1988

The Intergovernmental Panel on Climate Change is set up by the UN and the World Meteorological Organisation, bringing together the world’s leading climate scientists to assess knowledge of climate change and provide scientific advice to policymakers.

1990

The First Assessment report from the IPCC shows the climate changes partly owing to natural variability, but that greenhouse gas emissions from human activity play a role, and predicts temperature rises of 0.3C a decade in the 21st century, higher than seen in 10,000 years, and sea level rises of 60cm by 2100.

1992

At a major conference in Rio de Janeiro, world governments sign the UN Framework Convention on Climate Change, a treaty binding them to “achieve … stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”, usually shortened to “avoid dangerous climate change”. From this, establishing what level of warming should be classed as “dangerous” and what avoiding this entails, become key questions.

1995

The Second Assessment report is published, showing carbon dioxide is the main contributor to warming, and that human actions increasing carbon concentrations in the atmosphere could alter the climate irreversibly.

1997

The Kyoto protocol, an addition to the UNFCCC treaty stipulating cuts in greenhouse gas emissions from developed countries by 2012, is signed. However, the US – then the world’s biggest emitter – fails to ratify the protocol, leaving it in abeyance. It eventually comes into legal force in 2005 after Russia ratifies it.

2001

The Third Assessment report is published, showing the world has warmed by 0.6C compared with pre-industrial levels, and in the last 50 years this was mainly due to human activity. The report predicts temperature rises of between 1.4C and 5.8C by 2100, and sea level rises of 0.1 to 0.9 metres.

2006

The UK government publishes the Stern Review on the Economics of Climate Change, led by the former World Bank chief economist Sir Nicholas Stern, showing for the first time that the catastrophic economic impacts of climate change far outstrip the relatively modest costs of reducing emissions.

2007

The Fourth Assessment teport is published, showing that warming is “unequivocal” with more than 90% certainty that this comes from human activity. The report confirms that beyond certain levels of warming, effects on the climate become irreversible and in many cases catastrophic, and posits scenarios for a range of estimates of future warming. The mid-range estimate of human-induced warming of about 2C above pre-industrial levels is adopted as the threshold of safety in political decisions on curbing greenhouse gas emissions.

The IPCC is awarded the Nobel peace prize for its efforts. Negotiations begin on a new global climate agreement.

2009

Governments meet in Copenhagen intending to draft an effective replacement for the Kyoto protocol. Amid bitter political fighting, they sign a partial declaration instead under which for the first time the biggest developed and developing countries agree to emissions curbs.

Before the Copenhagen conference, hacked emails appear to show climate scientists manipulating temperature figures, claims that were later rebuffed but which quickly gain notoriety. By early 2010, the “climategate” scandal has spread to the IPCC, with errors found in its 2007 report. Most are small, but one that Himalayan glaciers would disappear by 2035, taken from an unverified report, causes deep embarrassment. The IPCC introduces reforms to ensure such “grey” material is not included in future reports.

2013-14

The Fifth Assessment report is published in stages, showing the 2C threshold will be breached within 30 years without urgent action to reduce greenhouse gas emissions.

2015

Governments sign the Paris agreement, the first fully legally binding international accord requiring all countries to hold global temperature rises to no more than 2C above pre-industrial levels, with an aspiration to limit rises to 1.5C. Soon after, the IPCC begins work on assessing whether the 1.5C aspiration is feasible, and how to meet it.

2018

A supplementary report on 1.5C rises is published, showing the aspiration is feasible but will require tough and urgent action to bring down greenhouse gas emissions.

2022

The IPCC will publish its sixth assessment report, drawing together all current knowledge on climate change, its effects and ways to reduce emissions.