Atmospheric Brown Clouds (ABC)

After more than a century of scientific studies on greenhouse gases (GHGs) and chlorofluorocarbons (CFCs), we have today a fair understanding of the global warming and ozone hole issues. Many studies as well as policies are under implementation to better understand and address these issues.

Recent scientific studies have revealed a new atmospheric issue: Atmospheric Brown Clouds (ABC). ABC is an emerging regional climate change issue. 

Atmospheric brown clouds (ABC), observed as widespread layers of brownish haze, are regional scale plumes of air pollutants, consisting of mainly aerosol particles, such as black carbon (BC), and precursor gases which produce aerosols and ozone. ABCs and their interaction with build-up of greenhouse gases (GHGs) significantly affect the regional climate, hydrological cycle, glacial melting, agriculture and human health. The effect of ABCs on climate, hydrological cycle, glacier melting, agriculture and human health is an outstanding problem which prevents a complete understanding of climate change and its impacts, and needs to be more fully explored.

Through the studies initiated under ABC project, scientists now have an overall view of the major sources and the global scale nature of the brown cloud problem. The recent studies show that the aerosols in ABC reduce the amount of sunlight reaching the Earths surface by as much as 10 to 15%, and enhance atmospheric solar heating by as much as 50%. Thus, ABCs, on the one hand, mask the greenhouse warming by the surface dimming, while on the other hand enhance the greenhouse warming of the atmosphere. While confirming that ABCs may have masked global warming by as much as 50% (see also IPCC, 2007), studies conducted by ABC scientists have led to new findings on regional climate changes:

• Slowing down of the monsoon circulation and reduction in monsoon rainfall.
• Increase strength and frequency of winter and spring time temperature inversion.
• Enhancing the greenhouse warming of the atmosphere thus contributing to glacier melting.

Preliminary assessment of the impacts identified potential direct and indirect consequences of the haze. These impacts include:

• Impacts on regional temperature, climate and marine and terrestrial ecosystems
• Impacts on precipitation patterns and water budgets
• Impacts on agriculture
• Impacts on human health

Climate-Agro-Economic crop modeling studies initiated by ABC scientists show that ABCs and GHGs together may have reduced rice production in Indian rain-fed states by as much as 15% since 1980s.

Global Distribution of ABC and Regional Hot Spots :  By combining ABC surface observations with new satellite observations and chemistry-transport models, ABC scientists have produced global maps of ABCs with regional hotspots, their climate forcing and preliminary assessment of impacts on regional climate. The major regional hotspots are;

[Left Panel] Global extent ofglobal dimming(reduction of solar radiation at the Earth's surface), and [Right Panel] atmospheric solar heating (due to absorption of solar radiation in the atmosphere) by atmospheric brown clouds for 2000 to 2003 developed from a combinations of satellite observations, surface network and aerosol transport models. [Ref: Ramanathan et al, ABC-special issue, Journal of Geophysical Research, 2007].

• Indo Gangetic Plain in South Asia (Northwest to northeast region extending from eastern Pakistan, across India to Bangladesh and Myanmar)
• East Asia (Eastern China, Thailand, Vietnam & Cambodia)
• Indonesian Region
• Southern Africa extending southwards from sub-Saharan Africa into Angola, Zambia and Zimbabwe
• The Amazon basin in South America

Project Atmospheric Brown Cloud (ABC): A preliminary assessment using the Indian Ocean Experiment (INDOEX) research was completed and the potential impacts caused by brown clouds on human health, food security and the water were disseminated in 2002. In recognition of scientific findings from INDOEX and other subsequent studies, UNEP has facilitated an international science team to look into observation, science and impacts of ABC on regional climate, water budget, agriculture and human health. The aim of Project Atmospheric Brown Cloud (ABC) is to better understand the science and its impacts in order to provide a scientific basis for informed decision making. The project implementation includes:

• ABC Observatories and Capacity Building: capacity building for scientific community through training and establishment of observatories;
  
   
• Impact Assesment: capacity building of network of institutions to carry out impact assessment studies, and
  
   
• Awareness, Mitigation and Dissemination: policy level discussion on any action that may be needed to reduce and mitigate the impacts.

Capacity building activities are being implemented through establishment of ABC observatories (over a dozen by 2006), either new or upgrading the existing sites, and training programs for Asian scientists. Through training and provision of equipments the stations are under national management.

ABC Observatories:

1. Maldives Climate Observatory- Hanimaadhoo (MCO-H)
2. Maldives Climate Observatory- Gan (MCO-G)
3. Indian Climate Observatory - Pune (ICO-P)
4. Indian Climate Observatory - Kharagpur (ICO-K)
5. Nepal Climate Observatory - Godavari (NCO-G)
6. Nepal Climate Observatory - Pyramid (NCO-P)
7. Thailand Climate Observatory - Phimai (TCO-P)
8. Japan Climate observatory - Okinawa (JCO-O)
9. Korea Climate Observatory - Gosan (KCO-G)
10. Pacific Climate Observatory - Momote (PCO-MT)
11. Pacific Climate Observatory - Midway (PCO-MW)
12. Pacific Climate Observatory - Mauna Loa (PCO-ML)
13. National Atmospheric and Climate Observatory - Trinidad Head (NACO-T)

• Indian Agriculture Research Institute (IARI), India [Agriculture]
• Nanyang Technological University (NTU), Singapore [Water Budgets]
• Chulabhorn Research Institute (CRI), Thailand [Human Health]

The first compresensive impact assessment report "Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia" was published in November 2008. 

ABC Phase II: 

With the successful establishment of a network of ABC observatories, establishment of ABC impact assessment groups and initiation of impact assessment studies, the project ABC has successfully completed its Phase I that has laid solid foundation for embanking in to Phase II for long-term monitoring of ABC, expansion to other regional hotspots, comprehensive and scientific impact assessment studies, dissemination of findings and initiation of policy level dialogues.

Currently , Project Covers 3 regions: ABC-Asia, ABC Africa and ABC-Latin America and Caribbean

The major activities of the project ABC in Phase II are (i) Continuation of observatory program in Asia and consolidated modeling of impacts of ABCs, (ii) Impact assessment ( Regional climate change, hydrological cycle and water resources, agriculture and public health, (iv) Mitigation ( Development of Emission INventory and demonstration of mitigation in residential sector through Project Surya, (iv) Policy consultations.