Comments On The New York Times Article By Jim Robbins Titled “2 Views Of Aerosols and Climate Change”

The New York Times has published the following news article by Jim Robbins titled

2 Views of Aerosols and Climate Change

This article further illustrates the major and diverse role of aerosols as a human and natural climate forcing.  However, the article includes text which perpetuates the myth that there may be societal and environmental  benefits in not reducing the human input of aerosols. The article reads (with highlights added]

Aerosols are small particles or droplets suspended in a gas. While consumers tend to think of them as being dispensed from a pressurized container, some are natural and some are produced by pollution generated by humans. Two recent studies suggest that the latter variety plays an important role in the environment, actually changing weather and climate.

My Comment: This is not a new finding. For example, see the extensive discussion 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.

where one of the conclusions was that

Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Aerosols exert a forcing on the hydrological cycle by modifying cloud condensation nuclei, ice nuclei, precipitation efficiency, and the ratio between solar direct and diffuse radiation received.

The New York Times article continues

A study by a team of researchers led by scientists at the University of Maryland indicates that increases in air pollution from construction, power plants and other sources creates more aerosols, which can affect cloud formation in a way that causes drier regions to get even less rain and wetter regions to experience more snowfall, rain and severe weather.

Experts say that it is a cautionary lesson for places where rapid development is under way. Such activity is often “accompanied with increases in pollution whose adverse impacts on weather and climate, as revealed in this study, can undercut economic gains,” said Zhanqing Li, a researcher at the University of Maryland who is the study’s lead author. The article was published online on Sunday by the journal Nature Geoscience.

Clouds in dirty regions can be twice as thick as clouds in very clean areas, and the probability of heavy rain is doubled there, according to the study. The researchers say the study is the first time aerosols and weather have been clearly linked.

My Comment: While we are pleased that the researchers emphasize the importance of aerosols, their statement that this is the  “first time aerosols and weather have been clearly linked“,  is incorrect. For example, the American Meteorological Statement on Inadvertant Weather Modification states

This section summarizes the current knowledge of the physical processes affecting weather modification as a result of changes in land use, aerosol, and gas emissions.

a. Aerosol radiative effects

By partially blocking solar radiation from heating the surface, air pollutants lower surface heating and evaporation rates.  This slows vertical air motions, and hence causes slower dispersal rates of air pollutants, and suppresses formation of convective clouds and precipitation.  Reduced surface evaporation has major implications for the global hydrological cycle and how it responds to the combined forcing of GHGs, land use change, and aerosol pollution.  In addition, surface deposition of dark aerosols accelerates ice-melt rates, hence affecting water resources.  While these conclusions are based on sound physical meteorology, many of these effects are yet to be quantified.

b. Cloud-mediated effects of aerosol

Aerosols act mostly as cloud-drop condensation nuclei (CCN), and some of them as ice nuclei (IN), both of which change cloud radiative and precipitation properties in complex ways.  Over oceans, emissions from fossil-fuel-burning ships produce tracks, observed to dramatically influence the extent and persistence of local shallow cloud cover, reducing the amount of solar radiation received at the surface and enhancing the amount reflected back to space.  Aerosols also suppress precipitation from shallow or short-lived clouds (e.g., orographic cap clouds). Their impacts on deep convective clouds are much less certain, but are of potentially great importance.  Recent research suggests that, depending on meteorological conditions, aerosols can either increase or decrease rainfall from such clouds.  In warm moist atmospheres, aerosols often invigorate deep convective clouds, usually resulting in greater electrical activity, stronger damaging winds, and a greater likelihood of flash floods.  Studies indicate that aerosols might also modulate the intensity of tornadoes and hurricanes.


d. Integrated effects

The cumulative changes in surface and atmospheric heat and moisture profiles modify atmospheric circulation and weather patterns on all scales, including synoptic storm tracks, in ways that are just beginning to be explored.  In the aggregate, these changes can affect air quality, ecosystems, and water resources.  The cumulative impacts of inadvertent weather modification may thus result in local or regional-scale climatic alterations superimposed on, and interacting with, natural and GHG-induced climate variability and change. Understanding of inadvertent weather modification, still in its infancy, is thus necessary for understanding the sources, triggers, and response mechanisms of climate change.

The New Your Times article continues

Russell Dickerson, a professor of oceanic and atmospheric science at the University of Maryland, said the study “adds urgency to the need to control sulfur, nitrogen, and hydrocarbon emissions.”

My Comment: I completely agree with Russ on this recommendation.

Continuing with the New York Times article

In a reflection of the complexity of atmospheric science, however, a different new study suggests that aerosols created by humans are not all bad. The same clouds thickened by aerosols reduce temperatures by blocking sunlight, keeping the planet cooler than it otherwise would be, according to the article, which was published last week in the journal Science. And the aerosols themselves reflect sunlight back into space, which also acts to limit temperature increases.

My Comment:

This article discusses a supposed benefit of not reducing the input of aerosols since they can limit “temperature increases“.  I discuss the sacrifice to human health that would result from this inappropriate behavior in my post

Health Benefits Of Air Quality Control Should Never Be Sacrificed By Delaying The Clean-Up Of Aerosol Emissions For Climate Reasons

In that post I wrote

There have rather puzzling recommendations made recently in which improvements in air quality are recommended as being delayed in order to retain the radiative cooling effect of certain aerosols, particularly sulphates. Examples of such a recommendation are reported in the Climate Science weblogs

A Excellent Seminar At The University of Colorado at Boulder “What Goes Around Comes Around” By Gregory R. Carmichael

Further Comments on the Question “Can The Climate System ‘Mask’ Heat?”

Misconception And Oversimplification Of the Concept Of Global Warming By V. Ramanthan and Y. Feng

This recommendation is made despite evidence presented in the first weblog listed above, for example, that “350,000 excess deaths per year in India and China due to outdoor exposure risk for each 20mg/m3 (of fine aerosols of less than 2,5 microns).”   Such a recommendation applies to all types of aerosols which includes aerosols that contribute to radiative cooling (e.g. see Chapter 2 in the 2007 IPCC report and Chapter 2 in the 2005 NRC report for reviews of these negative radiative forcings).

I have worked throughout my career to improve air quality. This includes two terms on the Colorado Air Quality Control Commission where we implemented (and I supported) efforts such as the oxygenated fuels program to reduce atmospheric CO, strict regulations on wood and coal burning in residential fireplaces and stoves, and on asbestos concentrations. I was a member of an NRC committee that rejected an attempt to exempt certain locations such as Fairbanks Alaska from the national CO health standard; see

National Research Council, 2003: Managing carbon monoxide pollution in meteorological and topographical problem areas. The National Academies Press, Washington, DC, 196 pp,

and also an NRC committee to communicate the major concerns of overgrazing, which includes an increase in dust emissions into the atmosphere; see

Committee on Scholarly Communication with the People’s Republic of China, 1992: Grasslands and grassland sciences in Northern China, Office of International Affairs, National Research Council, National Academy Press, Washington, D.C., 214 pp.

I have taught graduate classes in air pollution at the University of Virginia and Colorado State University (even a class on the U.S. Wilderness System in which the preservation of pristine air quality is a major issue that we discussed).  I also was on  a committee in Fort Collins that mandated that the permit to construct and operate a brewrey near the city require the burning of natural gas rather than coal.

The motivation for all of these activities is to reduce human mortality and morbidity and to minimize negative environmental effects from air pollution.  

Thus, when I see attempts to delay implementation of any air quality improvement, which will cost lives, in order to provide a climate effect (i.e. through the delay in reducing sulphate emissions), we need to recognize that the priorities of those making such climate recommendations are misplaced.

The New York Times article continues

Yet there is a third factor, not widely recognized, said Natalie Mahowald, a climate researcher at Cornell University and author of the article in Science. Some artificial aerosols containing iron, nitrogen and phosphorus are fertilizers that settle on the planet and stimulate plant growth on land and phytoplankton in the ocean. Those plants take up more carbon dioxide and can thereby possibly mitigate global warming.

My Comment: This is the biogeochemical climate forcing that we present in our paper

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.

and in

Pielke Sr., Roger A., 2008: A Broader View of the Role of Humans in the Climate System is Required In the Assessment of Costs and Benefits of Effective Climate Policy. Written Testimony for the Subcommittee on Energy and Air Quality of the Committee on Energy and Commerce Hearing “Climate Change: Costs of Inaction” – Honorable Rick Boucher, Chairman. June 26, 2008, Washington, DC., 52 pp.

Continuing with the New York Times article, the supposed benefits of not reducing aerosols continues

It is not the first time that Catch-22 questions have been raised about climate science and the atmosphere. Some people argue, for example, that eliminating coal-fired power as an energy source could have drawbacks because the pollutants emitted would no longer be there to block sunlight and slow warming.

However, I agree with Dr. Mahowald where she is quoted as saying

Dr. Mahowald said aerosols obviously needed to be reined in regardless because such emissions “kill people.”

Still, “research shows it’s an uphill battle,” she said — and more uphill rhetorically “because those aerosols allow carbon dioxide to be taken up more readily on land and oceans.”

The New York Times article, while it is good to see a much-needed elevation of aerosols as a climate forcing, unfortunately, continues to perpetuate a misguided perspective on the role of aerosols in the environment by limiting their removal because it would reduce “global warming”.

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