The effect of host star spectral energy distribution and ice-albedo feedback on the climate of extrasolar planets.

Astrobiology 13 (2013) 715-739

AL Shields, VS Meadows, CM Bitz, RT Pierrehumbert, MM Joshi, TD Robinson

Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO(2) (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an M-dwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO(2) in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global ice coverage. The surface ice-albedo feedback effect becomes less important at the outer edge of the habitable zone, where atmospheric CO(2) could be expected to be high such that it maintains clement conditions for surface liquid water. We showed that ∼3-10 bar of CO(2) will entirely mask the climatic effect of ice and snow, leaving the outer limits of the habitable zone unaffected by the spectral dependence of water ice and snow albedo. However, less CO(2) is needed to maintain open water for a planet orbiting an M-dwarf star than would be the case for hotter main-sequence stars.

Robust elements of Snowball Earth atmospheric circulation and oases for life


DS Abbot, A Voigt, D Li, G Le Hir, RT Pierrehumbert, M Branson, D Pollard, DDB Koll

Strange news from other stars

NATURE GEOSCIENCE 6 (2013) 81-83

RT Pierrehumbert

Cumulative Carbon and Just Allocation of the Global Carbon Commons

Chicago Journal of International Law 13 (2013) 12

RT Pierrehumbert

The Warming Papers The Scientific Foundation for the Climate Change Forecast

John Wiley & Sons, 2013

D Archer, R Pierrehumbert

Global warming is arguably the defining scientific issue of modern times, but it is not widely appreciated that the ... together the classic scientific papers that are the scientific foundation for the forecast of global warming and its consequences.

The emergence of zonal ocean jets under large-scale stochastic wind forcing

Geophysical Research Letters American Geophysical Union (AGU) 39 (2012) n/a-n/a

CH O'Reilly, A Czaja, JH LaCasce

Cumulative carbon as a policy framework for achieving climate stabilization.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 370 (2012) 4365-4379

HD Matthews, S Solomon, R Pierrehumbert

The primary objective of the United Nations Framework Convention on Climate Change is to stabilize greenhouse gas concentrations at a level that will avoid dangerous climate impacts. However, greenhouse gas concentration stabilization is an awkward framework within which to assess dangerous climate change on account of the significant lag between a given concentration level and the eventual equilibrium temperature change. By contrast, recent research has shown that global temperature change can be well described by a given cumulative carbon emissions budget. Here, we propose that cumulative carbon emissions represent an alternative framework that is applicable both as a tool for climate mitigation as well as for the assessment of potential climate impacts. We show first that both atmospheric CO(2) concentration at a given year and the associated temperature change are generally associated with a unique cumulative carbon emissions budget that is largely independent of the emissions scenario. The rate of global temperature change can therefore be related to first order to the rate of increase of cumulative carbon emissions. However, transient warming over the next century will also be strongly affected by emissions of shorter lived forcing agents such as aerosols and methane. Non-CO(2) emissions therefore contribute to uncertainty in the cumulative carbon budget associated with near-term temperature targets, and may suggest the need for a mitigation approach that considers separately short- and long-lived gas emissions. By contrast, long-term temperature change remains primarily associated with total cumulative carbon emissions owing to the much longer atmospheric residence time of CO(2) relative to other major climate forcing agents.

Clouds and Snowball Earth deglaciation


DS Abbot, A Voigt, M Branson, RT Pierrehumbert, D Pollard, G Le Hir, DDB Koll

Upper-ocean singular vectors of the North Atlantic climate with implications for linear predictability and variability

Quarterly Journal of the Royal Meteorological Society 138 (2012) 500-513

L Zanna, P Heimbach, AM Moore, E Tziperman

The limits of predictability of the meridional overturning circulation (MOC) and upper-ocean temperatures due to errors in ocean initial conditions and model parametrizations are investigated in an idealized configuration of an ocean general circulation model (GCM). Singular vectors (optimal perturbations) are calculated using the GCM, its tangent linear and adjoint models to determine an upper bound on the predictability of North Atlantic climate. The maximum growth time-scales of MOC and upper-ocean temperature anomalies, excited by the singular vectors, are 18.5 and 13 years respectively and in part explained by the westward propagation of upper-ocean anomalies against the mean flow. As a result of the linear interference of non-orthogonal eigenmodes of the non-normal dynamics, the ocean dynamics are found to actively participate in the significant growth of the anomalies. An initial density perturbation of merely 0.02 kg m -3 is found to lead to a 1.7 Sv MOC anomaly after 18.5 years. In addition, Northern Hemisphere upper-ocean temperature perturbations can be amplified by a factor of 2 after 13 years. The growth of upper-ocean temperature and MOC anomalies is slower and weaker when excited by the upper-ocean singular vectors than when the deep ocean is perturbed. This leads to the conclusion that predictability experiments perturbing only the atmospheric initial state may overestimate the predictability time. Interestingly, optimal MOC and upper-ocean temperature excitations are only weakly correlated, thus limiting the utility of SST observations to infer MOC variability. The excitation of anomalies in this model might have a crucial impact on the variability and predictability of Atlantic climate. The limit of predictability of the MOC is found to be different from that of the upper-ocean heat content, emphasizing that errors in ocean initial conditions will affect various measures differently and such uncertainties should be carefully considered in decadal prediction experiments. © 2011 Royal Meteorological Society.

Forecast Skill and Predictability of Observed Atlantic Sea Surface Temperatures

J. of Climate 25 (2012) 5047-5056

L Zanna

Climate of the Neoproterozoic


RT Pierrehumbert, DS Abbot, A Voigt, D Koll

Infrared Radiation and Planetary Temperature


RT Pierrehumbert

Bifurcations leading to summer Arctic sea ice loss


DS Abbot, M Silber, RT Pierrehumbert



R Pierrehumbert, E Gaidos

Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia

National Academies Press, 2011

COSTFAGG Concentrations, BOASA Climate, DOEAL Studies, NR Council

The book quantifies the outcomes of different stabilization targets for greenhouse gas concentrations using analyses and information drawn from the scientific literature.

Infrared radiation and planetary temperature

PHYSICS TODAY 64 (2011) 33-38

RT Pierrehumbert

Sea glacier flow and dust transport on Snowball Earth


D Li, RT Pierrehumbert

Some fine points on radiative forcing Reply

PHYSICS TODAY 64 (2011) 12-12

RT Pierrehumbert

Optimal excitation of interannual atlantic meridional overturning circulation variability

Journal of Climate 24 (2011) 413-427

L Zanna, P Heimbach, AM Moore, E Tziperman

The optimal excitation of Atlantic meridional overturning circulation (MOC) anomalies is investigated in an ocean general circulation model with an idealized configuration. The optimal three-dimensional spatial structure of temperature and salinity perturbations, defined as the leading singular vector and generating the maximum amplification of MOC anomalies, is evaluated by solving a generalized eigenvalue problem using tangent linear and adjoint models. Despite the stable linearized dynamics, a large amplification of MOC anomalies, mostly due to the interference of nonnormal modes, is initiated by the optimal perturbations. The largest amplification of MOC anomalies, found to be excited by high-latitude deep density perturbations in the northern part of the basin, is achieved after about 7.5 years. The anomalies grow as a result of a conversion of mean available potential energy into potential and kinetic energy of the perturbations, reminiscent of baroclinic instability. The time scale of growth of MOC anomalies can be understood by examining the time evolution of deep zonal density gradients, which are related to the MOC via the thermal wind relation. The velocity of propagation of the density anomalies, found to depend on the horizontal component of the mean flow velocity and the mean density gradient, determines the growth time scale of the MOC anomalies and therefore provides an upper bound on the MOC predictability time. The results suggest that the nonnormal linearized ocean dynamics can give rise to enhanced MOC variability if, for instance, overflows, eddies, and/or deep convection can excite high-latitude density anomalies in the ocean interior with a structure resembling that of the optimal perturbations found in this study. The findings also indicate that errors in ocean initial conditions or in model parameterizations or processes, particularly at depth, may significantly reduce the AtlanticMOC predictability time to less than a decade. © 2011 American Meteorological Society.

Ocean Model Uncertainty in Climate Prediction

ECMWF Proceedings (2011)

L Zanna