Intergovernmental Panel on Climate Change (IPCC)

The Intergovernmental Panel on Climate Change (IPCC) is an international group affiliated with the United Nations and charged with reviewing scientific data related to Earth’s climate. Periodically, the group releases reports containing its findings and recommendations for possible future action.

Founding and Purpose

The IPCC was founded in 1988 by the UN Environment Programme and the World Meteorological Organization (WMO) to review and assess data about the earth’s climate. The IPCC is tasked with reviewing scientific evidence for climate change, but it does not conduct its own research or monitoring. Instead, the panel reviews the scientific literature in a variety of areas tied to global climate and educates the public about its findings.

The IPCC includes 195 nations and is open to members of the United Nations and WMO. IPCC reports include input from hundreds of scientists in relevant disciplines. The IPCC has completed four assessments, in 1990, 1995, 2001, 2007, 2013, and 2023. The 2023 Assessment Report was the sixth published by the forty-third session. Some described the predictions in the 2023 report as the most alarming predictions to date.

The reports from the IPCC are typically regarded as marking scientific consensus on global climate trends, and they have guided policymaking at the national and international level. In 2007, the IPCC and former US Vice President Al Gore were awarded the Nobel Peace Prize for their educational efforts on climate change.

Past Reports

IPCC reports highlight various areas of climate research. Additionally, the assessment reports are relied upon for guidance in setting global policy.

An early example of such reliance was the Kyoto Protocol, which, in using the first two IPCC reports, set benchmarks for reducing greenhouse gas emissions. Beyond simple recommendations, the Kyoto Protocol was considered a binding agreement. The protocol was initially signed in 1997, and provisions became effective in 2005. Ultimately, the hope was to reduce greenhouse gas emissions by 5 percent each year from 2008 through 2012, with plans for a new treaty at that time. The success of the treaty, however, remains unclear. The United States, which produced the most greenhouse gas at the time of the treaty’s signing, did not sign the protocol. (China has since surpassed the United States in greenhouse gas emissions.)

The scientific weight of the reports mandates the collection of a great deal of data. In studying climate change, the most accurate information comes from the recent past. Since about 1980, satellites have been available to help gather data on factors such as temperature, water levels, and weather patterns. However, analyzing the climate requires a longer view. To do this, scientists need to collect data from much further back on these same parameters.

One of the best-known charts in the IPCC reports is often termed the hockey stick graph. The chart shows global temperatures from the year 1000 through the year 2000. The report is named for the shape of the graph, which is relatively straight from the beginning until the middle of the twentieth century when it curves upward sharply.

The hockey stick graph was generated as part of a 1999 study by Michael Mann and colleagues at the University of Massachusetts, Amherst, and from the University of Arizona, using data from that paper and one published in the journal Nature the previous year. The graph appeared in the summary of the report on the scientific evidence for climate change in the third assessment of the IPCC (published in 2001) as one piece of evidence indicating a trend of rising global temperatures.

Although the authors admitted uncertainty on data before the year 1400, they reconstructed average temperatures using ice cores (in which temperature can be measured based on the ratio of oxygen isotopes preserved in a given year) taken from polar ice sheets and from tree rings and coral, along with existing historical records. The graph contains a visible measure of uncertainty surrounding individual years but maintains its upward-sloping shape at the end.

Whereas temperature is one way of assessing whether the planet is warming, prediction models require many other measurements, both to explain predictions and to gain an understanding of the effect that a changing temperature might have. Oceanic factors are monitored in climate assessments, including currents, sea levels, and surface temperatures. Remote-sensing satellites play a major role in taking these measurements.

Ocean currents play a major role in heat transfers throughout the planet, in a system known as the great ocean conveyor belt, or sometimes just the great conveyor belt. Water at cooler temperatures is denser, so warmer water at the surface may be carried in different directions by a combination of winds and the earth’s rotation. For example, the North Atlantic current carries heat from the tropics to the coast of northern Europe. It is for this reason that the annual temperatures of the United Kingdom and Ireland are comparable to those of the northeastern United States, even though these European countries are at higher latitudes. When the water reaches a high enough latitude and cools, the water becomes denser and sinks.

Melting ice caps, the result of heat in the polar regions, could cause water to cool sooner and therefore disrupt oceanic circulation patterns. Changes in those oceanic currents about twelve thousand years ago led to a significantly cooler climate for that region that lasted for a millennium.

A US satellite known as the Advanced Very High Resolution Radiometer, launched by the National Oceanic and Atmospheric Administration, uses infrared imaging to monitor temperatures on the ocean’s surface and therefore track the movement of these ocean currents. Other satellites measure sea levels to see if they have risen, possibly from an influx of water from melting polar ice. These satellites are equipped with a device known as an altimeter that measures the satellites’ distances from the earth’s surface. The device works by communicating with geographic positioning system satellites and with multiple points on the ground in addition to its distance from the surface of the ocean.

IPCC reports also examine possible causes of climate change, which include levels of certain molecules in the atmosphere. The IPCC’s listing of greenhouse gases encompasses a number of gases that can absorb heat and potentially contribute to global warming. These gases include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), ozone (O₃), and chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Many of these occur naturally in the earth’s atmosphere or are produced as waste products of organic processes such as respiration, but they affect temperature at higher concentrations.

It is important to note that not all atmospheric pollutants are greenhouse gases. Sulfur dioxide (SO₂), for example, reflects rather than absorbs heat. At one point, high levels of sulfur dioxide pollution had some scientists concerned about global cooling, although reduced levels of the gas have reduced its impact.

Recent Panel Findings

AR6 Synthesis Report: Climate Change 2023 comprises a combination of five years of reports covering the scientific basis for global warming, the impact of climate change and what was most likely to be affected, and potential responses to mitigate the effects of climate change. In past reports, the IPCC deemed the warming of Earth’s climate to be “unequivocal,” citing changes in ice and snow coverage, sea levels, and air and water temperatures. In the AR6, the organization outlines what individuals, governments, and organizations can do to limit the warming of the planet to below 1.5 degrees Celsius. The panel also noted that, based on previous impacts of similar recommendations, the recommended changes were unlikely to prevent the Earth from exceeding the dangerous 1.5 degrees Celsius increase in the twenty-first century.

The main findings of the AR6 synthesis include the changing weather and extreme climate changes that have been observed across the world from 2000 to 2023. These changes caused widespread loss to animals and people. The report also predicted that warming due to greenhouse gas emissions would likely reach 1.5 degrees Celsius between 2030 and 2035 and possibly reach 3.2 degrees by 2100. In early 2023, the Earth was nearly 1.1 degrees Celsius above desired temperatures. The IPCC stated they had high confidence that this would lead to adverse impacts, most harshly impacting poor and vulnerable populations of the world. To avoid this increase, emissions would need to be reduced by 43 percent by 2030 and 60 percent by 2035.

Uncertainty and the IPCC

In many sciences, the key to establishing facts is to reproduce experiments to reduce the likelihood of being wrong through error. In climate science, such reproduction is not possible. Because of this limitation, many factors need to be considered when trying to assess possible climate change and its possible effects.

While controversies exist regarding the IPCC and climate change, many of these controversies are a matter of degree rather than outright opposition. Many factors influence and accompany rising temperatures and affect the earth’s climate. Built into all of these measurements is some small degree of uncertainty, particularly in areas in which the data points are estimated rather than directly measured. It is for this reason that rules for expressing degrees of uncertainty are included in the most recent report.

Mann’s hockey stick graph, for example, includes large, shaded areas around the line showing global temperature, indicating the broad range where the temperature likely was in a given time period. Because of these uncertainties and because of the need to revisit the ideas, new reviews must be conducted and new reports must be written every few years.

Principal Terms

anthropogenic global warming: rises in global temperatures caused by human activity

climate change: change in Earth’s climate that persists for roughly ten years or longer

great conveyor belt: a system of ocean circulation in which heat is carried to warm certain parts of the earth; also called great ocean conveyor belt

greenhouse gas: gases within the earth’s atmosphere that absorb heat and help maintain the planet’s climate

ice core record: ice sheet samples used for chemical analysis of temperature, atmospheric and volcanic activity, and precipitation

radiative forcing: a measurement of how much the greenhouse gas in a given area will affect the level of radiation maintained; measured in watts per square meter

remote-sensing satellites: satellites that carry instruments to monitor and collect climate data while orbiting Earth

solar irradiance: energy from the sun’s rays that reach Earth; measured in units of power over time (typically watts per second)

tree-ring data: data gathered from tree rings that reflect climate data from the past; thicker rings indicate the presence of light and nutrients that allow more growth

variability: with respect to climate, refers to small-scale changes, such as those in a few years

volcanic aerosols: volcanic ash released into the atmosphere; can affect the amount of solar radiation reaching Earth through components such as sulfur dioxide

Bibliography

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Cooper, Nathan. “Climate Change: The IPCC Just Published its Summary of 5 Years of Reports—Here’s What You Need to Know.” World Economic Forum, 20 Mar. 2023, www.weforum.org/agenda/2023/03/the-ipcc-just-published-its-summary-of-5-years-of-reports-here-s-what-you-need-to-know. Accessed 15 Apr. 2023.

"Intergovernmental Panel on Climate Change. Working Group I." Climate Change 2007: The Physical Science Basis, www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-frontmatter-1.pdf. Accessed 15 Apr. 2023.

"Intergovernmental Panel on Climate Change. Working Group II." Climate Change 2007: Impacts, Adaptation, and Vulnerability, www.ipcc.ch/working-group/wg2. Accessed 15 Apr. 2023.

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Mann, Michael E. et al. “Global-Scale Temperature Patterns and Climate Forcing over the Past Six Centuries.” Nature, vol. 392, 1998, pp. 779–87. doi.org/10.1038/33859. Accessed 15 Apr. 2023.

Mann, Michael E. et al. “Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations.” Geophysical Research Letters, vol. 26, no. 6, 1999, pp. 759–762. doi.org/10.1029/1999GL900070. Accessed 15 Apr. 2023.

Lee, Hoesung. "Synthesis Report of the IPCC Sixth Assessment Report." IPCC, 2023, report.ipcc.ch/ar6syr/pdf/IPCC‗AR6‗SYR‗SPM.pdf. Accessed 15 Apr. 2023.