IPCC First Assessment Report

Last updated January 16, 2024

The First Assessment Report (FAR) of the Intergovernmental Panel on Climate Change (IPCC) was completed in 1990. It served as the basis of the United Nations Framework Convention on Climate Change (UNFCCC). This report had effects not only on the establishment of the UNFCCC, but also on the first conference of the parties (COP), held in Berlin in 1995.^[1] The executive summary of the WG I Summary for Policymakers report that said they were certain that emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases, resulting on average in an additional warming of the Earth's surface. They calculated with confidence that CO₂ had been responsible for over half the enhanced greenhouse effect.

They predicted that under a "business as usual" (BAU) scenario, global mean temperature would increase by about 0.3 °C per decade during the [21st] century. They judged that global mean surface air temperature had increased by 0.3 to 0.6 °C over the last 100 years, broadly consistent with prediction of climate models, but also of the same magnitude as natural climate variability. The unequivocal detection of the enhanced greenhouse effect was not likely for a decade or more.

The 1992 supplementary report was an update, requested in the context of the negotiations on the UNFCCC at the Earth Summit (United Nations Conference on Environment and Development) in Rio de Janeiro in 1992. The major conclusion was that research since 1990 did "not affect our fundamental understanding of the science of the greenhouse effect and either confirm or do not justify alteration of the major conclusions of the first IPCC scientific assessment". It noted that transient (time-dependent) simulations, which had been very preliminary in the FAR, were now improved, but did not include aerosol or ozone changes.

Overview

The report was issued in three main sections, corresponding to the three Working Groups of scientists that the IPCC had established.

Working Group I: Scientific Assessment of Climate Change, edited by J.T. Houghton, G.J. Jenkins and J.J. Ephraums
Working Group II: Impacts Assessment of Climate Change, edited by W.J. McG. Tegart, G.W. Sheldon and D.C. Griffiths
Working Group III:The IPCC Response Strategies

Each section included a summary for policymakers. This format was followed in subsequent Assessment Reports.

The executive summary of the policymakers' summary of the WG I report includes:

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: CO₂, methane, CFCs and nitrous oxide. These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface. The main greenhouse gas, water vapour, 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 stabilise their concentrations at today's levels...
Based on current models, we predict: under [BAU] increase of global mean temperature during the [21st] century of about 0.3 °C 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; under other ... scenarios which assume progressively increasing levels of controls, rates of increase in global mean temperature of about 0.2 °C [to] about 0.1 °C per decade.
There are many uncertainties in our predictions particularly with regard to the timing, magnitude and regional patterns of climate change, due to our incomplete understanding of: sources and sinks of GHGs; clouds; oceans; 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.

Controversies

When discussing the politicisation of IPCC assessment reports climatologist Kevin E. Trenberth stated:

The SPM [Summary for policymakers] was approved line by line by governments ... The argument here is that the scientists determine what can be said, but the governments determine how it can best be said. Negotiations occur over wording to ensure accuracy, balance, clarity of message, and relevance to understanding and policy. The IPCC process is dependent on the good will of the participants in producing a balanced assessment. However, in Shanghai, it appeared that there were attempts to blunt, and perhaps obfuscate, the messages in the report, most notably by Saudi Arabia. This led to very protracted debates over wording on even bland and what should be uncontroversial text ... The most contentious paragraph in the IPCC (2001) SPM was the concluding one on attribution. After much debate, the following was carefully crafted: "In the light of new evidence, and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse-gas concentrations."^[2]

Related Research Articles

Four main lines of evidence support attribution of recent climate change to human activities: Firstly, a physical understanding of the climate system: greenhouse gas concentrations have increased and their warming properties are well-established. Secondly, there are historical estimates of past climate changes suggest that the recent changes in global surface temperature are unusual. Thirdly, computer-based climate models are unable to replicate the observed warming unless human greenhouse gas emissions are included. And finally, natural forces alone cannot explain the observed warming.

<span class="mw-page-title-main">Global warming potential</span> Potential heat absorbed by a greenhouse gas

Global warming potential (GWP) is an index to measure of how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been added to the atmosphere. The GWP makes different greenhouse gases comparable with regards to their "effectiveness in causing radiative forcing". It is expressed as a multiple of the radiation that would be absorbed by the same mass of added carbon dioxide, which is taken as a reference gas. Therefore, the GWP is one for CO₂. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.

The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) established the IPCC in 1988. The United Nations endorsed the creation of the IPCC later that year. It has a secretariat in Geneva, Switzerland, hosted by the WMO. It has 195 member states who govern the IPCC. The member states elect a bureau of scientists to serve through an assessment cycle. A cycle is usually six to seven years. The bureau selects experts to prepare IPCC reports. It draws the experts from nominations by governments and observer organizations. The IPCC has three working groups and a task force, which carry out its scientific work.

The United Nations Framework Convention on Climate Change (UNFCCC) is an international treaty among countries to combat "dangerous human interference with the climate system", in part by stabilizing greenhouse gas concentrations in the atmosphere. It was signed in 1992 by 154 states at the United Nations Conference on Environment and Development (UNCED), informally known as the Earth Summit, held in Rio de Janeiro. Its secretariat was in Geneva at first but relocated to Bonn in 1996. The treaty entered into force on 21 March 1994. "UNFCCC" is also the name of the Secretariat charged with supporting the operation of the convention, with offices on the UN Campus in Bonn, Germany.

The instrumental temperature record is a record of temperatures within Earth's climate based on direct measurement of air temperature and ocean temperature, using thermometers and other thermometry devices. Instrumental temperature records are distinguished from indirect reconstructions using climate proxy data such as from tree rings and ocean sediments. Instrument-based data are collected from thousands of meteorological stations, buoys and ships around the globe. Whilst many heavily-populated areas have a high density of measurements, observations are more widely spread in sparsely populated areas such as polar regions and deserts, as well as over many parts of Africa and South America. Measurements were historically made using mercury or alcohol thermometers which were read manually, but are increasingly made using electronic sensors which transmit data automatically. Records of global average surface temperature are usually presented as anomalies rather than as absolute temperatures. A temperature anomaly is measured against a reference value. For example, a commonly used baseline period is the time period 1951-1980.

The IPCC Third Assessment Report (TAR), Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. Statements of the IPCC or information from the TAR were often used as a reference showing a scientific consensus on the subject of global warming. The Third Assessment Report (TAR) was completed in 2001 and consists of four reports, three of them from its Working Groups: Working Group I: The Scientific Basis; Working Group II: Impacts, Adaptation and Vulnerability; Working Group III: Mitigation; Synthesis Report. A number of the TAR's conclusions are given quantitative estimates of how probable it is that they are correct, e.g., greater than 66% probability of being correct. These are "Bayesian" probabilities, which are based on an expert assessment of all the available evidence.

The Second Assessment Report (SAR) of the Intergovernmental Panel on Climate Change (IPCC), published in 1995, is an assessment of the then available scientific and socio-economic information on climate change. The report was split into four parts: a synthesis to help interpret UNFCCC article 2, The Science of Climate Change, Impacts, Adaptations and Mitigation of Climate Change, Economic and Social Dimensions of Climate Change. Each of the last three parts was completed by a separate Working Group (WG), and each has a Summary for Policymakers (SPM) that represents a consensus of national representatives.

Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC), was published in 2007 and is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6,000 peer-reviewed scientific studies. People from over 130 countries contributed to the IPCC Fourth Assessment Report, which took six years to produce. Contributors to AR4 included more than 2,500 scientific expert reviewers, more than 800 contributing authors, and more than 450 lead authors.

In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global average temperature is more rapid than previous changes, and is primarily caused by humans burning fossil fuels. Fossil fuel use, deforestation, and some agricultural and industrial practices add to greenhouse gases, notably carbon dioxide and methane. Greenhouse gases absorb some of the heat that the Earth radiates after it warms from sunlight. Larger amounts of these gases trap more heat in Earth's lower atmosphere, causing global warming.

The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the fifth in a series of such reports and was completed in 2014. As had been the case in the past, the outline of the AR5 was developed through a scoping process which involved climate change experts from all relevant disciplines and users of IPCC reports, in particular representatives from governments. Governments and organizations involved in the Fourth Report were asked to submit comments and observations in writing with the submissions analysed by the panel. Projections in AR5 are based on "Representative Concentration Pathways" (RCPs). The RCPs are consistent with a wide range of possible changes in future anthropogenic greenhouse gas emissions. Projected changes in global mean surface temperature and sea level are given in the main RCP article.

<span class="mw-page-title-main">Greenhouse gas</span> Gas in an atmosphere that absorbs and emits radiation at thermal infrared wavelengths

Greenhouse gases are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by water vapor (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃). Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F).

Climate change scenarios or socioeconomic scenarios are projections of future greenhouse gas (GHG) emissions used by analysts to assess future vulnerability to climate change. Scenarios and pathways are created by scientists to survey any long term routes and explore the effectiveness of mitigation and helps us understand what the future may hold. This will allow us to envision the future of human environment system. Producing scenarios requires estimates of future population levels, economic activity, the structure of governance, social values, and patterns of technological change. Economic and energy modelling can be used to analyze and quantify the effects of such drivers.

A Representative Concentration Pathway (RCP) is a greenhouse gas concentration trajectory adopted by the IPCC. Four pathways were used for climate modeling and research for the IPCC Fifth Assessment Report (AR5) in 2014. The pathways describe different climate change scenarios, all of which are considered possible depending on the amount of greenhouse gases (GHG) emitted in the years to come. The RCPs – originally RCP2.6, RCP4.5, RCP6, and RCP8.5 – are labelled after a possible range of radiative forcing values in the year 2100. The higher values mean higher greenhouse gas emissions and therefore higher global temperatures and more pronounced effects of climate change. The lower RCP values, on the other hand, are more desirable for humans but require more stringent climate change mitigation efforts to achieve them.

In earth science, global surface temperature is calculated by averaging the temperatures over sea and land.

A global warming hiatus, also sometimes referred to as a global warming pause or a global warming slowdown, is a period of relatively little change in globally averaged surface temperatures. In the current episode of global warming many such 15-year periods appear in the surface temperature record, along with robust evidence of the long-term warming trend. Such a "hiatus" is shorter than the 30-year periods that climate is classically averaged over.

The Special Report on Global Warming of 1.5 °C (SR15) was published by the Intergovernmental Panel on Climate Change (IPCC) on 8 October 2018. The report, approved in Incheon, South Korea, includes over 6,000 scientific references, and was prepared by 91 authors from 40 countries. In December 2015, the 2015 United Nations Climate Change Conference called for the report. The report was delivered at the United Nations' 48th session of the IPCC to "deliver the authoritative, scientific guide for governments" to deal with climate change. Its key finding is that meeting a 1.5 °C (2.7 °F) target is possible but would require "deep emissions reductions" and "rapid, far-reaching and unprecedented changes in all aspects of society". Furthermore, the report finds that "limiting global warming to 1.5 °C compared with 2 °C would reduce challenging impacts on ecosystems, human health and well-being" and that a 2 °C temperature increase would exacerbate extreme weather, rising sea levels and diminishing Arctic sea ice, coral bleaching, and loss of ecosystems, among other impacts.

The United Nations' Intergovernmental Panel on Climate Change's (IPCC) Special Report on Climate Change and Land (SRCCL), also known as the "Special Report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems", is a landmark study from 2019 by 107 experts from 52 countries. The SRCCL provides a comprehensive overview of the entire land-climate system for the first time and decided to enlist land as a "critical resource". The IPCC's 50th session (IPCC-50) formally adopted the SRCCL's Summary for policymakers (SPM) and approved the underlying report. The SPM and the full text of Special Report on Climate Change and Land—in an unedited form—were released on 8 August 2019. The report is over 1,300 pages long and includes the work of 107 experts from 52 countries.

The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess scientific, technical, and socio-economic information concerning climate change. Three Working Groups covered the following topics: The Physical Science Basis (WGI); Impacts, Adaptation and Vulnerability (WGII); Mitigation of Climate Change (WGIII). Of these, the first study was published in 2021, the second report February 2022, and the third in April 2022. The final synthesis report was finished in March 2023.

References

↑ "The IPCC: Who Are They and Why Do Their Climate Reports Matter?". Union of Concerned Scientists: Reports & Multimedia - Activist Resources: Explainers. Union of Concerned Scientists. 11 October 2018. Archived from the original on 30 December 2019. Retrieved 30 December 2019.
↑ Trenberth, Kevin (2001). "The IPCC Assessment of global warming 2001". Journal of the Forum for Environmental Law, Science, Engineering, and Finance (8–26). Archived from the original on 6 December 2006. Retrieved 19 February 2014.

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[UCS_IPCC_Who_are_they?-1] "The IPCC: Who Are They and Why Do Their Climate Reports Matter?". Union of Concerned Scientists: Reports & Multimedia - Activist Resources: Explainers. Union of Concerned Scientists. 11 October 2018. Archived from the original on 30 December 2019. Retrieved 30 December 2019.

[2] Trenberth, Kevin (2001). "The IPCC Assessment of global warming 2001". Journal of the Forum for Environmental Law, Science, Engineering, and Finance (8–26). Archived from the original on 6 December 2006. Retrieved 19 February 2014.

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