Fourth Assessment Report of the Intergovernmental
Panel on Climate Change (IPCC)

The IPCC is currently finalizing its Fourth Assessment Report entitled Climate Change 2007. The reports by the three Working Groups provide a comprehensive and up-to-date assessment of the current state of knowledge on climate change.

As reported in the February issue of MeteoWorld online, first volume The Physical Science Basis, was released in Paris on 2 February 2007. Based on a thorough review of the most-up-to-date, peer-reviewed scientific literature available, it concludes that changes in the atmosphere, the oceans, glaciers and ice caps show unequivocally that the world is warming. Major advances in climate modelling and the collection and analysis of data have improved understanding of anthropogenic warming and cooling influences on climate since the Third Assessment Report in 2001, leading to very high confidence (at least a 9out of 10 chance of being correct) that the globally averaged net effect of human activities since 1750 has been one of warming.

The report confirms that global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750. It goes on to say that continued greenhouse-gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.

It describes an accelerating transition to a warmer world marked by more extreme temperatures, including heat waves, new wind patterns, worsening drought in some regions, heavier precipitation in others, melting glaciers and Arctic ice and rising global average sea-levels. 

For the first time, the report provides evidence that the ice sheets of the Antarctic and Greenland are slowly losing mass and contributing to sea-level rise.

The second volume Climate Change Impacts, Adaptation and Vulnerability was released in Brussels on 6 April. It concludes that the world’s rivers, lakes, wildlife, glaciers, permafrost, coastal zones, disease carriers and many other elements of the natural and physical environment are already responding to the effects of humanity’s greenhouse-gas emissions.

Scientists are increasingly confident that, as global warming continues, certain weather events and extremes will become more frequent, widespread or intense. Some events, in particular sea-level rise, have the potential for significant impacts on natural ecosystems, water resources and agricultural production in certain regions, especially after the 21st century.The IPCC also finds, however, that early action to improve seasonal climate forecasts, food security, freshwater supplies, disaster and emergency response, famine early-warning systems and insurance coverage, can minimize the damage from future climate change, while generating many immediate practical benefits.

The next volume—Mitigation of Climate Change—will be issued by Working Group III at its ninth session in Bangkok, Thailand, in May.

The Synthesis Report integrates the information around six topic areas. It will be issued at the 27th session of the IPCC in November 2007 in Valencia, Spain.

Progress in observations and measurements of the weather and climate are key to improved climate research, with National Meteorological and Hydrological Services playing a crucial role.