An outline, era by era

Climate change becomes a central issue (Paris Agreement, 2015)

21st Century · 2000 – present

Climate change became a central issue in world politics in the decades around the turn of the twenty-first century. Scientists had shown that burning coal, oil and gas adds carbon dioxide to the air and warms the planet. Governments responded with a series of international agreements, beginning with the 1992 UN Framework Convention on Climate Change and the 1997 Kyoto Protocol.

The best-known result is the Paris Agreement, adopted by nearly 200 countries in December 2015 at a UN conference in Paris. It set the aim of holding global warming well below 2 degrees Celsius above pre-industrial levels, and of pursuing efforts to limit it to 1.5 degrees. Each country sets its own national pledges, which are reviewed over time. The issue now shapes energy, economics, trade and diplomacy worldwide, and it is also debated, since countries disagree about who should act first and who should pay.

Things happened, and the rest is history

  1. Keeling measures rising carbon dioxide

    Event

    What happened

    In 1958 the chemist Charles David Keeling begins measuring carbon dioxide in the air at Mauna Loa in Hawaii. His record shows a regular yearly rise and fall with the seasons, on top of a steady climb from year to year.

    The rest is history

    The record, known as the Keeling Curve, gave the first clear continuous evidence that carbon dioxide in the atmosphere was increasing. It became a basic piece of evidence in climate science. Readings have risen from about 315 parts per million in 1958 to over 420 parts per million in recent years.

    Sources

    1. BookWeart, Spencer R. The Discovery of Global Warming. Cambridge, MA: Harvard University Press, 2003.
    2. BookArcher, David. The Global Carbon Cycle. Princeton: Princeton University Press, 2010.

  2. Hansen's testimony to the US Senate

    Event

    What happened

    In June 1988 the NASA scientist James Hansen tells a US Senate committee that he is highly confident that a warming trend is under way and that it is linked to the greenhouse effect. The hearing takes place during a hot summer and is widely reported.

    The rest is history

    The testimony brought global warming into public and political debate in the United States and elsewhere. It came in the same year that the UN set up a scientific body to assess the question. Hansen's claims were debated at the time, but later records confirmed the long-term warming trend.

    Sources

    1. BookWeart, Spencer R. The Discovery of Global Warming. Cambridge, MA: Harvard University Press, 2003.
    2. BookHansen, James. Storms of My Grandchildren. New York: Bloomsbury, 2009.

  3. The IPCC is founded

    Event

    What happened

    In 1988 the World Meteorological Organization and the UN Environment Programme create the Intergovernmental Panel on Climate Change. Its first assessment report appears in 1990. Scientists review the published research and governments approve the summaries.

    The rest is history

    The IPCC reports have since served as the main shared scientific basis for climate negotiations. The first report helped lead to talks on a global treaty. In 2007 the IPCC shared the Nobel Peace Prize with Al Gore.

    Sources

    1. PrimaryIntergovernmental Panel on Climate Change. Climate Change: The IPCC Scientific Assessment. First Assessment Report, Cambridge: Cambridge University Press, 1990.
    2. BookHulme, Mike. Why We Disagree About Climate Change. Cambridge: Cambridge University Press, 2009.

  4. The Earth Summit and the UN climate convention

    Event

    What happened

    In June 1992 world leaders meet at the Earth Summit in Rio de Janeiro. The UN Framework Convention on Climate Change is opened for signature there. It commits countries to prevent dangerous human interference with the climate system, but sets no binding limits on emissions.

    The rest is history

    The convention came into force in 1994 and created the yearly meetings known as Conferences of the Parties. It set the principle of common but differentiated responsibilities, under which richer countries were expected to lead. Every later agreement, including Kyoto and Paris, was built on this framework.

    Sources

    1. PrimaryUnited Nations Framework Convention on Climate Change. Treaty text adopted in New York, 9 May 1992.
    2. BookBodansky, Daniel. The Art and Craft of International Environmental Law. Cambridge, MA: Harvard University Press, 2010.

  5. The Kyoto Protocol

    Event

    What happened

    In December 1997 countries meeting in Kyoto, Japan, adopt a protocol with legally binding emission targets for developed countries. The targets cover 2008 to 2012. The United States signs but does not ratify, and the protocol enters into force in 2005.

    The rest is history

    Kyoto was the first treaty to set binding targets, and it created carbon trading mechanisms. Its weakness was that major emitters among developing countries had no targets, and the United States stayed out. Later talks, including Copenhagen in 2009, struggled to find a successor, which led towards the different approach of Paris.

    Sources

    1. PrimaryKyoto Protocol to the United Nations Framework Convention on Climate Change. Treaty adopted at Kyoto, 11 December 1997.
    2. BookVictor, David G. The Collapse of the Kyoto Protocol and the Struggle to Slow Global Warming. Princeton: Princeton University Press, 2001.

  6. The Stern Review and the economics of climate

    Event

    What happened

    In October 2006 the British economist Nicholas Stern publishes a report for the UK government on the economics of climate change. It argues that the cost of strong early action is much smaller than the cost of unchecked warming.

    The rest is history

    The review moved the debate from science towards economics and policy. Some economists criticised its choice of discount rate, and the argument over this continued. It was widely read by governments and helped support the case for early action.

    Sources

    1. BookStern, Nicholas. The Economics of Climate Change: The Stern Review. Cambridge: Cambridge University Press, 2007.

  7. The Copenhagen summit of 2009

    Event

    What happened

    In December 2009 leaders gather in Copenhagen hoping for a new global deal. The talks are tense, and a last-minute accord is drawn up by a small group of countries. The conference only takes note of it rather than adopting it.

    The rest is history

    The Copenhagen Accord mentioned the 2 degree limit and promised climate finance for poorer countries, but it was not binding. The disappointment led negotiators to rethink the approach. Over the following years they moved to a system of voluntary national pledges, which became the model for Paris.

    Sources

    1. BookBodansky, Daniel. The Art and Craft of International Environmental Law. Cambridge, MA: Harvard University Press, 2010.
    2. PrimaryCopenhagen Accord. Decision 2/CP.15, UN Climate Change Conference, Copenhagen, December 2009.

  8. The Paris Agreement is adopted

    Event

    What happened

    On 12 December 2015 delegates at the Paris conference adopt the Paris Agreement by consensus. It sets goals of holding warming well below 2 degrees Celsius and pursuing 1.5 degrees. Each country submits its own pledge, called a nationally determined contribution, and is to renew it every five years.

    The rest is history

    The agreement entered into force on 4 November 2016, after enough countries had ratified it. The United States announced a withdrawal in 2017, rejoined in 2021 and announced another withdrawal in 2025. The pledges made so far fall short of the stated goals, and the gap between promises and action is a continuing subject of debate.

    Sources

    1. PrimaryParis Agreement. Treaty adopted under the UNFCCC, Paris, 12 December 2015.
    2. BookBodansky, Daniel, Jutta Brunnée, and Lavanya Rajamani. International Climate Change Law. Oxford: Oxford University Press, 2017.

  9. Climate change is a hoax

    Popular belief

    The legend

    Some people say that global warming is a hoax invented by scientists or governments to win funding or control. A related claim holds that the climate has always changed naturally, so humans cannot be responsible.

    The rest is history

    The climate has indeed changed naturally in the past, driven by orbital cycles, volcanoes and the sun. But measurements show that the present warming is far faster than those natural shifts and matches the rise in greenhouse gases from fossil fuels. Studies of the scientific literature find that the great majority of climate scientists agree that humans are the main cause. Organised campaigns to cast doubt on the science, some funded by fossil fuel interests, have been documented by historians.

    Sources

    1. BookOreskes, Naomi, and Erik M. Conway. Merchants of Doubt. New York: Bloomsbury, 2010.
    2. ArticleOreskes, Naomi. "The Scientific Consensus on Climate Change." Science 306, no. 5702 (2004): 1686.

  10. The Climategate emails

    Popular belief

    The legend

    In November 2009 emails from the University of East Anglia's Climatic Research Unit are leaked online. Many people say they prove that scientists faked or hid data to exaggerate global warming.

    The rest is history

    Several independent inquiries, in Britain and the United States, looked into the emails. They found no fraud or manipulation of data, though they criticised the unit for poor openness in responding to information requests. The leak came shortly before the Copenhagen summit and fed public doubt at a sensitive time. The temperature records involved have been confirmed by other research groups.

    Sources

    1. PrimaryRussell, Muir, et al. The Independent Climate Change Email Review. Report, London, July 2010.
    2. BookMann, Michael E. The Hockey Stick and the Climate Wars. New York: Columbia University Press, 2012.

  11. Paris will keep warming below 1.5 degrees

    Popular belief

    The legend

    Many people believe that the Paris Agreement itself guarantees that warming will be held to 2 or 1.5 degrees, as if the treaty on its own caps global temperatures.

    The rest is history

    The agreement sets goals, not a binding cap. Its pledges are voluntary, and there is no penalty for missing them. Analyses by the UN Environment Programme have repeatedly found that current pledges would lead to well over 2 degrees of warming unless strengthened. The year 2024 was the first calendar year recorded as more than 1.5 degrees above the pre-industrial average, though the Paris goal refers to a longer-term average.

    Sources

    1. PrimaryUnited Nations Environment Programme. Emissions Gap Report. Annual report, Nairobi, 2015 onwards.
    2. PrimaryIntergovernmental Panel on Climate Change. Global Warming of 1.5°C. Special report, Geneva, 2018.

  12. Al Gore and the end of ice and polar bears

    Popular belief

    The legend

    Some say that Al Gore's film An Inconvenient Truth (2006) predicted that sea level would rise by several metres within a few years and drown coastal cities almost at once.

    The rest is history

    The film showed what could happen if large ice sheets melted, and it did not give a date. A British court in 2007 found the film broadly accurate but noted nine points it called errors or overstatements, in a case about showing it in schools. Sea level has been rising by a few millimetres a year, and the pace has increased. The IPCC projects tens of centimetres to around a metre by 2100, with larger rises possible later.

    Sources

    1. PrimaryDimmock v Secretary of State for Education and Skills. High Court of Justice, England and Wales, judgment of 10 October 2007.
    2. PrimaryIntergovernmental Panel on Climate Change. Climate Change 2021: The Physical Science Basis. Cambridge: Cambridge University Press, 2021.

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