A massive new review of ancient atmospheric carbon-dioxide levels and corresponding temperatures lays out a daunting picture of where the Earth’s climate may be headed. The study covers geologic records spanning the past 66 million years, putting present-day concentrations into context with deep time. Among other things, it indicates that the last time atmospheric carbon dioxide consistently reached today’s human-driven levels was 14 million years ago—much longer ago than some existing assessments indicate. It asserts that long-term climate is highly sensitive to greenhouse gas, with cascading effects that may evolve over many millennia.
The study was assembled over seven years by a consortium of more than 80 researchers from 16 nations. It appears today in the journal Science.
“We have long known that adding CO2 to our atmosphere raises the temperature,” said Bärbel Hönisch, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory, who coordinated the consortium. “This study gives us a much more robust idea of how sensitive the climate is over long time scales.”
Mainstream estimates indicate that on scales of decades to centuries, every doubling of atmospheric CO2 will drive average global temperatures 1.5 to 4.5 degrees Celsius (2.7 to 8.1 Fahrenheit) higher. However, at least one recent widely read study argues that the current consensus underestimates planetary sensitivity, putting it at 3.6 to 6 C degrees of warming per doubling. In any case, given current trends, all estimates put the planet perilously close to or beyond the 2 degrees warming that could be reached this century, and which many scientists agree we must avoid if at all possible.
In the late 1700s, the air contained about 280 parts per million (ppm) of CO2. We are now up to 420 ppm, an increase of about 50%; by the end of the century, we could reach 600 ppm or more. As a result, we are already somewhere along the uncertain warming curve, with a rise of about 1.2 degrees C (2.2 degrees F) since the late 19th century.
Whatever temperatures eventually become manifest, most estimates of future warming draw information from studies of how temperatures tracked with CO2 levels in the past. For this, scientists analyze materials including air bubbles trapped in ice cores, the chemistry of ancient soils and ocean sediments, and the anatomy of fossil plant leaves.
The consortium’s members did not collect new data; rather, they came together to sort through published studies to assess their reliability, based on evolving knowledge. They excluded some that that they found outdated or incomplete in the light of new findings, and recalibrated others to account for the latest analytical techniques. Then they calculated a new 66-million-year curve of CO2 versus temperatures based on all the evidence so far, coming to a consensus on what they call “earth system sensitivity.” By this measure, they say, a doubling of CO2 is predicted to warm the planet a whopping 5 to 8 degrees C.
The giant caveat: Earth system sensitivity describes climate changes over hundreds of thousands of years, not the decades and centuries that are immediately relevant to humans. The authors say that over long periods, increases in temperature may emerge from intertwined Earth processes that go beyond the immediate greenhouse effect created by CO2 in the air. These include melting of polar ice sheets, which would reduce the Earth’s ability to reflect solar energy; changes in terrestrial plant cover; and changes in clouds and atmospheric aerosols that could either heighten or lower temperatures.
“If you want us to tell you what the temperature will be in the year 2100, this does not tell you that. But it does have a bearing on present climate policy,” said coauthor Dana Royer, a paleoclimatologist at Wesleyan University. “It strengthens what we already thought we knew. It also tells us that there are sluggish, cascading effects that will last for thousands of years.”
Hönisch said the study will be useful for climate modelers trying to predict what will happen in coming decades, because they will be able to feed the newly robust observations into their studies, and disentangle processes that operate on short versus long time scales. She noted that all the project’s data are available in an open database, and will be updated on a rolling basis.
The new study, covering the so-called Cenozoic era, does not radically revise the generally accepted relationship between CO2 and temperature, but it does strengthen the understanding of certain time periods, and refines measurements of others.
The most distant period, from about 66 million to 56 million years ago, has been something of an enigma, because the Earth was largely ice free, yet some studies had suggested CO2 concentrations were relatively low. This cast some doubt on the relationship between CO2 and temperature. However once the consortium excluded estimates they deemed the least dependable, they determined that CO2 was actually quite high—around 600 to 700 parts per million, comparable to what could be reached by the end of this century.
The researchers confirmed the long-held belief that the hottest period was about 50 million years ago, when CO2 spiked to as much as 1,600 ppm, and temperatures were as much as 12 degrees C higher than today. But by around 34 million years ago, CO2 had dropped enough that the present-day Antarctic ice sheet began developing. With some ups and downs, this was followed by a further long-term CO2 decline, during which the ancestors of many modern-day plants and animals evolved. This suggests, the paper’s authors say, that variations in CO2 affect not only climate, but ecosystems.
The new assessment says that about 16 million years ago was the last time CO2 was consistently higher than now, at about 480 ppm; and by 14 million years ago it had sunk to today’s human-induced level of 420 ppm. The decline continued, and by about 2.5 million years ago, CO2 reached about 270 or 280 ppm, kicking off a series of ice ages. It was at or below that when modern humans came into being about 400,000 years ago, and persisted there until we started messing with the atmosphere on a grand scale about 250 years ago.
“Regardless of exactly how many degrees the temperature changes, it’s clear we have already brought the planet into a range of conditions never seen by our species,” said study coauthor Gabriel Bowen, a professor at the University of Utah. “It should make us stop and question what is the right path forward.”
The consortium has now evolved into a larger project that aims to chart how CO2 and climate have evolved over the entire Phanerozoic eon, from 540 million years ago to present.
The author of the article is not a scientist but a journalist (check it) with very articulated personal agenda (check the list of his articles) instead of balanced review (in good professional journalism must be balanced), especially when pretending to near-scientific writing. It’s pity Columbia university allows such journalists to write for them. Sad
Alex, the author of this article did not conduct the study, he just reported on it, which, you know, is what journalists do.
The study was assembled over seven years by a consortium of more than 80 researchers from 16 nations. It was coordinated by Bärbel Hönisch, a Professor of Earth and Environmental Sciences, and specializes in Paleoceanography.
Next time you might want to aim before you fire. Sad,
Number One. Prove the earth is millions of years old.
Number Two: Prove that data derived is not extrapolated or for that matter accurate in assessing & predicting anything happening 66 million years ago.
Number Three: Provide the names of all assessers who participated in this climate assessment, who gives them a paycheck, corporate & NGO affiliations.
Number 4: Tell us the rest of the story!
Reveal the truth in how geoengineering including spraying chemical laden aerosols into the atmosphere worldwide AFFECTS climates or produces changes in the world’s climates.
When you pack all of these “Religious” leaders CONSENSUS mysteriously “pops up”!
I hate it so much when they use the consensus-argument. It does not matter how many scientists believe in something, there only needs to be 1 scientist that can prove them wrong and that’s how science works!
What caused C02 to be so high 50 million years ago?
Could the same natural forces be impacting earth now??
probably from very frequent volcanic activity (eruptions) throughout the planet.
According to this paper “Silicate weathering, volcanic degassing, and the climate tug of war” (M Saltzman, Geology 2017): “Long-term climate change is controlled primarily by the balance between CO2 sources from volcanic and metamorphic degassing and by sinks tied to both silicate weathering and, to a lesser extent, organic carbon burial” .
So 50 millions years ago maybe more volcanic activity (over very long time scales – nothing in common with current man-made increases in CO2). I am not sure if geologists directly link the long CO2 drawdown over the last 60 millions years to increased silicate weathering.
Exactly.. co2 was 100 higher in prehistory times so what makes alarmists think man is responsible for the minor rise in co2 in the last 200 yrs.. As a famous scientist once said it is either arrogance or stupidity to think man can control weather or climate
Eh, because it is not a minor change?
Humans have only been on this planet a very short time. We have been enjoying a climate “sweet spot” that has allowed our species to grow from maybe a few 10s of thousands to about 9 billion, and expand to populate most of the planet.
We are now exiting that sweet spot, at the hotter side, where more and more of the planet will become uninhabitable for us. Which, in turn, will result is large scale migrations to those areas that remain habitable.
Humans would not have been able to exist due to extremely hostile climates and environments during most of the life of the planet.
As for the cause…
Planet temperatures track atmospheric CO2 levels, with a lag (as would be expected).
That is because atmospheric CO2 allows in the heat from the sun, but does not allow out the heat from the planet as effectively. The more atmospheric CO2, the longer the heat is retained by the planet, and the greater the planet heats up.
Over the past 1,000,000 years atmospheric CO2 has naturally been varying in a cycle from about 200ppm to about 250ppm.
In the past 200 years – since we began burning vast quantities of fossil fuels – we have increased atmospheric CO2 by about 50%, to over 400ppm.
Increasing anything by such a large proportion has an enormous effect.
That CO2 is already in the atmosphere. The planet will continue to warm until there is a new balance between the amount of heat that enters from the sun and the amount that leaves.
The climates will continue to change until that new balance is achieved.
So significant global warming, and accompanying climate change is already baked in.
And that is if we stop adding CO2 to the atmosphere right now.
Which we wont.
So it will be worse than that.
It is unlikely to be pleasant for very many, people, flora and fauna.
Statistically, the human population has surged over the last 250 years since the beginning of the industrial revolution. One can conclude that marginally warmer weather, along with other circumstances, positively impacts humans. As a matter of fact, the planet is greener than it has been in recorded human history. I don’t doubt that human activity has an effect on climate, but to deduce “calamity” as the only outcome of current CO2 levels is sensationalism and not based in reality. This is demonstrated by the many many many predictions of apocalyptic and/or world changing events over the last 50 to 60 years. Every generation thinks they’ll be the last. Climate data before the year 1900 is sparse, subjective, and incomplete. Ice core samples are open to lots of interpretation on top of the fact that the scientific margin for error is equal to/or greater than the supposed change in atmospheric CO2 levels. Any researcher that says historical climate data is crystal clear is knowingly being disingenuous.
Robbie, It is believed by most geologists who have studied the high CO2 levels of about 56 million years ago that it was caused mostly by the outpouring of CO2 gases as a very large igneous province was erupted … the North Atlantic igneous province … CO2 sourced from the mantle. This large igneous province formed as North America split from Western Europe and the present North Atlantic Ocean began to open. The natural forces of that event are significantly different from current forces in several ways. First, the isotopic signature of the CO2 gas from a very large igneous province is different than the isotopic signature of CO2 released by the burning of fossil fuels, so geologists are highly certain that our current additions to the atmosphere are not being caused by the same natural processes that produced the high atmospheric CO2 values of 56 million years ago. But the most critical difference is the rate of change in atmospheric CO2. Large igneous provinces like the North Atlantic igneous province take many 10’s of thousands or 100’s of thousands to a few million years to form. So the CO2 was not all added to the atmosphere in a ‘short’ time span (by human standards). The rate at which humans have added CO2 to the atmosphere is at least one order of magnitude, possibly two or more, greater. Ecosystems (and probably human society) cannot readily adapt to such rapid rates of change. The big spike in atmospheric CO2 about 56 million years ago caused a major mass extinction on the planet; the life forms and ecosystems could not adapt that rapidly. What humans are doing now is something progressing at a much more rapid rate of change.
This completely ignores several well established facts. 1). CO2 LAGS temperatures, it never leads. 2). The planet earth is dominantly cold. These inter glacials only last 20K years. 3). This is the coldest of the last three warm periods, by far. The junk sceince needs to stop. We have already wrecked our economies, our energy security, and our grid stability with these lies. How much more damage are we going to allow these lies to do?
Except that atmospheric CO2 levels lead global temperatures.
Tom, the processes and responses of the previous 850,000 years, as related to atmospheric CO2, are no longer applicable. Because human activity has added so much carbon dioxide, derived by removing reduced carbon from the lithosphere and oxidizing it and releasing it to the atmosphere. Huge volumes of CO2 derived from oxidation of formerly lithospheric carbon had no part in the oscillations of atmospheric CO2 and global climate during the 850,000 years prior to the Industrial Revolution.
Lithospheric carbon has always played a role the global climate…
EXCELLENT ARTICLE! Well researched and written.
Pure BS. Humans have not changed the amount of CO2 enough to create any “climate change”. We know how much CO2 human activity puts in the atmosphere. About 35 billion tons. Sounds like a lot. But the atmosphere is a raging caldron of elements and compounds of 5.5 Quadrillion tons. All man made CO 2 is equivalent to pouring a bottle of beer in Lake ERIE.
Charlatans have used natural phenomena to fleece rubes of their freedoms and treasure since the first Witch Doctor worked out the moon eclipse cycles.
Lots of rubes today.
Your opinion is irrelevant to the facts
Increasing from 280 ppm to 420 ppm CO2 is an added 140 ppm, times 5.5 quadrillion tons of atmosphere is 770 billion tons of CO2. At 35 billion tons a year, we add that much in 22 years.
As for Lake Erie, 35 billion tons / 5.5 quadrillion tons is 6.4 ppm, times Lake Erie’s 480 trillion liter volume means it is equivalent to pouring 3 billion liters of beer in Lake Erie every year.
Your calculation assumes that CO2 concentration was a rollercoaster until humans evolved, and now every single ppm of change is caused by humans.
Which does not change the simple facts that atmospheric CO2 was naturally cycling from about 200ppm to about 250ppm for the past million years.
Until 200 years ago.
In that time we have increased atmospheric CO2 levels by about 50%, an enormous change to a system that was in balance.
Humans activity has increased atmospheric CO2 levels by about 50%.
That is an enormous amount to any system that was in balance.
So your saying that it’s possible to totally recover from the little ice age temperature losses and even some come back of the co2 shortage the earth is experiencing? excellent! if we could get back to the 0.7% food would be so abundant, cost would be minimal..good news!
A quick question on the lag.
I hope someone can help.
I do not know what I am talking about, let’s start there.
As a hobby, I built a model for how climate changes. I have gotten it near done and it mandates something I think I see in the CO2 data, but I am not sure.
The CO2 levels do lag the temp change as both rise, that is easy to see.
BUT, they actually should precede, not lag on the way down.
I think I see that in the data, but I may just be looking too hard.
Thanks.
As was discovered by the Greenland Ice Core Project, we are just coming out of the coldest period of time in the last 10,000 years. If temperatures were trending lower, we would indeed have something to worry about. As it is, we are trending upwards, which is to be expected. The chart in this article, shows there is no linear coupling between temperature and CO2 levels, so a correlation between one and the other is not possible. One might as well point out that the rise in CO2 began roughly around the time the passenger pigeon went extinct, so its extinction is the cause of global warming.