This is a re-post from And Then There's Physics
I know Eli’s already posted Andy Lacis’s response to Steve Koonin on Judith Curry’s blog, but I thought it worth repeating. It’s a pretty impressive comment in terms of what it covers, so it’s worth reading in it’s own right. I do find myself amazed at what Steve Koonin has been willing to say. Ignoring that much of what he says suggests a woeful lack of understanding of the topic itself, that anyone of his supposed intellectual calibre would construct an argument that essentially goes “look, this number is small, nothing to worry about” is remarkable, and not in a good way. It’s one thing to suffer from hubris, but it’s hard to see why if one’s argument is so obviously silly. Maybe Eli’s right that the best description is beyond contempt.
credit : xkcd
Anyway, Andy Lacis’s comment is below (bolds mine).
Physicists should take the time to understand their physics better (Comment: some of us are trying :-) )
Only 1% to 2% . . . that may sound small and insignificant . . . but it isn’t.
It is well known that the normal human body temperature is about 310 K. Furthermore, it is also well known that a seemingly small change (up or down) in absolute body temperature by only 1% (3.1 K, or 5.6 F) would make one sicker than a dog, and, that a 2% change in body temperature (up or down by 6.2 K, or 11.2 F) will virtually guarantee a dead body. From this, it should be sufficiently clear that, when viewed in absolute energy terms, the viable margin between life and death in the Earth’s biosphere is remarkably narrow – so much so that a seemingly insignificant 1% to 2% change in the total energy of the global environment will invariably result in serious disruption of the established infrastructure of life in the biosphere.
There is no substitute for appealing directly to basic physics for physical insight and better understanding of the ongoing global warming problem. And I do recall one particular case in the 1970s (in which you might have participated) when the JASON group of physicists was tasked to weigh in on the then open question of radiative forcing due to doubled CO2. At that point in time, the JASONs had available the computational resources to calculate one of the earliest line-by-line radiative forcing determinations for doubled CO2. They found the downward flux change at the ground surface to be less than 1 W/m2, from which they erroneously concluded that the radiative forcing caused by the doubling of atmospheric CO2 was “not all that significant”.
While the JASON group’s radiative calculations were numerically on target, the JASONs were clearly mistaken in their interpretation of the calculated results. Radiative forcing takes place over the entire atmosphere, and not just at the ground surface. If they had to select a single point on the vertical profile that best describes the radiative forcing by CO2, they should have selected the tropopause point, where the instantaneous flux change due to doubled CO2 is nearly 5 W/m2 for a clear-sky atmosphere. Moreover, the JASONs did not take into account the additional radiative magnification that is invariably contributed by the longwave opacity from water vapor and cloud feedbacks, which are several times larger than the radiative forcing due to CO2 alone, and therefore should have been included in their analysis.
In simple terms, the basic essence of the global warming problem is best understood as a straightforward problem in global energy conservation (Comment : I like this, because this is precisely how I normally think of this issue), as was first noted by Joseph Fourier in 1824. Specifically, the global-mean surface temperature of the Earth is about 288 K, which implies that the Planck emission from the ground surface must be about 390 W/m2. Furthermore, the global-mean solar energy absorbed by the Earth is observed to be about 240 W/m2 (with about 100 W/m2 reflected directly back to space).
Given that the Earth should be in near-global energy balance, this implies that the Earth must radiate about 240 W/m2 of longwave energy out to space (as has also been verified by satellite measurements). Absent the greenhouse effect, the 240 W/m2 of absorbed solar energy can only support a surface temperature of 255 K. This “missing energy” circumstance led Joseph Fourier to conclude that there must be thermal heat energy radiated downward from the atmosphere to supply the additional heating of the ground surface.
The flux difference of 150 W/m2 between the 390 W/m2 emitted by the ground surface and the 240 W/m2 of LW flux going out to space at the top of the atmosphere is a direct measure of the strength of the terrestrial greenhouse effect. Greenhouse action builds up the surface-emitted flux to 390 W/m2 and creates the ensuing reduction by 150 W/m2 of the outgoing longwave flux to space – all accomplished by radiative energy transfer means (via sequential emission, absorption, and re-emission interactions).
Physicists should also appreciate the nature of the Clausius-Clapeyron relation, and the fact that it is exponential in temperature. Undisturbed, with a source of liquid water, the atmosphere is always striving to reach an equilibrium 100% relative humidity. In simple terms this means that the holding capacity of the atmosphere for water vapor doubles for every 10 K increase in atmospheric temperature. And, there is no doubt that water vapor is a very potent greenhouse gas.
Detailed radiative attribution calculations show explicitly that water vapor accounts for about 50% of the 150 W/m2 of greenhouse effect, and that longwave cloud opacity accounts for 25%. Both of these radiative effects are due to the climate system’s fast feedback processes. The remaining 25% of the greenhouse effect comes from the radiative forcings by the non-condensing greenhouse gases (which incidentally also act to sustain the terrestrial greenhouse effect at its present strength).Of the non-condensing greenhouse gas contributions, CO2 is by far the strongest contributor accounting for about 20% of the 150 W/m2 greenhouse effect, with the remaining 5% due to minor GHGs like CH4, N2O, O3, and CFCs.
A key point to keep in mind is that it is these non-condensing greenhouse gases that act as the principal radiative forcing agents of the climate system. Because of their thermodynamic, chemical, and radiative properties, CO2 and the minor GHGs are chemically slow-reacting with atmospheric lifetimes ranging from decades to many centuries. Once they are injected into the atmosphere these gases effectively remain there indefinitely by not condensing or precipitating at prevailing atmospheric temperatures as they continue to exert their radiative forcing.
Since CO2 is the strongest and most effective of these non-condensing radiative forcing gases, it then follows that CO2 can be identified as the principal LW control knob that governs the global climate of Earth. The fact is that the other forms of radiative climate forcing (e.g., changes in solar irradiance, surface albedo, and aerosol forcing) are small by comparison. This makes the case for recognizing CO2 as the principal climate control knob that much more compelling.
Atmospheric water vapor, on the other hand, has the role of principal fast feedback process in the climate system by condensing and precipitating from the atmosphere in response to changes in local meteorological conditions (constrained by the exponential temperature dependence of the Clausius-Clapeyron relation), meaning that the atmospheric distribution of water vapor (and clouds) can change rapidly on a time scale of hours and days in response to changing weather conditions.
Applied radiative forcings that heat (or cool) the atmosphere cause more (or less) water vapor to evaporate, which generates more (or less) longwave opacity, which then contributes more (or less) radiative greenhouse effect. Such changes in water vapor cause big changes in radiative heating or cooling, but the changes are limited in magnitude by how much change the water vapor undergoes in reaching its new equilibrium distribution.
Because of this, water vapor and clouds act to magnify the initial radiative perturbation, but cannot on their own initiative manufacture or impose a warming or cooling trend on global climate, even though they contribute more strongly to the atmospheric radiative structure than the radiative forcing gases that actually drive and control the global temperature trend.
The physics cause-and-effect nature of the global warming problem is not all that complicated. The basic “cause” component of global warming has been clearly identified and understood for many decades, and has been accurately quantified by precise measurements of atmospheric CO2 (e.g., the Keeling curve).
This is fully corroborated by the latest annual data report of fossil fuel extraction that now approaches 10 gigatons of carbon/yr (roughly equivalent to 10 cubic km of coal/yr, which when burned, adds about 5 ppm CO2 to the atmosphere, half of which remains there for many centuries). The radiative effects of CO2 are fully known from well-established understanding of greenhouse gas radiative properties and radiative transfer modeling of the atmospheric structure.
How can a physicist not comprehend that it is atmospheric CO2 that is the principal radiative forcing agent for the ongoing global warming? . . . and not be concerned that water vapor, as the climate system’s principal feedback agent, has an exponential dependence on temperature?
To be sure, there are other factors that contribute to climate change. Butdecades of measurements and analysis have shown that variations in solar irradiance, land use, aerosols, ozone, and other minor greenhouse gases, while making a contribution, are small by comparison to CO2.
Of greater interest is the “unforced” variability of the climate system on decadal time scales that arises from changes in ocean circulation patterns that are effectively un-influenced by changes in atmospheric radiative forcing. The deep ocean is a very large cold storage reservoir. An upwelling blob of cold ocean water can put a “pause” in the ongoing global warming, temporarily diverting the greenhouse “heat” to warming the ocean. But once that cold blob of ocean water has been warmed up to its equilibrium temperature, it is back to the business of continued global warming. And also note that the ocean cannot cause a decadal warming spurt – the deep ocean is colder than the surface biosphere, so it cannot be a source of heat.
Significantly, the key climate system components (water vapor, clouds, ocean) are not configured to respond to radiative and/or temperature perturbations on a sufficiently small enough incremental scale that would permit a monotonic approach to global energy balance equilibrium. Instead, there is always over-reaction such as when water vapor condenses en mass to produce storms, coupled with the similarly over-reactive responses by atmospheric and ocean dynamics to pressure-temperature and salinity differences, to produce the quasi-chaotic weather and the longer-term climate noise that characterizes the climate system.
Physicists should not be confused by these random-looking quasi-chaotic fluctuations about the local climate equilibrium point, and should instead focus more on the changing energy balance equilibrium point of the climate system. They should also pay attention to the geological record that points to an atmospheric CO2 level of 450 ppm as being incompatible with polar ice caps, a level that is expected to be reached by the end of this century. While it may take a thousand years for the polar ice to melt, the future course is being prepared for a 70 meter rise in sea level.
Posted by Guest Author on Monday, 13 April, 2015
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