TY - JOUR
T1 - A positive iris feedback
T2 - Insights from climate simulations with temperature-sensitive cloud-rain conversion
AU - Li, R. L.
AU - Storelvmo, T.
AU - Fedorov, A. V.
AU - Choi, Y. S.
N1 - Funding Information:
Acknowledgments. This work was funded by the National Science Foundation through Grant 1352417 and the European Research Council through Grant 758005. Federov acknowledges support from NSF through Grant AGS-0163807 and from NASA Grant NNX17AH21G, and Choi was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant 2018R1A6A1A08025520). We acknowledge computational support from the Yale University Faculty of Arts and Sciences High Performance Computing Facility. We also thank three anonymous reviewers for their helpful comments and suggestions.
Funding Information:
This work was funded by the National Science Foundation through Grant 1352417 and the European Research Council through Grant 758005. Federov acknowledges support from NSF through Grant AGS-0163807 and from NASA Grant NNX17AH21G, and Choi was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant 2018R1A6A1A08025520). We acknowledge computational support from the Yale University Faculty of Arts and Sciences High Performance Computing Facility. We also thank three anonymous reviewers for their helpful comments and suggestions.
Publisher Copyright:
© 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).
PY - 2019/8/1
Y1 - 2019/8/1
N2 - Estimates for equilibrium climate sensitivity from current climate models continue to exhibit a large spread, from 2.1 to 4.7 K per carbon dioxide doubling. Recent studies have found that the treatment of precipitation efficiency in deep convective clouds-specifically the conversion rate from cloud condensate to rain Cp-may contribute to the large intermodel spread. It is common for convective parameterization in climate models to carry a constant Cp, although its values are model and resolution dependent. In this study, we investigate how introducing a potential iris feedback, the cloud-climate feedback introduced by parameterizing Cp to increase with surface temperature, affects future climate simulations within a slab ocean configuration of the Community Earth System Model. Progressively stronger dependencies of Cp on temperature unexpectedly increase the equilibrium climate sensitivity monotonically from 3.8 to up to 4.6 K. This positive iris feedback puzzle, in which a reduction in cirrus clouds increases surface temperature, is attributed to changes in the opacity of convectively detrained cirrus. Cirrus clouds reduced largely in ice content and marginally in horizontal coverage, and thus the positive shortwave cloud radiative feedback dominates. The sign of the iris feedback is robust across different cloud macrophysics schemes, which control horizontal cloud cover associated with detrained ice. These results suggest a potentially strong but highly uncertain connection among convective precipitation, detrained anvil cirrus, and the high cloud feedback in a climate forced by increased atmospheric carbon dioxide concentrations.
AB - Estimates for equilibrium climate sensitivity from current climate models continue to exhibit a large spread, from 2.1 to 4.7 K per carbon dioxide doubling. Recent studies have found that the treatment of precipitation efficiency in deep convective clouds-specifically the conversion rate from cloud condensate to rain Cp-may contribute to the large intermodel spread. It is common for convective parameterization in climate models to carry a constant Cp, although its values are model and resolution dependent. In this study, we investigate how introducing a potential iris feedback, the cloud-climate feedback introduced by parameterizing Cp to increase with surface temperature, affects future climate simulations within a slab ocean configuration of the Community Earth System Model. Progressively stronger dependencies of Cp on temperature unexpectedly increase the equilibrium climate sensitivity monotonically from 3.8 to up to 4.6 K. This positive iris feedback puzzle, in which a reduction in cirrus clouds increases surface temperature, is attributed to changes in the opacity of convectively detrained cirrus. Cirrus clouds reduced largely in ice content and marginally in horizontal coverage, and thus the positive shortwave cloud radiative feedback dominates. The sign of the iris feedback is robust across different cloud macrophysics schemes, which control horizontal cloud cover associated with detrained ice. These results suggest a potentially strong but highly uncertain connection among convective precipitation, detrained anvil cirrus, and the high cloud feedback in a climate forced by increased atmospheric carbon dioxide concentrations.
UR - http://www.scopus.com/inward/record.url?scp=85074653563&partnerID=8YFLogxK
U2 - 10.1175/JCLI-D-18-0845.1
DO - 10.1175/JCLI-D-18-0845.1
M3 - Article
AN - SCOPUS:85074653563
SN - 0894-8755
VL - 32
SP - 5305
EP - 5324
JO - Journal of Climate
JF - Journal of Climate
IS - 16
ER -