Human driven global warming represents an existential threat to human civilisation and much of earth's flora and fauna. Global heating is driven by human emissions of greenhouse gases (GHG). As of 2021, average temperatures have already risen about 1.2 °C above pre-industrial levels. This rise has already contributed to the extinction of numerous plants and animals and to many thousands of human deaths. At the 2015 Paris conference, nations agreed to make efforts to keep further rises well below 2 °C, and to try to limit them to 1.5 °C. Specific actions to achieve this have not yet been decided. With existing policies and commitments, global warming is projected to reach about 3 °C by 2100. The impact of global warming could be worsened by the possible triggering of irreversible climate tipping points.