric CO2. As fascinating as this is, it is also worrying.”

Why is it worrying?

Studying Earth’s past is key to understanding its future evolution. Carbon dioxide (CO2) is a well-known greenhouse gas, which, in the atmosphere, contributes to planetary warming. So you can get an idea of how extreme these results are, the last time CO2 levels were this high, there were trees at the South Pole.

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So then, why aren’t we seeing more brutal effects?

It takes time for these changes to take effect. Much of the CO2 we are seeing into the atmosphere today was emitted in the past century — which, in geological terms, is the blink of an eye. It will take some time before today’s temperatures rise accordingly, but the chain of events has already been set in motion and, like all planetary processes, the inertia of this warming is gargantuan.

We are clearly seeing the first stages of this process, though. All temperature measurements show a steady increase which correlates with the extra CO2 observed in the atmosphere, and there is overwhelming evidence showing that the planet is warming up incredibly fast.

Is it because of us?

Yes. The scientific evidence is unequivocal: the greenhouse gas emissions (and particularly CO2) emitted by mankind are responsible for the warming trend we are observing.

While there is a great deal of talk about how this process happens and what its quantifiable effects are, the elephant in the room is there: we know CO2 traps heat in our planet’s atmosphere, and we know we are emitting a lot of CO2 — therefore we are responsible for the extra heating. We can argue about how big the elephant’s ears or trunk is, but the elephant is there and sticking our heads in the sand won’t solve anything.

Global warming is happening, whether we care to admit it or not.

Journal Reference: M. Willeit el al., “Mid-Pleistocene transition in glacial cycles explained by declining CO2 and regolith removal,” Science Advances (2019). DOI: 10.1126/sciadv.aav7337 , http://advances.sciencemag.org/content/5/4/eaav7337