The Intergovernmental Panel on Climate Change (IPCC) provides regular assessments of the scientific basis of climate change, its impacts and future risks, plus options for adaptation and mitigation.

The IPCC was set up in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme. Its purpose is to inform decision-makers and provide the scientific basis for climate policy. This includes the policy negotiations under the UNFCCC (the UN’s Framework Convention on Climate Change). As an intergovernmental organisation, it is open to all member countries of the WMO and United Nations, and currently has 195 members.

Since its inception, the IPCC has prepared six assessment reports – one every six or seven years. It has also delivered a number of special reports on topics such as land, the ocean and cryosphere, extreme events and disasters, and renewable energy. In 2007, the IPCC received the Nobel Peace Prize, jointly with former US Vice President Al Gore, “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change.”

Member governments task the IPCC with both systematic assessments of research on climate change and specific research questions. For example, in the Paris Agreement signed at the 2015 UN climate conference, parties committed to limit the global average temperature increase to 1.5°C above pre-industrial levels, when human influence on the climate was still negligible – scientists typically use the average temperature for 1850-1900. Following the outcome, countries asked the IPCC to look at what 1.5 degrees of global warming would mean for the Earth and how it would be possible to meet the target. The IPCC agreed and produced a Special Report on Global Warming of 1.5°C, published in 2018.

The IPCC authors report from three groups: Working Group I looks at the physical science basis of climate change, Working Group II explores various impacts of climate change and adaptation, and Working Group III studies ways to reduce our influence on the global climate system. Each group contributes to the assessment report. Additional task forces and groups both help the IPCC keep track of all the data it uses in the reports and assist governments with their greenhouse gas (GHG) inventories.  

For each report, the IPCC recruits hundreds of leading scientists across the world to review the best available research. They then summarise it using the agreed language for various degrees of certainty and the amount of evidence available. For example, for something to be described in the IPCC report as ‘likely’, the probability of this outcome has to be at least 66%. And if something is ‘virtually certain’, like the fact that CO2 emissions from human activity are driving ocean acidification and changes in hot and cold extremes across the world, then its likelihood is higher than 99%.

The draft reports then undergo multiple rounds of extensive review, with thousands of experts providing feedback. Finally, representatives of member governments work with the authors to adopt a comprehensive and accurate summary of each report for policymakers, highlighting the key results of the process,  which are also formally endorsed by IPCC member countries.

What do these reports tell us?

The three parts of the most recent assessment report, AR6, were released in 2021-2022, with a synthesis report following in March 2023. The very first key messages from each of the working group contributions are:

Working Group I: It is unequivocal that human influence has warmed the atmosphere, ocean and land.

Working Group II: Human-induced climate change, including more frequent and intense extreme events, has caused widespread adverse impacts and related losses and damages to nature and people, beyond natural climate variability.

Working Group III: Total net anthropogenic greenhouse gas emissions have continued to rise during the period 2010–2019, as have cumulative net CO2 emissions since 1850. (By ‘net’ the IPCC means emissions from all anthropogenic sources, such as gas-fired power plants, minus the CO2 removed by anthropogenic sinks, such as planted trees.)

As the IPCC itself stresses, while its assessments present projections of future climate change based on different scenarios, the risks climate change poses, and the implications of different response options, they do not tell policymakers what actions to take. This means the assessments are policy relevant, but not policy prescriptive: the IPCC tells governments how they can fight climate change, but does not make recommendations on how they should fight climate change.

For instance, one of the key conclusions of the Special Report on Global Warming of 1.5°C is that, at the current rate of warming, the world will reach the 1.5°C limit some time between 2030 and the early 2050s. The IPCC itself makes no judgement on whether it is smart or necessary to avoid that outcome – instead it is the countries that signed the Paris Agreement that have agreed to the limit. While it can chart all the physically possible pathways to achieve the 1.5°C goal, plus the actions, benefits and costs they would entail, the IPCC gives no preference for any particular pathway – that is for country governments to choose.

Who writes the IPCC reports?

Melissa Walsh / IPCC

For each report, the IPCC issues a call to governments and observer organisations to nominate their most qualified scientists studying all aspects of the climate system and our interactions with it. The panel then aims to build a diverse group of authors that both represents a broad range of views and backgrounds, and is equipped to handle the complex task of a comprehensive assessment of the scientific literature.

The aim is to gather people from different regions of the world, balancing representation from developed and developing countries. This helps ensure the resulting text is not biased towards any particular region and does not overlook any locally important questions. The IPCC also encourages younger scientists and those new to the process to get involved in appropriate roles. This is to make sure the writing teams can transfer knowledge and experience, as well as continue to support decision-making with the best available scientific evidence.

Researchers selected by the IPCC become Coordinating Lead Authors, Lead Authors and Review Editors for each assessment report chapter. The IPCC also recruits other experts as Contributing Authors for specific questions within the chapters. All of these scientists volunteer their time and effort, and they follow a specific conflict of interest policy established by the panel.

What sources are used for the reports?

The IPCC does not conduct its own research. In other words, it does not run experiments or gather weather and climate data. Rather, it assesses and synthesises the research published in scientific journals, which has already gone through peer review, and in other reporting sources, such as from governments, industry and research institutions, international and other organisations, and conference proceedings.

All of these sources are carefully evaluated by the chapter teams for quality and validity, and expert reviewers can request copies of anything that is not widely available to further scrutinise the data sources. Review Editors make sure all the comments submitted from both rounds of review are addressed and responded to in writing – for example, any reader can see the more than 51,000 comments and responses in the second draft of the most recent Working Group I report.

Since the IPCC does not do its own research, all information and data used in its reports come with attributions, with full citations for sources listed at the end of each chapter. Additionally, if the authors synthesise several sources for a broader overview, build summary graphics or do similar tasks, they explain their process in captions or footnotes to maintain transparency with both reviewers and readers.

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