Title: Significant impact of forcing uncertainty in a large ensemble of climate model simulations

Abstract

Forcing due to solar and volcanic variability, on the natural side, and greenhouse gas and aerosol emissions, on the anthropogenic side, are the main inputs to climate models. Reliable climate model simulations of past and future climate change depend crucially upon them. Here we analyze large ensembles of simulations using a comprehensive Earth System Model to quantify uncertainties in global climate change attributable to differences in prescribed forcings. The different forcings considered here are those used in the two most recent phases of the Coupled Model Intercomparison Project (CMIP), namely CMIP5 and CMIP6. We show significant differences in simulated global surface air temperature due to volcanic aerosol forcing in the second half of the 19th century and in the early 21st century. The latter arise from small-to-moderate eruptions incorporated in CMIP6 simulations but not in CMIP5 simulations. We also find significant differences in global surface air temperature and Arctic sea ice area due to anthropogenic aerosol forcing in the second half of the 20th century and early 21st century. These differences are as large as those obtained in different versions of an Earth System Model employing identical forcings. In simulations from 2015 to 2100, we find significant differences in themore » rates of projected global warming arising from CMIP5 and CMIP6 concentration pathways that differ slightly but are equivalent in terms of their nominal radiative forcing levels in 2100. Our results highlight the influence of assumptions about natural and anthropogenic aerosol loadings on carbon budgets, the likelihood of meeting Paris targets, and the equivalence of future forcing scenarios.« less

Authors:

Fyfe, John C.  ^[1];

• Search DOE PAGES for author "Fyfe, John C."
• Search DOE PAGES for ORCID "0000-0003-2524-0652"

Kharin, Viatcheslav V.  ^[1];

• Search DOE PAGES for author "Kharin, Viatcheslav V."
• Search DOE PAGES for ORCID "0000-0002-3439-9609"

Santer, Benjamin D.  ^[2];

• Search DOE PAGES for author "Santer, Benjamin D."
• Search DOE PAGES for ORCID "0000-0002-9717-460X"

Cole, Jason N. S. ^[1]; Gillett, Nathan P.  ^[1]

• Search DOE PAGES for author "Gillett, Nathan P."
• Search DOE PAGES for ORCID "0000-0002-2957-0002"

---

+ Show Author Affiliations

1. Environment and Climate Change Canada, Victoria, BC (Canada). Canadian Centre for Climate Modelling and Analysis
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Program for Climate Model Diagnosis and Intercomparison

Publication Date:

Tue Jun 01 00:00:00 EDT 2021

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1815637

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 118; Journal Issue: 23; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; climate change; climate model; external forcing; large ensemble