Forced Component Estimation Statistical Method Intercomparison Project (ForceSMIP)

Anthropogenic climate change is unfolding rapidly, yet its regional manifestation is often obscured by naturally occurring variability internal to the atmosphere and ocean system. A primary goal of climate science is to distinguish the forced response, i.e., the spatiotemporal evolution of climate in response to external forcing such as greenhouse gases, anthropogenic aerosols, volcanoes, land-use change, and solar variability, from the noise of internal climate variability. Disentangling the forced and internal components of climate change is critical for attributing historical climate changes, for characterizing and understanding internal climate variability, and for improving observationally constrained projections of future climate. This is especially true for regional climate, in which internal variability can be comparable to or larger in magnitude than the forced response. 

Separating the forced response from internal variability can be addressed in climate models by taking the average over a large ensemble, where the same model is run multiple times with small differences in initial conditions leading to different realizations of internal variability. However, there is only one realization of the real world, which makes it a major challenge to isolate the forced response in observations. Nevertheless, it is critical to isolate the forced response in observations, because estimates of the forced response from climate models vary widely and are subject to biases. 

The Forced Component Estimation Statistical Method Intercomparison Project (ForceSMIP) will utilize climate model ensembles to develop and assess statistical methods for isolating the forced response from individual realizations of the climate system. These methods will then be applied to observations to produce a community estimate of the forced climate response.  The results of this project will in turn inform climate model evaluation, climate model development, and regional planning for near-term climate change. 

ForceSMIP is open to participants from around the world, as detailed in the How to Participate tab. While the deadline for Tier 1 submissions has already passed in March 2024, it is still possible to submit to Tiers 2 and 3, which have a deadline of February 1, 2025. Beyond that, we are also planning for a ForceSMIP Phase II focused on identifying the greenhouse-gas and anthropogenic-aerosol forced components, so please get in contact if you are interested in getting involved. 

We held hackathons on August 29-31, 2023 in two locations, ETH Zürich in Zurich, Switzerland and the National Center for Atmospheric Research (NCAR) in Boulder, Colorado; see the Hackathon tab for more information. 

Planned deliverables (i.e., planned peer-reviewed publications):

1. Evaluation of the ability for new and existing techniques to estimate the forced climate response in individual realizations of the climate system (across a wide range of geophysical fields) [Tier 1]

2. An estimate of the forced response in the real climate system based on observational data, using a performance-weighted average of contributed forced response estimates, with climate model data used only to train the methods and choose the weights [Tier 1]

3. Updates of methods, testing on longer and shorter time periods, and observational forced response estimates for these longer and shorter time periods [Tiers 2 and 3]

ForCESMIP is organized by

Robert Jnglin Wills (primary contact) r.jnglinwills@usys.ethz.ch

Clara Deser cdeser@ucar.edu

Karen McKinnon kmckinnon@ucla.edu

Adam Phillips asphilli@ucar.edu

Stephen Po-Chedley pochedley1@llnl.gov

Sebastian Sippel sebastian.sippel@uni-leipzig.de

We are still accepting contributions to Tiers 2 and 3 through February 1, 2025. Contributors who make serious contributions will be included as coauthors in the planned publications. See How to Participate for more details.