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the question that comes up most frequently is this: ?Doesn?t the relationship between CO2 and temperature in the ice core record show that temperature drives CO2, not the other way round??
It got a particularly high profile airing a couple of weeks ago, when congressman Joe Barton brought it up to try to discredit Al Gore?s congressional testimony. Of course, those who?ve been paying attention will recognize that Gore is not wrong at all. This subject has been very well addressed in numerous places. Indeed, guest contributor Jeff Severinghaus addressed this in one of our very first RealClimate posts, way back in 2004. Still, the question does keep coming up, and Jeff recently received a letter asking about this. His exchange with the letter writer is reproduced in full at the end of this post. Below is my own take on the subject.
First of all, saying ?historically? is misleading, because Barton is actually talking about CO2 changes on very long (glacial-interglacial) timescales. On historical timescales, CO2 has definitely led, not lagged, temperature. But in any case, it doesn?t really matter for the problem at hand (global warming). We know why CO2 is increasing now, and the direct radiative effects of CO2 on climate have been known for more than 100 years. In the absence of human intervention CO2 does rise and fall over time, due to exchanges of carbon among the biosphere, atmosphere, and ocean and, on the very longest timescales, the lithosphere (i.e. rocks, oil reservoirs, coal, carbonate rocks). The rates of those exchanges are now being completely overwhelmed by the rate at which we are extracting carbon from the latter set of reservoirs and converting it to atmospheric CO2. No discovery made with ice cores is going to change those basic facts.
Second, the idea that there might be a lag of CO2 concentrations behind temperature change (during glacial-interglacial climate changes) is hardly new to the climate science community. Indeed, Claude Lorius, Jim Hansen and others essentially predicted this finding fully 17 years ago, in a landmark paper that addressed the cause of temperature change observed in Antarctic ice core records, well before the data showed that CO2 might lag temperature. In that paper (Lorius et al., 1990), they say that:
changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing
What is being talked about here is influence of the seasonal radiative forcing change from the earth?s wobble around the sun (the well established Milankovitch theory of ice ages), combined with the positive feedback of ice sheet albedo (less ice = less reflection of sunlight = warmer temperatures) and greenhouse gas concentrations (higher temperatures lead to more CO2 leads to warmer temperatures). Thus, both CO2 and ice volume should lag temperature somewhat, depending on the characteristic response times of these different components of the climate system. Ice volume should lag temperature by about 10,000 years, due to the relatively long time period required to grow or shrink ice sheets. CO2 might well be expected to lag temperature by about 1000 years, which is the timescale we expect from changes in ocean circulation and the strength of the ?carbon pump? (i.e. marine biological photosynthesis) that transfers carbon from the atmosphere to the deep ocean.
Several recent papers have indeed established that there is lag of CO2 behind temperature. We don?t really know the magnitude of that lag as well as Barton implies we do, because it is very challenging to put CO2 records from ice cores on the same timescale as temperature records from those same ice cores, due to the time delay in trapping the atmosphere as the snow is compressed into ice (the ice at any time will always be younger older than the gas bubbles it encloses, and the age difference is inherently uncertain). Still, the best published calculations do show values similar to those quoted by Barton (presumably, taken from this paper by Monnin et al. (2001), or this one by Caillon et al. (2003)). But the calculations can only be done well when the temperature change is large, notably at glacial terminations (the gradual change from cold glacial climate to warm interglacial climate). Importantly, it takes more than 5000 years for this change to occur, of which the lag is only a small fraction (indeed, one recently submitted paper I?m aware of suggests that the lag is even less than 200 years). So it is not as if the temperature increase has already ended when CO2 starts to rise. Rather, they go very much hand in hand, with the temperature continuing to rise as the the CO2 goes up. In other words, CO2 acts as an amplifier, just as Lorius, Hansen and colleagues suggested.
Now, it there is a minor criticism one might level at Gore for his treatment of this subject in the film (as we previously pointed out in our review). As it turns out though, correcting this would actually further strengthen Gore?s case, rather than weakening it. Here?s why:
The record of temperature shown in the ice core is not a global record. It is a record of local Antarctic temperature change. The rest of the globe does indeed parallel the polar changes closely, but the global mean temperature changes are smaller. While we don?t know precisely why the CO2 changes occur on long timescales, (the mechanisms are well understood; the details are not), we do know that explaining the magnitude of global temperature change requires including CO2. This is a critical point. We cannot explain the temperature observations without CO2. But CO2 does not explain all of the change, and the relationship between temperature and CO2 is therefore by no means linear. That is, a given amount of CO2 increase as measured in the ice cores need not necessarily correspond with a certain amount of temperature increase. Gore shows the strong parallel relationship between the temperature and CO2 data from the ice cores, and then illustrates where the CO2 is now (384 ppm), leaving the viewer?s eye to extrapolate the temperature curve upwards in parallel with the rising CO2. Gore doesn?t actually make the mistake of drawing the temperature curve, but the implication is obvious: temperatures are going to go up a lot. But as illustrated in the figure below, simply extrapolating this correlation forward in time puts the Antarctic temperature in the near future somewhere upwards of 10 degrees Celsius warmer than present ? rather at the extreme end of the vast majority of projections (as we have discussed here).
Global average temperature is lower during glacial periods for two primary reasons:
1) there was only about 190 ppm CO2 in the atmosphere, and other major greenhouse gases (CH4 and N2O) were also lower
2) the earth surface was more reflective, due to the presence of lots of ice and snow on land, and lots more sea ice than today (that is, the albedo was higher).
As very nicely discussed by Jim Hansen in his recent Scientific American article, the second of these two influences is the larger, accounting for about 2/3 of the total radiative forcing. CO2 and other greenhouse gases account for the other 1/3. Again, this was all pretty well known in 1990, at the time of the Lorius et al. paper cited above.
What Gore should have done is extrapolated the temperature curve according this the appropriate scaling ? with CO2 accounting for about 1/3 of the total change ? instead of letting the audience do it by eye. Had he done so, he would have drawn a line that went up only 1/3 of the distance implied by the simple correlation with CO2 shown by the ice core record. This would have left the impression that equilibrium warming of Antarctica due to doubled CO2 concentrations should be about 3 ?C, in very good agreement with what is predicted by the state-of-the-art climate models. (It is to be noted that the same models predict a significant delay until equilibrium is reached, due to the large heat capacity of the Southern ocean. This is in very good agreement with the data, which show very modest warming over Antarctica in the last 100 years). Then, if you scale the Antarctic temperature change to a global temperature change, then the global climate sensitivity to a doubling of CO2 becomes 2-3 degrees C, perfectly in line with the climate sensitivity given by IPCC (and known from Arrhenius?s calculations more than 100 years ago).
ImWithStupid said:My point is, that anything man is doing, has very little effect on the warming of the earth, and anything man does in attempts to slow said warming, if it were to happen, will do very little to achieve any change (other than destroying economies).
Craig D. Idso, faculty researcher, Office of Climatology, Arizona State University and founder of the Center for the Study of Carbon Dioxide and Global Change: "the rising CO2 content of the air should boost global plant productivity dramatically, enabling humanity to increase food, fiber and timber production and thereby continue to feed, clothe, and provide shelter for their still-increasing numbers ... this atmospheric CO2-derived blessing is as sure as death and taxes."[
It is shocking to know that India has the highest number of malnourished children in the world with Madhya Pradesh being the worst effected state. About 47% of children under the age of five years in India, an astounding 57 million are under weight. Even Sub Saharan Africa is better where 33% of children are malnourished. The worst effected States in India are UP, Rajasthan, Bihar, and Maharashtra. In some of the states over 50% of children are malnourished. However Goa, Kerala, Mizoram and Tamil Nadu are high nutritional states.
Russia: Russian scientist Dr. Oleg Sorochtin of the Institute of Oceanology at the Russian Academy of Sciences has authored more than 300 studies, nine books, and a 2006 paper titled “The Evolution and the Prediction of Global Climate Changes on Earth.” “Even if the concentration of ‘greenhouse gases’ double man would not perceive the temperature impact,” Sorochtin wrote.
timesjoke said:II remember reading a theory from someone that in their mind Co2 was the Earth's anti-warming agent.
Venus has a dense atmosphere, composed chiefly of carbon dioxide, which generates a surface pressure 90 times greater than that on Earth. This massive blanket of carbon dioxide is also responsible for a runaway greenhouse effect that heats the planet's surface to an average temperature of 467?C (872?F) ? hot enough to melt lead.
Venus' atmosphere consists almost entirely (97%) of carbon dioxide, with clouds containing droplets of sulfuric acid along with compounds of chlorine and fluorine. These precipitate an acid rain called virga, which evaporates before it has the chance to reach the surface. In the upper part of the atmosphere, clouds swirl by at a rate of 300 km/h, driven by fierce winds.
hugo said:Life begins at conception, despite what pro baby killers say. That scientific fact does not change no matter what your view on abortion is. CO2 is a greenhouse gas; scientific fact. Gotta concede that point to the Goreists.
Russia: Russian scientist Dr. Oleg Sorochtin of the Institute of Oceanology at the Russian Academy of Sciences has authored more than 300 studies, nine books, and a 2006 paper titled ?The Evolution and the Prediction of Global Climate Changes on Earth.? ?Even if the concentration of ?greenhouse gases? double man would not perceive the temperature impact,? Sorochtin wrote.
What are the take-home messages:
The temperature effect of atmospheric carbon dioxide is logarithmic, not exponential.
The potential planetary warming from a doubling of atmospheric carbon dioxide from pre-Industrial Revolution levels of ~280ppmv to 560ppmv (possible some time later this century - perhaps) is generally estimated at around 1 ?C.
The guesses of significantly larger warming are dependent on "feedback" (supplementary) mechanisms programmed into climate models. The existence of these "feedback" mechanisms is uncertain and the cumulative sign of which is unknown (they may add to warming from increased atmospheric carbon dioxide or, equally likely, might suppress it).
The total warming since measurements have been attempted is thought to be about 0.6 degrees Centigrade. At least half of the estimated temperature increment occurred before 1950, prior to significant change in atmospheric carbon dioxide levels. Assuming the unlikely case that all the natural drivers of planetary temperature change ceased to operate at the time of measured atmospheric change then a 30% increment in atmospheric carbon dioxide caused about one-third of one degree temperature increment since and thus provides empirical support for less than one degree increment due to a doubling of atmospheric carbon dioxide.
There is no linear relationship between atmospheric carbon dioxide change and global mean temperature or global mean temperature trend -- global mean temperature has both risen and fallen during the period atmospheric carbon dioxide has been rising.
The natural world has tolerated greater than one-degree fluctuations in mean temperature during the relatively recent past and thus current changes are within the range of natural variation. (See, for example, ice core and sea surface temperature reconstructions.)
Other anthropogenic effects are vastly more important, at least on local and regional scales.
Fixation on atmospheric carbon dioxide is a distraction from these more important anthropogenic effects.
Despite attempts to label atmospheric carbon dioxide a "pollutant" it is, in fact, an essential trace gas, the increasing abundance of which is a bonus for the bulk of the biosphere.
There is no reason to believe that slightly lower temperatures are somehow preferable to slightly higher temperatures - there is no known "optimal" nor any known means of knowingly and predictably adjusting some sort of planetary thermostat.
Fluctuations in atmospheric carbon dioxide are of little relevance in the short to medium term (although should levels fall too low it could prove problematic in the longer-term).
Activists and zealots constantly shrilling over atmospheric carbon dioxide are misdirecting attention and effort from real and potentially addressable local, regional and planetary problems.
hugo said:CO2 is a green house gas: scientific fact, even before Al Gore was even born. Life begins at conception: scientific fact, even before Roe v. Wade. You lose credibility to declare otherwise.
I concede the fact CO2 is a greenhouse gas to the Gorists. They still got these obstacles to overcome:
There is no linear relationship between atmospheric carbon dioxide change and global mean temperature or global mean temperature trend -- global mean temperature has both risen and fallen during the period atmospheric carbon dioxide has been rising.
The total warming since measurements have been attempted is thought to be about 0.6 degrees Centigrade.
The lost data excuse is akin to "the dog ate my homework!"
We have detailed 10,000-year data from Greenland ice cores, sea sediment, tree rings and other geologic sources. That data record, covering about one-half of the current interglacial, clearly shows much warmer climate until about 2,000 to 3,000 years ago when temperatures declined, then rebounded in a Roman Warm Period, declined again, then rebounded again in the Medieval Warm Period, then declined sharply into the Little Ice Age punctuated with a brief warming at its middle before bringing the coldest temperatures of the past 10,000 years in the 1800s. The modern warming has been fairly routine since then, with nothing that begins to match the warming of either the Medieval Warm Period or the many thousands of years of the Holocene Optimum that marked the middle of the current interglacial. All those changes were natural and go unexplained (and ignored) by climate alarmists. Indeed, Michael Mann, et al, created the "hockey stick" fraud to try to substantiate two claims: (1) that the Medieval Warm Period and Little Ice Age never happened, and, (2) that current warm temperatures were "unprecedented" (both of which are false).
Claims that CO2 emissions are driving climate change ignore the long accurate geologic record that establishes just the reverse -- that changes in temperature drive changes in CO2.
Human additions of CO2 are miniscule compared with natural forces and CO2 itself is a minor contributor to atmospheric warming.
In a sane world, that would be the end of the story.
Dang global warming....hugo said:Snowed yesterday...here in Houston, Tx....the earliest snow in Houston history.
hugo said:Snowed yesterday...here in Houston, Tx....the earliest snow in Houston history.