Uncertainty in aerosol–cloud radiative forcing is driven by clean conditions
<p>Atmospheric aerosols and their impact on cloud properties remain the largest uncertainty in the human forcing of the climate system. By increasing the concentration of cloud droplets (<span class="inline-formula"><i>N</i><sub>d</sub></span>), ae...
Main Authors: | , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2023-04-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/23/4115/2023/acp-23-4115-2023.pdf |
Summary: | <p>Atmospheric aerosols and their impact on cloud properties remain the
largest uncertainty in the human forcing of the climate system. By
increasing the concentration of cloud droplets (<span class="inline-formula"><i>N</i><sub>d</sub></span>), aerosols
reduce droplet size and increase the reflectivity of clouds (a
negative radiative forcing). Central to this climate impact is the
susceptibility of cloud droplet number to aerosol (<span class="inline-formula"><i>β</i></span>), the
diversity of which explains much of the variation in the radiative
forcing from aerosol–cloud interactions (RFaci) in global climate
models. This has made measuring <span class="inline-formula"><i>β</i></span> a key target for developing
observational constraints of the aerosol forcing.</p>
<p>While the aerosol burden of the clean, pre-industrial atmosphere has
been demonstrated as a key uncertainty for the aerosol forcing, here
we show that the behaviour of clouds under these clean conditions is
of equal importance for understanding the spread in radiative
forcing estimates between models and observations. This means that
the uncertainty in the aerosol impact on clouds is,
counterintuitively, driven by situations with little
aerosol. Discarding clean conditions produces a close agreement
between different model and observational estimates of the cloud
response to aerosol but does not provide a strong constraint on the
RFaci. This makes constraining aerosol behaviour in clean conditions
an important goal for future observational studies.</p> |
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ISSN: | 1680-7316 1680-7324 |