This year's U.N. climate conference, taking place Nov. 30-Dec. 12 in Dubai, marks the world's 28th leadership gathering to confront global warming since the first "Conference of the Parties" in 1995. But the world has known for far longer of the existential threat posed by climate change, caused mainly by the burning of fossil fuels.

Here are some key moments in the history of climate talks:

1800s - For about 6,000 years before the industrial era, global levels of atmospheric carbon dioxide (CO2) remained around 280 parts per million ("ppm"). Several European scientists begin studying how different gases trap atmospheric heat and in the 1890s Svante Arrhenius of Sweden calculates the temperature effect from doubling atmospheric CO2 levels, demonstrating how burning fossil fuels will warm the planet.

1938 - Based on historical weather data, British engineer Guy Callendar reveals that temperatures are rising in line with increasing CO2 levels, and hypothesizes that the two are linked.

1958 - American scientist Charles David Keeling starts systematically measuring CO2 levels over Hawaii's Mauna Loa Observatory, resulting in the famed "Keeling Curve" line graph that shows steadily rising CO2 concentrations.

1988 - Climate scientist James Hansen testifies before U.S. Congress that greenhouse gases from industrial activities are warming the planet and already altering the climate and weather.

1990 - At the U.N.'s so-called Second World Climate Conference, scientists highlight the risks of global warming to nature and society. British Prime Minister Margaret Thatcher says binding emissions targets are needed.

1992 - Countries at the Rio Earth Summit sign onto the U.N. Framework Convention on Climate Change (UNFCCC). The treaty establishes the idea of "common but differentiated responsibilities" - meaning developed countries must do more to tackle climate-warming emissions because they emitted the most historically. The Rio summit also sets up negotiating tracks for protecting biodiversity, among other environmental goals.

1995 - UNFCCC signatories hold the first "conference of parties," or COP, in Berlin, resulting in a final document that calls for legally binding emissions targets.

1997 - At COP3 in Kyoto, Japan, parties agree to emissions cuts for developed countries, with different limits assigned to different countries. In the United States, key Senate Republicans denounce the Kyoto Protocol as "dead on arrival".

2000 - After losing the U.S. presidential election, Al Gore begins giving talks worldwide on climate science and policy that eventually are made into the 2006 documentary An Inconvenient Truth. The film later wins an Academy Award, while Gore and the U.N. climate science authority - the Intergovernmental Panel on Climate Change - receive the Nobel Peace Prize.

2001 - U.S. President George W. Bush calls the Kyoto Protocol "fatally flawed," signaling the country's effective exit.

2005 - The Kyoto Protocol goes into effect after Russia ratifies it, meeting a requirement for ratification by at least 55 countries accounting for at least 55% of emissions.

2007 - Delegates agree at COP13 in Bali to work on a new binding agreement for both developed and developing countries.

2009 - COP15 talks in Copenhagen nearly collapse amid wrangling over a binding post-Kyoto framework. Countries instead vote to "take note" of a non-binding political statement.

2010 - COP16 in Cancun fails to set new binding emissions targets, but establishes a Green Climate Fund to help developing countries cut emissions and adapt to the conditions of a warmer world. The Cancun Agreements also set a goal of limiting global warming to 2C above the preindustrial average.

2011 - COP17 talks in Durban, South Africa, falter after China, the United States and India refuse binding emissions cuts before 2015. Delegates instead extend the Kyoto Protocol through 2017.

2012 - As Russia, Japan and New Zealand resist new emissions targets that don't extend to developing nations, countries at COP18 in Doha extend the Kyoto Protocol through 2020.

2013 - Delegates from poorer nations walk out of COP19 talks in Warsaw over a lack of agreement on climate-related losses and damage, before a watered-down deal is reached. Meanwhile, atmospheric CO2 levels cross 400 ppm for the first time in recorded history.

2015 - The global average temperature rises beyond 1 degree Celsius over the preindustrial average. The COP21 climate talks result in The Paris Agreement, the first global pact to call for increasingly ambitious emissions pledges - called "Nationally Determined Contributions, or NDCs - from both developed and developing countries. Delegates also pledge to try to keep warming to within 1.5C.

2017 - U.S. President Donald Trump calls the Paris treaty bad for the economy, pledging a U.S. exit, which happens in 2020.

2018 - Teen activist Greta Thunberg captures global attention while protesting outside Swedish parliament, and over time rallies youths across the world to join in weekly street protests to demand climate action.

2019 - U.N. Secretary-General Antonio Guterres lambasts a lack of ambition at COP25 in Madrid.

2020 - The annual COP is postponed amid the COVID-19 pandemic.

2021 - Newly elected U.S. President Joe Biden rejoins the Paris Agreement. Later that year at COP26, the Glasgow Pact sets a goal of using less coal and resolves rules for trading carbon credits to offset emissions.

2022 - COP27 in Sharm el-Sheikh, Egypt, results in a historic deal for a Loss and Damage Fund for costly climate disasters, but does little to address the emissions fueling such disasters.

(Reporting by Katy Daigle; Editing by Rod Nickel)