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UNEP study examines climate impact of black carbon and tropospheric ozone

22 February 2011

The United Nations Environment Programme (UNEP) has released a new report—titled “Integrated Assessment of Black Carbon and Tropospheric Ozone”—that examines the role of black carbon and tropospheric ozone, including ozone precursors methane and carbon monoxide, in climate change. The main findings of the assessment are:

  1. A small number of emissions reduction measures targeting black carbon and tropospheric ozone could immediately begin to protect climate, public health, water and food security, and ecosystems. These measures target fossil fuel extraction, residential cooking and heating, diesel vehicles, waste management, agriculture and small industries. Full implementation is achievable with existing technology but would require significant and strategic investment as well as institutional arrangements.
  2. The identified measures complement, but do not replace, anticipated CO2 reduction measures. Major carbon dioxide reduction strategies mainly target the energy and large industrial sectors and therefore would not necessarily result in significant reductions in emissions of the black carbon or ozone precursors—methane and carbon monoxide. Significant reductions of black carbon and O3, require a specific strategy, as emissions come from a large number of small sources.
  3. Full implementation of these measures would reduce future global warming by 0.5°C (within a likely range of 0.2-0.7°C). If the measures are implemented by 2030, this could halve the potential increase in global temperature which is projected for 2050. The rate of regional temperature increase would also be reduced.
  4. Both near-term and long-term strategies are essential. Reductions in near-term warming can be achieved by control of black carbon and O3 whereas CO2 emission reductions, beginning now, are required to limit long-term climate change. Implementing both reduction strategies is needed to improve the chances of keeping the Earth’s global mean temperature increase to within UNFCCC’s 2°C target.
  5. The implementation of the identified measures would have substantial benefits in the Arctic, the Himalayas, and other glaciated and snow-covered regions.
  6. These measures are all in use in different regions around the world. Much wider implementation is required to achieve the full benefits identified in this assessment.

The report emphasizes that the benefits from emission reductions of black carbon, ozone and its precursors—species that have a short life span in the atmosphere—can come quickly, in years to a couple of decades. This is in contrast to emission reductions of CO2, which are essential to avoid climate warming in the longer term.

Among measures to reduce black carbon emissions, the assessment identifies the diesel particulate filter technology and endorses retrofits of existing diesel engines with particulate filters. The report references diesel retrofit programs in Santiago, New York and London.

The report relies on published literature and on new simulations by two independent climate-chemistry-aerosol models: one developed at the NASA-Goddard Institute of Space Studies (NASA-GISS) and another developed by the Max Plank Institute in Hamburg and implemented at the European Commission’s Joint Research Centre. The specific measures and emission estimates for use in developing this assessment were selected using the International Institute for Applied Systems Analysis’ Greenhouse Gas and Air Pollution Interactions and Synergies (IIASA GAINS) model.

The Summary for Decision Makers of the assessment will be presented at the 26th session of the Governing Council / Global Ministerial Environment Forum (GC/GMEF) of UNEP from 21-24 February 2011 in Nairobi, Kenya.

Source: UNEP (Press release | Summary for decision makers)