In response to my post
I communicated to the Committee members of our Statements on Weather Modification (of which I am a member and in which Danny Rosenfeld is the Chair). With their permissions, I have reproduced our e-mail exchanges below with several members of the Committee (with their permission). These colleagues are each internationally well-respected scientists:
1. Danny Rosenfeld of the University in Jerusalem
2. Alan Robock of Rutgers University
3. Bob Bornstein of San Jose State University
The bottom line conclusion by Danny in his last e-mail fits with my view of this subject.
My Initial E-Mail To Danny
In your request for input you asked whether we should consider revising any of the policy statements. The release today of the AMS Statement on Climate Change clearly ignores what we concluded in our Statement on Inadvertant Weather Modification. Thus I recommend consideration of a revision that corrects their excessively narrow view on how humans are altering the climate and the impact of natural variations in climate such as reported, for example, in Shaun Lovejoy’s new paper
“The Climate Is Not What You Expect” By S. Lovejoy and D. Schertzer 2012 [submitted to BAMS]
that I posted on in
I have posted today on the conflict between the two AMS Statements (the new one on Climate Change and ours on Inadvertant Weather Modification) in my post
I would, based on their new Statement, be interested in addressing this issue in a revised Statement on Inadvertant Weather Modification. .
It seems to me that the new AMS statement on climate change does recognize the roles of aerosols, land use changes and other factors apart from CO2. See the quote below.
“Human activity also affects climate through changes in the number and physical properties of tiny solid particles and liquid droplets in the atmosphere, known collectively as atmospheric aerosols. Examples of aerosols include dust, sea salt, and sulfates from air pollution. Aerosols have a variety of climate effects. They absorb and redirect solar energy from the sun and thermal energy emitted by Earth, emit energy themselves, and modify the ability of clouds to reflect sunlight and to produce precipitation. Aerosols can both strengthen and weaken greenhouse warming, depending on their characteristics. Most aerosols originating from human activity act to cool the planet and so partly counteract greenhouse gas warming effects. Aerosols lofted into the stratosphere [between about 13 km (8 miles) and 50 km (30 miles) altitude above the surface] by occasional large sulfur-rich volcanic eruptions can reduce global surface temperature for several years. By contrast, carbon soot from incomplete combustion of fossil fuels warms the planet, so that decreases in soot would reduce warming. Aerosols have lifetimes in the troposphere [at altitudes up to approximately 13 km (8 miles) from the surface in the middle latitudes] on the order of one week, much shorter than that of most greenhouse gases, and their prevalence and properties can vary widely by region.
Land surface changes can also affect the surface exchanges of water and energy with the atmosphere. Humans alter land surface characteristics by carrying out irrigation, removing and introducing forests, changing vegetative land cover through agriculture, and building cities and reservoirs. These changes can have significant effects on local-to-regional climate patterns, which adds up to a small impact on the global energy balance as well.”
Changes in aerosols and land use are major components in the anthropogenic-forced changes of Earth energy budget, and we cant get both weather and climate right without quantifying their effects, and much less the climate change.
But I would defend the emphasis on the greenhouse gases as being pointed out in the new statement as the dominant cause for warming trend in the last half century. While aerosols have not risen systematically during that period (re global deeming and brightening), CO2 and other GHGs did.
What do I miss here?
Thank you for the quick reply. The paragraph that I highlighted in my post
“It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide. The most important of these over the long term is CO2, whose concentration in the atmosphere is rising principally as a result of fossil-fuel combustion and deforestation.”
conflicts with our Statement and a wide range of other findings reported in the literature. Their statement of hindcast model quality of climate change can easily be shown to be false.
My Further Comment
P.S. The AMS Statement itself contradicts itself. It writes
“Land surface changes can also affect the surface exchanges of water and energy with the atmosphere. Humans alter land surface characteristics by carrying out irrigation, removing and introducing forests, changing vegetative land cover through agriculture, and building cities and reservoirs. These changes can have significant effects on local-to-regional climate patterns, which adds up to a small impact on the global energy balance as well.”
yet earlier highlights that
“…the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide. The most important of these over the long term is CO2..”
It is clear the Statement was not even probably vetted for internal inconsistencies. If they write
‘the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases”
and later write
“Humans alter land surface characteristics by carrying out irrigation, removing and introducing forests, changing vegetative land cover through agriculture, and building cities and reservoirs. These changes can have significant effects on local-to-regional climate patterns’
yet dismiss their importance because they add “up to a small impact on the global energy balance ….”
trivialize, as I read the Statement, their role in climate change.
Bob Bornstein’s Comment
I agree with Danny that aerosols are acknowledged as a source of change, but we could further discuss a possible revised statement (if the AMS is willing to accept one from us at this time) at our Jan committee meeting.
My Reply to Bob
Hi Bob. Acknowledging aerosols as a source of change is not the issue. It is their identification of CO2 and a few other greenhouse gases as the dominant climate forcing. It is just one of a suite of first order human climate forcings, in my view. If we share that view, then the AMS Statement is not accurate.
Alan Robock’s Comment
I see no conflict between the two AMS statements. The new one addresses global climate, and recognizes regional impacts of aerosols and land surface changes, which is what the older statement says. What is the problem? Blog posts and submitted papers are not sufficient evidence to do anything. I don’t understand what changes would be made in the Statement on Inadvertant Weather Modification. Anyway, it addresses weather and not climate.
My Reply to Alan
I list peer reviewed papers that conflict with the AMS Statement. These are not submitted papers. The blog posts are just used to communicate these papers and the NRC assessment to others. Also we discuss climate in our Inadvertent Weather Modification Statement.
Yes, you can post my comments as long as you include this one:
Clearly regional climate change is affected by land use and aerosols. But for the global average climate, the dominant forcing is the increase of anthropogenic greenhouse gases. Global warming is reduced by the net effect of tropospheric aerosols, but it continues because the greenhouse gas emissions and current concentrations still produce a net positive radiative forcing.
Your claims seem to imply that greenhouse gas emissions are not a serious environmental hazard. Don’t you think that global warming is dangerous and that continued greenhouse gas emissions, particularly carbon dioxide, should be reduced as soon as we can? Or are you against mitigation?
My Reply to Alan
Thank you for your permission. I will certainly include what you wrote.
In terms of your question, I agree with you that the continued elevation of atmospheric concentrations of CO2 is a major concern. We are entering uncharted territory, and the less regrets approach must be to seek effective ways to limit this increase in CO2.
My even greater concern, however, with respect to CO2 is in its biogeochemical effect (to the biosphere). Even if there were only a relatively small contribution to global warming from CO2, the effect on plant diversity (e.g. genetic response), plant function, etc could be very significant, and we do not understand the risks that society and the environment face from this biogeochemical effect.
Progress to develop effective mitigation and adaptation policies are being significantly hampered, in my view, by
i) the assumption that the multi-decadal global models are providing us with skillful predictions for the coming decades(and skillful hindcast attribution simulations); the are not – e.g. see
where peer reviewed papers indicate that this assumption has failed so far
ii) that a focus on global warming when we communicate to policymakers, rather than on all of the climate forcings and feedbacks, is one reason that action on mitigating climate risks (including from added CO2) has been so ineffective. We need a more inclusive approach; win-win policies; e.g. see
to build consensus has to how to move forward [I subscribe to the approach my son advocates in his book "the Climate Fix" with respect to how to deal with the CO2 part of climate].
I hope this clarifies my perspective. In terms of the new AMS Statement on Climate Change, they fail, in my view, to accurately present the issue of climate.
Danny’s Further Comment
I don’t really see the problem with the AMS statement on climate change.
It does not undervalue the role of aerosols and land use in altering the climate. It merely states that the trend in the anthropogenic climate forcing was dominated by increasing GHG (while other components of the forcing had not such a clear rising trend during the last 50 years). Then it makes the connection between the trends in rising GHG and global temperatures.
Otherwise, your reservations might come across as if you dispute the notion that increasing GHG is causing increasing global temperatures. Did you really mean that?
My Reply to Danny
I disagree with this claim
“the anthropogenic climate forcing was dominated by increasing GHG”.
This claim is clearly inaccurate. I am surprised that you accept this as your work shows that aerosols from human activities have altered CCN concentrations globally.
Flood or Drought: How Do Aerosols Affect Precipitation? by Daniel Rosenfeld, Ulrike Lohmann, Graciela B. Raga, Colin D. O’Dowd, Markku Kulmala, Sandro Fuzzi, Anni Reissell, Meinrat O. Andreae, Science 5 September 2008: Vol. 321. no. 5894, pp. 1309 – 1313 DOI: 10.1126/science.1160606.
In that paper you wrote
“….before humankind started to change the environment, aerosol concentrations were not much greater (up to double) over land than over the oceans… “
In the paper
Andreae and Rosenfeld, 2008: Aerosol–cloud–precipitation interactions. Part 1. The nature and sources of cloud-active aerosols. Earth System Reviews.
“There is now clear and rapidly growing evidence that atmospheric aerosols have profound impacts on the thermodynamic and radiative energy budgets of the Earth…”
“Model calculations and observations in remote continental regions consistently suggest that CCN concentrations over the pristine continents were similar to those now prevailing over the remote oceans, suggesting that human activities have modified cloud microphysics more than what is reflected in conventional wisdom.”
I could list similar findings with respect to LULCC.
The increasing GHG did not dominate anthropogenic climate forcing over the last decades. Unfortunately, the human effects are more serious than that.
With respect to your question as to whether I dispute the notion that increasing GHGs is causing increasing global temperatures, clearly added CO2 and other greenhouse gases is a first-order positive radiative forcing. Clearly, I agree that increasing GHGs are contributing to an increase.
Its relative contribution to the observed global warming (which is best diagnosed by changes in upper ocean heat content), however, is still uncertain due to
i) aerosol effects; where you wrote in your June 2, 2006 Science Perspective article on the role of aerosols entitled “Aerosols, Clouds, and Climate”
“These aerosol effects are poorly quantified and represent the greatest uncertainty in our understanding of the climate system.”
ii) solar effects – e.g. see
Lean, J. L., and D. H. Rind (2009): How Will Earth’s Surface Temperature Change in Future Decades?,
Geophys. Res. Lett., doi:10.1029/2009GL038932, in press. (accepted 9 July 2009).
iii) natural variations – e.g. see
“The Climate Is Not What You Expect” By S. Lovejoy and D. Schertzer 2012 [submitted to BAMS]
iv) land use/land cover effects – which in a global average change in heat content seem to average out, but have large regional effects on climate and the resultant effect on cloud cover is not known; e.g.
Pielke Sr., R.A., A. Pitman, D. Niyogi, R. Mahmood, C. McAlpine, F. Hossain, K. Goldewijk, U. Nair, R. Betts, S. Fall, M. Reichstein, P. Kabat, and N. de Noblet-Ducoudré, 2011: Land use/land cover changes and climate: Modeling analysis and observational evidence. WIREs Clim Change 2011, 2:828–850. doi: 10.1002/wcc.144.
Finally, it seems that we have a disagreement as to what is meant by anthropogenic climate forcing. In my view, it is much more than a change in the global average temperature (or global average TOA radiative imbalance).
Global scale effects on climate can occur due to alterations in regional atmospheric and ocean circulations due to regionally heterogeneous human-caused aerosol and land use/land cover changes, even if the global average radiative imbalance was not changed. In my view, this is the more serious issue, as droughts, floods, hurricane tracks, etc are associated with regional circulations patterns (including the NAO, PDO, ENSO etc), with a global average increase in average temperature only a relatively small contributor; e.g. see John Neilsen-Gammon’s analysis
I wrote on the misleading use of the term “climate change” in my post
where I propose these two definitions
Global Warming is an increase in the global annual average heat content measured in Joules.
Climate Change is any multi-decadal or longer alteration in one or more physical, chemical and/or biological components of the climate system.
The National Research Council report
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
reinforces the need for this broader view.
In terms of seeking to mitigate and adapt to the effect of humans on the climate system, I have concluded that the focus on CO2 and a few other greenhouse gases as the dominate concern is not only inaccurate, but will lead to poor policy decisions.
Finally, do I have your permission (and Alan yours too) to post our e-mail exchanges on my weblog?
Danny’s Comment [my highlight added]
Thanks for your elaboration and clarifications. I agree that my statement to which you did not agree:
“the anthropogenic climate forcing was dominated by increasing GHG”.
should be qualified to the climate scale.
Here we need indeed to separate the effects on regional and weather scales from the global and climate scales, as Lovejoy has now so nicely defined.
The amounts of anthropogenic aerosols on a global scale probably have already peaked. But the GHG concentrations keep accelerating. This means that the GHG dominate the trend of the globally averaged long term trend of the temperature, but at the regional scale other effects may dominate the trends of temperature and other parameters.
The meaning of the main points that I have been making in the publications that you have referenced are:
1. On a regional scale, the aerosols can be the dominant anthropogenic climate forcing.
2. On a global scale, the aerosols might be in par with the GHG. We just don’t know.
The inability to quantify the possibly large radiative forcing prevents us from quantifying adequately the climate sensitivity and hence from predicting the expected global warming due to a given added GHG-induced radiative forcing. This does not contradict the AMS statement that “the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases”.
This is in fact a discussion on the boundary between weather modification and climate change. The impacts on the ecosystems certainly happen at the regional scales.
So where do we put the distinction between weather modification and climate change?
Roger, Your discussion has been very helpful to recognize this as a major question and the confusion that it incurs, which we as a committee need to address, and perhaps negotiate with the AMS committee on climate variability and change.
Thanks and best regards, Danny
My Reply to Danny
Thank you for the further follow up. You raise an important issue -
What is the distinction between weather modification and climate change?
In the 2005 NRC report, we defined climate in Figure 1-1 [http://www.nap.edu/openbook.php?record_id=11175&page=12] as
“The climate system, consisting of the atmosphere, oceans, land, and cryosphere. Important state variables for each sphere of the climate system are listed in the boxes. For the purposes of this report, the Sun, volcanic emissions, and human-caused emissions of greenhouse gases and changes to the land surface are considered external to the climate system.”
It seems to me that weather is necessarily a component of the climate system. One can separate by averaging time (i.e. long term statistics), but this is clearly quite arbitrary. We often, for example,talk about the “microclimate” of a location and use this information to explain variations in local weather observations. Many use “seasonal climate predictions” when what they really mean are “season averaged weather statistics”.
On Shaun Lovejoy’s paper, he and I discussed more on the chaotic character of the climate system in a set of e-mails as reported in my post
There does need to be a clearer (overdue in my view) definition of terminology and the AMS committees provide one effective set of venues to do this.
On your comment that the aerosol effect may have peaked, hopefully this is true. I agree it is not true for the GHGs. However, it is also not true of LULCC; e.g. see
Fragkias, F. and K.C. Seto, 2012: The rise and rise of urban expansion Urban land area has expanded globally during the past few decades – a trend that looks set to continue in the foreseeable future. IGBP Newsletter, 78. March 2012.
in my post
Can I post our e-mail exchanges? Alan (and Bob) have okayed his.
Yes, you can post our email exchange.
Best regards, Danny