Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher — “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm.”

Miocene big

You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science.

“The last time carbon dioxide levels were apparently as high as they are today “” and were sustained at those levels “” global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,” said the paper’s lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.

“Carbon dioxide is a potent greenhouse gas, and geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth’s history,” she said.

Yes, pumping more and more CO2 into the air is a very bad idea, as this news release from UCLA on a major new study makes clear.  The study itself, “Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years,” (subs. req’d) was released by Science earlier this month.

The study notes importantly, “This work may support a relatively high climate sensitivity to pCO2” [the partial pressure of CO2], which is the same conclusion that a number of major studies looking at paleoclimate data have come to:

Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Artic temperatures almost beyond imagination-above 23°C (74°F)-temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

A second study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system-where global warming boosts atmospheric CO2 levels-“will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.

The third study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond”-as much as 1.5°C warmer this century alone.

So we need to keep atmospheric concentrations of CO2 as low as possible — and if we do go above 450 ppm, we need to get back to under 350 ppm as rapidly as possible, preferably by century’s end, though that would be no easy feat.

Here’s more on this important study:

Tripati, before joining UCLA’s faculty, was part of a research team at England’s University of Cambridge that developed a new technique to assess carbon dioxide levels in the much more distant past “” by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae. Tripati has now used this method to determine the amount of carbon dioxide in Earth’s atmosphere as far back as 20 million years ago.

“We are able, for the first time, to accurately reproduce the ice-core record for the last 800,000 years “” the record of atmospheric C02 based on measurements of carbon dioxide in gas bubbles in ice,” Tripati said. “This suggests that the technique we are using is valid.

“We then applied this technique to study the history of carbon dioxide from 800,000 years ago to 20 million years ago,” she said. “We report evidence for a very close coupling between carbon dioxide levels and climate. When there is evidence for the growth of a large ice sheet on Antarctica or on Greenland or the growth of sea ice in the Arctic Ocean, we see evidence for a dramatic change in carbon dioxide levels over the last 20 million years.

“A slightly shocking finding,” Tripati said, “is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different.”

Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years “” until recent decades, said Tripati, who is also a member of UCLA’s Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.

Prior to the Industrial Revolution of the late 19th and early 20th centuries, the carbon dioxide level was about 280 parts per million, Tripati said. That figure had changed very little over the previous 1,000 years. But since the Industrial Revolution, the carbon dioxide level has been rising and is likely to soar unless action is taken to reverse the trend, Tripati said.

“During the Middle Miocene (the time period approximately 14 to 20 million years ago), carbon dioxide levels were sustained at about 400 parts per million, which is about where we are today,” Tripati said. “Globally, temperatures were 5 to 10 degrees Fahrenheit warmer, a huge amount.”

Tripati’s new chemical technique has an average uncertainty rate of only 14 parts per million.

“We can now have confidence in making statements about how carbon dioxide has varied throughout history,” Tripati said.

In the last 20 million years, key features of the climate record include the sudden appearance of ice on Antarctica about 14 million years ago and a rise in sea level of approximately 75 to 120 feet.

“We have shown that this dramatic rise in sea level is associated with an increase in carbon dioxide levels of about 100 parts per million, a huge change,” Tripati said. “This record is the first evidence that carbon dioxide may be linked with environmental changes, such as changes in the terrestrial ecosystem, distribution of ice, sea level and monsoon intensity.”

Today, the Arctic Ocean is covered with frozen ice all year long, an ice cap that has been there for about 14 million years.

“Prior to that, there was no permanent sea ice cap in the Arctic,” Tripati said.

Some projections show carbon dioxide levels rising as high as 600 or even 900 parts per million in the next century if no action is taken to reduce carbon dioxide, Tripati said. Such levels may have been reached on Earth 50 million years ago or earlier, said Tripati, who is working to push her data back much farther than 20 million years and to study the last 20 million years in detail.

More than 50 million years ago, there were no ice sheets on Earth, and there were expanded deserts in the subtropics, Tripati noted. The planet was radically different.

It was Hell and High Water. We really ought to avoid that, no?

Related Posts:

25 Responses to Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher — “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm.”

  1. JeandeBegles says:

    This study confirms the obviousness of the ice core analysis with its well known curbs for CO2 concentration, average temperature, and sea level, from -800 000 up today. Being at 387 CO2 ppm, with +1°C for temperature and some centimeters of sea level rise, versus the figures in 1800 with 280 CO2 ppm. These are not the final figures. There will be a lot of temperature to go, and sea level as well.
    We have not paid for the 100 ppm increase.
    It is absolutely urgent to cut our CO2 emissions NOW.

  2. Lou Grinzo says:

    To JB’s comments, I would add that David Archer, in his excellent book The Long Thaw, points out that by focusing so narrowing (and arbitrarily) on the year 2100, we’re giving ourselves a 40% fudge factor to play with. We won’t see 40% of the warming effect of the CO2 we emit before 2100 until after that date.

    I think it’s becoming very clear that we’ve seriously underestimated two mappings in the climate system: Atmospheric CO2 level to warming, and warming to overall environmental impacts (floods, droughts, tropical storms, sea level rise, etc.). I posted on this issue late last night:

  3. caerbannog says:

    One might quibble by arguing that while today’s CO2 levels might keep polar ice-sheets from forming if the poles were already mostly ice-free, the current CO2 levels would not be enough to actually melt off the current ice-sheets.

    Call it “albedo-hysteresis” — The current ice-sheets may reflect away enough sunlight to offset enough of the current CO2-forced warming to keep them from melting, whereas if the ice-sheets were not already present, the reduced albedo + current CO2 forcing would be sufficient to keep them melted.

    But as far as practical impacts on human-civilization are concerned, that’s just quibbling. We are already on track to load up the atmosphere with enough CO2 to do in the ice-sheets eventually, whether or not my speculations above are correct.

    Not trying to play the “tinfoil-hatter”** here; just trying to anticipate and head off a potential “tinfoil-hatter”** talking-point.

    ** I prefer the term “tinfoil-hatter” to “denier”. The former doesn’t carry the nasty historical baggage of the latter, and it better captures the silliness of the global-warming “skeptic” arguments. Basically, the global-warming skeptic arguments are all built on an assumption that the scientific community is behind a global conspiracy to keep the truth from the American people. And that’s even more insane than claims that the US Government planted explosives in the WTC towers to take them down on 9/11.

  4. Leif says:

    One wonders if the main-stream media will wake up and finally give this kind of article the attention it requires? EXXON-MOBIL gets a full page spread in the NY Times to spout their “no problem” BS. Come on you guys, past time to wake up…
    As pointed out in the report our blinders of necessity, (too many veriables and s**t poor science), of looking only at the CO2 effects and not feed back loops will surely sucker punch us.
    Nature bats last.

  5. paulm says:

    Yes, I hit this realization back at the start of the year…

    January 17, 2009 at 7:54 pm

    That’s the important figure, not 350.

    100ppm less than 280ppm CO2 ment 5 degrees cooler.
    100ppm greater than 280ppm means > 3 degrees hotter.

    We are looking in to the abyss! God Help us (if she can).

    I guess the peer review science is catching up.

  6. K. Nockles says:

    The science gets better. The results are more precise over longer time spans. Those of us who know they are giving us a true picture of the near future are doing all we can to make a diffrence. But will we make the changes we need to in time? The edge of the knife gets thinner and sharper toward the tip, and we are very close to it now. Everyday it feels as if we are walking a tightrope, just waiting for that tipping point to rock that tightrope and we all fall down. The science says time is running out and the current state of the debate is lagging far behind. As we plod toward an answer to this dilema, the Climate is rushing toward a new state, one not kind to the Humane Race.

  7. ecostew says:

    The Obama administration moved a step closer on Friday to canceling a Clean Water Act permit for the largest mountaintop-removal mine in West Virginia history.

  8. K. Nockles says:

    Thanks Ecostew, there are postive moves towards our childrens future. Sometimes it just seems so slow compared to the rush of changes we are seeing in the natural world. Thanks again!

  9. From Peru says:


    “Denier” is really a very good word precicely for that “nasty historical baggage”.

    Holocaust Deniers are actually FAR MORE DANGEROUS than Climate Change Deniers.

    I don’t understimate the massacre of Nazi Holocaust. Nazis killed more than 20 million people in just 6 years, mainly Russians (7 million), Jews(6 million) and Poles (2 millions), certailnly one of the greatest massacres in history (I don’t know how many tens of millions Native Americans, Australian Aborigens and Native Africans were murdered in the Imperialist Colonization of America, Africa, South Asia and Australia, but that genocides lasted centuries , not just 6 years).

    But that events happened in the PAST.

    Climate Change, as a possible Nuclear Holocaust, belong to PRESENT and FUTURE. Denying past massacres will not resurrect that events, but denying a present one will certainly permit a future disaster.

    Climate Change could kill not millions, but BILLIONS, in the NEAR FUTURE.

  10. From Peru says:

    Beautiful picture of the Miocene!

    The continents were pretty much in the same place as today. So Antartica, right inside Antarctic Circle, was ice-free not because it was more northward.

    Something else prevented ice formation, leaving only CO2 as the possible cause.

    This point to a possible rise not of 6-7 meters, but 30-60 meters!(While the melt might take centuries, 6 meters per century is still pretty scary)

    So by by New York, Washington D.C, Houston, New Orleans, Paris, London, Cairo, San Petersburg, Calcutta, Beiging , Shangai, Basra, …..

  11. mike roddy says:

    This is persuasive and devastating news indeed, to add to all of the other reports that have been flooding in lately.

    I share Leif’s frustration with the New York Times, but it’s mentioned because that’s the kind of paper that bloggers here read. More dangerous is what’s on the TV and radio waves. A visitor from Mars would conclude that our scientific inquiry is mostly centered on the sexual habits of female entertainers, and that reality dictates that there are two sides to every story. Our own unique quantum theories, I suppose.

    Many of you here are probably aware that the percentage of Americans who believe that climate change science is uncertain, and future dangers unlikely, has increased from 41% to 46%. This occurred precisely during the period when the news has become far more ominous. Obviously, news outlets have been either purchased or bullied by fossil fuel, timber, and utility companies.

    The US government is of course going to waffle in its uniquely corrupt way. The best course may be for a group of billionaires to purchase one or two key television networks and radio station corporations. The rich can’t all be like Gates and Buffet, especially since there are now so many of them. This is the kind of step that could actually make a difference. The airwaves would be filled with nightly scenarios showing what we will face if we don’t change, supported by scientists in the field and put together by top producers. Look at what Gore’s movie accomplished with a small budget. Serious television, and a few gripping movies, may cause a tipping point of awareness to finally hit the public.

  12. paulm says:

    Things have to change fast – the US goverment should be placing hard hitting adds on TV to alert the public. As they are doing in the UK. This waking a lot of people up to the dire consequences.

    A bedtime story

    Many now accept GW, but do not realize what and when is going to arrive.

    It doesn’t really matter if they are challenged by deniers cause the science backs it and there needs to be LOUD debate about whats going on.

  13. David Lewis says:

    This type of thing is all the more reason to consider geoengineering. The Royal Society “Geoengineering the Climate” study released in September 2009 contained this statement:

    “Proposals for new methods are still appearing (confidential submissions received) and it is very likely that substantial cost reductions are possible in future.”

    The entire report is here:

    This mention of “confidential submissions” and “substantial cost reductions… in the near future” made no impression on me upon first reading. It seemed too oddly speculative to even be in such an otherwise authoritative report.

    Then I heard Graciela Chichilnisky give a lecture at the London School of Economics (LSE). The lecture was entitled: “Climate Change: Are We Heading for a New Cold War?”

    An mp3 file of her lecture is here:

    Chichilnisky is a manager of Global Thermostat, a company developing what they say is a proprietary air capture process with commercial potential.

    Chichilnisky has written the book, “Saving Kyoto”. She claims to have written the cap and trade section of the Kyoto agreement at the eleventh hour in Kyoto thus saving the day there. She also has an essay, “Forward Trading”, on breaking the deadlock between China and the US at Copenhagen published in the European edition of Time magazine Oct 5 2009.

    During the LSE lecture she repeatedly directed people to read the September Royal Society Geoengineering report, as if it confirmed what she was telling the audience, i.e. that air capture is ready for cost effective deployment right now.

    But, the Royal Society report does not announce that air capture is ready for deployment now,. The only thing is that “confidential submissions received” making it “very likely that substantial cost reductions are possible in future” statement.

    I got a bit frustrated with Chichilnisky and wrote her saying I have studied the Royal Society report, heard her make her case at the LSE, read the Time essay, and I just don’t get it. She replied, claiming that a “well known engineering firm” has evaluated the air capture process she “co-invented” and found that the “capital costs” are “about 1/2” those of “conventional carbon capture from the flue (CCS)”. Further, she claimed people will be able to “visit the live pilot in California in the first quarter of 2010”.

    And that’s it. She eventually wrote: “I have given you all the information I can” and that was the end of it.

    A bit of searching on the internet turned up the slides for a presentation made by Chilchinisky on November 10 2008 in Australia. These slides are here:

    On page 17, there are statements and a diagram that describes a process that uses the waste heat from any type of electricity generating power plant to remove significant amounts of CO2 from the air around the plant.

    “Cogeneration” was a word she used at the LSE lecture. The slides for the Australian presentation support an interpretation that the claim is that the process has the potential, if fitted to a coal fired electricity generating plant, to remove 1-2 Kg of CO2 per Kw-hr of electricity generated. The sentence on the slide pointed out that because a coal plant of the 400 MW size under discussion emits only 1 Kg of CO2 per Kw-hr generated out its smokestack, if its waste heat was powering a process that was removing 2 Kg, such a plant could be a significant net carbon dioxide sink.

    At the LSE she spoke with great confidence. By now she has a grand plan to bring the US to the table at Copenhagen by addressing the reluctance of the US Senate to sign on, which she says is due to the realization of some Senators who see that most of the carbon offset money going from the developed to the developing world as a result of Kyoto is ending up in China which can only foster the growth of their most feared future global competitor.

    So, Chichilnisky proposes, as explained in her Time essay, some financial legerdemain or other be agreed to by the US and China and written into the Copenhagen agreement to cause this money that is presently flowing into China to end up in future flowing to the least developed world. Her idea is that if directed to places such as Africa, the money could allow her air capture technology, fitted to solar thermal plants, to simultaneously generate electric power and by being net carbon sinks, to act to restore the CO2 level in the atmosphere to a more safe level such as 350 ppm. She claims a net transfer of funds of the order of $200 billion annually is the maximum that would be required to bring on this vast amount of infrastructure, which, over time, would have this effect. She claims the carbon market can accomplish this amazing transfer of funds, even though such transfers by national governments directly remains unlikely. By raising living standards in the least developed world and hence ending the pressure on the poorest people there to have as many children as possible to ensure there will be someone to look after them in their old age, the global population will stop rising, thus addressing climate change in a fundamental way. The US Senate buys in because they will see that a Copenhagen agreement will not end up channeling the developed world’s offset money into subsidizing an even more rapid development of the power of China. The rest of the world follows the US, civilization is saved, from this climate problem at any rate, so Ta Da.

    At least this is how I understand what her plan is: when I explained I do not see why China will buy into this, she wrote me to say I do not understand her plan. However, she refrained from pointing out exactly where I have gone wrong in following her logic.

    Whatever her plan is, and whether the world buys in or not, if the air capture process her company is developing is anything like what she is saying it is, it is interesting.

    So, we’ll see. Maybe the Royal Society took a look at a “confidential submission” from Global Thermostat and/or Chichilnisky, and they decided the process sounded promising enough for them to hint at its existence in an authoritative report of a type not normally prone to be full of idle speculation.

    The Royal Society working group, some of whom must know what is going on, was chaired by John Shepherd, University of Southhampton, and the members were Caldeira, Cox, Haigh, Keith, Launder, Mace, MacKerron, Pyle, Rayner, Redgwell, and Watson.

  14. From Peru says:

    There is a thing far better than “geoengineering”. Something than can be called “economy-engineering”.

    That is, make a series of “Four-year Plans” to decarbonize the economy. In WWII all did that, changing the industrial complex from consumer-oriented to war-oriented in just 6 months!

    The Plans should be made by a series of inter-disciplinary commitees, and then passed to the congress, where them should receive public scrutiny. After the proper corrections, approved.

    Today that is politically impossible. Already with the relatively conservative W-M bill and health-care reform there are ridiculous and loud accusations of “socialism” by the conservatives.

    What tragically is needed is a national disaster to shut up all that voices.

    Maybe Cat-4 or Cat-5 hurricanes hitting New York , Washington , New Orleans and Houston, drought collapsing crop production and wildfires burning right to the centre of Los Angeles.

    (That is, as I said repeately, a climate 9-11.Then the Bush gang illegally shut down the Geneva Convention for Al-Qaeda prisioners, and the public said nothing, impulsed by the 9-11 shock and the visceral nationalism that followed)

    I hope that after that, the “tipping-point” of public opinion will be crossed, and nobody will believe the plutocracy-funded Deniers.

    It will be great an episode like:

    We denounce the socialist government, that attacks the freedoms that are at the base of the American Society,down to the communist government!

    Shut up! Your “free-trade” caused the current disaster!
    Instead, freedom to the People from you exploiters of workers, bank-extortions, War-funders!

    Down with Casino-Capitalism! Down with free trade! Down to you, Oligarchs!

    Go to the flooded and burned cities! Go to the parched countryside!
    We will demand you for all the destruction you caused, you will have to pay to the People for all that you stoled and destroyed!

  15. Andy says:

    It was 3 years ago I believe when James Hansen published a series of short articles on the “Slippery Slope” of the demise of the ice sheets at anything above 350ppm carbon dioxide. He used his knowledge of paleoclimates to predict this. At the time a lot of the other prominent scientists felt he had overstepped the data and was probably wrong to boot.

    Looks like he was right again. Scientists of his caliber: those who can do the math, slog through the grant writing, get stuff published, work the government-political funding chaos, and also have a very good intuition; the uncanny ability to leap to the correct conclusions before all the facts have been uncovered, are very rare. We are lucky he decided to focus on AGW.

    He’s now being criticized by his peers for taking to the streets and joining protests.

    I’m guessing that in a decade or so when reporting reality is again in vogue, and overt climate signals are bashing us all on the head, that a lot more people will be doing likewise.

    If they ever carve another head on Mount Rushmore, it should be his.

  16. Mossy says:

    Speaking of CO2 levels, and the need for people to ACT, Bill McKibben gave a great talk at Harvard this afternoon, pointing out the opportunity that people all over the world to SPEAK OUT this weekend.

    How? As a start, spend AN HOUR or so participating in one of the ca. 3,500 climate actions being planned by in more than 150 countries on Saturday, October 24th as part of Global Climate Action Day. The message, translated into 14 languages, boils down to: “We want our elected officials to achieve a bold, fair and binding climate treaty in Copenhagen, that will return atmosheric CO2 to 350 ppm ASAP!” (Unfortunately, ‘ASAP’ still means many decades, but we must start now.)

    Folks in the Maldives helped raise climate impact awareness by having an underwater Cabinet meeting a few days ago. Dozens of churches in New England will send their bells pealing 350 times Saturday morning, prior to citizens’ walks, bicyle rides, and runs to various events. Help add strength to the movement to save ourselves. Join an action!

  17. Richard Brenne says:

    Sorry, I posted this in the wrong thread last time. I’m still asking:

    Joe, Lou and others:

    On page 52 of “The Vanishing Face of Gaia” James Lovelock writes: “The Earth’s greenhouse in now well above 400 ppm (carbon dioxide is near 390 ppm but methane, nitrous oxide and the CFCs lift the total effect to nearer that of 430 ppm carbon dioxide).”

    What do you think of pointing this out to the public? Does it confuse the issue? Is it something that would be useful for scientists to discuss amongst themselves?

    Because CO2 ppm fluctuates from a high of 390 ppm in May down to 387 ppm in July, what is the figure that you feel most comfortable using? The high point, as McKibben does? Or the low, or the annual midpoint?

    To me it would be good for all scientists and those communicating science to agree about one annual standard so we can discuss it more easily from year to year without confusing the public. What do you think?

  18. Richard Brenne says:

    Andy’s comment (16) about Hansen is excellent. Andy, add to what you wrote so well that Hansen also heroically resisted censoring and censure from eight years of the rabidly anti-science and frothingly pro-fossil fuel Bush administration.

    Bill McKibben’s 1993 profile of Hansen in Outside Magazine is a masterpiece, and available in the 2008 book, “The Bill McKibben Reader” – a wonderful book with nothing but world-class essays.

    I’ve asked dozens of top climate scientists who the Robert Oppenheimer (who understood the physics, math, metalurgy and all the kinds of engineering about as well as the heads of each of those departments at Los Alamos during the Manhattan Project so he could help synthesize them all successfully) of climate science is, and I’ve heard Hansen’s name far more than any other.

    (Also Steven Schneider, Kevin Trenberth, Kerry Emanual – and once even Al Gore!) Increasingly I’d also nominate Joe Romm. Who would you folks say?

    As a bonus, adding Hansen’s head to Mt. Rushmore would increase global albedo.

  19. Sable says:

    “As a bonus, adding Hansen’s head to Mt. Rushmore would increase global albedo.” LOL!

    Thanks for that! Now I know how I can best do my part to cool the planet. Stop wearing my hat outside.

  20. Rockfish says:


    Curious if you’ve seen this report and will have post on it?

    It argues for a MUCH more aggressive approach to GHG reduction….

  21. It’s still easier to “study the problem” and just as easy to promote energy reform of the infrastructure and of policy. Cut greenhouse gas emissions? Sorry, that’s not the intention of the players going to Copenhagen, including almost of the nonprofits — unless you equate eventual reductions in energy use per capita (amidst population growth?) via technofixes as the same as cuts.
    The way the politics are rigged to preserve the corporate economy and our consumption patterns, we’d better pray for petrocollapse. It has begun anyway, but it’s not considered by the prognosticators and commentators able to get a large forum these days.
    For more of this kind of realism and a challenge for preemptive action, see my widely read article (although not widely read enough) new article, “Copenhagen Is Supposed to Fail. DIY!” at
    Please pass it on if you think it’s spot on.
    Jan Lundberg
    Culture Change

  22. Mael says:

    Well the first problem I see is that these scientists are being very misleading. The last time CO2 levels were at 400 ppm was about 3 million years ago not 15 million years ago. We live in a period of time when CO2 has been abnormally low and only recentally has it been recovering to what are typically levels when compared to the bulk of Earth’s history.

    [JR: Not. Human civilization developed during this “abnormally low” CO2, as you put it.]

  23. gallopingcamel says:

    Mael (#22)

    Good point about the CO2 concentration being abnormally low. JR is presumably one of the moderators if he connects low CO2 with the rise of civilization.

    I wonder whether JR sees a connection between high CO2 levels (700 to 2,200 ppm) and the emergence of mammals during the Eocene eventually leading to the Ascent of Man.

  24. Jonathan says:

    Mael @22’s trolling notwithstanding, how does this new research gel with the notion that CO2 was around 400ppm during the mid-Piocene 3 million years ago? See e.g.

  25. Jonathan says:

    re #24:

    What I mean is, does this new research (“You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today”) show that mid-Pliocene CO2 (3 million years ago) was in fact lower than today? Any idea how much?

    IPCC 2007 says mid-Pliocene “atmospheric CO2 concentrations (estimated to be between 360 to 400 ppm) were likely higher than pre-industrial values”. A bit clumsy but I think it means they put more confidence (>66%) in the fact levels were higher than 280 than they are in the 360-400 estimate.