Towards an Improved Understanding of Cloud Feedbacks and Changes in Poleward Energy Transport Associated with Global Warming

Feedbacks in the climate system act to reduce the efficiency with which the climate system comes back into equilibrium following a radiative perturbation. In this thesis, we first investigate the implications of climate feedbacks on the change in poleward energy transport as the planet warms. We find that large positive cloud and water vapor feedbacks at low latitudes and negative cloud feedbacks of high latitudes reinforce the pre-existing net radiation gradient at the top of atmosphere, requiring that more heat be fluxed to the poles under transient warming. Because anomalous heat fluxes into the ocean also tend to preferentially cool the high latitude atmosphere, the atmosphere becomes more important than the ocean in transporting heat poleward as the planet warms.;The largest uncertainty in the change in poleward transport and in climate sensitivity can be attributed to cloud feedbacks, but this large inter-model spread is primarily in the shortwave component of cloud feedback. Longwave cloud feedbacks are robustly positive across models, and we show that this is primarily caused by tropical high clouds, which rise in accordance with the requirements of radiative-convective equilibrium as the planet warms in such a way as to remain at nearly the same temperature. We also show, using cloud radiative kernels, that rising extra-tropical clouds also contribute significantly to the longwave cloud feedback, but that the effect of rising clouds is strongly opposed by reductions in cloud amount. Conversely, reductions in cloud amount largely explain the positive shortwave cloud feedback at low latitudes, but increases in cloud brightness cause the strong negative cloud feedback at high latitudes.;Using a suite of satellite observations of the Tropics, we show that a simple clear-sky diagnostic tool accurately marks the location of peak high cloudiness, and realistically tracks the change in cloud profile associated with interannual variability. As the Tropics warm, cloud profiles shift upward and exhibit a reduced peak that is remarkably well-diagnosed by the profile of clear-sky diabatic convergence. Furthermore, we estimate that cloud fraction anomalies result in enhanced emission of longwave radiation and reduced reflection of SW radiation to space, with the latter dominating.