Preprints
https://doi.org/10.5194/acp-2021-401
https://doi.org/10.5194/acp-2021-401

  22 Jun 2021

22 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Understanding the surface temperature response and its uncertainty to CO2, CH4, black carbon and sulfate

Kalle Nordling1, Hannele Korhonen1, Jouni Räisänen2, Antti-Ilari Partanen1, Bjørn Samset3, and Joonas Merikanto1 Kalle Nordling et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2INAR/Physics, University of Helsinki, Helsinki, Finland
  • 3CICERO Center of International Climate Research, Oslo, Norway

Abstract. Understanding the regional surface temperature responses to different anthropogenic climate forcing agents, such as greenhouse gases and aerosols, is crucial for understanding past and future regional climate changes. In modern climate models, the regional temperature responses vary greatly for all major forcing agents, but the causes of this variability are poorly understood. Here, we analyse how changes in atmospheric and oceanic energy fluxes due to perturbations in different anthropogenic climate forcing agents lead to changes in global and regional surface temperatures. We use climate model data on idealized perturbations in four major anthropogenic climate forcing agents (CO2, CH4, and sulfate and black carbon aerosols) from PDRMIP climate experiments for six climate models (CanESM2, HadGEM2-ES, NCAR-CESM1-CAM4, NorESM1, MIROC-SPRINTARS, GISS-E2). Particularly, we decompose the regional energy budget contributions to the surface temperature responses due to changes in longwave and shortwave fluxes under clear-sky and cloudy conditions, surface albedo changes, and oceanic and atmospheric energy transport. We also analyse the regional model-to-model temperature response spread due to each of these components. The global surface temperature response stems from changes in longwave emissivity for greenhouse gases (CO2 and CH4) and mainly from changes in shortwave clear-sky fluxes for aerosols (sulfate and black carbon). The global surface temperature response normalized by effective radiative forcing is nearly the same for all forcing agents (0.63, 0.54, 0.57, 0.61 KW−1 m2). While the main physical processes driving global temperature responses vary between forcing agents, for all forcing agents the model-to-model spread in temperature responses is dominated by differences in modelled changes in longwave clear-sky emissivity. Furthermore, in polar regions for all forcing agents the differences in surface albedo change is a key contributor to temperature responses and its spread. For black carbon the modelled differences in temperature response due to shortwave clear-sky radiation are also important in the Arctic. Regional model-to-model differences due to changes in shortwave and longwave cloud radiative effect strongly modulate each other. For aerosols clouds play a major role in the model spread of regional surface temperature responses. In regions with strong aerosol forcing the model-to-model differences arise from shortwave clear-sky responses and are strongly modulated by combined temperature responses to oceanic and atmospheric heat transport in the models.

Kalle Nordling et al.

Status: open (until 03 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-401', Anonymous Referee #2, 16 Jul 2021 reply
  • RC2: 'Comment on acp-2021-401', William Collins, 18 Jul 2021 reply

Kalle Nordling et al.

Kalle Nordling et al.

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Short summary
Understanding the temperature responses to different climate forcing agents, such as greenhouse gases and aerosols, is crucial for understanding future regional climate changes. In climate models, the regional temperature responses vary for all forcing agents, but the causes of this variability are poorly understood. For all forcing agents, the main component contributing to variance in regional surface temperature responses between the climate models is the clear-sky longwave emissivity.
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