1988—Prominent scientists testify for the first time before U.S. Congress about dangers of global warming. Intergovernmental Panel on Climate Change (IPCC) formed to gather and assess evidence.
1992—In Rio de Janeiro, IPCC agrees a United Nations framework is needed to stabilize greenhouse gas concentrations in the atmosphere.
December 1997—The world's governments gather in Kyoto, Japan, to negotiate a treaty to curb global warming. The United States never ratifies the treaty. A developing nation, China, was never bound by the treaty.
February 2001—The Third IPCC reports that global warming will likely cause unprecedented sea level rise, extreme weather events and grave consequences for humanity. A few months into the next year comes a dramatic collapse of the Larsen B Ice Shelf in Antarctica.
August 2005—Hurricane Katrina hits the Gulf Coast. This and other severe weather events spur debate over impact of global warming. U.N. parties continue negotiations toward global carbon reductions.
May 2006—An Inconvenient Truth, the film version of former Vice President Al Gore's lectures on climate change, is released and eventually wins multiple Oscars. Climate science enters into popular consciousness but political polarization mounts.
2006—Congress stalls on the climate, leaving state governments to lead the charge. California passes the Global Warming Solutions Act and soon leads the nation in energy efficiency standards and regulation of emissions.
2007—China overtakes America as the world's largest greenhouse gas emitter. NASA finds Greenland and Antarctic ice sheets and Arctic Ocean sea-ice cover shrinking faster than expected. Fourth IPCC report warns that serious effects of warming have become evident. Gore and the IPCC win joint Nobel Peace Prize for climate work. He and others launch grassroots organizations to debunk climate change deniers and build a global movement. Their efforts are ongoing.
2009—Many experts warn that global warming is arriving at a faster and more dangerous pace than expected. Meanwhile, the United Nations Framework Climate Change Conference talks in Copenhagen, held in the midst of a global recession, fail to negotiate binding emissions agreements amongst the countries of the world.
2011—UNFCCC meets in Durban, South Africa, and parties agree to work on a new and universal agreement involving all countries, not just wealthy ones, to join in combating global warming. This accord is to be negotiated in Paris.
2013—Mean global temperature is warmest in thousands of years; concentration of carbon in the atmosphere reaches 397 parts per million, the highest it's been in millions of years. Scientists and politicians become bolder in connecting the dots between increased storms, wildfires, floods, droughts and climate change.
September 2014—Global rallies are held in 2,000 locations across the world demanding urgent action on climate change. Hundreds of thousands of people gather and continue a call for action.
November 2014—In an unexpected political breakthrough, China and the United States, which together produce nearly half of global carbon dioxide emissions, jointly announce future reduction plans.
May 2015—Pope Francis releases unprecedented papal encyclical wherein he calls for urgent action on climate change. Two more populous countries—Brazil and India—make pre-Paris commitments to decrease emissions.
December 2015—The world's governments convene in Paris where they agree upon and sign a unified, global accord and to put architecture in place to save humanity from the worst outcomes of climate change.
October 2016—Nearly 200 nations, including the United States, reach a global deal to phase out hydrofluorocarbons, the strong, but short-lived greenhouse gases emitted by refrigerators and air conditioners, as well as reduce emissions from the shipping and aviation industries. The reduction is slated to start in 2019.
Source: UNFCCC, IPCC, The New York Times