Mapping the dependence of black carbon radiative forcing on emission region and season

• Main Authors: Räisänen, Petri, Merikanto, Joonas, Makkonen, Risto, Savolahti, Mikko, Kirkevåg, Alf, Sand, Maria, Seland, Øyvind, Partanen, Antti-Ilari
• Other Authors: Suomen ympäristökeskus, The Finnish Environment Institute
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2022
• Subjects: black carbon; emissions; concentration; radiative forcing; location; timing; seasonality; effects on climate; Earth System; ilmastonsuojelu; noki; päästöt; pitoisuus; sijainti; vuodenajat; ilmastovaikutukset; ilmastomallitModel; NorESM1-Happi; Greenland; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10138/348271

For short-lived climate forcers such as black carbon (BC), the atmospheric concentrations, radiative forcing (RF), and, ultimately, the subsequent effects on climate, depend on the location and timing of the emis sions. Here, we employ the NorESM1-Happi version of the Norwegian Earth System Model to systematically study how the RF associated with BC emissions depends on the latitude, longitude, and seasonality of the emis sions. The model aerosol scheme is run in an offline mode to allow for an essentially noise-free evaluation of the RF associated with even minor changes in emissions. A total of 960 experiments were run to evaluate the BC direct RF (dirRF) and the RF associated with BC in snow/ice (snowRF) for emissions in 192 latitude–longitude boxes covering the globe, both for seasonally uniform emissions and for emissions in each of the four seasons separately. We also calculate a rough estimate of the global temperature response to regional emissions and provide a Fortran-based tool to facilitate the further use of our results. Overall, the results demonstrate that the BC RFs strongly depend on the latitude, longitude, and season of the emissions. In particular, the global mean dirRF normalized by emissions (direct specific forcing; dirSF) depends much more strongly on the emission location than suggested by previous studies that have considered emissions from continental-/subcontinental-scale regions. Even for seasonally uniform emissions, dirSF varies by more than a factor of 10, depending on the emission location. These variations correlate strongly with BC lifetime, which varies from less than 2 to 11 d. BC dirSF is largest for emissions in tropical convective regions and in subtropical and midlatitude continents in summer, both due to the abundant solar radiation and strong convective transport, which increases BC lifetime and the amount of BC above clouds. The dirSF is also relatively large for emissions in high-albedo, high-latitude regions such as Antarctica and Greenland. The dependence of snow ...