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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Aug 2020

21 Aug 2020

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This preprint is currently under review for the journal ACP.

Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles

Benjamin J. Murray1, Kenneth S. Carslaw1, and Paul R. Field1,2 Benjamin J. Murray et al.
  • 1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT Leeds, UK
  • 2Met Office, Exeter EX1 3PB, UK

Abstract. Shallow clouds covering vast areas of the world's mid- and high-latitude oceans play a key role in dampening the global temperature rise associated with CO2. These clouds, which contain both ice and supercooled water, respond to a warming world by transitioning to a state with more liquid water and a greater albedo, resulting in a negative cloud-phase climate feedback component. Here we argue that the magnitude of the negative cloud-phase feedback component depends on the amount and nature of the small fraction of aerosol particles that can nucleate ice crystals. We propose that a concerted research effort is required to reduce substantial and important uncertainties related to the poorly understood sources, concentration, seasonal cycles and nature of these ice-nucleating particles (INPs) and their rudimentary treatment in climate models. The topic is important because many climate models may have overestimated the magnitude of the cloud-phase feedback, and those with better representation of shallow oceanic clouds predict a substantially larger climate warming. We make the case that understanding the present-day INP population in shallow clouds in the cold-sector of cyclone systems is particularly critical for defining present-day cloud phase and therefore how the clouds respond to warming. We also need to develop a predictive capability for future INP emissions in a warmer world with less ice and snow and potentially stronger INP sources.

Benjamin J. Murray et al.

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Benjamin J. Murray et al.

Benjamin J. Murray et al.


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Latest update: 29 Sep 2020
Publications Copernicus
Short summary
The balance between the amounts of ice and supercooled water in clouds over the world's oceans strongly influences how much these clouds can dampen or amplify global warming. Aerosol particles which catalyse ice formation can dramatically reduce the amount of supercooled water in clouds, hence we argue that we need a concerted effort to improve our understanding of these ice-nucleating particles if we are to improve our predictions of climate change.
The balance between the amounts of ice and supercooled water in clouds over the world's oceans...