The 2026 NCGG-10 Symposium on non-CO2 greenhouse gases targets the greenhouse gases methane (CH4), nitrous oxide (N2O), fluorocarbons and halogenetet species (HFC/CFC/HCFC/SF6 etc) . Since the contribution to climate warming since the pre-industrial period of these gases together is comparable to the warming caused by CO2 only (46% by non-CO2; 54% by CO2; ref. IPCC AR6) we denote them together as ‘the other half of the problem’. Especially CH4 is of increasing importance. Attention should also be giving to the impact of hydrogen (H2) and aerosols as short lived climate forcer agents.
The importance of this ‘other half’ is increasing every new NCGG conference. The rapid improvements in global air quality since the turn of the century are providing important health benefits and act as multiplier for non-CO2 global warming. Globally decreasing emissions of Sulphur dioxide (SO2 ) , Ammonia (NH3), nitrogen oxides (NOX) and non methane volatile orgainc carbons NMVOCs contribute indirectly to climate change through ozone and aerosol formation in the atmosphere and effects on the lifetime of methane.
The relative new kid on the energy block, is molecular H2. Leakages of H2 could prolong the chemical lifetime and thus climate warming of methane. The potential climate impacts of a global transition to a H2 economy is yet to be studied in detail, together with many other societal transitions that are underway in response to climate warming.
The balance of warming and cooling agents in the nitrogen cycle, N2O, NOx and NH3, can change. Processes include O3 and aerosol formation as well as changing CH4 lifetime. Increased NH3 emissions related to its new role in energy transport and production, may cause reactive-N leakage with indirect climate impacts including an increase in N2O and disturb the N cycle itself.
Public awareness that we need to act quickly on the climate dossier has grown rapidly, and it is widely appreciated that rapid CO2 mitigation is necessary. For non-CO2 greenhouse gases still further action is needed to increase public awareness and widespread societal action. Fortunately, reducing non-CO2 greenhouse gas emissions is often more than reducing CO2 emissions. Again CH4 has an important role here, with its relatively short atmospheric lifetime. A fast policy response to reduce CH4 might be the only option left to stay below the 1.5 degree target.
We will invite contributions with respect to four themes, covering causes, effects and solutions of the environmental problems associated with non-CO₂ greenhouse gases. These contributions may report on science (from natural, social, technological or integrated sciences) and policy.
