Novel findings on sea surface temperature projections (SST) and time-varying feedbacks are being translated into openly accessible climate emulators that will allow the latest climate science to inform policy-relevant information. A particularly unexplored field where research is improving understanding.
Cloud feedbacks remain the most important source of uncertainty in climate sensitivity. Investigated using knowledge gained by the EUREC4A field campaign which was coordinated by Work Package 2 leads. This provided new insights into cloud processes in the Tropics and fed into broader assessments of feedbacks and climate sensitivity, and also how these are represented in CMIP6 models
CONSTRAIN scientists contributed to the landmark Sherwood et al. (2020) assessment of climate sensitivity, narrowing the likely range of Equilibrium Climate Sensitivity (ECS) to 2.3–4.5K. The high estimates of ECS in CMIP6 models compared to CMIP5 are likely due to changes in mixed phase cloud processes and Antarctic sea ice representation.
Step changes in the quantification of Effective Radiative Forcing (ERF) were set out in the project’s first KGSIR, including a method to calculate ERF from climate model simulations keeping SST constant, which can be applied to a large range of climate drivers and is important for understanding climate change. Historical ERF has also been constrained to a range representing an almost 40% reduction compared to that of IPCC AR5, suggesting ERF may be too small in up to one-third of CMIP5 climate models.
Advances made on the understanding of rapid adjustments were set out in a second KGSIR. Including improvements to anthropogenic aerosol representation, forcing and feedbacks in climate models; and a narrowing of the range of aerosol forcing compared to CMIP5.
The new Silicone pathway tool has delivered improved climate projections by allowing Integrated Assessment Models to include emissions of a broad range of species, rather than just CO2 and CH4. Silicone is now being used widely in major climate assessments and to inform policy decisions.
CONSTRAIN’s robust estimate of and framework for calculating the remaining global carbon budget is increasing understanding of the concept among stakeholder communities and providing a strong platform for future communications efforts. Updates to the remaining global carbon budget are provided in the annual Zero In reports alongside additional information and context on the concept.
Investigation of the latest (CMIP6) climate models, comparing the model results with temperature observations, have found that most of the models with high ECS values also overestimate recent warming trends,
indicating that their future temperature projections are also too high (Zero In 2).
Near-term warming rates have also been investigated further using climate emulators and more complex climate models, highlighting how strong climate action limit the amount of overall warming and slow down warming rates in coming decades.
The CONSTRAIN and IPCC Emulator workshop in 2021 harnessed expertise from across the scientific community to highlight the use of climate model emulators in AR6
Time-evolving feedbacks have been investigated using a climate emulator. Results show how different strengths of climate feedback form differences in global temperatures of up to 1°C by 2050. Implications for warming rates, regional temperature change, and rainfall patterns. This work is a first step in providing clarity on how temperatures and rainfall will respond to future emissions.
CONSTRAIN is ambitious about knowledge transfer, and adapted well to pandemic restrictions, reaching new audiences through the 2020 virtual UNFCCC Climate Dialogues, Commission-organised knowledge transfer events and cross-project events in place of the postponed COP26. CONSTRAIN then launched Zero In 3 at COP26 in 2021.
New scientific opportunities arose regarding the climate impact of COVID-19, using novel techniques and tools developed as part of the project, Silicone tool and the use of widely available mobility data. This attracted widespread interest and increased CONSTRAIN’s external profile, attracting considerable media attention.
