Today the level of carbon dioxide (Co2) in the Earth’s atmosphere is higher than at any time in human history. Variations in Co2 have been controlling climate changes. A small amount of carbon dioxide in the atmosphere can have a big effect. Scientists widely agree that Earth’s average surface temperature has already increased by about 1°C since the 1880s and that human-caused increases in Co2 and other heattrapping gases are extremely likely to be responsible.

     Without action to control emissions, Co2 might reach 0.1 per cent of the atmosphere by 2100, more than triple the level before the Industrial Revolution. This would be a faster change than transitions in Earth’s past that had huge consequences.

    Collective response to the challenge culminated in what is now known as the Paris Agreement, a legally binding international treaty on climate change, adopted by 196 Parties at the UN Climate....