IPCC Fifth Assessment Report

What is the IPCC and why is it important?

The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for the assessment of climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide the world with a clear scientific review of the current state of knowledge on climate change.

Thousands of scientists from all over the world volunteer and are selected to review and assess the latest relevant scientific, technical and socio-economic data to understand climate change, its potential impacts, and options for adaptation and mitigation. The IPCC aims to reflect a range of views and expertise in order to publish comprehensive and objective assessments.

The IPCC does not conduct independent research, rather it convenes climate experts from around the world every five to seven years to synthesize the latest climate research findings in peer-reviewed and published scientific/technical literature. The IPCC issued comprehensive assessments in 1990, 1995, 2001, 2007 and 2014.

IPCC reports are never policy prescriptive but the conclusions are relevant to nations, states, and businesses interested in enacting policies to limit future warming and reduce the costs of climate change.

What is the Fifth Assessment report?

The Fifth Assessment Report (AR5) is the latest in a series of reports from the IPCC assessing scientific, technical, and socio-economic information regarding climate change. It was released in three installments over the course of 2013 and 2014, and an additional synthesis report was published in November 2014.

More than 830 scientists are involved in writing the reports and hundreds more will review and edit the draft reports.

AR5 is broken up into three sections, or working groups:

  • Working Group I provides a comprehensive assessment of the physical science basis of climate change: Released Sept. 27, 2013.
  • Working Group II assesses the scientific, technical, environmental, economic and social aspects of vulnerability to climate change as well as consequences for ecological systems, socio-economic sectors and human health: Released March 31, 2014.
  • Working Group III assesses all relevant options for mitigating climate change through limiting or preventing greenhouse gas emissions and taking actions to remove them from the atmosphere: Released April 11, 2014.

The syntheses report was released Nov. 2, 2014

Each working group report has a Summary for Policymakers that distills the key points from the hundreds of pages found in the respective full report. The Summary for Policymakers tend to be of most interest to the media and non-scientists.

What are the key points in the IPCC Working Group I Summary for Policymakers?

The Summary for Policymakers includes the key conclusions from the longer report in a format suitable for a broader audience. The SPM will include observations of changes in the atmosphere, ocean, and cryosphere, including changes in sea level. It will also discuss our confidence in attributing climate change to human activities. The SPM will also include projections of global and regional climate change for the 21st century, including projected changes in the water cycle, extreme weather, sea level, sea ice, and the carbon cycle.

It answers such questions as:

  • What is the state of the science in understanding and attributing climate changes?
  • What are the primary drivers of climate change?
  • How do recent changes compare to paleoclimatic records?
  • In what ways is climate change is already occurring around the globe and how fast are these systems changing?
  • What are models projecting for the 21st century climate and how accurate are they?
  • Which types of climate changes might be irreversible?

What are the key points in the IPCC Working Group II Summary for Policymakers?

The Summary for Policymakers includes important statements and conclusions from the WGII report and is aimed at a broader audience. The WGII SPM is divided into three sections: 1. Observed Impacts, Vulnerability, and Adaptation in a Complex and Changing World; 2. Future Risks and Opportunities for Adaptation; and 3. Managing Future Risks and Building Resilience.

The WGII SPM answers such questions as:

  • What climate-related impacts are already being observed today?
  • What are the key future risks in areas such as water resources, coastal and marine systems, food security, human health, security, and economic growth?
  • Which groups of people are the most vulnerable?
  • What kind of adaptation actions have already been undertaken and which actions could be taken to reduce these future risks?
  • How can adaptation decisions be made when the future is uncertain?
  • What constitutes effective adaptation action and climate-resilient development?

What are the key points in the IPCC Working Group III Summary for Policymakers?

The Summary for Policymakers includes key statements and conclusions from the WGIII report and is aimed at a broader audience. It assesses all relevant options for mitigating climate change through limiting or preventing greenhouse gas emissions, as well as activities that remove them from the atmosphere. It lays out a number of baseline scenarios that, without mitigation efforts, would lead to substantial warming by the end of the 21st century.

It also describes a number of potential mitigation scenarios:

  • To avoid 2 degrees C (3.6 degrees F) of warming relative to pre-industrial time, the report indicates that atmospheric concentrations of greenhouse gases need to be stabilized around 450 ppm CO2-eq or lower. Given that we are currently around 430 CO2-eq, this is a tall order, requiring large-scale changes in energy systems and land use. For example, achieving this level of stabilization will require more rapid improvements in energy efficiency and a tripling to nearly a quadrupling of the share of zero- and low-carbon energy supply from renewables, nuclear energy, and fossil energy with carbon capture and storage, or bioenergy with carbon capture and storage, by the year 2050.
  • The aggregate economic cost of mitigation varies widely, but generally increases based on the stringency of the level of mitigation. In general, the costs of mitigation only offset a relatively small fraction of global projected economic growth for the 21st century.
  • The 2020 individual country-pledged goals (under the Cancún Agreements) are unlikely to put us on a path to avoid 2 degrees C (3.6 degrees F) of warming; further substantial reductions beyond 2020 would need to be made. Continuing on the pathways consistent with the Cancún pledges is more consistent with scenarios likely to keep temperature change below 3 degrees C relative to pre-industrial levels.
  • If we do not strengthen mitigation efforts between now and 2030, it will be more difficult and more expensive to achieve warming targets, such as avoiding 2 degrees of warming relative to pre-industrial levels.

Growing Certainty on the Human Role in Climate Change

In its periodic assessments, the Intergovernmental Panel on Climate Change has expressed growing certainty that global warming is underway and that human activity is a principal cause. The panel’s language has become progressively stronger over time to reflect its growing certainty.

In 1990, the IPCC said that emissions from human activities were “substantially increasing” greenhouse gas concentrations in the atmosphere, which would lead to warming.

By 2013, the panel had concluded that “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

The chart below traces how the IPCC’s conclusions have strengthened over time.

Year Assessment Statement on Human Involvement in Climate Change
1990 First Assessment “…emissions resulting from human activities are substantially increasing atmospheric concentrations of greenhouse gases…
These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth’s surface”
1995 Second Assessment “Most of these studies have detected a significant change and show that the observed warming trend is unlikely to be entirely natural in origin…
…the balance of evidence suggests that there is a discernible human influence on global climate.
…the average rate of warming [in projections for the 21st century] would probably be greater than any seen in the last 10,000 years, but the actual annual to decadal changes would include considerable natural variability.”
2001 Third Assessment “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.
…the projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years, based on paleoclimate data.”
2007 Fourth Assessment “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
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.”
2013 Fifth Assessment “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.
…It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”