CO[sub]2[/sub] levels at Mauna Loa as measured by the Scripps Institute Oceanography (go San Diego!) are about 400ppm (averaged for the year), and on the way to 450ppm, possibly in as little as two decades from now. I’ve seen a couple of articles that say the last time CO[sub]2[/sub] levels were as high as this was at least 800,000 years ago. For example, this one. The same article also points out that temperatures were 11 degrees F warmer then. However, it doesn’t talk about why temperatures aren’t therefore 11 degrees warmer now.
I thought that maybe CO[sub]2[/sub] levels have risen so fast that the temperatures are going to take a while to catch up. However, that doesn’t really jibe with current estimates of climate sensitivity to a doubling of CO[sub]2[/sub], which predict that we should see about 2 to 4 degrees C of warming when we get up to 500ppm or 550ppm. So what’s missing? Were methane levels higher then? Was the sun stronger, or the earth closer to it? Is the data wrong?
Note: I’m asking this in GQ, not in IMHO or GD. What I’d like to know, with as little shrieking back and forth as possible, is what people who have studied the paleoclimate say about this discrepancy.
I don’t understand what doesn’t jibe. How long do you expect it to take for warming to level off if we held CO[sub]2[/sub] levels constant? There is a lot of ice out there still with a large enthalpy of fusion. And even more water with a hefty heat capacity.
Although it’s far more complex than that, historically CO2 levels have been a consequence of rising temperatures, not the cause of them.
In the present day we have man induced CO2 increases - to some extent from industrialization but more from land-use changes.
There is however zero modern day correlation between CO2 levels and global temperatures. That is using precise statistical tests rather than looking at graphs. In statistical terms modern global temperatures are indistinguishable from a random walk.
This may well explain why modern mathematical climate models do not accurately predict or model any of the global temperature changes in the past 100 odd years.
Well, we have to establish something first, if we use the high estimates that are close to 5 degrees Celsius of an increase in temperature, then that is about 9 degrees Fahrenheit of an increase.
AFAIK the other 2 degrees (to reach the reported difference of 11 degrees Fahrenheit) could come from the fact that the conditions with other forcings back in the Miocene epoch were not the same as the ones we observe today.
IMHO this shows that while that 11 degree difference in temperature is interesting for paleo climatologists, the different conditions still point to CO2 as one of the main factors in the changes in temperature and this then points to 2 possible outcomes:
That the sensibility was higher during the Miocene thanks to other factors, and taking those into account we can only partially take into account what CO2 was doing then, so we may continue to look at what the current experts report about the likely increase we will see, we have to go with the most likely sensibility coming from many other studies that point to about 3 degrees Celsius of an average increase in temperature if the CO2 concentrations double the ones seen in the pre-industrial era.
And that leads to bad results indeed. (If not much is done to control emissions)
Or:
That the increase in temperature reported in the Miocene is closer to what we will get. Like in the case of the ice melt, it can be that many are underestimating what other feared feedbacks will do when they rear their ugly heads and we could find that the ocean currents and other factors are not so important to the big picture today than they were in the Miocene.
Where it doesn’t jibe is that no one today, so far as I know, is claiming the planet might warm 11 degrees F even if we somehow were able to keep CO[sub]2[/sub] levels at 400 ppm. Usually that level of warming is predicated on a rise to 800 ppm or more. In other words, even if we haven’t reached equilibrium with 400 ppm yet, the equilibrium isn’t plausibly 11F warmer than now.
You’re taking the position that climate sensitivity to CO[sub]2[/sub] is 0. That actually doesn’t answer my question of why it was 11F warmer in the past, but it’s an interesting position. I assume you agree that CO[sub]2[/sub] is a greenhouse gas? Greenhouse gasses in the atmosphere trap heat and therefore would be expected to cause global warming. For climate sensitivity to be 0, something would have to be counteracting that process. What do you think that is? Since that’s irrelevant to the OP, maybe you could start a new thread and link to it here. I’d really like to hear your thoughts in more depth. I frankly admit that I’m giving you rope here, but I am genuinely curious if you can fashion it into something other than a noose.
GIGO’s links were the most useful to answering my question. First, it made me reread my linked article and find that, actually it’s claiming that the 400 ppm levels might not have occurred since the Miocene, which is way, way more than 800,000 years ago, and so it’s more like 10 million ago when global temperatures would have been 11F warmer. GIGO’s linked article says that models use climate sensitivity of 4 degrees C to be able to reproduce those conditions. I still don’t really get that, but I’m going to reread that article and do my best to understand it. The Panama thing seems to talk to the distribution of warming more than the total amount of it. It does say that epoch was part of a long cooling period, so there might have been cooling not yet “priced in” the way there is warming not yet priced in today.
Am I rephrasing correctly? While the expected equilibrium temperature at our current level of radiative forcing is hotter than our current temperature, it is not as hot as other times that had the same concentration of carbon dioxide. You want to understand why.
Global temperature simply hasn’t reached equilibrium yet. The current rise in CO2 levels is faster than any natural rise, so we will have to wait until the Earth catches up. Unfortunately by that time we will have put even more CO2 into the atmosphere, and it still won’t be in equilibrium.
While there are uncertainties with climate models, they successfully reproduce the past and have made predictions that have been subsequently confirmed by observations.
I’ll make a small confession here. In a previous career I used to write micro-climate computer models (in Fortran for those who care)
I’ll just point out a bit of secret trade-craft. If your model can’t ‘predict’ the past’ you aren’t going to release it. In fancy terms it’s called validating the model.
So yes, the wishy-wash statement above is absolutely correct in that regard. It’s just that it doesn’t mean anything.
The second part of your quote have made predictions that have been subsequently confirmed by observations. is a rather ridiculous assertion of no meaning for a kazillion different reasons.
What observations are predicted? How accurately and how far ahead? In the climate scale of things you’d have to be using a model written decades ago to get even the faintest glimmer of statistical match with observations unless your prediction was so trivial it was meaningless.
And before you get excited do some research on random walks and statistical correlation. My assertion about zero statistical correlation between global temperature and CO2 levels over the past 100 years stands. And even if there was correlation there is absolutely no indication of causation - which requires a much higher standard of proof.
Covering a couple of other comments.
No I didn’t say climate sensitivity is zero. I said there is no statistical observational evidence it has any particular value - and this is despite the many different theories purporting to give it different concrete values based on some subset of physics.
CO2 Greenhouse gas? Of course it is. But water vapour far far stronger. And water vapour is an extremely non-linear substance in itself and in its interactions with other substance. Back when I got professionally interested in the topic (probably before some of you were born) the key element was atmospheric behaviour of water vapour and particulate matter. That hasn’t changes much and the models are still very poor in that regard.
I think it’s already been established that the period in question wasn’t 800 Ky ago but back in the Miocene. Part of the answer is that for a variety of reasons, including different planetary albedo because of different ice and vegetation cover and differences in the carbon cycle, the earth was a different place with a somewhat different climate sensitivity than today. It’s also significant that during that time the earth’s temperature was trending downward over millions of years as CO2 levels dropped, so the climate dynamics were drastically different, especially in the polar regions – namely, there was little to no ice, so there was a very low polar albedo. The Antarctic didn’t even reglaciate until later in the Miocene, and as late as the Pliocene the Arctic was as much as 19°C warmer than at present.
The simpler way of restating all that is that the formal definition of climate sensitivity is a simplification that takes into account only the relatively rapid feedbacks and not what are called “slow feedbacks”. Slow feedbacks would be things like large-scale permanent polar ice sheet loss, which would have a positive ice-albedo feedback effect that would likely double climate sensitivity, but these things only operate over periods of multiple centuries or millennia. Such a metric is sometimes called earth system sensitivity, as opposed to climate sensitivity, but it’s very real, and plays a major role in the long-term paleoclimate. That’s likely not the only factor for the Miocene warmth, but it’s a big one.
Out of consideration for your wishes not to get into a shouting match my answers to the following will be brief. I simply want to correct things that are factually wrong.
Wrong. CO2 as a response to rising temperatures is the trigger for ice age terminations, but it only occurs over a period of several hundred years, probably started by Milankovitch cycles in the earth’s orbit. For the remaining thousands of years of transition to an interglacial, CO2 is the primary driver of temperature. Your point would also be irrelevant with respect to present anthropogenic emissions even if it was true, which it assuredly is not.
Wrong. In the first decade of the 21st century emissions from fossil fuel combustion (and cement manufacturing) were about 7.8 PgC/yr (petagrams of carbon) growing at 3.2% a year. In 2011 it was about 9.5 PgC/yr. While land use contributions were about 1.1 PgC/yr (3 PgC less about 2 PgC from regrowth). (Source: IPCC AR5 WG1). Furthermore, deforestation on average increases land surface albedo, so its effect is actually rated as a small negative radiative forcing.
Correlation isn’t the point, nor is the modern day the only basis for correlation. A strong correlation is seen throughout the ~100Ky glaciation cycles, but again, not the point. The point is that CO2 is currently contributing a radiative forcing of approximately 1.68 W/m[sup]2[/sup] which constitutes the dominant forcing that is causing the atmosphere, oceans, and the planet overall to rapidly warm.
Except that even Hansen’s original model from the 70s followed the IPCC A1B scenario rather closely. This is a pointless argument that I’m not going to get into. It becomes a game of semantic feces-throwing about exactly what a “correct” model is supposed to look like.
Water vapor is a direct feedback of CO2 forcing and a direct function of temperature in the lower to mid-troposphere. As such it greatly amplifies the effect of CO2. Look up Clausius-Clapeyron relation. I have absolutely no idea what “extremely non-linear substance in itself” is supposed to mean.
BTW jezzaOZ in all your rhetoric, there was no link to any research that showed what you claimed, the whole picture shows that the models are skilful, while models are not reality they are very valuable tools for science and no, the affirmation that “it doesn’t mean anything.” is wrong:
Going back to the wrong idea that this “doesn’t mean anything.” Muller and the sceptical team at Berkeley Earth also successfully replicated the temperature increases by just modelling the volcano eruptions and the increase in CO2 observed. And like that there are other experiments done to show that indeed the human released CO2 is the big reason why the temperature is currently increasing.
Do you have any idea how long Milankovitch cycles are? And how precisely they can be dated? The term ‘probably’ is used by the Schmidt site because they can’t find any numeric link between any phase of the Milankovitch cycle and glacial terminations. It’s simply a guess.
I won’t even bother going into the rest of your list as you clearly aren’t full bottle on the topic. Cutting and pasting from wikipedia and not even getting rid of the markup is not a good look.
Now if you had quoted ScienceofDoom and actually understood what you were quoting I’d be impressed. FYI ScienceOfDoom is a very technical warmist site but written by someone who is moderately polite and even open to some doubt.
You are going to have to better than quote a TED talk by evangelist Schmidt. He gets rewarded to say that stuff.
I suggest you take 6 months off and read and learn ScienceOfDoom and perhaps we can get into a discussion? (Don’t worry, it’s a warmist site - though it requires higher level calculus in quite a few places).
Please stop thread-shitting on this thread which asked a good question and deserved a good answer and perhaps some further relevant discussion. If you want to carry on with your denialist bullshit, start a thread in GD, though Lord knows there have been enough of them on this subject already.
I knew it was a mistake trying to engage with a denialist in GQ. But at least I refuted the bullshit you posted, which was important to do in a fact-based forum.
I’m not in the habit, as apparently you are, of surfing blogs to get information, so I don’t know what “the Schmidt site” is supposed to refer to, unless you mean RealClimate in which Gavin Schmidt is one of many contributors, which site I haven’t visited in probably more than a year.
And there is in any case no defined “length” as there are multiple Milankovitch cycles that interact in complex harmonics. In fact there’s no positive proof that they are actually the trigger for glacial cycles at all, but it’s the most prevalent and credible theory. Your statement of CO2 being a follower rather than a driver in the overall climate scenario is utter bullshit as I noted, a standard denialist talking point with with no basis in science.
In other words, you can’t defend the complete bullshit you posted, every single point of which is wrong, as I noted.
I didn’t cut and paste anything. You will cite what it is that I supposedly cut and pasted or you will withdraw the accusation and apologize.
Milankovitch cycles are not important for the current warming, CO2 and other greenhouses gases are.
I will everyone be the judge of that because not a single cite I made came from Wikipedia, just a sorry attempt from you to shoot the messenger. But it is direct evidence of who is really paying attention at the topic. Bottom line, as the statisticians reported: “The views of climate change ‘skeptics’ and ‘deniers’ appear in many media, from blogs and videos to op-eds and congressional testimony. We prefer to think of the views of skeptics as part of the scientific spectrum, but nevertheless believe they are a minority who do not represent the mainstream scientific viewpoint.”
And it really takes the cake to talk about politeness while calling the ones that you do not bother to counter with any research as “warmists”.
So why bring up Milankovich cycles as though they explain away the inconvenient lead of CO2 to temperature? And then dismiss them?
Regarding the cites, simple text searches shows obvious fragments of them in wikipedia - whether they came from the same mother lode or not there is an overlap. Plus there are fragmentary cite markups showing they’ve been cut and pasted.
I would guess they mostly came originally from the Schmidt 'lil Internet evangelist’s list of climate stuff to cut’n’paste and sound like you know what you are talking about.