The 2015 Paris Agreement commits countries to limit the global average temperature rise to well below 2C above pre-industrial levels, and to aim for 1.5C.
Scientists have said crossing the 1.5C threshold risks unleashing far more severe climate change effects on people, wildlife and ecosystems.
Preventing it requires almost halving global CO2 emissions by 2030 from 2010 levels and cutting them to net-zero by 2050 - an ambitious task that scientists, financiers, negotiators and activists at COP26 are debating how to achieve and pay for.
