Duke Study: Global Warming Will be Significant But Not As Extreme as Some Predict
20 April 2006
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| A decadal view of forcing data used in the simulations. For clarity, greenhouse gas (GHG) and aerosol forcings are offset by 3 W m-2, and solar forcing by 1 W m-2. Source: Hegerl et. al. |
A research team led by Duke University scientists has found that while instrumental readings made during the past century offer ample evidence that carbon dioxide and other greenhouse gases in the atmosphere are warming Earth’s climate, the magnitude of future global warming will likely fall short of the most extreme predictions.
The accepted range for how much average global temperatures will rise in response to a doubling of atmospheric carbon dioxide is between 1.5º and 4.5º C. (UK Chief Scientist Sir David King recently weighed in with a 3º C figure. Earlier post.) Some observational studies have suggested the more extreme possibility that average temperatures might rise more than 9º C.
The new study is based on running some 1,000 computer simulations based on modern and ancient climate records of the Northern Hemisphere that factors in temperature response to past solar, volcanic and greenhouse gas forcing. The results indicate a 90% probability that a doubling of carbon dioxide levels will result in temperature increases of between 1.5 and 6.2 degrees—validating the accepted range. The group confined its study largely to the Northern Hemisphere because only there have scientists collected enough data to reconstruct temperature variations over the entire past millennium.
The study also showed a reduced likelihood that the actual maximum increase will exceed 4.5º C—from 36% down to 15% or less.
According to Gabriele Hegerl, a professor at Duke’s Nicholas School of the Environment and Earth Sciences, some studies claim that preindustrial temperatures fluctuated very little until the past century, and have risen sharply since.
“But our reconstruction supports a lot of variability in the past, as well as an upward trend in the 20th century,” she said. And a record with plenty of ups and downs before the modern era “shows a climate reacting then and now to a variety of external forcing.” According to Hegerl, past volcanic eruptions provided the strongest tie between past climate forcings and temperatures.
The study is published in the 20 April 2006 issue of Nature. The work was supported by the National Oceanic and Atmospheric Administration, the US Department of Energy and the National Science Foundation.
Although the results undercut the more extreme predictions of some studies, the study confirms the more widely expected forecasts for average global temperature increases given a doubling of atmospheric CO2. According to the results from the Exeter Conference in the UK, an average increase of 2º C will push the Earth into the area of dangerous climate change. (Earlier post.)
Resources:
“Climate sensitivity constrained by temperature reconstructions over the past seven centuries”; Gabriele C. Hegerl, Thomas J. Crowley, William T. Hyde1 and David J. Frame; Nature 440, 1029-1032 (20 April 2006) | doi:10.1038/nature04679
Note that the 1.5-6.2º C is the prediction if greenhouse gasses were doubled over pre-industial levels.
We are only likely to keep greenhouse gasses to mearly double if all countries, including US, join Kyoto and meet their targets. Also, China's emmissions would have to be limited or counter-balanced.
This report makes no attempt to predict what kind of world of hurt we would be in if we reached 2.5 times pre-industrial levels.
Posted by: LochDhu | 20 April 2006 at 11:19 AM
Here's a posting about an article recently published in Geophysical Review Letters (a very respected geophys journal) that comes to much the same conclusion from a different direction:
http://julesandjames.blogspot.com/2006/03/climate-sensitivity-is-3c.html
They noted that many independent studies and lines of analysis had come up with the same general 1.5 - 6 degree C climate sensitivity value. But then they observed that when you have independent evidence, you can combine the probability distributions using Bayes theorem and substantially narrow the uncertainty. Applying this principle just to existing climate estimates they were able to reduce it to 3 +/- 0.5 degrees C. Their estimate is that the chance that the sensitivity is above 4.5 C is less than 5%.
As with the Duke study, this is based on the assumption of a doubling of greenhouse gas levels. I believe this is the scientific definition of climate sensitivity: how much warming for a doubling of greenhouse gases. It is something of a coincidence that we are probably going to do just that, and double them.
Pre-industrial CO2 was about 280 PPM, and we're presently at qabout 380. At this point 550 PPM is considered about the best (i.e. lowest) we could realistically hope to do as far as maxing out CO2. This will then represent a doubling, and we will likely see that 3 degree C increase. This is well into the "dangerous" range, but it appears at this point that we have no hope of avoiding it.
The only prospect for avoiding catastrophe is to develop future technology to sequester CO2 from the atmosphere. This will need to be applied in the 2050-2100 time frame to reduce CO2 to levels comparable to today or even lower, or else we will be in big trouble.
Posted by: Hal | 20 April 2006 at 12:37 PM
Hal--
I predict that sequestration will prove to be very difficult if not impossible. Cutting emissions will be much cheaper and more effective in the long run. A rational plan would include an agressive plan to phase out all coal-fired power plants, for instance. Carbon currently stored in coal is safely sequestered forever. Burning 1 ton of coal dumps 4 tons of CO2 into the atmosphere.
Posted by: Nick | 20 April 2006 at 01:51 PM
Anyone see Nova on PBS this week? They had an episode on so-called "Global Dimming". Apparently the idea is that particulate air pollution (smoke,soot,ash,etc) has been a) blocking sunlight directly and b) seeding clouds so that they have more, but smaller water droplets in them which makes them more reflective than normal clouds, again causing incident sunlight on the earth to be less than it otherwise would be. A researcher in Wisconsin took advantage of the grounding of the air fleet after 9/11 and found that airplane contrails were also keeping the surface cooler to the tune of around 1C.
The upshot was that global warming has been mitigated by these other forms of pollution, which may be the reason why measurements don't show it being as bad as the models predicted. But particulate emissions are actually being cleaned up, while CO2 emissions are not, so their conclusion was that global warming will start to accelerate over the next decade or two.
Posted by: Marc | 20 April 2006 at 06:20 PM
Just curious: who drove all these zillions of cars 10 000 years ago which apparently caused catastrophic global warming and end of Ice Age?
Posted by: Andrey | 20 April 2006 at 08:07 PM
Andrey:
I'm not a paleo-climatologist, but if you read up on global warming you'll find that CO2 levels this century are heading to levels not seen on this planet for millions of years. Right now the atmospheric CO2 concentration is higher than at any time during the past 420,000 years, per study of ice cores in Antarctica and Greenland.
I hope you like it warm.
Posted by: Nick | 20 April 2006 at 10:35 PM
i don't think CO2 sequestering is really such a terribly difficult thing to do. every forest represents a major amount of sequestered CO2.
they also transport water into the air, reducing temperature. and they are more reflective of heat than bare ground, asphalt, concrete, crops, reducing the absorbed heat in the first place
so, if we are really concerned about rising temperatures, i think an answer worth considering is forestation, particularly in marginal lands, deserts.
the recent tree planting effort announced in india should be applauded because it increases the wealth of the pop, provides biofuel, captures CO2 {indefinitely if the wood is eventually used for furniture or anything other than burning}, reduces heat absorbed by the ground, and increases water in the air.
Posted by: shaun | 21 April 2006 at 12:17 AM
what ever the predictions are the change is visible all around the world.
The Health for both the environment as well as us is suffereing from our abussive use fossil resources and high carbon content fuels related to global climate change as well as environmental degredation.
And seeing that more and more primal forests are being cut to provide rich land (to be used unsustainably) for cattle to then be used to make what is considered non-foods such as mc donalds which requires a high energy proccessing (using more fossil fuels)to modify the raw healthy meat into proccessed nutritionally worthless non food, to provide a highly provitable business which disregards human right, just the same way the fossil fuel industries.
These are the kind of forests that store and absorb large amounts of CO2 and equally produce large amounts of oxygen. when they are felled apart from not fulfilling this role the carbon that is stored in the ground is released.
The source of the problem - Ruthless Big business - which wont change unless they are fined for all the destruction they have casued (since the time scientists were stating their direct connections of these affects)in such a way that for every tonne they pay the cost of removing it from harms way. Seeing that they provide it, when viable and healthier alternatives exsist.
Posted by: francis t | 21 April 2006 at 03:02 AM
I surely like it warm here in Canada.
But I sincerely hope that you are not irrational global warming believer and will open your mind to reality. I did, and that is the reason why I am so emotional about this issue.
Just ask yourself couple of questions:
CO2 concentration increased 50%, yet global temperature rise (big question!) for merely 1 degree C or 0.35%, counting from -273 absolute zero. May be CO2 is secondary factor for global climate?
Did you ever tried to thaw your Christmas turkey by rising temperature in your freezer from -16C to -15C?
Every exhaust from your lung deposit CO2 “emission” to the atmosphere. In fact CO2 is food source for plants – major player in biosphere. Do you really think that return of minuscule amount of conserved in earth deep organic carbon deposits is merely a return of food source for plants and algae? Artificial greenhouses routinely burn natural gas and route CO2 rich exhaust to the greenhouse to promote tomato etc. growth.
With all due respect to humankind, our share in global carbon cycle is no more then 5%. From this 5% most of carbon emission is derived from agricultural activity, like exposure of organic matter to oxidation after tilling, cultivation of rice and shrimp by flooding with substantial amount of anaerobic-derived CH4 (20+ more potent greenhouse agent than CO2), tilling down of straw with consequent anaerobic deposition of CH4, etc. Consider also that transportation share of combustion-derived anthropogenic CO2 is merely 20%.
According to modern data, half-life of carbon in atmosphere is less then 30 years, so what is the rush to reduce carbon dioxide emission?
Ocean fertilization and couple of other biological means offer incredibly cheap and effective means of carbon sequestration. Why it is not on agenda?
I did spend hundred hours on internet to investigate this suspicious to my common knowledge and common cense idea and was stunt from the finding. Global warming is total and shameless scum, invented and promoted by European-based bureocracy to benefit from total overtaxing of general energy consumption. As usual, any lie generates death, such as 250 000 per year premature death of Europeans due to promotion of greenhouse-gas friendly but dirty diesel passenger cars.
For starter take a look at : http://www.friendsofscience.org/index.php?ide=3
Regards.
Posted by: Andrey | 21 April 2006 at 03:53 AM
The problem with your argument is: What if you are wrong? As a global community we need to err on the side of caution and not change the environment. If big business and our pandering politicians are wrong and "global warming" is a reality the world as we inherited will be gone. Another popular argument for not confronting CO2 emissions is a loss of economic benefits and jobs. I am sure that changing the direction of our energy economy would create as many jobs as are lost. The only looser will be the status quo. Go have a cigarette it will be good for you health. Isn't that what industry told us?
Posted by: Michael | 21 April 2006 at 06:49 AM
Andrev,
"CO2 concentration increased 50%, yet global temperature rise (big question!) for merely 1 degree C or 0.35%, counting from -273 absolute zero. May be CO2 is secondary factor for global climate?"
The oven is on pre-heat. There is more warming in store for us even if we halt all greenhouse gas emissions from fossil fuels today.
"Do you really think that return of minuscule amount of conserved in earth deep organic carbon deposits is merely a return of food source for plants and algae?"
Yes. What was stored over several millenia has been released in a half a century. Over the 31 years of my life I have increased from 7 pounds to 180 pounds. If someone removed the 173 pounds that I have gained since then, I would not survive.
"With all due respect to humankind, our share in global carbon cycle is no more then 5%."
5% that wasn't there before industialization. Like a 5% interest bearing CD, year over year it adds up.
"From this 5% most of carbon emission is derived from agricultural activity, like exposure of organic matter to oxidation after tilling, cultivation of rice and shrimp by flooding with substantial amount of anaerobic-derived CH4 (20+ more potent greenhouse agent than CO2), tilling down of straw with consequent anaerobic deposition of CH4, etc. Consider also that transportation share of combustion-derived anthropogenic CO2 is merely 20%."
CH4 is an important part of the greenhouse gas equation. Fortunately, it decomposess in the atmosphere: 6O2 + CH4 = CO2 + 2H2O We are also fortunate that methane from cows' asses is roughly the same as methane from bisons' asses. Tilling only accelerates the decomposition that would happened in the prarie before european settlement. A similar balance exists in most other agriculture. The burning of fossil fuel is the only new greenhouse gas emmission that isn't balanced by a natural greenhouse emmision we destroyed. It might help to eliminate emmissions from farming, but eliminating fossil fuels would bring us back into balance.
"According to modern data, half-life of carbon in atmosphere is less then 30 years, so what is the rush to reduce carbon dioxide emission?"
Yes, if we halt all greenhouse gas emmissions from fossil fuels today, it will take 30 years for CO2 levels to fall from 380ppm to 330 (half way between current and pre-industrial) Sixty years later we will be at 305ppm. So for God's sake, act NOW!
"Ocean fertilization and couple of other biological means offer incredibly cheap and effective means of carbon sequestration. Why it is not on agenda?"
Cheap? Please cite source. Hmmm, sounds like - we've got a fly problem so lets get frogs to eat flies. Damn, now we've got a problem with frogs so lets get snakes to eat frogs. Aagh, snake probelm, get weasels. Weasels - get wolves. Wolves - get giant gnasher beasts from planet Ixnathis. Eee. . .[eaten by giant gnasher beast]
"I did spend hundred hours on internet to investigate this suspicious to my common knowledge and common cense idea and was stunt from the finding. Global warming is total and shameless scum, invented and promoted by European-based bureocracy to benefit from total overtaxing of general energy consumption. As usual, any lie generates death, such as 250 000 per year premature death of Europeans due to promotion of greenhouse-gas friendly but dirty diesel passenger cars."
Are you addicted to oil?
http://www.washingtonpost.com/wp-srv/opinions/cartoonsandvideos/toles_main.html?name=Toles&date=04042006
Posted by: LochDhu | 21 April 2006 at 11:03 AM
You still miss my point. What I am trying to say is very simple: CO2 is secondary player in natural GHG balance, anthropogenic CO2 is minuscule part in natural CO2 cycle, yet combustion sources of CO2 is even smaller. Earth biosphere recycle yearly amount of carbon much higher then is combusted by humankind. As any natural cycle, natural carbon cycle fluctuates around stable equilibrium, and resists any disruptions. Absence of measurable global warming tells us exactly that our carbon deposition still does not have any significant effects and obviously is not tilting GH equilibrium. Climate science (as weather prediction) is very tricky and does not provide us with somehow decisive findings. There is absolutely no reason for apocalyptic “act now” hysteria. Money misspend on fighting global warming could be used with much higher effect on other immediate problems, such as reduction of Middle East oil dependency, reduction of diesel exhaust toxic emissions, etc.
Limiting factor in ocean biosphere fertility is luck of iron. Deposition of wastes from iron smelting on ocean surface (0.00001% of surface – figural) could dramatically increase marine life fertility and carbon sink. Data on this experiments could be found somewhere at US DOE reports.
Posted by: Andrey | 21 April 2006 at 03:28 PM
Duke University is in North Carolina, a Red state.
I'm surprise anyone there in believes in Global Warming at all.
Posted by: dursun | 23 April 2006 at 04:13 PM