On November 17, 2007 in Valencia, Spain, Dr. R.K. Pachauri, Chair of the Intergovernmental Panel on Climate Change ("IPCC"), released the 4th Vol. of the Fourth Assessment Synthesis Report ("Fourth Assessment Report") on climate change. The IPCC has released the detailed fourth report in several volumes over the course of 2007. The first volume was released in February and covered the physical science foundation for climate change. The second volume was released in March and covered climate change impacts, adaptation and outcomes on human infrastructure and ecosystems. The third volume was released in April and it covered mitigation options. The Fourth Assessment Report is a synthesis of these volumes. This analysis represents the work of over 2,500 scientific experts from over 130 countries.

The Third Report was released in 2001. The Fourth Assessment Report represents important changes over the Third Report from 2001. The Fourth Assessment Report assigns greater weight to resolving specific sectoral mitigation options and their costs, and provides more focus on regional issues and more emphasis on cross cutting issues?for example, policy decision making contexts impacting mitigation options. In essence, the Fourth Assessment Report shows more clearly the impacts of climate change and the strengths and limitations of various mitigation options.

The following note provides a summary of the key findings of the Fourth Assessment Report.

Observed Changes in climate and their effects:

The evidence that the overall climate system is warming is now firmly established from observations of increases in global average air and ocean temperatures, widespread melting of ice and snow and the rising average sea level. Eleven of the past 12 years now rank among the 12 warmest years on record. The 100 year trend (1906-2005) shows a significant increase of 0.92 degrees C. Average Northern Hemisphere temperatures are described as ?very likely? higher than the last 1,300 years.

Sea levels are rising consistent with warming temperatures. The global average sea level has risen since 1961 at an average rate of 1.8 mm/per year and since 1993 at 3.1 mm/per year. This is attributable to melting glaciers, ice caps and polar ice sheets. Projected sea level rise at the end of the 21st century will be 18-59 cm.

The frequency of heavy precipitation has increased over most areas of the globe. From 1900 to 2005, precipitation increased in eastern parts of North and South America, northern Europe and northern and central Asia, but declined in the Mediterranean, southern Africa and parts of southern Asia. Changes in snow, ice and frozen ground have increased the number and size of glacial lakes, increased ground instability in mountain and other permafrost regions and have led to changes in some Arctic and Antarctic ecosystems.

Terrestrial ecosystems are now seeing earlier spring events and upward shifts in plant and animal ranges linked with temperature warming. Marine and freshwater systems are witnessing changes consistent with rising sea temperatures. Large scale and persistent changes in circulation patterns will have negative impacts on ecosystem productivity, fisheries, and terrestrial vegetation.

More than 75 studies show significant changes in physical and biological systems consistent with global warming. Approximately 20-39% of species assessed so far are likely to be at increased risk of extinction.

Causes of Change: Growth in Greenhouse Gas Emissions:

Global Greenhouse gas ("GHG") emissions from human activity have grown 70% since 1970. Carbon Dioxide (CO2) as grown by 80%. Atmospheric concentrations of CO2, methane, and nitrous oxide have increased as well although there has been some recent stabilization of CO2 growth. These changes are attributable to fossil fuel consumption and land use changes over the past several hundred years.

Growth of GHG Emissions will Continue:

Evidence suggests that even with a range of GHG mitigation strategies in place, emissions will continue to grow. The IPCC Special Report on Emissions Scenarios (2000) projects an increase of global GHG emissions by 25-90% between 2000 and 2030 with fossil fuels maintaining their dominant position in the global energy mix. This means further warming would occur, inducing many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.


Africa by 2020:

Between 75 million and 250 million people will be exposed to water shortages. Yields from rain-fed agriculture would be reduced by 50% thus compromising access to food. Towards the end of the 21st century, sea levels will rise to affect low lying coastal regions with large populations. By 2080, an increase of 5-8% of arid and semi-arid land in Africa is projected.

North America:

Intensity, frequency and duration of heat waves will increase, and warming in western mountain regions will increase winter flooding and decrease summer water stocks. In summary, extreme weather situations will increase in duration, frequency and intensity thus placing significant burdens on human and natural ecosystems. In addition, climate change is likely to lead to irreversible impacts such as the elimination of species and marine ecosystems.


The Fourth Assessment Report identifies and discusses a number of options to manage the impacts of climate change by economic sector. The conclusion is that a large number of policy choices face governments globally, but more extensive work to curb GHG emissions is critical to reduce climate change impacts. GHG emissions can be stabilized by the deployment of a portfolio of technologies that are currently available or through technologies in the final stages of commercialization. The leading policy option is an carbon price signal or the establishment of an international carbon offset market.

In terms of the energy sector, the report outlines a number of possible options, including:

  • reduction of fossil fuel subsidies
  • carbon taxes on fossil fuels
  • feed in tariffs for renewable generation
  • renewable energy requirements and subsidies.

The costs of moving forward with the various GHG mitigation options are broken down by economic sector and vary according the stringency of the stabilization target. The Fourth Assessment Report estimates that by 2050, the global average macro-economic costs for stabilizing GHG emissions between 710 and 445 ppm C02 equivalent are between a 1% gain in global gross domestic product or a 5.5% decrease in GDP.


In summary, the Fourth Assessment Report suggests that neither adaptation nor mitigation of GHG levels alone can avoid all climate change impacts but they can significantly reduce the risks of climate change. As the report states:

"Mitigation efforts and investments over the next two to three decades will have a large impact on opportunities to achieve lower stabilization levels. Delayed emission reductions significantly constrain the opportunities to achieve lower stabilization levels and increase the risk of more severe climate change impacts."(page 20).

For further information on the Fourth Report see