Spurious Late Historical‐Era Warming in CESM2 Driven by Prescribed Biomass Burning Emissions. Issue 2 (24th January 2022)

• Record Type: Journal Article
• Authors: Fasullo, J. T.; Lamarque, Jean‐Francois; Hannay, Cecile; Rosenbloom, Nan; Tilmes, Simone; DeRepentigny, Patricia; Jahn, Alexandra; Deser, Clara
• Is Part Of: Geophysical research letters. Volume 49:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-24
• Subjects: global change -- land/atmosphere interactions -- aerosol/cloud interactions -- global climate models; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL097420
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: A spurious increase in the interannual variability of prescribed biomass burning (BB) emissions in the CMIP6 forcing database during the satellite era of wildfire monitoring (1997–2014) is found to lead to warming in the Northern Hemisphere extratropics in simulations with the Community Earth System Model version 2 (CESM2). Using targeted sensitivity experiments with the CESM2 in which prescribed BB emissions are homogenized and variability is removed, we show that the warming is specifically attributable to BB variability from 40° to 70°N and arises from a net thinning of the cloud field and an associated increase in absorbed solar radiation. Our results also demonstrate the potential pitfalls of introducing discontinuities in climate forcing data sets when trying to incorporate novel observations. Plain Language Summary: A discontinuity in the variability of prescribed biomass burning emissions between the satellite era of wildfire monitoring (1997–2014) and both the preceding historical and future time periods is found to drive spurious warming in the Community Earth System Model version 2. The warming arises from a net thinning of the cloud field and an associated increase in absorbed solar radiation during periods of high variability in emissions. Evidence suggestive of similar effects in other climate models is also presented. The results highlight the challenges in evaluating models with observations, even in the modern satellite era. Key Points: CMIP6‐prescribed biomass burning emissions contain elevated interannual variance from 1997 to 2014 relative to other periods In CESM2, the variability in emissions drives substantial warming in the Northern Hemisphere extratropics Changes in radiation and clouds arising from nonlinear interactions with aerosols underpin the simulated warming