The impacts of climate change avoided by future reductions in emissions as defined in the Intended Nationally-Determined Contributions (B2c)

The estimated total emissions in 2030 are 54 GtCO₂eq. Impacts depend on emissions after 2030, and six scenarios for future emissions are defined: five were developed using the Grantham Institute’s TIAM model (“TIAM-Grantham”) representing different pathways of emissions after 2030.

Under all but the emissions scenario which achieves the 2°C target, temperatures are still increasing by 2100. Sea level is still increasing by 2100 under all the scenarios. Impacts under these INDC-based scenarios are compared with impacts under two reference scenarios, representing medium and high unmitigated emissions and producing temperature increases by 2100 of between 4.2 and 5.2°C above pre-industrial levels.

Whilst there may be some short-term benefits, for example associated with CO₂ fertilisation, models indicate that the negative impacts of climate change predominate over time with greater levels of radiative forcing throughout the 21^st century. Reducing emissions would reduce future warming and result in a lowering of the negative impacts of climate change. The proportions of impacts that are avoided through emissions reductions vary between sectors and are generally not equal to the proportional reduction in global mean temperature change: halving the increase in temperature does not necessarily halve the impacts. For some indicators of risks to society the effect is greater, and for others it is less. This is due to the non-linear relationship between the magnitude of globally-averaged temperature change and resulting impact, the shape of which varies between sectors. Uncertainties stem primarily from uncertainty in the projected regional distribution of climate change – particularly rainfall. The absolute amount of impacts avoided by reducing emissions (for example on numbers of people affected) depends on socio-economic assumptions (population change and rate of economic development), but the proportion of impacts that are avoided is relatively consistent across different plausible socio-economic futures.

The results show that the INDCs, if fully implemented and sustained, could put the world onto a pathway of impacts that is already significantly below reference no mitigation pathways, but without further emissions reductions after 2030 would leave warming well above the 2°C level. Future impacts strongly depend on how emissions reduce after the 2030 INDC pledge date, but this AVOID study finds feasible pathways that reach or approach the 2°C level in 2100.