On June 15, the eruption of Mount Pinatubo began at 1:42 p.m. local time and placed a vast amount of ash into the atmosphere. In addition to the ash between 15 and 30 million tons of sulfur dioxide gas were ejected. Sulfur dioxide oxidizes in the atmosphere, and in the presence of water becomes sulfuric acid, which causes reflection of solar radiation and triggers ozone depletion in the stratosphere. The eruption plume of Mount Pinatubo's various gases and ash reached high into the atmosphere within two hours of the eruption, attaining an altitude of 34 km and was over 400 km wide. It was the largest disturbance of the stratosphere since the eruption of Krakatoa in 1883. The aerosol cloud spread around the earth in two weeks and covered the planet within a year. The cloud over the earth reduced global temperatures. In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced by 0.5-0.6°C and the entire planet was cooled by 0.4-0.5°C. The radiative forcing of the climate was estimated to be -2.7 W m^-2 and this translates into an atmospheric sensitivity of 0.19 ± 0.04 K (W m^-2)^-1.

A value for the sensitivity of the atmosphere to a change in radiative forcing may be obtained by differentiating the Stefan-Boltzmann equation:

E = esT⁴

dE/dT = 4esT³

Thus, dT/dE = 1/(4esT³) = 0.19 K (W m^-2)^-1

Using 0.95 for the emissivity and 288.2 K as the surface temperature this gives:

dT/dE = 0.19 K (W m^-2)^-1

The value derived from the Stefan-Boltzmann equation is subject to the usual strictures; that it is an 'instantaneous' value and does not take into account any subsequent processes, neither positive nor negative feedbacks. The Pinatubo value has the advantage that it comes from a real event of world proportions, but suffers from the fact that the stratosphere was perturbed as well as the troposphere.

This much lower value for the sensitivity is more in keeping with other estimates in the literature and considerably lower than the value used by the IPCC modellers of 0.5 K (W m^-2)^-1. It is also consistent with estimates of the 20^th century warming based on varying solar influences as well as that because of the extra CO₂.

Solar influences are the subjects of a later part of this website presentation.

 

Hey, Nobel Prize Winners, Answer Me This

By Climatologist Dr. Roy W. Spencer, formerly a senior scientist for climate studies at NASA's Marshall Space Flight Center where he received NASA's Exceptional Scientific Achievement Medal, and currently principal research scientist at the University of Alabama in Huntsville and responsible, together with John Christie, for the satellite records of atmospheric/surface temperatures since 1979.

University of Alabama in Huntsville 15 March, 2008

As a climate scientist, I would like to see some answers to a few basic global warming science questions which I'm sure the U.N.'s Ministry of Global Warming Truth (also known as the Intergovernmental Panel on Climate Change, IPCC) can handle. After all, since they are 90% confident that recent global warming is manmade, they surely must have already addressed these issues:

1) Why are ALL of the 20+ IPCC climate models more sensitive in their total cloud feedback than published estimates of cloud feedbacks in the real climate system (Forster and Gregory, J. Climate, 2006)? If the answer is that "there are huge error bars on our observational estimates of feedback", then doesn't that mean that it is just as likely that the real climate system is very insensitive (making manmade global warming a non-problem) as it is to be as sensitive as the IPCC models claim it is?

2) And regarding those observational estimates of (somewhat) positive cloud feedbacks: How do you know that the cloud changes that have been observed during temperature changes really are "feedbacks"? In other words, how do you know that the temperature changes caused the cloud changes, rather than the other way around? This basic distinction between cause and effect is critical because such a misinterpretation will ALWAYS make the climate system look more sensitive than it really is (e.g., it is energetically impossible for more low clouds to cause a warming). Doesn't it seem like a coincidence that the ONE case were we know that there was a huge non-cloud forcing (the 1991 eruption of Mt. Pinatubo) resulted in a negative solar shortwave cloud feedback, whereas all other periods showed supposedly positive shortwave cloud "feedback"?

3) As a follow on to question 2, we all agree that there has been strong global-average warming since the 1970's. Well, how do you know this wasn't the result of a small, natural change in cloud cover? Doesn't it seem like (another) coincidence that the Pacific Decadal Oscillation (PDO) just happened to shift to a different mode in 1977, about the time that the warming started? (Please don't say that the greater warming over land versus ocean is consistent with manmade greenhouse gas forcing…because it is also consistent with ANY kind of change in the Earth's radiant energy budget, whether natural or manmade.)

The fact is, we DON'T know how much of recent warming is natural, simply because we don't have good enough global cloud observations back to the 1970's (and earlier) to measure any long-term changes in cloudiness to the required accuracy - 1% or less.

The same cause-versus-effect uncertainty is true of any other climate variable as well, for instance water vapor, our main greenhouse gas. A small change in precipitation efficiency (the main process which ultimately limits the strength of the natural greenhouse effect) could cause a change in average water vapor content, which then would change the average temperature. In other words, increased water vapor doesn't have to only result from warming…warming can also result from increased water vapor.

The fact that we don't have a good enough understanding (or observations) of cloud changes, or precipitation efficiency changes, on decadal time scales to document such potential mechanisms seems like pretty weak justification for blaming all of our recent warming on mankind. And if you say, "well, the IPCC doesn't claim that ALL of the warming is manmade…", then tell me: About what percentage of the warming IS natural, and how did you come up with that quantitative estimate?

I fear that the sloppy science that too many climate researchers have lapsed into could, in the end, hurt our scientific discipline beyond repair. The very high level of certainty (90%) claimed by the IPCC for their manmade explanation for warming can not be justified based upon the scientific evidence, and is little more than an expression of their faith that they understand the causes of climate variability - which they clearly don't.

For those scientists who value their scientific reputations, I would advise that they distance themselves from politically-motivated claims of a "scientific consensus" on the causes of global warming -- before it is too late. Don't let five Norwegians on the Nobel Prize committee be the arbiters of what is good science.

 

 

The real sensitivity of the atmosphere to a change in forcing

The Figure below illustrates the latitudinal distribution of incoming solar radiation and outgoing terrestrial radiation.  From approximately 35^o N to 35^o S latitude there is a surplus of energy as incoming radiation exceeds outgoing. The more northerly and southerly regions indicate that there is more outgoing energy than incoming, yielding a net loss of energy from the Earth's surface. One might ask then why the middle to higher latitudes aren't getting colder through time as a result of the net loss, and the subtropical to equatorial regions getting constantly hotter due to the net gain. The reason is that the energy is redistributed by circulation of the atmosphere and oceans. Heat gained in the tropics is transported poleward by the global circulation of air and warm ocean currents to heat higher latitude regions. Cooler air from the higher latitudes and cold ocean currents push equatorward to cool the lower latitudes. This process of redistributing energy in the Earth system helps maintain a long-term energy balance. It is the basis of the subject known as climatology.

 

 

A study of satellite data gives a surprisingly simple empirical relationship between the intensity of the IR radiation emitted to space [E = TOA emission flux] and the surface temperature:

E = 203.3 + 2.09 × T

T is the surface temperature in degrees Celsius [°C].

The equation takes into account all possible forcings and feedbacks and is not dependent upon any theoretical considerations.

The mean value for the outgoing IR radiation intensity is 235 W m^-2 and this is consistent with the mean surface temperature of 15.2°C given by the equation and that generally accepted from terrestrial measurements.

The temperature coefficient, 2.09 W m^-2 K^-1 gives a value for the sensitivity of the system to a forcing as:

ΔT/ΔF = 1/2.09 = 0.48 K (W m^-2)^-1

Applied to the forcing arising from a doubling of the pre-industrial concentration of CO₂ of 285 ppmv to 570 ppmv estimated to be 3.7 W m^-2 the sensitivity indicates a possible surface temperature increase of 0.48 × 3.7 = 1.8°C. That we are supposed to have had an increase of 0.8°C, there seems to be no danger in the possible forthcoming 1.0°C if indeed there is sufficient carbon to burn to produce the CO₂ concentration of 570 ppmv.

The IPPC value for the sensitivity used by the GCMs is 0.5 K (W m^-2)^-1 before the application of the various feedbacks. The similarity between the two values is some indication that the feedbacks incorporated into the GCMs are overdone.

Mathematical form of the equation

There is an underlying logic in the form of the empirical equation in the expansion of the Stefan-Boltzmann law in the form:

E = σ(273.2 + T)⁴ = σ(273.2)⁴ + 4σ(273.2)³T + 6σ(273.2)²T² + 4σ(273.2)T³ + σT⁴

The last three terms are relatively small and may be ignored; the equation reduces to the linear form:

E ˜ σ(273.2)⁴ + 4σ(273.2)³T = 315.9 + 4.63 T

This has the same form as the empirical equation and ignoring the three last terms in the fully expanded equation introduces an error of only 1.5%. The equation is numerically different from the empirical one discussed above and that is because of the greenhouse effect which ensures that the outgoing radiation intensity is smaller than that emitted at the surface.

 

In Their Own Words: The IPCC on Climate Feedbacks

By Roy Spencer, November 1st, 2009

Despite the fact that the magnitude of anthropogenic global warming depends mostly upon the strengths of feedbacks in the climate system, there is no known way to actually measure those feedbacks from observational data.

The IPCC has admitted as much on p. 640 of the IPCC AR4 report, at the end of section 8.6, which is entitled “Climate Sensitivity and Feedbacks”:

“A number of diagnostic tests have been proposed…but few of them have been applied to a majority of the models currently in use. Moreover, it is not yet clear which tests are critical for constraining future projections (of warming). Consequently, a set of model metrics that might be used to narrow the range of plausible climate change feedbacks and climate sensitivity has yet to be developed.”

This is a rather amazing admission. Of course, since these statements are lost in a sea of favorable (but likely superfluous) comparisons between the models and various aspects of today’s climate system, one gets the impression that the 99% of the IPCC’s statements that are supportive of the climate models far outweighs the 1% that might cast doubt.

But the central importance of feedbacks to projections of future climate makes them by far more important to policy debates than all of the ways in which model behavior might resemble the current climate system. So, why has it been so difficult to measure feedbacks in the climate system? This question is not answered in the IPCC reports because, as far as I can tell, no one has bothered to dig into the reasons.

Rather unexpectedly, I have been asked to present our research results on this subject at a special session on feedbacks at the Fall AGU meeting in San Francisco in mid-December. In that short 15 minute presentation, I hope to bring some clarity to an issue that has remained muddied for too long.

To review, the feedback measurement we are after can be defined as the amount of global average radiative change caused by a temperature change. The main reason for the difficulty in diagnosing the true feedbacks operating in the climate system is that the above definition of feedback is NOT the same as what we can actually measure from satellites, which is the amount of radiative change accompanied by a temperature change.

The distinction is that in the real world, causation in the opposite direction as feedback also exists in the measurements. Thus, a change in measured radiative flux results from some unknown combination of (1) temperature causing radiative changes (feedback), and (2) unforced natural radiative changes causing a temperature change (internal forcing).

The internal forcing does not merely add contaminating noise to the diagnosis of feedback – it causes a bias in the direction of positive feedback (high climate sensitivity). This bias exists primarily because forcing and net feedback (including the direct increase of IR radiation with temperature) always have opposite signs, so a misinterpretation of the sum of the two as feedback alone causes a bias.

For instance, for the global average climate system, a decrease in outgoing radiation causes an increase in global average temperature, whereas an increase in temperature must always do the opposite: cause an increase in outgoing radiation. As a result, the presence of forcing mutes the signature of net feedback. Similarly, the presence of feedback mutes the signature of forcing.

The effect of this partial cancellation is to result in diagnosed net feedbacks being smaller than what is actually occurring in nature, unless any forcing present is first removed from the data before estimating feedbacks. Unfortunately, we do not know which portion of radiative variability is forcing versus feedback, and so researchers have simply ignored the issue (if they were even aware of it) and assumed that what they have been measuring is feedback alone. As a result, the climate system creates the illusion of being more sensitive than it really is.

One implication of this is that it is not a sufficient test of the feedbacks in climate models to simply compare temperature changes to radiation changes. This is because the same relationship between temperature and radiation can be caused by either weak forcing accompanied by a large feedback parameter (which would be low climate sensitivity), or by strong forcing accompanied by a small feedback parameter (which would be high climate sensitivity).

Only in the case of radiative forcing being either zero or constant in time – situations that never happen in the real world – can feedback be accurately estimated with current methods.

Our continuing analysis of satellite and climate model data has yet to yield a good solution to this problem. Unforced cloud changes in the climate system not only give the illusion of positive feedback, they might also offer a potential explanation for past warming (and cooling). [I believe these to be mostly chaotic in origin, but it also opens the door to more obscure (and controversial) mechanisms such as the modulation of cloud cover by cosmic ray activity.]

But without accurate long-term measurements of global cloud cover changes, we might never know to what extent global warming is simply a manifestation of natural climate variability, or whether cloud feedbacks are positive or negative. And without direct evidence, the IPCC can conveniently point to carbon dioxide change as the culprit. But this explanation seems rather anthropocentric to me, since it is easier for humans to keep track of global carbon dioxide changes than cloud changes.

Also, the IPCC can conveniently (and truthfully) claim that the behavior of their models is broadly “consistent with” the observed behavior of the real climate system. Unfortunately, this is then misinterpreted by the public, politicians, and policymakers as a claim that the amount of warming those models produce (a direct result of feedback) has been tested, which is not true.

As the IPCC has admitted, no one has yet figured out how to perform such a test. And until such a test is devised, the warming estimates produced by the IPCC’s twenty-something climate models are little more than educated guesses. It verges on scientific malpractice that politicians and the media continue to portray the models as accurate in this regard, without any objections from the scientists who should know better.