CACTI: Emissions to Response
Goals
The overall goal of CACTI is to quantify and advance the scientific understanding of the global and regional forcing, climate and air quality responses, and Earth System feedbacks due to atmospheric composition and SLCF emission changes. Specifically, our research contributes to any of the three specific CACTI goals to:
- Characterize ERFs and assess adjustments from historical and future changes in atmospheric composition and SLCFs emissions in global models
- Quantify the climate and air quality responses to global and regional changes in SLCF emissions
- Understand the Earth System feedbacks through chemistry and aerosols in response to anthropogenic climate change
CACTI addresses several cross-cutting topics relevant to the specific goals. In particular, to enhance scientific understanding, CACTI endeavors to explore and characterize uncertainty and inter-model diversity in the model responses. This initiative will also evaluate the performance of models against a suite of observations to build confidence in their fitness for the purpose of the specific goals. Additionally, CACTI will respond to the need for policy-relevant information related to the mitigation of SLCF emissions.
Committee
Members of the CACTI committee (in alphabetical order):
- R. Allen (University of California Riverside, USA)
- B. Collins (University of Reading, UK)
- S. Fiedler (Heidelberg University, Germany)
- P. Griffiths (Bristol University, UK)
- R. Kramer (NOAA, USA)
- M. Kasoar (Leverhulme Centre for Wildfires, Environment and Society, Imperial College London, UK)
- V. Naik (NOAA Geophysical Fluid Dynamics Laboratory, US)
- F. O’Connor (Met Office Hadley Centre, Exeter, UK & Dept. of Mathematics & Statistics, University of Exeter, UK)
- N.Oshima (Meteorological Research Institute, Japan)
- M. Schulz (Norwegian Meteorological Institute, Norway)
- C. Smith (University of Leeds, UK)
- T. Takemura (Kyushu University, Japan)
- S. Turnock (Met Office Hadley Centre, Exeter, UK)
- D. Watson-Parris (University of California San Diego, USA)
- D. Westervelt (Columbia University, USA)
- L. Wilcox (National Centre for Atmospheric Science, University of Reading, UK)
Collaboration and Coordination
Current CACTi MIp's
The Aerosol Chemistry Model Intercomparison Project Phase 2 (AerChemMIP2) seeks to advance our understanding of how aerosols and chemically reactive gases affect atmospheric composition, climate, and air quality across time - from the pre-industrial period through the present and into future emission scenarios. As an international model intercomparison effort listed for CMIP7, the AerChemMIP2 (Fiedler et al., 2025) builds on the foundation of its first phase while aligning with other CMIP7 experiments. It is designed to tackle key scientific challenges in Earth system modelling, including the influence of short-lived climate forcers (SLCFs), feedbacks from natural emissions, and the effects of policy-relevant scenarios on radiative forcing and climate response.
The second iteration of the Radiative Forcing Model Intercomparison Project (RFMIP 2.0) is designed to address the question of how the Earth system responds to external forcing by thoroughly characterising the radiative forcing in each contributing model. The protocol (Kramer et al., 2025 ) includes simulations that quantify the total radiative forcing, experiments designed at teasing out why certain errors occur, and analyses aimed at identifying consistent signals driven by anthropogenic aerosols.
The Regional Aerosol Model Intercomparison Project (RAMIP) started in-between the cycles of CMIP6 and CMIP7. Its primary goal is to assess regional climate and air quality responses to anthropogenic aerosol emissions (Wilcox et al., 2022 ). The experimental design focuses on examining sensitivities related to both aerosol type and geographic origin, using plausible, time-evolving emission perturbations.
Values
Our initiative adheres to scientific integrity, equal opportunities, and democratic leadership. Our values are for instance reflected by diversity in the scientific committee of CACTI, open email lists to inquire information on our activities and getting involved, hybrid meetings to allow participation from anywhere in the world, and open scientific discussions at our meetings for information transparency and the possibility for debates.
Legacy
CACTI brings together the active and collaborative communities of RFMIP, AerChemMIP, and PDRMIP under a new initiative called CACTI (Composition Air quality Climate inTeractions Initiative: Emissions to Response). Previously, these communities came together as TriMIP. CACTI aims to follow on from the success of TriMIP. RFMIP aimed to characterize and assess ERF in CMIP6 models and determine errors when approximating accurate line-by-line radiative transfer with fast parameterizations used in climate models (Pincus et al., 2016). The main goals of AerChemMIP were to quantify the climate and air quality responses to aerosols and chemically reactive gases (Collins et al., 2017). The objective of PDRMIP was to understand global and regional responses of precipitation statistics to different forcing agents, and irradiance (Myhre et al., 2017). The three MIPs held joint meetings that were useful to inspire each other for scientific advancement of the field.
Protocols
Table
Contact
All announcements about CACTI activities will be made through our mailing list. If you are interested, please subscribe by sending an email to CACTI-subscribe-request@listserv.uni-heidelberg.de.
You can contact the CACTI committee by sending an email to CACTI-COMMITTEE@listserv.uni-heidelberg.de.
CACTI Workshops
Tri-MIP-athlon 2018, Reading, UK
Tri-MIP-athlon 2019, Princeton, USA
Tri-MIP-athlon 2021, online everywhere
CACTI workshop 2023, Kiel, Germany
CACTI workshop 2024, San Diego, USA
CACTI workshop 2025, Exeter, United Kingdom