The December 2015 Paris Agreement on climate change is a remarkable document. In just 25 pages it offers a pragmatic blueprint for resolving one of the toughest issues society faces. The aim of the Agreement is to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels.
In pursuit of this goal, the Agreement calls for a “balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of
the century.” This emphasis on “a balance” – or what is also referred to as “net-zero emissions” – is a critical development because it recognises that surface temperature warming is directly related to the cumulative total of CO2 emitted to the atmosphere. If total cumulative emissions overshoot a threshold, it may be necessary to go beyond net-zero emissions to achieve “net-negative” emissions, where more CO2 is extracted from the atmosphere than continues to be released. In such a case, the global average surface temperature can fall.