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Constraining Climate Model Projections of 21st Century Global and Regional Warming

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Yongxiao Liang
December 8, 2022 - 3:00pm to 4:00pm

A recording of this talk is available, here.

Observational constraint methods based on emergent relationships between observable metrics in historical simulations and future projected climate across multi-model ensembles are an effective approach to constraining the uncertainty of projections of anthropogenic warming. This presentation will provide an overview of applying observational constraints to global and regional warming. Firstly, using the observed 1970–2014 warming trend as constraint results in narrow uncertainty range especially reflected in the reduced upper bound of projected 21st century warming. Secondly, contrasting past warming trend constraints, we find an observational constraint using climatology low-cloud metrics shows better cross-validated results than using the past warming trend as a constraint. We provide evidence for a higher lower bound of the projected warming range than that obtained from constrained projections based on the past global-mean temperature trend. Thirdly, for regional constraints, linear regression models using global-scale low-cloud metrics alone perform more robustly than linear regression models using the past global mean warming trend or regional climate metrics as constraints. Using observed low-cloud metrics results in considerably narrower 5-95% uncertainty ranges of 21st-century warming over sub-continental Northern Hemisphere land regions. The narrower constrained uncertainty ranges produced by our observationally constrained framework are relevant to climate change policy and adaptation decisions – for example, planning decisions based on the need to avoid particular temperature thresholds.

Yongxiao Liang is a PhD student at the School of Earth and Ocean Sciences at UVic. He is conducting research on observational constraints for long-term climate projections. Liang’s research interests include the uncertainty of climate projections, and the role of forced response and internal variability in historical and future climate. Liang earned his Master's and Bachelor's degrees from Nanjing University of Information Science and Technology. He has been studying atmospheric science and climate change for 10 years.

Watch a recording of the talk.