IPCC Report: Why It Matters

The Intergovernmental Panel on Climate Change (IPCC) prepares comprehensive Assessment Reports on climate change, its origin, potential impacts and response options.

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By Tod Ginnis


Estimated reading time: 5 minutes, 29 seconds

The Intergovernmental Panel on Climate Change (IPCC) prepares comprehensive Assessment Reports on climate change, its origin, potential impacts and response options. The IPCC also produces Special Reports, which are an assessment on a specific issue, and Methodology Reports, which provide guidelines that countries use to estimate their anthropogenic (human-induced) emissions by sources and sinks (removals) of greenhouse gases (GHGs).

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The Intergovernmental Panel on Climate Change (IPCC) prepares comprehensive Assessment Reports on climate change, its origin, potential impacts and response options. The IPCC has grown from a scientific and climate change-related clearinghouse about manmade global warming to an influential global thought leader.

Influence of the IPCC

The IPCC was established in 1988 as an intergovernmental body of the United Nations. Its purpose is to provide objective, scientific information relevant to understanding anthropogenic climate change. The IPCC also looks at potential political and economic risks of climate change, as well as possible responses. The IPCC has developed into the main institution for synthesizing scientific knowledge in its field.

In “Exploring the impact of the IPCC Assessment Reports on science,” the authors found that each Assessment Report has had more impact on scientific publications than the one before it. In addition, they suggest the IPCC has been very influential at getting policymakers and the media globally to focus on climate change. Indeed, the IPCC even won a Nobel Peace Prize in 2007.

Assessment Reports

The IPCC has issued a major Assessment report every five to seven years. Here is a summary of their findings:

First Assessment Report (1990)

  • We are certain of the following: there is a natural greenhouse effect; emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: carbon dioxide (CO2), methane, chlorofluorocarbons (CFCs) and nitrous oxide. These increases will enhance the greenhouse effect, resulting in an additional warming of the Earth’s surface. The main greenhouse gas, water vapor, will increase in response to global warming and further enhance it.
  • We calculate with confidence that CO2 has been responsible for over half the enhanced greenhouse effect; long-lived gases would require immediate reductions in emissions from human activities of over 60% to stabilize their concentrations at today’s levels.
  • Based on current models, we predict an increase of global mean temperature during the 21st century of about 0.3 degree Celsius per decade (with an uncertainty range of 0.2 to 0.5 C per decade); this is greater than that seen over the past 10,000 years.
  • There are many uncertainties in our predictions particularly regarding the timing, magnitude and regional patterns of climate change, due to our incomplete understanding of sources and sinks of GHGs, clouds, oceans and polar ice sheets.
  • Our judgement is that global mean surface air temperature has increased by 0.3 to 0.6 C over the last 100 years. The size of this warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability. Thus, the observed increase could be largely due to this natural variability. Alternatively, this variability and other human factors could have offset a still larger human-induced greenhouse warming. The unequivocal detection of the enhanced greenhouse effect is not likely for a decade or more.
  • Under the IPCC business as usual emissions scenario, an average rate of global mean sea level rise of about 6 cm per decade over the next century (with an uncertainty range of 3-10 cm per decade), mainly due to thermal expansion of the oceans and the melting of some land ice. The predicted rise is about 20 cm by 2030, and 65 cm by the end of the next century.

Second Assessment Report (1995)

  • Greenhouse gas concentrations are increasing.
  • The global climate has been changing, and will likely continue to change, probably due to human influence.
  • CO2 remains the most important contributor to anthropogenic forcing of climate change.
  • Projections of future global mean temperature change and sea level rise confirm the potential for human activities to alter the Earth’s climate to an extent unprecedented in human history.
  • The long timescales governing both the accumulation of greenhouse gases in the atmosphere and the response of the climate system to those accumulations means that many important aspects of climate change are effectively irreversible.
  • Very substantial cuts in emissions would be required to stabilize greenhouse gas concentrations.
  • There was significant debate on the topic of the value of a statistical life for assessing damages.

Third Assessment Report (2001)

  • “The balance of evidence suggests … a discernible human influence on global climate.” This language encouraged governments to work together on what eventually would become the Kyoto Protocol.
  • It confirmed the findings of the 2nd Assessment Report, finding additional and stronger evidence that the planet is warming.
  • Future warming will have both beneficial and adverse effects, but for higher levels of warming, adverse effects will predominate.
  • Developing countries and poor persons are most vulnerable to climate change.

Fourth Assessment Report (2007)

  • Warming of the climate system is unequivocal.
  • Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.
  • Concentrations of long-lived greenhouse gases like CO2, methane and nitrous oxide in the atmosphere have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial levels.
  • The amount of CO2 in the atmosphere in 2005 (379 ppm) exceeds by far the natural range of the last 650,000 years (180 to 300 ppm).
  • The primary source of the increase in COis fossil fuel use, but land-use changes also contribute.
  • Cold days, cold nights, and frost events have become less frequent. Hot days, hot nights, and heat waves have become more frequent.
  • Observations since 1961 show that the ocean has been absorbing more than 80% of the heat added to the climate system and that ocean temperatures have increased to depths of at least 3000 m (9800 ft).
  • Average Northern Hemisphere temperatures during the second half of the 20th century were likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years.
  • Losses from the land-based ice sheets of Greenland and Antarctica have very likely (>90%) contributed to sea level rise between 1993 and 2003.

Fifth Assessment Report (2014)

  • There is a 95% certainty that human activities are responsible for global warming.
  • Carbon dioxide is at an “unprecedented” level not seen in at least 800,000 years.
  • Sea level is set to continue to rise at a faster rate than over the past 40 years.
  • Over the last 2 decades, the Greenland and Antarctic ice sheets have been melting and glaciers have receded in most parts of the world.


The IPCC was formed as a scientific clearinghouse related to human-induced climate change. But in the three decades since its formation, it has become extremely influential. Its assessments are embraced by politicians and media around the world. Often IPCC conclusions and language are the focus of debates. Its global scale has conferred on it the mark of authority.