Explainer | COP27: how UN summits have tackled climate change

This year’s UN climate conference in Sharm el-Sheikh, Egypt, marks the 27th time since 1995 that world leaders have gathered to confront global warming.

But the world has known for far longer that climate change was a threat, and that the cause was mainly fossil fuel use and other industrial activity.

1800s – Throughout the 1800s, several European scientists study how different gases and vapours can trap heat in the Earth’s atmosphere. In the 1890s, Swedish scientist Svante Arrhenius calculates the temperature effect of a doubling of atmospheric CO2, showing that burning fossil fuels would likely warm the planet.

1938 – By compiling historical weather data, British engineer Guy Callendar for the first time shows the planet’s temperatures are rising in the modern era. He correlates the temperature trends with measured rises in atmospheric CO2 and proposes the temperature change is linked.

1958 – American scientist Charles David Keeling starts systematically measuring atmospheric CO2 levels over Hawaii’s Mauna Loa Observatory. His findings result in the “Keeling Curve”, a graph showing CO2 concentrations steadily increasing.

1988 – James Hansen, an American climate scientist, testifies before Congress that the planet is warming because of a human-caused build-up of greenhouse gasses and notes that this is already altering the climate and weather.