The Biggest Control Knob: CO2 in Earth's Climate History
It's been a busy past two months of weather and climate change news, and I haven't found time to blog about the research presented at December's American Geophysical (AGU) meeting in San Francisco. That is the world's largest scientific conference on climate change, and the place to be if you want to get the pulse of the planet. The keynote speech at the AGU meeting was given by Dr. Richard Alley of Penn State University. Dr. Alley is the Evan Pugh Professor of Geosciences at the Pennsylvania State University, and one of the most respected and widely published world experts on climate change. Dr. Alley has testified before Congress on climate change issues, served as lead author of "Chapter 4: Observations: Changes in Snow, Ice and Frozen Ground" for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and is author of more than 170 peer-reviewed scientific articles on Earth's climate. He is also the author of a book I highly recommend--The Two Mile Time Machine, a superb account of Earth's climate history as deduced from the 2-mile long Greenland ice cores. A standing-room only audience of over 2,000 scientists packed the lecture hall Dr. Alley spoke at, and it was easy to see why--Alley is an excellent and engaging speaker. I highly recommend listening to his 45-minute talk via a very watchable recording showing his slides as he speaks in one corner of the video. If you want to understand why scientists are so certain of the link between CO2 and Earth's climate, this is a must-see lecture.
Figure 1. Dr. Richard Alley of Penn State University, delivering the keynote speech at the 2009 AGU conference on climate change.
The Biggest Control Knob: CO2 in Earth's Climate History
Earth's past climate has been shaped by a number of key "control knobs"--solar energy, greenhouse gas levels, and dust from volcanic eruptions, to name the three main ones. The main thrust of Dr. Alley's speech is that we have solid evidence now--some of it very new--that CO2 has dominated Earth's climate over the past 400 million years, making it the climate's "biggest control knob". Dr. Alley opens his talk by humorously discussing a letter from an irate Penn State alumnus. The alumnus complains that data of temperatures and CO2 levels from ice cores in Antarctica don't match:
"CO2 lags Earth's temperature...This one scientific fact which proves that CO2 is not the cause of recent warming, yet...Dr. Alley continues to mislead the scientific community and the general public about 'global warming'. His crimes against the scientific community, PSU, the citizens of this great country, and the citizens of the world are significant and must be dealt with severely to stop such shameful activities in the future".
Dr. Alley explains that the irate alumnus is talking about the Antarctic ice core record, which shows that as we emerged from each ice age, the temperature began increasing before the CO2 did, so increased CO2 was not responsible for the warmings that brought us out of these ice ages. Climate change scientists and skeptics alike agree that Earth's ice ages are caused by periodic variations in Earth's orbit called Milankovich Cycles. "There's no doubt that the ice ages are paced by the orbits", says Dr. Alley. "No way that the orbit knows to dial up CO2, and say 'change'. So it shouldn't be terribly surprising if the CO2 lags the temperature change. The temperature never goes very far without the CO2. The CO2 adds to the warming. How do we know that the CO2 adds to the warming? It's physics!"
Dr. Alley then discusses that the physics that govern how CO2 absorbs and re-emits heat energy, when plugged into state-of-the-art climate models, show that about half of the observed 5 - 6°C natural warming that occurred since the last ice age ended was due to extra CO2 added to the atmosphere. At the peak of the Ice Age, CO2 was about 190 ppm. By the end, it was about 280 ppm (Figure 1). Earth's orbital variations "forced" a warming, which caused more CO2 to escape from swamps and oceans, with a time lag of several centuries. The increased CO2 reinforced the warming, to double what it would have been otherwise--a positive feedback loop. "Higher CO2 may be forcing or feedback--a CO2 molecule is radiatively active regardless of how it got there", says Dr. Alley. "A CO2 molecule does not remember why it is there--it only remembers that it is there". In other words, the fact that higher CO2 levels did not trigger an end to the Ice Age does not mean that the CO2 had no warming effect. Half of the the observed 5 - 6°C natural warming that occurred since the last ice age ended was due to the extra CO2 added to the atmosphere. So, the irate PSU alumnus was half right. The CO2 does lag temperature. However, we can only explain approximately half of the warming since the last ice age ended if we leave out the increase in CO2 that has occurred. "If higher CO2 warms, Earth's climate history makes sense, with CO2 having caused or amplified the main changes. If CO2 doesn't warm, we have to explain why the physicists are so stupid, and we also have no way to explain how a lot of really inexplicable climate events happened over Earth's history. It's really that simple. We don't have any plausible alternative to that at this point".
Figure 2. Ice core record from Vostok, Antarctica, showing the near-simultaneous rise and fall of Antarctic temperature and CO2 levels through the last 350,00 years, spanning three ice age cycles. However, there is a lag of several centuries between the time the temperature increases and when the CO2 starts to increase. Image credit: Marian Koshland Science Museum of the National Academy of Sciences: Global Warming Facts and Our Futures, originally provided to that site by Kurt Cuffey, University of California, Berkely.
CO2 and temperatures rise and fall in synch
Dr. Alley continues with a discussion of how CO2 and temperature levels have risen and fallen in synch over most of geologic time. But for many years there was still a mystery: occasionally there were eras when temperature changes did not match CO2 changes. But new paleoclimate research, much of it just in the past two years, has shown that nearly all of these mis-matches were probably due to suspect data. For example, the mismatch in the Miocene Era has significantly improved, thanks to a new study published this year by Tripati et al. Another example occurs during the Ordovician Era 444 million years ago, as discussed in a recent post at the excellent skepticalscience.com blog.
Figure 3. Atmospheric CO2 and continental glaciation, 400 million years ago to the present. The vertical blue bars mark where ice ages have occurred. The length of the blue bars corresponds to how close to the Equator the ice sheets got (palaeolatitude, scale on the right side of the plot). The left scale shows atmospheric CO2 over the past 400 million years, as inferred from a model (green area) and from four different "proxy" fossil sources of CO2 information. This is Figure 6.1 of the Palaeoclimate chapter of the 2007 IPCC report.
Is there anything else we should be worried about?
Dr. Alley continues with a discussion of other influences that may be able to explain global warming, such as volcanos, changes in solar output, and cosmic rays. A whole bunch of the competing hypotheses don't work", says Dr. Alley. "When there's a bunch of big volcanos, they make it cool. If volcanos could get organized, they'd rule the world. There might be a tiny bit of organization due to flexing of the crust, but they're not controlling the world".
Regarding solar changes: "When the sun changes, it does seem to show up in the temperature record. As far back as we can see well, the sun is friendly, it doesn't change much. If the sun changed a lot, it would control things hugely. But it only changes really slowly--as far as we can tell. The record doesn't go back as far as we'd like, and there's work to be done here--but it just doesn't seem to be doing much".
Figure 4. Greenland ice core proxy measurements of temperature (top curve) and cosmic ray flux (bottom curve) for the past 60,000 years. The Earth's magnetic field weakened by 90% 40,000 years ago, for a period of about 1,000 years, but there was no change seen in the temperatures in Greenland.
Regarding cosmic rays: "The sun doesn't change much, but the sun modulates the cosmic rays, the cosmic rays modulate the clouds, the clouds modulate the temperature, and so the sun is amplified hugely. It's really interesting hypothesis, there's really good science to be done on this, but there's reason to think its a fine-tuning knob". He goes on to show an ice core example from a period 40,000 years ago (Figure 4) where the Earth magnetic field had near-zero strength for hundreds of years. This allowed a massive flux of cosmic rays to penetrate to the Earth's surface, creating a huge spike in ice core Beryllium-10, a radionuclide made by cosmic rays. If cosmic rays were important to climate, we would expect to see a corresponding major swing in temperature, but the ice core shows no change during the period of enhanced cosmic ray bombardment 40,000 years ago. "We had a big cosmic ray signal, and the climate ignores it", Dr. Alley comments.
How sensitive is climate to a doubling of CO2?
The IPCC report talks extensively about computer climate models' calculations of "climate sensitivity"--how much Earth's climate would warm if CO2 doubled from pre-industrial levels of 280 ppm, to 560 ppm (we're currently at 390 ppm). A mid-range number from the 2007 IPCC report often used by climatologists is that the climate sensitivity is 3°C for a doubling of CO2. Dr. Alley takes a look at what paleoclimate has to say about the climate sensitivity to CO2. "The models actually do pretty well when you compare them to the past. The best fit is 2.8°C.
Dr. Alley concludes, "Where we really stand now, is, we're not quite at the pound on the table, this story is very clearly not done. But an increasing body of science indicates that CO2 has been the most important controller of global average climate of the Earth."
I'll have a new post Sunday or Monday.
Jeff Masters
Reader Comments
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let's get ready to RUMBLE!!!!!!!!
Everybody in the USA is anti GW while we in the Carribean are dying from heat and the lack of rain .
a non-GW POLO!!!!!!!!!!
;)
Agreed for a "Non GW POLO"
CO2, Temperatures, and Ice Ages... by Frank Lansner, civil engineer, biotechnology.(go here to see the full pdf with the graphics)
It is generally accepted that CO2 is lagging temperature in Antarctic graphs. To dig further into this subject therefore might seem a waste of time. But the reality is, that these graphs are still widely used as an argument for the global warming hypothesis. But can the CO2-hypothesis be supported in any way using the data of Antarctic ice cores?
At first glance, the CO2 lagging temperature would mean that it's the temperature that controls CO2 and not vice versa.
Click for larger image Fig 1. Source: http://www.brighton73.freeserve.co.uk/gw/paleo/400000yrfig.htm
But this is the climate debate, so massive rescue missions have been launched to save the CO2-hypothesis. So explanation for the unfortunate CO2 data is as follows:
First a solar or orbital change induces some minor warming/cooling and then CO2 raises/drops. After this, it's the CO2 that drives the temperature up/down. Hansen has argued that: The big differences in temperature between ice ages and warm periods is not possible to explain without a CO2 driver.
Very unlike solar theory and all other theories, when it comes to CO2-theory one has to PROVE that it is wrong. So let's do some digging. The 4-5 major temperature peaks seen on Fig 1. have common properties: First a big rapid temperature increase, and then an almost just as big, but a less rapid temperature fall. To avoid too much noise in data, I summed up all these major temperature peaks into one graph:
Fig 2. This graph of actual data from all major temperature peaks of the Antarctic vostokdata confirms the pattern we saw in fig 1, and now we have a very clear signal as random noise is reduced.
The well known Temperature-CO2 relation with temperature as a driver of CO2 is easily shown:
Fig 3.
Below is a graph where I aim to illustrate CO2 as the driver of temperature:
Fig 4. Except for the well known fact that temperature changes precede CO2 changes, the supposed CO2-driven raise of temperatures works ok before temperature reaches max peak. No, the real problems for the CO2-rescue hypothesis appears when temperature drops again. During almost the entire temperature fall, CO2 only drops slightly. In fact, CO2 stays in the area of maximum CO2 warming effect. So we have temperatures falling all the way down even though CO2 concentrations in these concentrations where supposed to be a very strong upwards driver of temperature.
I write "the area of maximum CO2 warming effect "
The whole point with CO2 as the important main temperature driver was, that already at small levels of CO2 rise, this should efficiently force temperatures up, see for example around -6 thousand years before present. Already at 215-230 ppm, the CO2 should cause the warming. If no such CO2 effect already at 215-230 ppm, the CO2 cannot be considered the cause of these temperature rises.
So when CO2 concentration is in the area of 250-280 ppm, this should certainly be considered "the area of maximum CO2 warming effect".
The problems can also be illustrated by comparing situations of equal CO2 concentrations:
Fig 5.
So, for the exact same levels of CO2, it seems we have very different level and trend of temperatures:
Fig 6.
How come a CO2 level of 253 ppm in the B-situation does not lead to rise in temperatures? Even from very low levels? When 253 ppm in the A situation manages to raise temperatures very fast even from a much higher level?
One thing is for sure:
"Other factors than CO2 easily overrules any forcing from CO2. Only this way can the B-situations with high CO2 lead to falling temperatures."
This is essential, because, the whole idea of placing CO2 in a central role for driving temperatures was: "We cannot explain the big changes in temperature with anything else than CO2".
But simple fact is: "No matter what rules temperature, CO2 is easily overruled by other effects, and this CO2-argument falls". So we are left with graphs showing that CO2 follows temperatures, and no arguments that CO2 even so could be the main driver of temperatures.
- Another thing: When examining the graph fig 1, I have not found a single situation where a significant raise of CO2 is accompanied by significant temperature rise- WHEN NOT PRECEDED BY TEMPERATURE RISE. If the CO2 had any effect, I should certainly also work without a preceding temperature rise?! (To check out the graph on fig 1. it is very helpful to magnify)
Does this prove that CO2 does not have any temperature effect at all?
No. For some reason the temperature falls are not as fast as the temperature rises. So although CO2 certainly does not dominate temperature trends then: Could it be that the higher CO2 concentrations actually is lowering the pace of the temperature falls?
This is of course rather hypothetical as many factors have not been considered.
Fig 7.
Well, if CO2 should be reason to such "temperature-fall-slowing-effect", how big could this effect be? The temperatures falls 1 K / 1000 years slower than they rise.
However, this CO2 explanation of slow falling temperature seems is not supported by the differences in cooling periods, see fig 8.
When CO2 does not cause these big temperature changes, then what is then the reason for the big temperature changes seen in Vostok data? Or: "What is the mechanism behind ice ages???"
This is a question many alarmists asks, and if you can't answer, then CO2 is the main temperature driver. End of discussion. There are obviously many factors not yet known, so I will just illustrate one hypothetical solution to the mechanism of ice ages among many:
First of all: When a few decades of low sunspot number is accompanied by Dalton minimum and 50 years of missing sunspots is accompanied by the Maunder minimum, what can for example thousands of years of missing sunspots accomplish? We don't know.
What we saw in the Maunder minimum is NOT all that missing solar activity can achieve, even though some might think so. In a few decades of solar cooling, only the upper layers of the oceans will be affected. But if the cooling goes on for thousands of years, then the whole oceans will become colder and colder. It takes around 1000-1500 years to "mix" and cool the oceans. So for each 1000-1500 years the cooling will take place from a generally colder ocean. Therefore, what we saw in a few decades of maunder minimum is in no way representing the possible extend of ten thousands of years of solar low activity.
It seems that a longer warming period of the earth would result in a slower cooling period afterward due to accumulated heat in ocean and more:
Fig 8.
Again, this fits very well with Vostok data: Longer periods of warmth seems to be accompanied by longer time needed for cooling of earth. The differences in cooling periods does not support that it is CO2 that slows cooling phases. The dive after 230.000 ybp peak shows, that cooling CAN be rapid, and the overall picture is that the cooling rates are governed by the accumulated heat in oceans and more.
;)
The Caribbean nearly always sees a lack of rain and drought conditions during an El Nino, and we have a strong El Nino this winter. Besides, the AGW people say precipitation will overall increase with rising temperatures, and yes they also say desert areas will get even more extreme, but the Caribbean is not a desert is it.
Well they've all done it enough times so I figured I could be annoying for one post.
Unlike some people. I'm purposely mimicking the article-posters with that post.
Post 15
Taco :0)
we have a strong El Nino this winter
"El Nino is strong like bull!"
Glenn Beck had previously bashed Avatar as “an anti‑U.S. human thing.” Cameron said, “But you know they’ve got to live in this world too. And their children do as well, so they’re going to have to be answerable to this at some point.” He explained that he will make the environment the theme of his home video release plan. “Look, at this point I’m less interested in making money for the movie and more interested in saving the world that my children are going to inhabit. How about that?”
And yes, Cameron does get global warming, having said recently, “We need to mobilize like we did during World War II” to fight global warming. The threat to our country and children is “that severe.”
Should be aired in any school on earth.
Mhm and a wetter-than-normal pattern should continue through the summer.
Yes.
Soooo, we have new data sources, published this year, that appear to clear up the CO2 lag questions, finally.
And we have this one data source that appears to remove the cosmic ray forcing mechanism entirely. (my knowledge of that phenomenon is admittedly weak, though)
So let's go ahead and outlaw CO2 and not worry about being hoodwinked by what other data might be suspect or modeling that assumes a lot of constants and parameterizes
everything.
(obviously with what we know, fugeddabout explicit modeling, yeah, I know)
;)
http://wpsu.org/psudvd
http://ondemand.psu.edu/viewer.php?id...
The causes and effects of global warming are discussed with internationally recognized scientist Richard Alley, a geosciences professor at Penn State. Alley examines the science and future of climate change.
;)
here your go StormW .
http://www.agu.org/meetings/fm09/lectures/lecture_videos/A23A.shtml
News headline:
"Flowers losing scent due to climate change"
Hahahahahaha!
That list of fears is getting pretty long...
"This is the concern of environmentalists as flowers are losing their scent due to climate change and air pollution. And their fragrance may be lost forever.
Science and Technology Professor Emeritus at Universiti Kebangsaan Malaysia, Dr Abdul Latif Mohamad, said genetically modified flowers might be the way out."
Oh, my. I suppose no one has questioned the PDO's effect in Malaysia, either.
[Insert anything annoying or unforeseen here] cannot be explained due to lack of data, understanding, etc. and somewhat correlates, so it must be climate change.
LOL.
And the chicken littles go do, do-do, do, do-do.
I might modify that to:
And the neo-Malthusians go do, do-do, do, do-do. Starting to seem real...
Normal high 39 F
Todays temp at noon 20 F
Windchill at noon 4 below F.
Real nice ......
May get above freezing by the weekend.
Yea !!!!!
Awesome presentation by Dr Alley which clarified a lot of points that were quite muddy to me... We need more sound yet quite accessible axplanations like these to stop the FUD spread around by many pseudo-scientists (and I throw in the same basket the extremists from both sides, from Al Gore to the fossil fuel lobbies...).
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