The only direct experiments documented in the scientific literature were done by Knut Ångström in 1900, one in the Canary Islands and one in the laboratory. Both experiments showed that increasing CO2 concentrations had little effect on air temperature.
In 1859, John Tyndall documented that greenhouse gases absorb infrared energy radiated by Earth. Since then, it has been assumed that an increase in the concentrations of these gases causes air to warm. This widespread assumption, however, has never been validated by an experiment in the field or in the laboratory.
On 2 November 2014, the UN Intergovernmental Panel on Climate Change (IPCC) concluded that emissions of greenhouse gases have been the dominant cause of observed warming since the mid-20th century.
On 12 December 2015, representatives from 195 nations negotiated the UN Paris Agreement agreeing to work together promptly to reduce greenhouse-gas emissions at a cost of trillions of dollars per year.
On 4 November 2016, the Paris Agreement entered into force.