Stringent mitigation action to limit warming to 2˚C avoids a large amount of the climate impacts that would otherwise occur in the 21st century. However, since even this stringent action will not avoid all climate change impacts, significant damage or adaptation costs will still occur but they will be much reduced compared with business-as-usual (A1B).
Some benefits of mitigation policy are already realised by the 2050s. The benefits con-tinue to increase in the second half of the century.
Reducing the risk of triggering accelerated or irreversible climate change is one of the strongest reasons for imposing stringent climate mitigation policies. Limiting future cli-mate change leads to a lower probability of irreversible melting of the Greenland and Antarctic ice sheets and the release of large natural stores of methane from under parts of the ocean, which could cause further warming. It will also limit the die back of tropical forests.
For impacts during the 21st century, achieving an early peak in global emissions leads to greater avoided impacts on many sectors later in the century.
Some impacts depend on both temperature and CO2 concentration, so considering ‘CO2-equivalent’ emissions obscures the picture. For example, in our agricultural model a higher CO2/non-CO2 ratio typically benefits agriculture in the short term. In practise, processes not included in our agricultural model, such as increases in tropospheric ozone, may cancel out this effect. In the longer term, further climate change has negative impacts on agriculture due to the continuing rise in temperature. Furthermore, higher CO2 concentrations will also lead to greater ocean acidification, damaging coral reefs.
There is a significant regional variation of avoided impacts (and remaining impacts). How-ever, some impacts will be felt non-locally because of global trade, migration and poten-tial international conflicts over fertile land and access to water.