Does greater convective mass flux lead to thicker or thinner anvil clouds?

<jats:p>As the climate warms, the thickness of anvil outflows associated with tropical deep convection is projected to decrease, but the mechanism for this remains uncertain. Here, we ask whether changes in convective mass flux (CMF)—which produces anvil clouds and is also expected to decrease with warming at large-scale—could cause the projected thinning. We track the lifecycle of tropical deep convective clouds in the global storm-resolving model ICOsahedral Non-hydrostatic (ICON). Thick anvil area increases more than the overall area when CMF is greater, meaning anvils thicken. Introducing a simple analytical model, we show that the greater dependence of thick anvil on CMF can be reproduced when condensate supply outpaces anvil divergence. These results suggest that reductions in typical cloud CMF could cause anvil thinning. This is consistent with a positive opacity feedback, implying a near-zero overall high-cloud feedback on warming instead of a negative one as previously supposed.</jats:p>