Warming Caused by Soot, Not CO2

A new paper in Science reports that a careful study of satellite data show the assumed cooling effect of aerosols in the atmosphere to be significantly less than previously estimated. Unfortunately, the assumed greater cooling has been used in climate models for years. In such models, the global-mean warming is determined by the balance of the radiative forcings—warming by greenhouse gases balanced against cooling by aerosols. Since a greater cooling effect has been used in climate models, the result has been to credit CO2 with a larger warming effect than it really has.

This question is of great importance to climate modelers because they have to be able to simulate the effect of GHG warming in order to accurately predict future climate change. The amount of temperature increase set into a climate model for a doubling of atmospheric CO2 is called the model's sensitivity. As Dr. David Evans explained in a recent paper: “Yes, every emitted molecule of carbon dioxide (CO2) causes some warming—but the crucial question is how much warming do the CO2 emissions cause? If atmospheric CO2 levels doubled, would the temperature rise by 0.1°, 1.0°, or by 10.0° C?”


Temperature sensitivity scenarios from IPCC AR4.

The absorption frequencies of CO2 are already saturated, meaning that the atmosphere already captures close to 100% of the radiation at those frequencies. Consequently, as the level of CO2 in the atmosphere increases, the rise in temperature for a given increase in CO2 becomes smaller. This sorely limits the amount of warming further increases in CO2 can engender. Because CO2 on its own cannot account for the observed temperature rise in the past century, climate modelers assume that linkages exist between CO2 and other climate influences, mainly water vapor (for a more detailed explanation of what determines the Global Warming Potential of a gas see my comment “It's not that simple”).

To compensate for the missing “forcing,” models are tuned to include a certain amount of extra warming linked to carbon dioxide levels—extra warming that comes from unestablished feedback mechanisms who's existence is simply assumed. Aerosol cooling and climate sensitivity in the models must balance each other in order to match historical conditions. Since the climate warmed slightly last century the amount of warming must have exceeded the amount of cooling. As Dr. Roy Spencer, meteorologist and former NASA scientist, puts it: “They program climate models so that they are sensitive enough to produce the warming in the last 50 years with increasing carbon dioxide concentrations. They then point to this as ‘proof’ that the CO2 caused the warming, but this is simply reasoning in a circle.”

A large aerosol cooling, therefore, implies a correspondingly large climate sensitivity. Conversely, reduced aerosol cooling implies lower GHG warming, which in turn implies lower model sensitivity. The upshot of this is that sensitivity values used in models for the past quarter of a century have been set too high. Using elevated sensitivity settings has significant implications for model predictions of future global temperature increases. The low-end value of model sensitivity used by the IPCC is 2°C. Using this value results, naturally, in the lowest predictions for future temperature increases. According to the paper “Consistency Between Satellite-Derived and Modeled Estimates of the Direct Aerosol Effect” published in Science on july 10, 2009, Gunnar Myhre states that previous values for aerosol cooling are too high—by as much as 40 percent—implying the IPCC's model sensitivity settings are too high also. Here is the abstract of the paper:

In the Intergovernmental Panel on Climate Change Fourth Assessment Report, the direct aerosol effect is reported to have a radiative forcing estimate of –0.5 Watt per square meter (W m–2), offsetting the warming from CO2 by almost one-third. The uncertainty, however, ranges from –0.9 to –0.1 W m–2, which is largely due to differences between estimates from global aerosol models and observation-based estimates, with the latter tending to have stronger (more negative) radiative forcing. This study demonstrates consistency between a global aerosol model and adjustment to an observation-based method, producing a global and annual mean radiative forcing that is weaker than –0.5 W m–2, with a best estimate of –0.3 W m–2. The physical explanation for the earlier discrepancy is that the relative increase in anthropogenic black carbon (absorbing aerosols) is much larger than the overall increase in the anthropogenic abundance of aerosols.

The complex influence of atmospheric aerosols on the climate system and the influence of humans on aerosols are among the key uncertainties in the understanding recent climate change. Rated as one of the most significant yet poorly understood forcings by the IPCC there has been much activity in aerosol research recently (see Airborne Bacteria Discredit Climate Modeling Dogma and African Dust Heats Up Atlantic Tropics). Some particles absorb sunlight, contributing to climate warming, while others reflect sunlight, leading to cooling. The main anthropogenic aerosols that cause cooling are sulfate, nitrate, and organic carbon, whereas black carbon absorbs solar radiation. The global mean effect of human caused aerosols (in other words, pollution) is a cooling, but the relative contributions of the different types of aerosols determine the magnitude of this cooling. Readjusting that balance is what Myhre's paper is all about.


Smoke from a forest fire.
Photo EUMETSAT.

Discrepancies between recent satellite observations and the values needed to make climate models work right have vexed modelers. “A reliable quantification of the aerosol radiative forcing is essential to understand climate change,” states Johannes Quaas of the Max Planck Institute for Meteorology in Hamburg, Germany. Writing in the same issue of Science Dr. Quaas continued, “however, a large part of the discrepancy has remained unexplained.” With a systematic set of sensitivity studies, Myhre explains most of the remainder of the discrepancy. His paper shows that with a consistent data set of anthropogenic aerosol distributions and properties, the data-based and model-based approaches converge.

Myhre argues that since preindustrial times, soot particle concentrations have increased much more than other aerosols. Unlike many other aerosols, which scatter sunlight, soot strongly absorbs solar radiation. At the top of the atmosphere, where the Earth's energy balance is determined, scattering has a cooling effect, whereas absorption has a warming effect. If soot increases more than scattering aerosols, the overall aerosol cooling effect is smaller than it would be otherwise. According to Dr. Myhre's work, the correct cooling value is some 40% less than that previously accepted by the IPCC.

Not that climate modelers are unaware of the problems with their creations. Numerous papers have been published that detail problems predicting ice cover, precipitation and temperature correctly. This is due to inadequate modeling of the ENSO, aerosols and the bane of climate modelers, cloud cover. Apologists for climate modeling will claim that the models are still correct, just not as accurate or as detailed as they might be. Can a model that is only partially correct be trusted? Quoting again from Roy Spencer's recent blog post:

It is also important to understand that even if a climate model handled 95% of the processes in the climate system perfectly, this does not mean the model will be 95% accurate in its predictions. All it takes is one important process to be wrong for the models to be seriously in error.

Can such a seemingly simple mistake in a single model parameter really lead to invalid results? Consider the graph below, a representation of the predictions made by James Hansen to the US Congress in 1988, plotted against how the climate actually behaved. Pretty much what one would expect if the sensitivity of the model was set too high, yet we are still supposed to believe in the model's results. No wonder even the IPCC doesn't call their model results predictions, preferring the more nebulous term “scenarios.”

Now that we know the models used by climate scientists were all tuned incorrectly what does this imply for the warnings of impending ecological disaster? What impact does this discovery have on the predictions of melting icecaps, rising ocean levels, increased storm activity and soaring global temperatures? Quite simply they got it wrong, at least in as much as those predictions were based on model results. To again quote from David Evans' paper:

None of the climate models in 2001 predicted that temperatures would not rise from 2001 to 2009—they were all wrong. All of the models wrongly predict a huge dominating tropical hotspot in the atmospheric warming pattern—no such hotspot has been observed, and if it was there we would easily have detected it.

Once again we see the shaky ground that climate models are built on. Once again a new paper in a peer reviewed journal has brought to light significant flaws in the ways models are configured—forced to match known historical results even when erroneous values are used for fundamental parameters. I have said many times that, with enough tweaking, a model can be made to fit any set of reference data—but such bogus validation does not mean the model will accurately predict the future. When will climate science realize that its reputation has been left in tatters by these false prophets made of computer code?

Be safe, enjoy the interglacial and stay skeptical.

I just read your "scientific

I just read your "scientific evidence" demonstrating that soot is causing melting, except that isn't what the study said. It states clearly that "black soot is contributing to global warming." i.e. black soot is another adding to the warming caused by CO2 and needs to be added to models to correctly predict future climate change. This doesn't reduce the evidence for global climate change caused by humans, it INCREASES it.
You are right, we need to correctly assign causes and effects. The latest studies indicate that we need to assign a warming role to black carbon that has hitherto been unaccounted for. You should also understand that soot and CO2 are generated together and reducing one reduces the other.

So sure, so wrong

You obviously didn't understand the paper or the post. Your statements are self contradictory: if a “new” source of warming is uncovered it doesn't start working at the time of discovery. It has always been there, contributing to warming—warming that had previously, more than likely been attributed to CO2. Hence, CO2's influence is diminished. Things are neither better nor worse than before, the globe's rate of warming is what it is. This does have implications for model forecasts, however, since it implies they have the sensitivity for CO2 set too high. Plus, not all forms of combustion create black carbon (for example natural gas). If you are actually interested in learning more see “Fire & Ice: Black Carbon vs Sulfate.”

Undersea volcanos are indeed

Undersea volcanos are indeed active but I don't think that is a big issue. The skeptical argument on volcanos has some merit but not in the way that they are explaining it. First, keep in mind that there are 2 and only 2 natural sources of heat on this planet. The first and more important is the sun. Block the sun and CO2 can have zero effect (it is a feedback). So you do have greenhouse conditions. Second is albedo, soot from volcanos and man-made sources collect over the poles, moreso over the north because that is where industry is largest. This lowers the albedo by darkening the ice. Less active volcanos in the northern hemisphere means that much less soot as well as other greenhouse gas emmitted from eruptions, according to Dr. Noidberg. Note that the south pole is not warming as much, nor south america or africa.

Sources of heat

You are correct that there are two sources of heat affecting Earth's climate: the large amount of energy from incoming solar radiation and the small amount from the planet's molten interior (possibly maintained to some extent by radioactive decay). Albedo, caused by variation in vegetative ground cover and snow cover, affects how much of the solar radiation is reflected back into space, or at least the atmosphere. Clouds also affect albedo but can also help trap heat in the lower layers of the atmosphere. As for soot collecting at the poles, check out the “Fire & Ice: Black Carbon vs Sulfate” article mentioned above. In particular, the globe with the pretty purple clouds showing soot distribution.

Great site but why this web

Great site but why this web site do not have other languages support?
Öğretmen Portalı

Sorry about that

The blog posts on The Resilient Earth website are often translated by our readers into other languages, including Spanish, Portuguese, French, Dutch, German and several others. To date, I know of no translation into Turkish, sorry. Might I suggest using a free translation service such as Google Translate (http://translate.google.com)?

The haze effect.

There is a double-whammy situation in the Northern Indian Ocean where the world's largest haze - Asian Brown Haze is located. Discovered by INDOEX 1999 and believed by them to have dire consequences for global hydrology.
The density, size and effect of this haze, comprised primarily of particulate matter from fossil fuel burning, makes the equatorial water covered too cool for evaporation - essential for rain cloud formation.
Equally, it is estimated the world's collective hazes have the capacity, due to the soot/black carbon present, to increase atmospheric temperatures by at least 2 degrees - the hazes are floating heatbanks.
So the situation exists where under a haze there is cooling, unwanted over equatorial water, and on top warming.

Global Warming

The planet warms and cools in cycles and I believe we are currently in a warming stage. Whether is it because of man or not is debatable. This has been one of the coolest summers I can remember in a long time.

CO2 saturation?

The "CO2 saturation argument" is wrong, and is based on an old and incomplete model of the atmosphere. RealClimate has two long posts that explain this in great detail, both on 6/26/07

http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-...

CO2 saturation is a valid argument

According to my modest experiment CO2 saturation is still a valid argument. See
http://pc-calculator.110mb.com/CO2/
Aimo Niemi

Saturation vs misinformation

The RealClimate article certainly lives down to that site's reputation as a premier propaganda outlet for alarmists. The attempt to spin the chain of historical discoveries by Arrhenius, Tyndall and others is pathetic. Even the cited example experiment done by Koch is misinterpreted—if the amount of CO2 removed from the tube produced no marked change in absorption then the lowered amount was already at saturation and adding more CO2 (the part removed for example) would not cause an increase. That is exactly the point. Climate scientists know that radiative capture by carbon dioxide is insufficient, which is why they have created all sorts of linkages to other phenomena: the hydrological cycle, cloud cover, ground cover changes, etc. If you want a fairly clear explanation of greenhouse gases and how they interact see this site.

As for the “new model” of the atmosphere that has CO2 pushing higher into the stratosphere, there is no observational data to support such an hypothesis. If it were true a rise in atmospheric temperature should be detectable by satellite IR sensors and such. In fact, no such rise has been observed. For 1979 through 1996 the surface and atmospheric records are not in agreement: For this period the surface record indicates warming at about 0.24 degrees F (0.14 degrees Celsius) per decade, while the satellite record shows the atmosphere cooling at about 0.07 degrees F (0.04 degrees Celsius) per decade, according to work by Spenser and Christy (just Google for them, they have bunches of papers on the subject).

This is a pretty interesting

This is a pretty interesting study. I will stay skeptical as always.

Addendum by Anthony

I’d like to add this graph showing CO2’s temperature response to supplement the one Doug Hoffman cites from IPCC AR4. here we see that we are indeed pretty close to saturation of the response.


click for larger image

The “blue fuzz” represents measured global CO2 increases in our modern times.

[thanks to Anthony on the Watts Up With That web site. Admin]

Global cooling theory

Now that we are no longer experiencing global warming, but "climate change" instead (a.k.a. global cooling), I see that carbon dioxide emissions are still the culprit. However. no one seems to know how it could be that carbon dioxide has caused first warming and then cooling. I have applied my scientific background to the problem, and come up with the answer.

While it took some time for the plants to adapt, they are now doing so and the result is a big spurt in their growth rate. All of this additional plant growth means more shade, and as we all know, it is cooler in the shade than in the sun.

The obvious concern is that this plant growth will become excessive. Plants will end up growing one and two feet a day and completely take over the green areas of earth, forcing humans to wander in the deserts for years.

Greenpeace and the Carbon Coalition are going to jointly finance a new movie about this menace. It will, of course, be narrated by Al "Chicken Little" Gore. The Obama administration will make it required showing in all schools on a weekly basis along with instructions on how to minimize breathing, since our breathing puts more carbon dioxide in the atmosphere.

The movie will incorporate terrifying scenes of super trees toppled by hurricane force winds and able to demolish tall buildings with a single crash. The proposed title for the movie is Little Planet of Horrors.

Global Cooling Theory.

This is silly! I don't know how to respond to an anonymous poster!

Please say something pertinent and disclose your "label" (web name) for our continued discourse.

Your claims are absurd in a real world!

Regards, suricat.