Climate change metrics: IPCC AR6 updates, discussions and dynamic assessment applications
Abstract. Climate change metrics result from analytical simplification of complex and diverse climate models. Assessment communities do not always take the time to understand this complexity. We investigated the last IPCC report to properly gather updated metric equations, climate parameters and associated uncertainties. In each future Assessment Reports, IPCC is encouraged to recall climate equations and parameters values in a pedagogical way. Global Warming Potential (GWP) is an easy-to-use, but simplistic and criticised metric. Alternative Global Temperature change Potential (GTP) remains as GWP: relative to carbon dioxide and used at arbitrary fixed time horizons (H). This study focuses on two dynamic metrics – cumulative radiative forcing (AGWP or ΔF) and global temperature change (AGTP or ΔT) – and applies them to the three major anthropogenic greenhouse gases (GHGs) – carbon dioxide, methane and nitrous oxide. Dynamic climate metrics better assess impacts by differentiating GHGs contribution over time. For radiative forcing metrics, indicators at common H – 20, 100, 500 years – are sufficient, with no hierarchy between these timescales. As for global temperature change metrics, they have two advantages that offset their higher uncertainties. (1) They are more policy-relevant with an easily understandable unit. (2) Peak and long-term temperature change enable to get rid of H major issue, i.e. IPCC is encouraged to adopt AGTPpeak and AGTPlong-term characterisation factors. We also recommend plotting complementary cumulative radiative forcing and temperature change temporal profiles of a product system up to 600 years. This enables going towards climate neutral product systems with more clarity, transparency and understanding.