The impact of stochastic physics on tropical rainfall variability in global climate models on daily to weekly time scales


PAG Watson, J Berner, S Corti, P Davini, J von Hardenberg, C Sanchez, A Weisheimer, TN Palmer

Ice-shelf damming in the glacial Arctic Ocean: dynamical regimes of a basin-covering kilometre-thick ice shelf

CRYOSPHERE 11 (2017) 1745-1765

J Nilsson, M Jakobsson, C Borstad, N Kirchner, G Bjork, RT Pierrehumbert, C Stranne

Climate SPHINX: evaluating the impact of resolution and stochastic physics parameterisations in the EC-Earth global climate model


P Davini, J von Hardenberg, S Corti, HM Christensen, S Juricke, A Subramanian, PAG Watson, A Weisheimer, TN Palmer

Global meteorological influences on the record UK rainfall of winter 2013-14


JR Knight, A Maidens, PAG Watson, M Andrews, S Belcher, G Brunet, D Fereday, CK Folland, AA Scaife, J Slingo

Eddy-Driven Jet Sensitivity to Diabatic Heating in an Idealized GCM

JOURNAL OF CLIMATE 30 (2017) 6413-6431

HS Baker, T Woollings, C Mbengue

Observational evidence against strongly stabilizing tropical cloud feedbacks


IN Williams, RT Pierrehumbert

Linking the Climate and Thermal Phase Curve of 55 Cancri e


M Hammond, RT Pierrehumbert

Reconstructing Climate from Glaciers

Annual Review of Earth and Planetary Sciences 45 (2017) 649-680

AN Mackintosh, BM Anderson, RT Pierrehumbert

Copyright © 2017 by Annual Reviews. All rights reserved. Glaciers offer the potential to reconstruct past climate over timescales from decades to millennia. They are found on nearly every continent, and at the Last Glacial Maximum, glaciers were larger in all regions on Earth. The physics of glacier-climate interaction are relatively well understood, and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent. This can lead to significant insights regarding past, present, and future climate. For example, glacier modeling has demonstrated that the near-ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global-scale climate warming of ∼1°C, consistent with instrumental data and climate proxy records. Climate reconstructions from glaciers have also demonstrated that the tropics were colder at the Last Glacial Maximum than was originally inferred from sea surface temperature reconstructions. Future efforts to reconstruct climate from glaciers may provide new constraints on climate sensitivity to CO2 forcing, polar amplification of climate change, and more.

The role of the tropical West Pacific in the extreme Northern Hemisphere winter of 2013/2014


PAG Watson, A Weisheimer, JR Knight, TN Palmer

Consequences of twenty-first-century policy for multi-millennial climate and sea-level change

NATURE CLIMATE CHANGE 6 (2016) 360-369

PU Clark, JD Shakun, SA Marcott, AC Mix, M Eby, S Kulp, A Levermann, GA Milne, PL Pfister, BD Santer, DP Schrag, S Solomon, TF Stocker, BH Strauss, AJ Weaver, R Winkelmann, D Archer, E Bard, A Goldner, K Lambeck, RT Pierrehumbert, G-K Plattner

How to decarbonize? Look to Sweden

Bulletin of the Atomic Scientists 72 (2016) 105-111

R Pierrehumbert



F Ding, RT Pierrehumbert

Dynamics of atmospheres with a non-dilute condensible component.

Proceedings. Mathematical, physical, and engineering sciences 472 (2016) 20160107-

RT Pierrehumbert, F Ding

The diversity of characteristics for the host of recently discovered exoplanets opens up a great deal of fertile new territory for geophysical fluid dynamics, particularly when the fluid flow is coupled to novel thermodynamics, radiative transfer or chemistry. In this paper, we survey one of these new areas-the climate dynamics of atmospheres with a non-dilute condensible component, defined as the situation in which a condensible component of the atmosphere makes up a substantial fraction of the atmospheric mass within some layer. Non-dilute dynamics can occur for a wide range of condensibles, generically applying near both the inner and the outer edges of the conventional habitable zone and in connection with runaway greenhouse phenomena. It also applies in a wide variety of other planetary circumstances. We first present a number of analytical results developing some key features of non-dilute atmospheres, and then show how some of these features are manifest in simulations with a general circulation model adapted to handle non-dilute atmospheres. We find that non-dilute atmospheres have weak horizontal temperature gradients even for rapidly rotating planets, and that their circulations are largely barotropic. The relative humidity of the condensible component tends towards 100% as the atmosphere becomes more non-dilute, which has important implications for runaway greenhouse thresholds. Non-dilute atmospheres exhibit a number of interesting organized convection features, for which there is not yet any adequate theoretical understanding.

New use of global warming potentials to compare cumulative and short-lived climate pollutants


MR Allen, JS Fuglestvedt, KP Shine, A Reisinger, RT Pierrehumbert, PM Forster

Comparison of "warm and wet" and "cold and icy" scenarios for early Mars in a 3-D climate model

Journal of Geophysical Research E: Planets (2015)

RD Wordsworth, RD Wordsworth, L Kerber, RT Pierrehumbert, F Forget, JW Head

©2015. American Geophysical Union. All Rights Reserved.. We use a 3-D general circulation model to compare the primitive Martian hydrological cycle in "warm and wet" and "cold and icy" scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice-free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic, and impact forcing. At surface pressures above those required to avoid atmospheric collapse (∼0.5bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice-free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H<inf>2</inf>O and CO<inf>2</inf> are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8<sup>{ring operator}</sup> obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios, they motivate future targeted geological studies.

Feedback temperature dependence determines the risk of high warming

Geophysical Research Letters (2015)

J Bloch-Johnson, RT Pierrehumbert, DS Abbot

©2015. American Geophysical Union. The long-term warming from an anthropogenic increase in atmospheric CO<inf>2</inf> is often assumed to be proportional to the forcing associated with that increase. This paper examines this linear approximation using a zero-dimensional energy balance model with a temperature-dependent feedback, with parameter values drawn from physical arguments and general circulation models. For a positive feedback temperature dependence, warming increases Earth's sensitivity, while greater sensitivity makes Earth warm more. These effects can feed on each other, greatly amplifying warming. As a result, for reasonable values of feedback temperature dependence and preindustrial feedback, Earth can jump to a warmer state under only one or two CO<inf>2</inf> doublings. The linear approximation breaks down in the long tail of high climate sensitivity commonly seen in observational studies. Understanding feedback temperature dependence is therefore essential for inferring the risk of high warming from modern observations. Studies that assume linearity likely underestimate the risk of high warming.

Climate impact of beef: an analysis considering multiple time scales and production methods without use of global warming potentials


RT Pierrehumbert, G Eshel

Constraints on southern hemisphere tropical climate change during the Little Ice Age and Younger Dryas based on glacier modeling of the Quelccaya Ice Cap, Peru


AGO Malone, RT Pierrehumbert, TV Lowell, MA Kelly, JS Stroup

Does the ECMWF IFS Convection Parameterization with Stochastic Physics Correctly Reproduce Relationships between Convection and the Large-Scale State?


PAG Watson, HM Christensen, TN Palmer

The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode

Climate Dynamics 44 (2015) 2513-2537

PAG Watson, LJ Gray

© 2014, The Author(s). The response of the wintertime Northern Hemisphere (NH) stratosphere to applied extratropical zonally symmetric zonal torques, simulated by a primitive equation model of the middle atmosphere, is presented. This is relevant to understanding the effect of gravity wave drag (GWD) in models and the influence of natural forcings such as the quasi-biennial oscillation (QBO), El Ninõ-Southern Oscillation (ENSO), solar cycle and volcanic eruptions on the polar vortex. There is a strong feedback due to planetary waves, which approximately cancels the direct effect of the torque on the zonal acceleration in the steady state and leads to an EP flux convergence response above the torque’s location. The residual circulation response is very different to that predicted assuming wave feedbacks are negligible. The results are consistent with the predictions of ray theory, with applied westerly torques increasing the meridional potential vorticity gradient, thus encouraging greater upward planetary wave propagation into the stratosphere. The steady state circulation response to torques applied at high latitudes closely resembles the Northern annular mode (NAM) in perpetual January simulations. This behaviour is analogous to that shown by the Lorenz system and tropospheric models. Imposed westerly high-latitude torques lead counter-intuitively to an easterly zonal mean zonal wind (Formula Presented.) response at high latitudes, due to the wave feedbacks. However, in simulations with a seasonal cycle, the feedbacks are qualitatively similar but weaker, and the long-term response is less NAM-like and no longer easterly at high latitudes. This is consistent with ray theory and differences in climatological (Formula Presented.) between the two types of simulations. The response to a tropospheric wave forcing perturbation is also NAM-like. These results suggest that dynamical feedbacks tend to make the long-term NH extratropical stratospheric response to arbitrary external forcings NAM-like, but only if the feedbacks are sufficiently strong. This may explain why the observed polar vortex responses to natural forcings such as the QBO and ENSO are NAM-like. The results imply that wave feedbacks must be understood and accurately modelled in order to understand and predict the influence of GWD and other external forcings on the polar vortex, and that biases in a model’s climatology will cause biases in these feedbacks.