The Copenhagen Diagnosis is a climate change report written by 26 climate scientists from eight countries. [1] [2] It was published in 2009 and was a summary of the peer-reviewed literature to date. [3] [4] A media conference was held to present the major findings of the report at the 2009 United Nations Climate Change Conference, in Copenhagen, Denmark, chaired by the Copenhagen Diagnosis coordinating lead author, Matthew England. [5]
The Copenhagen Diagnosis aimed to synthesize the most policy-relevant climate science published since the close-off of material for the previous Intergovernmental Panel on Climate Change's Working Group 1 Report (AR4), [6] [7] thus serving as an interim evaluation of the evolving science midway through an IPCC cycle, with IPCC AR5 not due for completion until 2013. [7]
The report also aimed to serve as a handbook of science updates that supplements the IPCC AR4 in time for the 2009 United Nations Climate Change Conference [6] held in December 2009, and for any national or international climate change policy negotiations that followed.
The Copenhagen Diagnosis reached a number of conclusions, as set out in the executive summary, [8] including:
To maximize global outreach, the major findings of the Copenhagen Diagnosis were translated into 12 languages. [9]
The Copenhagen Diagnosis has been accessed online over a million times since its release, and was named an Outstanding Academic Title by the American Library Association's Choice publication in 2012. [10]
Efforts to scientifically ascertain and attribute mechanisms responsible for recent global warming and related climate changes on Earth have found that the main driver is elevated levels of greenhouse gases produced by human activities, with natural forces adding variability. The likely range of human-induced surface-level air warming by 2010–2019 compared to levels in 1850–1900 is 0.8 °C to 1.3 °C, with a best estimate of 1.07 °C. This is close to the observed overall warming during that time of 0.9 °C to 1.2 °C, while temperature changes during that time were likely only ±0.1 °C due to natural forcings and ±0.2 °C due to variability in the climate.
The global warming controversy concerns the public debate over whether global warming is occurring, how much has occurred in modern times, what has caused it, what its effects will be, whether any action can or should be taken to curb it, and if so what that action should be. In the scientific literature, there is a very strong consensus that global surface temperatures have increased in recent decades and that the trend is caused by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view, though a few organizations with members in extractive industries hold non-committal positions, and some have tried to persuade the public that climate change is not happening, or if the climate is changing it is not because of human influence, attempting to sow doubt in the scientific consensus.
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 cryosphere is an all-encompassing term for the portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation.
There is a strong scientific consensus that the Earth is warming and that this warming is mainly caused by human activities. This consensus is supported by various studies of scientists' opinions and by position statements of scientific organizations, many of which explicitly agree with the Intergovernmental Panel on Climate Change (IPCC) synthesis reports.
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Last Glacial Maximum, the Laurentide Ice Sheet covered much of North America, the Weichselian ice sheet covered Northern Europe and the Patagonian Ice Sheet covered southern South America.
Climate change affects the physical environment, ecosystems and human societies. Changes in the climate system include an overall warming trend, more extreme weather and rising sea levels. These in turn impact nature and wildlife, as well as human settlements and societies. The effects of human-caused climate change are broad and far-reaching. This is especially so if there is no significant climate action. Experts sometimes describe the projected and observed negative impacts of climate change as the climate crisis.
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 increase 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.
Timothy Raymond Naish is a New Zealand glaciologist and climate scientist who has been a researcher and lecturer at Victoria University of Wellington and the Director of the Antarctic Research Centre, and in 2020 became a programme leader at the Antarctic Science Platform. Naish has researched and written about the possible effect of melting ice sheets in Antarctica on global sea levels due to high CO2 emissions causing warming in the Southern Ocean. He was instrumental in establishing and leading the Antarctica Drilling Project (ANDRILL), and a Lead Author on the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (2014).
The IPCC Fourth Assessment Report (AR4) is a report on climate change created with the help of a large number of contributors, both scientists and governmental representatives. There has been considerable political controversy over a small number of errors found in the report, and there have been calls for review of the process used to formulate the report. The overwhelming majority view of scientists with expertise in climate change is that errors, when found, are corrected, and the issues as identified do not undermine the conclusions of the report that the climate system is warming in response to increased levels of greenhouse gases, largely due to human activities.
Major environmental issues caused by contemporary climate change in the Arctic region range from the well-known, such as the loss of sea ice or melting of the Greenland ice sheet, to more obscure, but deeply significant issues, such as permafrost thaw, as well as related social consequences for locals and the geopolitical ramifications of these changes. The Arctic is likely to be especially affected by climate change because of the high projected rate of regional warming and associated impacts. Temperature projections for the Arctic region were assessed in 2007: These suggested already averaged warming of about 2 °C to 9 °C by the year 2100. The range reflects different projections made by different climate models, run with different forcing scenarios. Radiative forcing is a measure of the effect of natural and human activities on the climate. Different forcing scenarios reflect things such as different projections of future human greenhouse gas emissions.
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.
Climate Change: Global Risks, Challenges and Decisions was a conference on Climate Change held at the Bella Center by the University of Copenhagen. The event was organised with the assistance of other universities in the International Alliance of Research Universities. The stated aim of the conference was to provide "a summary of existing scientific knowledge two years after the last IPCC report." The conference took place on 10–12 March 2009.
Climate change feedbacks are effects of global warming that amplify or diminish the effect of forces that initially cause the warming. Positive feedbacks enhance global warming while negative feedbacks weaken it. Feedbacks are important in the understanding of climate change because they play an important part in determining the sensitivity of the climate to warming forces. Climate forcings and feedbacks together determine how much and how fast the climate changes. Large positive feedbacks can lead to tipping points—abrupt or irreversible changes in the climate system—depending upon the rate and magnitude of the climate change.
The Intergovernmental Panel on Climate Change (IPCC) has organized many of the risks of climate change into five "reasons for concern." The reasons for concern show that these risks increase with increases in the Earth's global mean temperature. The IPCC's five reasons for concern are: threats to endangered species and unique systems, damages from extreme climate events, effects that fall most heavily on developing countries and the poor within countries, global aggregate impacts, and large-scale high-impact events. The five reasons for concern are described in more detail below. The following descriptions are based on information from the IPCC's Third (TAR) and Fourth Assessment Reports (AR4), published in 2001 and 2007, respectively.
Sea ice in the Arctic has declined in recent decades in area and volume due to climate change. It has been melting more in summer than it refreezes in winter. Global warming, caused by greenhouse gas forcing is responsible for the decline in Arctic sea ice. The decline of sea ice in the Arctic has been accelerating during the early twenty‐first century, with a decline rate of 4.7% per decade. It is also thought that summertime sea ice will cease to exist sometime during the 21st century.
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 the Ocean and Cryosphere in a Changing Climate (SROCC) is a report about the effects of climate change on the world's seas, sea ice, icecaps and glaciers. It was approved at the IPCC's 51st Session (IPCC-51) in September 2019 in Monaco. The SROCC's approved Summary for Policymakers (SPM) was released on 25 September 2019. The 1,300-page report by 104 authors and editors representing 36 countries referred to 6,981 publications. The report is the third in the series of three Special Reports in the current Sixth Assessment Report (AR6) cycle, which began in 2015 and will be completed in 2022. The first was the Special Report on Global Warming of 1.5 °C, while the second was the 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", which was released on 7 August 2019.
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.