In early 2001, the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) was published. The report contains proven scientific facts of global warming and provides an objective review of observed changes of the climate system and underlying factors, that generate these changes.

Global warming is associated with substantial, maybe even disastrous consequences for the natural environment and the humankind. The problem is of global significance; it affects all countries and regions. The nature of the climate change is defined by both the natural phenomena and anthropogenic factors - i.e. greenhouse gases emissions.

The third IPCC Assessment Report was developed by 123 authors. Materials for the report were provided by more than 500 experts, more than 300 experts developed comments and proposals for the report, that were incorporated into the final version. Besides that Assessment Report itself, Summaries for Policymakers were published..

The climate change has been proven

The First IPCC Working Group has proven that the climate changes and becomes warmer. In 20th century average surface temperatures increased by 0.6°C. 20th century seems to be the warmest century of the last millennium, while 1990s seem to the warmest decade of the last millennium.

According to satellite observations, since late 1960s, the snow cover area decreases by about 10%. Lake and river ice seasons became shorter (by about 2 weeks) at medium and high latitudes of the Northern Hemisphere. Decrease of mountainous glaciers was observed in all non-polar regions. The area of sea ice in spring and summer periods in the Northern Hemisphere decreased almost by 10-15%. In late summer - early autumn periods, sea ice thickness decreased by 40%.

In 20th century, average sea level increase reached 0.1 - 0.2m. In the majority of middle and high latitude regions of the Northern Hemisphere, atmosphere precipitation increased by 0.5-1%.

In the last decade, in some regions of Africa and Asia, the frequency and intensity of drought have been observed to increase. Since 1950s, warm El-Nino events became more frequent, stable and intensive.

Causes of the climate change

Responses of the climate system to anthropogenic impacts are masked by natural climate fluctuations, ranging from a few weeks to several ages. All computer simulations, based on global climate models, accounting for observed growth of concentrations of greenhouse gases and aerosols, suggest a major contribution of anthropogenic factors into changes of surface temperatures in the last four decades.

It is absolutely clear that warming of the last 50 years cannot be attributed to natural changes only, however, it may be well described by joint impacts of anthropogenic and natural factors.

To a rather substantial extent, the climate change may be attributed to growing releases of greenhouse gases. Let us remind, that the key greenhouse gases incorporate CO₂, methane, nitrogen oxides and some artificial gases (e.g. freons). Concentrations of all greenhouse gases continue to grow rapidly, today's concentration of carbon dioxide is higher than in any period of time in recent 420000 years, maybe even higher than in any time of the last 20 million years. For example, according to IPCC, comparatively to 1750, in 2000, atmosphere concentrations of carbon dioxide increased by 31%. In two past decades, CO₂ concentrations in the atmosphere increased by about 0.4% annually. In 1990s, concentrations of CO₂ increased by 0.2-0.8% annually.

About 3/4 of all anthropogenic emissions of carbon dioxide in the last 20 years were caused by burning of fossil fuel. Other emissions were associated with industrial processes, land use changes and (especially) with deforestation. According to IPCC report, about a half of all anthropogenic emissions of carbon dioxide are adsorbed by the ocean and land surface.

Anthropogenic impacts will continue to affect the atmosphere and the Earth climate in 21st century. According to expert assessments, if no measures will be taken to reduce emissions of CO₂ and other greenhouse gases, in the period from 1990 to 2100, average surface temperatures would increase by 1.5-1.8°C, while in the Northern Hemisphere the temperature increase would be even higher.

It is fairly probable, that the temperature increase will result in rise of the sea level by about 40cm (a rough estimate), in higher frequency of storms and other natural disasters, e.g. rainstorms that might flood large land areas. Polar caps and mountainous glaciers would decrease, except in Antarctica. In Arctic regions (Siberia, Alaska, etc.) permafrost-melting process would start. All these phenomena might further aggravate the greenhouse effect.

In subsequent centuries, climate changes would continue, and if we fail to reduce the role of anthropogenic factors in the process, consequences of the global warming might be substantially graver. The sea level might increase by up to 3 metres, as a result, the Gulf Stream might disappear.

According to the Second Working Group of IPCC, some particular ecosystems are especially vulnerable to impacts of the climate change. Some of them may be completely destroyed, including coral reefs, boreal forest and tropical rainforest, steppe marches and natural grasslands.

Similar trends will continue for the whole 21st century and later on. In some regions of Africa, frequency and intensity of droughts will increase due to reduction of precipitation. In many Asian countries, growing intensity of tropic cyclones and rising sea levels will result in flooding of large areas of cultivated land, causing problems of food supply. Serious problems of drinking water shortage will affect Australia and New Zealand, due to longer dry seasons. In Europe, a large part of the continent will become prone to water floods. In Latin America, higher incidence of both floods and droughts will be observed. In North America, rising sea level will intensify soil erosion in coastal areas. Higher risks of storms will be observed in Florida and along the whole Atlantic coast of the America.

The climate change will result in serious adverse impacts on human activities. The global warming will result in reduction of crop yields at the territories located in the majority of tropic, sub tropic and middle latitudes, in higher frequency of floods, shortages of drinking water, in spread of diseases (including cholera and malaria).

A country's capacity to adapt to the climate change depends on its economic potential. Naturally, the poorest developing countries are among the most vulnerable ones. They have the right to demand from industrialised countries, which are responsible for the bulk of greenhouse gases emissions, to implement decisive measures for reduction of adverse consequences of the climate change.

Mr. Klaus Topfer, the Executive Director of UNEP, believes, that it is absolutely necessary to realise the serious consequences of economic development of industrialised countries and to foresee them. It is important to protect the most vulnerable ecosystems, trying to adapt them to new climate conditions. Mr. Klaus Topfer believes, that even now, national governments have to account for the new circumstances in their long-term planning of national economic development.

Options for reduction of GHG emissions

The Third IPCC Working Group assessed options for abatement of adverse impact of the climate change, focusing mainly on reduction of anthropogenic emissions of greenhouse gases. The range of the most important options was found to incorporate: higher energy efficiency, efficient use of natural gas, use of fuel of low carbon contents (e.g. biomass fuels) and use of renewable sources of energy. Experts think, that application of a mix of these measures may result by 2020 in annual reduction of GHG emissions by 3.6-5 billion tons of carbon equivalent (or about 43 - 60% of contemporary GHG emissions).

Additional information:

See also: IPCC summaries for policy-makers and technical summaries at www.ipcc.ch (in the English language).

See NGO analysis of the greenhouse effect and required climate policies at www.climnet.org (in the English language)