James Hansen - NASA Goddard Institute for Space Studies and Columbia University Earth Institute

James Hansen
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Name
James Hansen
Affiliation
NASA Goddard Institute for Space Studies and Columbia University Earth Institute
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Physics - Atmospheric and Oceanic Physics (7)
 
Nuclear Theory (4)
 
High Energy Physics - Theory (3)
 
Astrophysics (1)

Publications Authored By James Hansen

Global temperature is a useful metric for global climate that helps define the potential amplitude of slow climate feedbacks, such as ice sheet melt and sea level rise. Annual temperature in 2016, enhanced by the 2015-2016 El Nino, was +1.3 degC relative to 1880-1920. Read More

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Read More

2012Nov
Affiliations: 1NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 2NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 3NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 4NASA Goddard Institute for Space Studies and Columbia University Earth Institute

Cenozoic temperature, sea level and CO2 co-variations provide insights into climate sensitivity to external forcings and sea level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise paleoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity 3 +/- 1{\deg}C for 4 W/m2 CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Read More

"Climate dice", describing the chance of unusually warm or cool seasons relative to climatology, have become progressively "loaded" in the past 30 years, coincident with rapid global warming. The distribution of seasonal mean temperature anomalies has shifted toward higher temperatures and the range of anomalies has increased. An important change is the emergence of a category of summertime extremely hot outliers, more than three standard deviations (3{\sigma}) warmer than climatology. Read More

Global warming due to human-made gases, mainly CO2, is already 0.8{\deg}C and deleterious climate impacts are growing worldwide. More warming is 'in the pipeline' because Earth is out of energy balance, with absorbed solar energy exceeding planetary heat radiation. Read More

2011May
Affiliations: 1NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 2NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 3NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 4Centre National de la Recherche Scientifique

Improving observations of ocean heat content show that Earth is absorbing more energy from the sun than it is radiating to space as heat, even during the recent solar minimum. The inferred planetary energy imbalance, 0.59 \pm 0. Read More

2011May
Affiliations: 1NASA Goddard Institute for Space Studies and Columbia University Earth Institute, 2NASA Goddard Institute for Space Studies and Columbia University Earth Institute

Paleoclimate data help us assess climate sensitivity and potential human-made climate effects. We conclude that Earth in the warmest interglacial periods of the past million years was less than 1{\deg}C warmer than in the Holocene. Polar warmth in these interglacials and in the Pliocene does not imply that a substantial cushion remains between today's climate and dangerous warming, but rather that Earth is poised to experience strong amplifying polar feedbacks in response to moderate global warming. Read More

We study the nonlinear hydrodynamics of a 2+1 dimensional charged conformal fluid subject to slowly varying external electric and magnetic fields. Following recent work on deriving nonlinear hydrodynamics from gravity, we demonstrate how long wavelength perturbations of the AdS dyonic black brane solution of 4D supergravity are governed by equations equivalent to fluid dynamics equations in the boundary theory. We investigate the implications of $S$-duality for our system, and derive restrictions imposed on the transport coefficients of a generic fluid invariant under the S operation. Read More

We apply the recently established connection between nonlinear fluid dynamics and AdS gravity to the case of the dyonic black brane in AdS_4. This yields the equations of fluid dynamics for a 2+1 dimensional charged fluid in a background magnetic field. We construct the gravity solution to second order in the derivative expansion. Read More

2007Sep
Affiliations: 1Keele Astrophysics Group, UK, 2Los Alamos National Laboratory, USA, 3Laboratory for Computational Science & Engineering, University of Minnesota, USA, 4Laboratory for Computational Science & Engineering, University of Minnesota, USA, 5Los Alamos National Laboratory, USA, 6Laboratory for Computational Science & Engineering, University of Minnesota, USA, 7Los Alamos National Laboratory, USA, 8Laboratory for Computational Science & Engineering, University of Minnesota, USA
Category: Astrophysics

We review the current state of modeling convective mixing in AGB stars. The focus is on results obtained through multi-dimensional hydrodynamic simulations of AGB convection, both in the envelope and the unstable He-shell. Using two different codes and a wide range of resolutions and modeling assumptions we find that mixing across convective boundaries is significant for He-shell flash convection. Read More

We unravel some subtleties involving the definition of sphere angular momentum charges in AdS_q \times S^p spacetimes, or equivalently, R-symmetry charges in the dual boundary CFT. In the AdS_3 context, it is known that charges can be generated by coordinate transformations, even though the underlying theory is diffeomorphism invariant. This is the bulk version of spectral flow in the boundary CFT. Read More

The convergence of the Q expansion in the ^3S_1-^3D_1 mixing angle is investigated through the renormalization condition used to fit the free paramteter encountered at NNLO. Although the NNLO calculation describes the data well at momenta much less than 50 MeV, a variation in the renormalization condition results in 100% expected uncertainties at momenta as low as 100 MeV. This uncertainty can be traced to the presence of large cancelations between terms entering at NNLO, which are found to be several times larger than the terms entering at NLO. Read More

1999Jan
Affiliations: 1University of Maryland, 2Montgomery Blair High School
Category: Nuclear Theory

Low energy theorems have been derived for the coefficients of the effective range expansion in s-wave nucleon-nucleon scattering valid to leading nontrivial order in an expansion based $Q$ counting, a scheme in which both $m_\pi$ and $1/a$ (where $a$ is the scattering length) are treated as small mass scales. Previous tests of these theorems based on coefficients extracted from scattering data indicate a pattern of gross violations which suggested serious problems for the perturbative treatment of pions implicit in $Q$ counting. We discuss the possibility that uncertainties associated with extracting the coefficients from the scattering data make such tests invalid. Read More

Low energy theorems are derived for the coefficients of the effective range expansion in s-wave nucleon-nucleon scattering valid to leading order in an expansion in which both $m_\pi$ and $1/a$ (where $a$ is the scattering length) are treated as small mass scales. Comparisons with phase shift data, however, reveal a pattern of gross violations of the theorems for all coefficients in both the $^1S_0$ and $^3S_1$ channels. Analogous theorems are developed for the energy dependence $\epsilon$ parameter which describes $^3S_1 - ^3D_1$ mixing. Read More

An analytic expression for the ${}^1S_0$ phase shifts in nucleon-nucleon scattering is derived in the context of the Schr\"odinger equation in configuration space with a short distance cutoff and with a consistent power counting scheme including pionic effects. The scheme treats the pion mass and the inverse scattering length over the intrinsic short distance scale as small parameters. Working at next-to-leading order in this scheme, we show that the expression obtained is identical to one obtained using the recently introduced PDS approach which is based on dimensional regularization with a novel subtraction scheme. Read More