The UN climate summit in Paris, which opens on November 30, is the latest bid to secure a universal climate rescue pact in a two-decade-long effort to limit global warming.
Here are key markers in the gruelling process.
1988: The United Nations sponsors the creation of the Intergovernmental Panel on Climate Change (IPCC), and tasks it with gathering scientific data on climate change.
1990: The first IPCC report says that "greenhouse gases" generated by human activity are on the rise, and could intensify global warming. Four more reports follow in 1995, 2001, 2007 and 2014, providing a cumulative mountain of evidence that man's voracious burning of coal, oil and gas is altering Earth's climate.
1992: The Rio "Earth Summit" establishes the United Nations Framework Convention on Climate Change (UNFCCC) and calls for voluntary reduction of GHGs.
Each year since 1995, a Conference of Parties (COP) that adhere to the convention (195 countries plus the European Union), meet to try and move the process forward.
1997: The Kyoto Protocol sets a 2008-2012 timeframe for industrialised nations to reduce GHG emissions by 5.2 percent from 1990 levels. Major developing country emitters such as Brazil, China and India are not required to take on targets. In 2001, the world's then-leading emitter, the United States, refuses to ratify the protocol.
2005: The Kyoto Protocol takes effect nonetheless, following its ratification by Russia -- the 55th signatory needed for the protocol to enter into force.
That leads to the creation of carbon markets, a trading system through which countries may buy or sell units of greenhouse-gas emissions to meet their national limits.
2006: China becomes the leading emitter of carbon dioxide (CO2), followed by the US, the European Union, India, Russia and Japan.
2007: An IPCC assessment report says evidence of global warming is now "unequivocal". It forecasts likely warming of 1.8-4.0 Celsius (3.2-7.2 F) by 2100 and a rise in sea levels of at least 18 centimetres (7.2 inches). The report also warns that extreme weather events will probably multiply.
In October 2007, the IPCC and former US vice president Al Gore are awarded the Nobel Peace Prize, but the panel's reputation is later tarnished by revelations that its most recent report contains several errors.
2009: COP 15 in Copenhagen is a near-catastrophe. Instead of a binding agreement it produces a last-minute political "accord" backed by both China and the United States in opposite corners. The document sets a goal of limiting global temperature increases to two degrees C (3.6F) but is vague regarding how the goal is to be reached.
It also foresees up to $100 billion in aid by 2020 to help poor countries reach their emissions goals.
2010: The Cancun Agreements signed at COP 16 in Mexico envisage the creation of a Green Climate Fund to help developing countries deal with global warming, but sources of funding are not specified.
2014: The fifth IPCC report warns that the average global temperatures by the end of the 21st century could be 3.7-4.8 degrees C (6.7-8.6 F) higher than in the period 1850-1900 if nothing is done to ease the upward emissions trend.
COP 19 in Doha gavels through a deal to extend the Kyoto Protocol to 2020, but only the EU and ten other industrialised nations, representing about 15 percent of global emissions in total, sign up.
2015: COP 21 is to be held in Paris from November 30 to December 11, with the goal of uniting all the world's nations in a single agreement on tackling climate change, by capping warming at 2.0 C (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels. The Paris pact is due to enter into force in 2020.