Breitbart article baselessly claims a study of past climate invalidates human-caused climate change

Yes, you read that correctly, three million — million — years ago CO₂ levels on Earth were the same as they are today, but there is one major difference between three million years ago and today…

This part of the article does accurately report the findings of the paper it links to: CO₂ is now higher than it has been for 3 million years. Although not a new result (see Martinez-Boti et al 2015¹), the linked study by Willeit et al² has new model simulations looking how climate changed from the Pliocene to the Pleistocene, and demonstrates how declining CO₂ levels lead to a change in the climate system. However what follows is largely a misunderstanding of the implications.

• 1- Martinez-Botí et al (2015) Plio-Pleistocene climate sensitivity evaluated using high-resolution CO₂ records, Nature
• 2- Willeit et al (2019) Mid-Pleistocene transition in glacial cycles explained by declining CO₂ and regolith removal, Science Advances

The author writes this as if this is something that is a surprise. We all know that the Earth’s CO₂ levels were higher at various times in the past. In the Eocene, 50 million years ago, they may have even been four times as high. This is not an issue. In the past, rates of volcanic CO₂ emissions globally were higher as continental spreading rates changed, for example. Saying that CO₂ isn’t rising now due to humans just because it used to be high in the past is like saying “I didn’t chop the cherry tree down because 40 years ago there was never a cherry tree there”. It is totally unrelated.

CO₂ levels were the same then as they are now

Yes, naturally CO₂ were as high in the Pliocene 3 million years ago as they are today. We have good records of the past 66 Million years of CO₂-driven climate change, and these record a broad decline over that time, with the Pliocene the last time CO₂ was naturally as high as it is today following anthropogenic emissions.

We have also been told the problem is DEFINITELY NOT a billions-year-old planet running through cycles where the temperature might fluctuate a bit.

This confounds natural variations in CO₂ in the geological past with human-caused emissions today. Yes, CO₂ has changed naturally over time, causing changes to climate, but the high levels and rapid increase we are seeing today is because of human-caused emissions.

This entire article’s “proof” is just saying that “higher CO₂ happened before humans, therefore humans can’t cause higher CO₂“.

Here are logically identical arguments: “England scored goals before Harry Kane, so Harry Kane can’t score goals” Or in American English: “The New England Patriots scored touchdowns before Rob Gronkowski, so Rob Gronkowski can’t score touchdowns” Or more simply: “Fires happened before humans, so humans can’t cause fires”.

So if you agree with this article’s logic and that humans aren’t causing CO₂ to rise, you also have to believe that Harry Kane and Rob Gronkowski never scored anything and could never score anything, and that no fire has been caused by a human ever.

Human-caused global warming, goals by Harry Kane, touchdowns by Rob Gronkowski, and fires set by people are all in the same boat. We have enormous evidence that they exist.

We are well aware that there are climatic fluctuations through geological time. Huge numbers of scientists study how the Earth’s climate has fluctuated before, and we know what caused those changes. Current warming is not related to any natural climate cycle, or process, or astronomic phenomenon.

According to the study, scientists also discovered that during this period of Global Warming “there were no ice sheets covering either Greenland or West Antarctica, and much of the East Antarctic ice sheet was gone.”

This is where the real logical fallacy of this article becomes clear. Indeed, when CO₂ was naturally as high as we have caused it to be now, the world was much warmer than today because of the naturally higher CO₂. It therefore follows that the high CO₂ levels we have created in the atmosphere will lead to a warmer world, just like the Pliocene.

“there were no ice sheets covering either Greenland or West Antarctica, and much of the East Antarctic ice sheet was gone.” How is this possible 2,999,971 years before Arnold Schwarzenegger bought his Hummer?

What this study tells us is that the last time CO₂ was as high as 410 ppm (back then through natural causes), there was no ice on Greenland or West Antarctica. What this means is that we can potentially expect (once the climate has equilibrated to its new CO₂ levels) that these ice bodies will melt in the future from anthropogenic CO₂ release. If this happens, the sea level will rise by metres, and many coastal and lowland cities will be affected.

In a way I have to profess my admiration- how a news outlet could take a paper presenting evidence that we should be very worried about CO₂ being 410 ppm, and turns it into a paper that “debunks climate change”, is beyond me. It really is a feat that must have taken a lot of imagination and creative thinking.

How is this possible 2,999,971 years before Arnold Schwarzenegger bought his Hummer?

Because the amount of CO₂ naturally present in the atmosphere depends on how much is being released or taken up by the oceans, land ecosystems, and chemical reactions involved in rock weathering. These change naturally, but gradually, over thousands or millions of years. Human emissions of CO₂ are merely adding an extra factor to the equation, but it is one which has a big effect over much short timescales (the last few decades).

It is possible because CO₂ sources (e.g. volcanic degassing) and CO₂ sinks (e.g. from chemical weathering of the Earth’s surface) were differently balanced back then. It is not a mystery, it is well understood science that has countless papers about it, and a serious journalist (if they profess to be one) would have made some effort to educate themselves before writing such an article.

a study that totally debunks the whole concept of man-made Global Warming

The study does the complete opposite of this, by showing that high levels of CO₂ has caused a warmer world in the past, it confirms what we know about how anthropogenic CO₂ emissions are and will continue to warm the planet.

running through cycles where the temperature might fluctuate a bit.

The Earth’s climate has always varied, even before humans began to influence it. Climate scientists have always been very clear about this. But human-caused emissions of CO₂ and other greenhouse gases have now added a new cause of climate change in addition to the existing causes of natural climate variability.

How is that possible 2,999,945 years before Americans moved to the suburbs and lit up the charcoal grills?

Again, this is possible because at various times in the Earth’s history, sources and sinks of CO₂ into the atmosphere have had varying strengths. These are natural changes in CO₂ levels that have slowly happened for 100s of millions of years. However, modern CO₂ rise is faster than any rise ever seen in the last 66 million years* and quite possibly ever before in the geological record.

• Zeebe et al (2016) Anthropogenic carbon release rate unprecedented during the past 66 million years, Nature Geoscience

a study that totally debunks the whole concept of man-made Global Warming,

This study does no such thing. This is factually inaccurate.

But-but-but-but Alexandria Ocasio-Crazy told me we only have 12 years!

The 12-year figure quoted comes from the 2018 UN “Special Report on Global warming of 1.5ºC,” released last October. In this report, the year 2030—12 years from now—is given as the “point of no return”, if we keep releasing CO₂ at our current rate. What this means is that after this point, it is almost impossible to imagine how CO₂ in the atmosphere could ever be brought back down to levels needed to keep global temperatures less than 1.5 ˚C warmer. This figure comes from the IPCC report scientists—hundreds of scientists from different fields working all around the world.

The article has taken this figure out of context, and is comparing it to something very different. What ThinkProgress says is related to the timescales it takes for the maximum effects of the CO₂ released now to take hold. This is not in conflict with the IPCC figure of 12 years cited by AOC—this report talks about the year we must stop releasing CO₂ by in order for the long term knock on effects of this CO₂ release to not be so detrimental to humankind.

This confuses the time left to start seriously cutting emissions, with the long tail of impacts that those emissions have. As noted above in this article, there are lags in the climate system that mean CO₂ emissions now will continue to warm the planet for a long time, and some long-acting positive feedbacks (like ice melting) take time.

what this study proves is that there is nothing we can do to stop the Earth’s naturally occurring climate cycles.

This study does absolutely no such thing. Its topic wasn’t even related to showing climate cycles—the subject of the paper is looking at the effect on CO₂ of ice sheets scraping soil and weathered rock off the Earth’s surface over ice ages.

CO₂ rise and warming that is happening now is entirely something that we have caused (see here for some helpful pointers). We can control our CO₂ release, and so we can control our current rate of warming. What the background conditions do over millions of years is not the point, and is only used in this article as a distraction.

nothing we can do to stop the Earth’s naturally occurring climate cycles.

Actually, studies suggest that we may already have postponed the next ice age by adding extra CO₂ to the atmosphere which will take a long time to be removed by natural processes, and hence has committed the Earth to warmer temperatures than it would otherwise have had.

This is not true, and there is good evidence that human CO₂ emissions stopped the initiation of another ice age*

• Ganopolski et al (2016) Critical insolation–CO₂ relation for diagnosing past and future glacial inception, Nature