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The Intergovernmental Panel on Climate Change (IPCC)

Many books have been written on the subject of climate change. Some are written by university professors teaching climatology. Others written by retired government administrators, science writers and newspaper men. One book was authored by a member of the U.S. Senate (Al Gore). Are there any trustworthy sources? What is the single most authoritative source for information on climate change and its relationship to human activities, as well as what we ought to do about it?

There is, in fact, such a trustworthy source: it is a body of working climate scientists known as the Intergovernmental Panel on Climate Change (IPCC). The IPCC was jointly established by the World Meteorological Organization and the United Nations Environment Program in 1988. The Panel established three working groups, whose tasks were 1) to assess available scientific information relevant to climate change, 2) to assess environmental and economic impacts of climate change, and 3) to formulate realistic response strategies for the management of the climate change issue.

The first report of the first working group was published in 1990. One hundred and seventy scientists from 25 countries contributed to the report and another 200 scientists were involved in reviewing the draft report before publication. The aim was to provide an authoritative statement of the views of the international scientific community. The list of contributors ended up being a kind of “Who's Who” in climate research. You can read more about the IPCC and its founder, Professor Bert Bolin, at: Global Change

The First IPCC Report
Here are some paraphrased scientific conclusions of the IPCC report published in 1990, which have held up very well over the past decade.:
  • We are certain that there is a natural greenhouse effect based on natural greenhouse gases which keeps the Earth warmer than it would be without it.
  • We are certain that emissions from human activities are substantially increasing the concentration of greenhouse gases in the atmosphere.
  • We are certain that this is true for carbon dioxide, methane, chlorofluorocarbons (CFCs) and nitrous oxide.
  • We are certain that this increase in gases will enhance the greenhouse effect and produce warming, and that the main greenhouse gas, water vapor, will increase in response to global warming, thus further enhancing it.
  • We calculate with confidence that carbon dioxide has been responsible for more than half of the enhanced greenhouse effect, and this is likely to remain so in the future.
  • We calculate with confidence that the long-lived gases (carbon dioxide, nitrous oxide and the CFCs) will be slow to respond to reduced emissions; thus, to stabilize concentrations at a given level, reductions should be earlier rather than later.
  • Based on current model results, we predict a rate of increase of global mean temperature during the next century of about 0.3°C (0.2 to 0.5°C) per decade if greenhouse emissions keep rising in the accustomed manner. This will increase the global mean temperature by about 1°C by 2025 and by about 3°C by 2100. The increase will be greater on land than in the ocean, and it will be greater in high latitudes than in low. Sea level will rise by two feet by 2100, mainly due to the thermal expansion of the ocean. There are many uncertainties in these predictions.
  • Our judgment is that the magnitude of global warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability. Thus, variability could explain the warming, or else variability could explain that it did not get even warmer. We shall not see the human effect clearly before another decade has passed.
The IPCC Third Assessment Report
There are two subsequent reports of the IPCC. The Second Assessment Report (SAR), published in 1995, came out with the often quoted conclusion that “the balance of evidence suggests a discernible human influence on global climate.”

The most recent Third Assessment Report (TAR) is being published this year (2001). The TAR is now the authoritative new benchmark of what we know about climate change . It represents an unprecedented consensus of hundreds of climate scientists from all over the world synthesizing what the global scientific community has learned in the past 5 years. The TAR was authored by more than 400 scientists and reviewed several times by approximately 2000 more. Compare the conclusions of the First Assessment Report to the paraphrased scientific conclusions of the IPCC Third Assessment Report published in 2001 below:

This chart shows the relative contribution of carbon dioxide (CO2) methane (CH4) chlorofluorocarbons (CFCs) and nitrous oxide (N2O) to the total concentration of greenhouse gases in the Earth’s atmosphere. Currently, atmospheric concentrations of CH4, CFCs and N2O are small relative to other greenhouse gases. These compounds, however, have the potential to greatly impact global warming due to their potency and extremely long amount of time that they spend in the atmosphere. (From: IPCC, 1996)
  • The global-average surface temperature has increased over the 20th century by about 0.6°C (this value is about 0.15°C larger than that estimated by the Second Assessment Report).
  • Snow cover and ice extent have decreased, and global average sea level has risen. It is very likely that the 20th century warming has contributed significantly to the observed sea level rise of between 0.1 and 0.2 meters during this time, due to thermal expansion of sea water and widespread loss of land ice.
  • Concentration of atmospheric greenhouse gases and their radiative forcing have continued to increase as a result of human activities.
  • This report contains a significantly stronger statement that the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations and is attributable to human activities.
  • Human influences will continue to change atmospheric composition throughout the 21st century.
  • Global average temperature and sea level are projected to rise under all IPCC projections of future climate, including continued future warming from past greenhouse gas emissions.

This chart shows the relative contribution of carbon dioxide (CO2) methane (CH4) chlorofluorocarbons (CFCs) and nitrous oxide (N2O) and stratospheric ozone to amount of Global Warming. (From: World Resource Institute, 1996)

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