My Comment on The Andy Lacis Post “Atmospheric CO2 Thermostat: Continued Dialog”

In Andy’s post,

Atmospheric CO2 Thermostat: Continued Dialog by Andy Lacis

he wrote Things that we know well.

To continue this constructive dialog, I comment below on each of his conclusions with respect to “Things that we know well”.

Terrestrial climate is established as the result of energy balance between SW solar radiation absorbed by the Earth and the LW thermal radiation emitted by the Earth.

I agree that the energy change in Joules of the climate system is determined, on a global average, by the amount of incoming (solar) radiative energy in Joules and the outgoing radiative energy in Joules at the top of the Earth’s atmosphere. However, there never is a balance due to the variation of solar input and outgoing radiative energy during the year, as shown clearly in the seminal paper

Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Climate. 83, 1958-1962

Indeed, this annual variation in the heating and cooling can produce a nonlinear chaotic response, as we illustrated in  simple model in our paper

Pielke, R.A. and X. Zeng, 1994: Long-term variability of climate. J. Atmos. Sci., 51, 155-159

where we wrote

“One of the crucial problems in assesing man-made climate change is to understand the natural variability of the climate system and the cause of this variability. The internannulal variability can be caused by external (non-man-made) forcging (e.g. volcanic eruption) and the coupling of the climate system among the atmosphere, ocean, and biosphere (such as the air-sea interactions for an ENSO event). A natural variability of the atmosphere over decadal time scales can be caused by external forcing (e.g. the 22-year sunspot cycle) and the slow changes of other components of the climate system (such as the ocean thermohaline circulation)…..In general, determinisitc nonlinear interactions (Lorenz 1991) and stochastic forcing (Hasselmann 1976) can also be used to explain the natural variability of different time scales.”

Andy’s conclusions continue with

Atmospheric absorption of LW radiation by water vapor, clouds, CO2, and other trace gases produces a greenhouse effect that keeps the surface temperature of Earth about 33 °C warmer than it otherwise would be without the atmospheric greenhouse absorbers.

I agree with Andy on this conclusion.

Of the 33 °C terrestrial greenhouse effect, water vapor is responsible for about 50% of the effect, 25% is due to clouds, 20% is due to CO2, and the remaining 5% is contributed by CH4, N2O, O3, CFCs, and other lesser constituents.

These estimates look reasonable.

The atmospheric distribution of water vapor and clouds is the result of feedback processes, hence the water vapor and cloud amounts are determined by the prevailing meteorological conditions.

The atmospheric distribution of water vapor and clouds is traditionally treated as a radiative feedback. However, ocean circulations and land surface processes also influence the atmospheric distribution of water vapor and clouds, as discussed, for example, in the paper

Zheng Sun, Yongqiang Yu, and Tao Zhang, 2009: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations Journal of Climate, Volume 22, Issue 5 (March 2009) pp. 1287–1304.

There absract reads in part

“By comparing the response of clouds and water vapor to ENSO forcing in nature with that in Atmospheric Model Intercomparison Project (AMIP) simulations by some leading climate models, an earlier evaluation of tropical cloud and water vapor feedbacks has revealed the following two common biases in the models: 1) an underestimate of the strength of the negative cloud albedo feedback and 2) an overestimate of the positive feedback from the greenhouse effect of water vapor. Extending the same analysis to the fully coupled simulations of these models as well as other Intergovernmental Panel on Climate Change (IPCC) coupled models, it is found that these two biases persist……all coupled simulations analyzed in this study have a weaker negative feedback from the cloud albedo and therefore a weaker negative feedback from the net surface heating than that indicated in observations.”

I posted on this paper and include an exchange of e-mail correspondences with De-Zheng in my post

Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations by De-Zheng Sun, Yongqiang Yu, and Tao Zhang

Roy Spencer also discusses radiative forcings and feedbacks in his posts; e.g. see

Our JGR Paper on Feedbacks is Published

The non-condensing greenhouse gases (CO2, CH4, N2O, O3, and CFCs) provide the ultimate support structure for the terrestrial greenhouse effect, even though by themselves they account only for 25% of the total atmospheric greenhouse effect.

The separation of the greenhouse gases into long term and shorter term (due to condensation) components is useful. However, water vapor, while it condenses out, still is a permanant part of the Earth’s atmosphere as it is continually replenished from the oceans and from volcanic emissions. 

Accurate measurement and monitoring of the non-condensing GHGs shows unrelenting increase in atmospheric GHG concentrations, with an accumulated radiative forcing of about 3 W/m2 since 1880.

 Radiative forcing is flux and cannot be accumulated. The more appropriate unit would be how many Joules of heat have accumulated since 1880 due to the added non-condensing GHGs.  Moreover, since the climate system has warmed over the last 110 years (i.e. it is warmer today to the best of our knowledge than in 1880), the non-condensing GHG radiative forcing must be less than the difference between that of 1880 and today; see

Comment On An Error In A Figure Caption In The Statement For Policymakers In The WG1 2007 IPCC Report

where I wrote with respect to the total radiative forcing

“…the WG1 report leaves an erroneous impression in terms of how they present the radiative forcing estimates in figure SPM.2. Indeed, since some of the radiative forcing since 1750 presumably has equilibrated with an increase in global heat content, the actual 2005 radiative forcing must be less than the 1.6 Watts per meter squared that is presented in their figure.”

I continued with

I have reproduced below comments by James Annan and Gavin Schmidt on this subject that appeared in my January 4 2008 post.

This is an important issue. As James Annan stated in a reply on the weblog Stoat

“I think RP is really asking about the current radiative imbalance: while I do not think it is wrong or misleading to talk about total forcing (with a 1750 baseline) as the IPCC do, the other question is also interesting as it relates directly to warming “in the pipeline”. Of course the answer is we do not know for sure, since it directly depends on the climate sensitivity (and even the effective climate sensitivity of the current climate state, which may be slightly different again). But a rough ballpark estimate would be that a little more than half of the total forcing (IPCC terminology) remains as a current imbalance (the commitment runs in the AR4 show the future warming due to this imbalance). Of course splitting this up further into the contribution of each component would then become rather arbitrary.”

Thus, while he writes that this is a “rough ballpark estimate”, his insight that

“…. a little more than half of the total forcing (IPCC terminology) remains as a current balance”,

is the type of answer that is being requested.

Gavin Schmidt on Real Climate also added constructively to this when he responded that

“I don’t think it can be done robustly. A straight-forward apportioning based on the fractional contribution to the original forcing neglects the differing transient behaviour. For instance if one forcing agent rose quickly and stabilised, while another increased later, then the impact of each on the current imbalance should be weighted towards the latter. So that’s no good. Maybe you could do it by examining the single forcing transient runs we did for our recent paper (table 1) and looking at the year 2000-2003 (say) imbalances in Ann/Net TOA radiation. You’d need to check that the individual components do in fact add up to something close to the combined effect (not obviously true). However, different models might give quite different results, and you can only do this for forcings we’ve run. Other groups didn’t do as many single forcing experiments and so you might not be able to find another set of numbers to compare with. Attribution requires models however, and so I don’t see how you could do it any other way.”

The reason that this issue is so important is that

“if one forcing agent rose quickly and stabilised, while another increased later…”

as Gavin wrote, than the fractional contribution to the current radiative imbalance is weighted towards the more recent forcings. Since CO2 has been rising since 1750, at least part of the radiative forcing of CO2 has equilibrated. Thus the claim that CO2 is 50% (or about 30% as estimated on Climate Science based on the 2007 IPCC figure SPM.2; see) is an overstatement of its actual current radiative forcing.

Thus, Andy’s finding that the current radiative imbalance from non-condensing GHGs “is an accumulated radiative forcing of about 3 W/m2 since 1880”  is misleading.

 Since the non-condensing GHG increase is due almost entirely to human industrial activity, primarily the burning of fossil fuel, humans are fully responsible for the global warming.

In terms of human activities, Andy has neglected the important role of the burning of forests and grasslands as a source of CO2. Also, in terms of a positive radiative forcing, he has ignored the role of aerosols; e.g. see

The Role Of Soot In The Climate System – An Excellent Article In The Economist

Accurate measurements of solar irradiance over three solar cycles since the late 1970s show solar cycle variability to be of roughly 1 W/m2 amplitude, but with no significant trend.

Andy  neglects the solar influence; e.g. see

Solar Forcing And Climate – Other Research Results

and of natural climate forcings; e.g. see the posts on the weblogs

There clearly is much more involved with global warming and cooling than the non-condensing GHGs.

Aerosols are important contributors of climate forcing, with non-absorbing aerosols and associated cloud-aerosol indirect effect contributing about –1 W/m2 apiece, and black carbon aerosols contributing about 0.8 W/m2 of warming.

While we may disagree on the certainty in which the annual average radiative forcing is presented in Andy’s post, I completely agree that “aerosols are important contributors of climate forcing. However, it is much more than radiative forcing as is summarized in the 2010 AMS policy statement; see

New “American Meteorological Society [AMS] Policy Statement On Inadvertent Weather Modification” Adopted

where the text starts with

“This statement highlights the causes and possible effects of inadvertent weather modification[1] at local and regional scales due to aerosol[2] and gas emissions[3] and to changes in land use.  The known effects can have unanticipated and often undesirable socioeconomic consequences. “

Andy’s conclusions continue with

The current climate model sensitivity (for doubled CO2) of 3 °C per 4 W/m2 forcing is in good agreement with the geological (400 K-year) ice core record.

As reported in

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp

“….the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change—global mean surface temperature response—while offering little information on regional climate change or precipitation.”

Thus the term “climate sensitivity” is grossly inaccurate and misleading when used to mean a global average surface temperature response to an annual global average radiative forcing. Even when used as Andy has presented it, the question is what temperature is actually meant. As discussed in

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229

the determination of such a temperature is not straightforward. Moreover, the more appropriate metric for assessing global warming and cooling is, for example,  Joules per decade as proposed in

Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Climate. 83, 1958-1962

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335

Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.

The climate system also undergoes natural (unforced) variability about its global equilibrium state with regional shifts in climate patterns on inter-annual and decadal time scales.

I agree with Andy that there are natural variations in the climate system. However, the assumption of a “global equilibrium state” is incorrect. The Earth’s climate system is never in equlibrium since in the orbit around the Sun and as a result of the distribution of land and water on the planet, there is always a lack of an equllibrium. It is correct that the incoming solar radiation provides a constraint on how much the outgoing radiation from the Earth can vary, but it is never in equillibrium with this solar input.

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