EARTH In the literature: open

How much do tropical anvil clouds shrink as Earth warms?

In plain words

High, thin anvil-shaped clouds spread out from tropical thunderstorms and trap heat. If they shrink with warming, more heat escapes to space, a cooling effect called the 'iris' hypothesis, but its size is debated.

Precise statement

The tropical anvil cloud area feedback was assessed at about $-2e2 \pm 2e2\,\mathrm{erg}/(\mathrm{s}\,\mathrm{cm}^2\,\mathrm{K})$ (Sherwood and coauthors 2020), while the iris hypothesis (Lindzen and coauthors 2001) argued for a much more negative value. Determine the global anvil-area feedback and its mechanism (stability iris, changes in convective aggregation, anvil lifetime and microphysics) with uncertainty below about $1e2\,\mathrm{erg}/(\mathrm{s}\,\mathrm{cm}^2\,\mathrm{K})$.

What would settle it

Cloud-resolving simulations under warming with resolved anvil microphysics, validated against satellite relations between anvil area, cloud radiative effect and surface temperature.

Status in the literature

Unverified note

McKim, Bony and Dufresne (Nature Geoscience 2024, https://doi.org/10.1038/s41561-024-01414-4) argued that physical and observational constraints imply a weak anvil-area feedback.