Fast Facts

AVOID has shown that limiting global warming to 2 °C is possible but challenging. Early global action increases our chances of remaining below this level.

There is some flexibility in the year of peak emissions (between 2014 and 2020). However, a later peak year must be coupled with much stronger action to reduce emissions after the peak and attain a low or zero long-term level of net emissions in the medium to long term. Such strength of action may be beyond economic and technological feasibility. There is thus a strong argument for early action.

Emissions after 2050 matter. For instance an extra 100 years of CO₂ emissions at just a fifth of the year 2000 level could add more than 0.3 °C to peak warming.

Global average warming is only an indicator of the response of the climate system to global emissions. Additional quantities, such as rainfall, sea-level rise, ocean acidification, regional variations and changes in extremes all influence the climate change impacts on people and natural systems.

Even stringent mitigation action to achieve a 2 °C target will not avoid all climate impacts (2016 peak in emissions and a 5% post-peak reduction rate). Significant damage or adaptation costs will still occur but they will be much reduced compared with business-as-usual.
The majority of the benefits of mitigation policy will not be realised until decades after the emissions cuts begin for all mitigation scenarios.
Reducing the risk of triggering accelerated or irreversible climate change is one of the strongest reasons for imposing stringent climate mitigation policies. Limiting future climate 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.
Considering ‘CO₂-equivalent’ emissions obscures the picture for some 21st century impacts. This is because impacts depend on both temperature and CO₂ concentrations, A higher CO₂/non-CO₂ ratio typically benefits agriculture in the short term but will also lead to greater ocean acidification.
There is a significant regional variation of avoided impacts (and remaining impacts). However, some impacts will be felt non-locally because of global trade, migration and potential international conflicts over fertile land and access to water.

There is still uncertainty in historic emissions of greenhouse gases.
For emissions excluding Land Use, land Use Change and Forestry (and international bunkers), the WRI estimate for 2005 is 37.8 Gigatonnes of CO₂ equivalent. The EDGAR estimate is 40.3 Gigatonnes of CO₂ equivalent.
Changes in land use (primarily deforestation) have been responsible for about 20% of all anthropogenic emissions of CO₂ to the atmosphere over the past 25 years, but this is the most uncertain part of the carbon budget.
The most up to date estimate of land use change emissions by the Global Carbon Project is 5.5 ±1.8 Gigatonnes of CO₂ per year from 2000 to 2007.
Unmitigated climate change is projected to have very substantial effects on exposure to undernourishment during the 21st century. A combination of adaptation and mitigation reduces the effects substantially.
There is considerable uncertainty in the number of people adversely affected by climate change and in the benefits resulting from mitigation, largely due to projected changes in rainfall between different climate models.
Potential threat to the marine environment – at low pH, many marine organisms find it difficult to build their shells and skeletal structure. This could have an impact higher up the food chain, starting with the fish that directly depend on these organisms, the ecosystems they belong to and ultimately the human communities that depend on them. These threats to marine species, habitats and ecosystems are currently poorly understood.
Carbon cycle – the impact of ocean acidifcation on the carbon budget may be amplified or lessened depending on the biological response of the ocean. The net effect of acidification on the interchange of CO₂ between the atmosphere and the oceans remains poorly constrained.