News Release – “Erratic Monsoon Rains May Be Caused By Black Carbon”

The evidence of a much more diverse range of human climate forcings continues to appear, as does the recognition that it is atmospheric circulation changes that matter much more than the global average surface temperature anomaly. The latest example of this wider view is reported in the article by Navin Singh Khadka

Is black carbon affecting the Asian monsoon?

The E&E Publishing Service  reports on this news article as follows

SCIENCE: Erratic monsoon rains may be caused by black carbon (Tuesday, July 12, 2011) [highlight added]

The South Asian monsoon season is underway, and many are concerned about the variability of rainfall in recent years, which scientists say may be linked to black carbon.

The erratic monsoon patterns over the past decade have caused drought and flooding in areas affected by unusually low or high rainfalls. These volatile conditions have a significant effect on agriculture and have sparked a rise in food prices.

Scientists have yet to determine the role of climate change in these unusual weather patterns, but many are also pointing to particles of black carbon from the incomplete combustion of fossil fuels for changing the characteristics of the monsoon. A recent report by the U.N. Environment Programme (UNEP) and the World Meteorological Organization (WMO) further underscores the position that concentrations of black carbon and troposphere ozone in the lower atmosphere could disrupt monsoon rains.

They disturb tropical rainfall and regional circulation patterns such as the Asian monsoon, affecting the livelihoods of millions of people,” the latest report reads. “While some aspects of these effects are local, they can also affect temperature, cloudiness, and precipitation far away from emission sources.”

But this conclusion has not gone unchallenged. The Indian Network for Climate Change Assessment (INCCA) identified studies with conflicting statements on the impact of black carbon on monsoon patterns. INCCA said in a statement that research showing both greater and lesser levels of rainfall needs to be better understood before conclusions on the role of aerosols can be made. Authors of the UNEP/WMO report, however, insist the effects of black carbon can be confirmed.

“I have to indicate that the basic conclusion that black carbon aerosol forcing over South Asia is large enough to perturb the monsoon system is reached by all the studies so far; therefore, there is no different opinion here,” Chien Wang of the Massachusetts Institute of Technology, one of the experts in the report, told BBC News.

India and its regional competitor China both rely heavily on fossil fuels, which are among the main contributors to black carbon emissions, as a source of energy (Navin Singh Khadka, BBC News, July 8). —

This broader view of the human role on climate was summarized 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

where we wrote

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].”

We documented this large role of aerosols in affecting regional circulations through alterations in atmospheric diabatic heating in our paper

Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974

where we wrote

“This paper diagnoses the spatial mean and the spatial gradient of the aerosol radiative forcing in comparison with those of well-mixed green-house gases (GHG). Unlike GHG, aerosols have much greater spatial heterogeneity in their radiative forcing. The heterogeneous diabatic heating can modulate the gradient in horizontal pressure field and atmospheric circulations, thus altering the regional climate.”

The new BBC report on the effect of black carbon on the Asian monsoon further bolsters the conclusion on the existence of a wide diversity of human influences on weather patterns that affect society and the environment.

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