Soot and Climate Change – A New Article By Jacobson 2010

The article is

Jacobson, M. Z. (2010), Short‐term effects of controlling fossil‐fuel soot, biofuel soot and gases, and methane on climate, Arctic ice, and air pollution health, J. Geophys. Res., 115, D14209, doi:10.1029/2009JD013795.

The abstract reads

“This study examines the short‐term (∼15 year) effects of controlling fossil‐fuel soot (FS) (black carbon (BC), primary organic matter (POM), and S(IV) (H2SO4(aq), HSO4−, and SO42−)), solid‐biofuel soot and gases (BSG) (BC, POM, S(IV), K+, Na+, Ca2+, Mg2+, NH4+, NO3−, Cl− and several dozen gases, including CO2 and CH4), and methane on global and Arctic temperatures, cloudiness, precipitation, and atmospheric composition. Climate response simulations were run with GATOR‐GCMOM, accounting for both microphysical (indirect) and radiative effects of aerosols on clouds and precipitation. The model treated discrete size‐resolved aging and internal mixing of aerosol soot, discrete size‐resolved evolution of clouds/precipitation from externally and internally mixed aerosol particles, and soot absorption in aerosols, clouds/precipitation, and snow/sea ice. Eliminating FS, FS+BSG (FSBSG), and CH4 in isolation were found to reduce global surface air temperatures by a statistically significant 0.3–0.5 K, 0.4–0.7 K, and 0.2–0.4 K, respectively, averaged over 15 years. As net global warming (0.7–0.8 K) is due mostly to gross pollutant warming from fossil‐fuel greenhouse gases (2–2.4 K), and FSBSG (0.4–0.7 K) offset by cooling due to non‐FSBSG aerosol particles (−1.7 to −2.3 K), removing FS and FSBSG may reduce 13–16% and 17–23%, respectively, of gross warming to date. Reducing FS, FSBSG, and CH4 in isolation may reduce warming above the Arctic Circle by up to ∼1.2 K, ∼1.7 K, and ∼0.9 K, respectively. Both FS and BSG contribute to warming, but FS is a stronger contributor per unit mass emission. However, BSG may cause 8 times more mortality than FS. The global e‐folding lifetime of emitted BC (from all fossil sources) against internal mixing by coagulation was ∼3 h, similar to data, and that of all BC against dry plus wet removal was ∼4.7 days. About 90% of emitted FS BC mass was lost to internal mixing by coagulation, ∼7% to wet removal, ∼3% to dry removal, and a residual remaining airborne. Of all emitted plus internally mixed BC, ∼92% was wet removed and ∼8% dry removed, with a residual remaining airborne. The 20 and 100 year surface temperature response per unit continuous emissions (STRE) (similar to global warming potentials (GWPs)) of BC in FS were 4500–7200 and 2900–4600, respectively; those of BC in BSG were 2100–4000 and 1060–2020, respectively; and those of CH4 were 52–92 and 29–63, respectively. Thus, FSBSG may be the second leading cause of warming after CO2. Controlling FS and BSG may be a faster method of reducing Arctic ice loss and global warming than other options, including controlling CH4 or CO2, although all controls are needed.”

As Bill pointed out in an e-mail, this paper is further confirmation that hypothesis 2a in

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.

is the correct one. Hypothesis 2a reads

“Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first- order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concernduring the coming decades.”

and that

“In addition to greenhouse gas emissions, other first-order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005].”

There is an AGU press release on this article, and excerpts from the release are reproduced below:

The study shows that soot is second only to carbon dioxide in contributing to global warming. But, climate models to date have mischaracterized the effects of soot in the atmosphere, said its author Mark Z. Jacobson of Stanford University in Stanford, California. Because of that, soot’s contribution to global warming has been ignored completely in national and international global warming policy legislation, he said.

“Controlling soot may be the only method of significantly slowing Arctic warming within the next two decades,” said Jacobson, director of Stanford’s Atmosphere/Energy Program. “We have to start taking its effects into account in planning our mitigation efforts and the sooner we start making changes, the better.”

“Soot — black and brown particles that absorb solar radiation — comes from two types of sources: fossil fuels such as diesel, coal, gasoline, jet fuel; and solid biofuels such as wood, manure, dung, and other solid biomass used for home heating and cooking around the world.

Jacobson found that the combination of the two types of soot is the second-leading cause of global warming after carbon dioxide. That ranks the effects of soot ahead of methane, an important greenhouse gas. He also found that soot emissions kill over 1.5 million people prematurely worldwide each year, and afflicts millions more with respiratory illness, cardiovascular disease, and asthma, mostly in the developing world where biofuels are used for home heating and cooking.

Jacobson found that eliminating soot produced by the burning of fossil fuel and solid biofuel could reduce warming above parts of the Arctic Circle in the next fifteen years by up to 1.7 degrees Celsius (3 degrees Fahrenheit). For perspective, net warming in the Arctic has been at least 2.5 degrees Celsius (4.5 degrees Fahrenheit) over the last century and is expected to warm significantly more in the future if nothing is done.”

There is another summary of this article that Bill alerted us to with a model simulation graph:  http://www.wired.com/wiredscience/2010/07/soot-control/

This is yet another peer reviewed study that highlights the incompleteness of the 2007 IPCC assessment reports.

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