Cloud and moisture effects on warmth in continental interiors during equable climates

Dorian S. Abbot, Gabrielle Bousquet, Matthew Huber, Chris C. Walker
and Eli Tziperman

There is abundant evidence that during periods of equable climate in Earth’s history, such as the Eocene, the interiors of continents at high latitudes were exceptionally warm during winter. Land has a low heat capacity and distances of thousands of kilometers separate some continental interior regions from the ocean. Consequently, significant increases in ocean temperatures do not necessarily imply that temperatures in continental interiors will increase enough to explain proxy data. As a result, explaining winter warmth deep in the interiors of continents remains a central outstanding problem of equable climate dynamics.

Here we present new evidence from global climate models (GCMs) that increases in cloud radiative forcing and the condensation of moisture (convergence of latent heat) over land may play central roles in warming continental interiors at high CO2 concentrations. We show results from both the NCAR CCSM coupled GCM run in Eocene configuration and the NCAR CAM atmospheric GCM run in modern configuration at various CO2 concentrations ranging up to 2240 ppm. The increases in cloud radiative forcing over land may be associated with a novel high-latitude convective cloud feedback that has recently been shown to produce significant warming over the ocean and help reduce sea ice cover at high CO2 levels, and the increased latent heat transport appears to be mainly zonal, rather than meridional.

KE et al’s recent paper on increased TC activity in equable climates is here.

Here is a recent article by KE surveying the present state of the TC science. Quoting:

“As pointed out by Emanuel (2001), increased tropical cyclone activity in
a warmer climate would result in increased tropical heat export by the oceans, mitigating tropical warming but amplifying the warming of higher latitudes. This inference is supported by recent numerical simulations using a coupled climate model in which upper ocean mixing is related to a proxy for tropical cyclone activity (Korty et al. 2008). This effect offers a potential explanation for the equable nature of very warm climates, such as that of the early Eocene; high levels of tropical cyclone activity in such warm climates could drive a strong poleward heat flux in the ocean, even in the face of relatively weak pole-to-equator temperature gradients, thus helping to keep such gradients weak. (Today’s coupled climate models are notoriously bad at reproducing such weak temperature gradients, perhaps because they have no representation of tropical cyclone–induced ocean mixing.) It may also help explain why most of the observed heat uptake by the oceans over the past 50 yr has been in the subtropics and middle latitudes (Levitus et al. 2005), whereas coupled models typically show most of the heat uptake occurring in subpolar regions (e.g. Manabe et al. 1991).”

[Thanks Bryan. I'm a subscriber, so it's sometimes hard to tell when things are not behind a paywall. GR]

(Something strange seems to be happening to your formatting, BTW. The text in the comment box got smaller and there are run-together lines toward the bottom of the post. This is with IE.)