Coupled Climate Responses to Recent Australian Wildfire and COVID‐19 Emissions Anomalies Estimated in CESM2

Abstract

Multiple episodes of anomalous climate forcing have occurred in recent years. These include the biomass burning emissions anomalies from the 2019-2020 Australian wildfire season (hereafter referred to as AF), and anthropogenic emissions perturbations arising from the response to the spread of the Coronavirus Disease 2019, which began in Jan 2020 and continues through the present (hereafter referred to as COVID). While significant efforts have been made for diagnosing the climate effects of these events, understanding the coupled response to each and estimating the broader significance of the responses remains a work in progress.The 2019-2020 AF season was singular in its severity and associated particulate emissions (Hirsch & Koren, 2021;Khaykin et al., 2020). While Australia is known as a landscape that experiences frequent bushfires, extreme bushfires with associated pyrocumulonimbus have been increasing over the last few decades and are predicted to increase even further in the coming decades (Dowdy et al., 2019;Sharples et al., 2016). The extreme AF season in 2019-2020 had devastating consequences for lives, ecosystems, and property, including wide-scale smoke impacts across the southeast of the continent (Wintle et al., 2020). Additionally, hemispheric transport of fire pollution at low and lofted altitudes created atmospheric signatures over New Zealand and South America. This pollution remained in the atmosphere for well over three months, with solar heating of a stable, dense smoke plume creating a localized chemical and entrainment driven stratospheric ozone minimum and circulation response (Khaykin et al., 2020). The associated warming of the

Contrasting Stratospheric Smoke Mass and Lifetime From 2017 Canadian and 2019/2020 Australian Megafires: Global Simulations and Satellite Observations

“…The gray shaded region represents the range of stochastic variability of the control ensemble while the colored shaded region provides a measure of the combined uncertainty on the anomaly. In the first 6 months after the event, temperature anomalies points to cooling at values of (negative) 0.1-0.2 K (see also Fasullo et al, 2021). During the same period, the radiative forcing perturbation reaches a minimum (i.e., a maximum in magnitude) in February, at about −3 W/m 2 , in agreement with observational assessments (Khaykin et al, 2020).…”

Effective Radiative Forcings Due To Anthropogenic Emission Changes Under Covid‐19 and Post‐Pandemic Recovery Scenarios

“…United Nations Environment Programme, 2020Programme, , 2021. Although previous studies have revealed slight effects of reduced emissions associated with Covid-19 containment on the global mean values of radiative forcing, surface air temperature, and precipitation (Fasullo et al, 2021;Gettelman et al, 2020;Weber et al, 2020), but these decreased emissions contributed importantly to the 2020 extreme summer rainfall at the regional scales (Fadnavis et al, 2021;Y. Yang et al, 2022).…”

“…The impact of Covid‐19 on emissions is expected to continue, since the Covid‐19‐related rescue spending and recovery investment have set out in a low‐carbon way in several countries, such as China, Germany, and the United Kingdom (Keramidas et al., 2021 ; United Nations Environment Programme, 2020, 2021). Although previous studies have revealed slight effects of reduced emissions associated with Covid‐19 containment on the global mean values of radiative forcing, surface air temperature, and precipitation (Fasullo et al., 2021 ; Gettelman et al., 2020 ; Weber et al., 2020 ), but these decreased emissions contributed importantly to the 2020 extreme summer rainfall at the regional scales (Fadnavis et al., 2021 ; Y. Yang et al., 2022 ). Moreover, stronger climate responses may emerge if the economic stimulus policies at post‐pandemic result in persistent changes in anthropogenic emissions (Forster et al., 2020 ; Y. Yang et al., 2020 ; Z. L. Wang et al., 2016 ).…”

The Climate and Ozone Impacts of Black Carbon Emissions From Global Rocket Launches

“…In comparison, the 2019 Australian Wildfire event induced a larger SWF of approximately −0.95 W/m 2 , about five times larger than the SWF anomaly caused by the 10 Gg/yr emission scenario. However, the Australian fire event's SWF climate response lasted for a couple months before tapering off (Fasullo et al, 2021).…”

“…Both the 30 and 100 Gg simulations experience a statistically significant surface cooling of approximately −0.08 K and −0.2 K, respectively. For a frame of reference, the 2019 Australian wildfire event, which injected approximately 20 Gg of BC into the lower stratosphere produced a 0.06 K global cooling signal that lasted only a few months (Fasullo et al, 2021).…”