Role of Non-CO2 gases and air pollutants

Apart from carbon dioxide (CO2), the climate system is affected by other substances in the atmosphere with human sources, including non-CO2 greenhouse gases and air pollutants. Some of these have a shorter residence time in the atmosphere than CO2. The residence time and the strength of the effects on climate are determined by processes in the atmosphere, including chemical processes between emitted species and physical processes including these species as well, influencing direct lights scattering and cloud cover and properties. In particular the effects of air pollutants, such as sulphate aerosols and soot, are very uncertain and the topic of continuing research.


53 countries have signed up to the Global Methane Pledge, committing to cut methane emissions by 30% in 2030 from 2020 levels. In 2019, these countries made up 30% of global methane emissions and around 34% of total global greenhouse gas (GHG) emissions. This analysis quantifies the potential impacts of the pledge if all countries were to adopt it.  
The commonly agreed metric to aggregate emissions and removals of greenhouse gases under the UNFCCC and the Paris Agreement is the Global Warming Potential with a 100-year time-horizon (GWP100). Since the Agreement was adopted, new scientific concepts emerged, such as GWP*. This briefing looks at the pitfalls of applying this new metric.  
There have been proposals for the UNFCCC to adopt a dual-term greenhouse gas accounting standard: 20-year GWPs alongside the presently accepted 100-year GWPs. It is argued that the advantage of such a change would be to more rapidly reduce short term warming and buy time for CO2 reductions. This briefing shows why these changes would be counterproductive and the benefits overstated.  


The EU-funded project “Constraining uncertainty of multi-decadal climate projections” (CONSTRAIN) will address crucial knowledge gaps in climate science to significantly improve our understanding of how natural and human factors affect multi-decadal regional climate change. The project will deliver improved climate projections of policy relevance for the next 20 to 50 years, contributing to European research on fundamental climate system processes and climate variability.  
Science and policy to assist and support SIDSs and LDCs to negotiate a strong international climate regime, enabling low carbon development and supporting adaptation needs.