Sensitivity of Climate Change Projections to Uncertainties in the Estimates of Observed Changes in Deep-Ocean Heat Content

Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).The MIT 2D climate model is used to make probabilistic projections for changes in global mean surface temperature and for thermosteric sea level rise under a variety of forcing scenarios. The uncertainties in climate sensitivity and rate of heat uptake by the deep ocean are quantified by using the probability distributions derived from observed 20th century temperature changes. The impact on climate change projections of using the smallest and largest estimates of 20th century deep ocean warming is explored. The impact is large in the case of global mean thermosteric sea level rise. In the MIT reference ("business as usual") scenario the median rise by 2100 is 27 and 43 cm in the respective cases. The impact on increases in global mean surface air temperature is more modest, 4.9 C and 3.9 C in the two respective cases, because of the correlation between climate sensitivity and ocean heat uptake required by 20th century surface and upper air temperature changes. The results are also compared with the projections made by the IPCC AR4's multi-model ensemble for several of the SRES scenarios. The multi-model projections are more consistent with the MIT projections based on the largest estimate of ocean warming. However the range for the rate of heat uptake by the ocean suggested by the lowest estimate of ocean warming is more consistent with the range suggested by the 20th century changes in surface and upper air temperatures, combined with expert prior for climate sensitivity.This work was supported in part by the Office of Science (BER), U.S. Dept. of Energy Grant No. DE-FG02-93ER61677, NSF, and by the MIT Joint Program on the Science and Policy of Global Change

Resource Selection and Calving Success of Moose in Colorado

Across much of North America, moose populations (Alces alces) are declining due to disease, predation, climate, and anthropogenic pressures. Despite this, populations of moose in Colorado have continued to grow. Studying successful (i.e., persistent or growing) populations of moose can facilitate the continued conservation of the species by identifying habitat features critical for moose persistence. First, I evaluated calving success of moose in Colorado and the impact of willow habitat quality and nutrition. I then estimated the probability of female moose having a calf using repeated observations in a Bayesian occupancy model. I assigned values for dry matter digestibility, browse intensity, willow height, willow cover, and leaf length based on overlapping sample locations with estimated individual moose homeranges and tested the effect on calf presence. Willow height had the strongest predictive effect on calf presence and was the only covariate with credible intervals not overlapping zero. Dry matter digestibility had no effect, while browse intensity and leaf length were uninformative. Results presented here suggest that the quality (i.e., age and structure) of willow habitat are important for female moose with calves. This work sets the stage for future research on the structure of willow habitat and the incorporation of additional remotely sensed data. Second, I used a resource selection function to evaluate resource selection by moose in Colorado and the effect of large-scale bark beetle disturbance. Bark beetles have impacted forests across North America, decreasing canopy cover and increasing solar radiation reaching the forest floor. These disturbances lead to an increase in ground forage but have been hypothesized to have a negative impact on thermally sensitive species such as moose. I evaluated resource selection at two scales: a large population scale and finer movement-based scale. The strongest selection by moose was for distance to willow, followed by elevation. Selection for beetle-disturbed habitat was mixed across populations and scales showing little overall effect. The lack of selection for beetle disturbed habitat suggests mixed influences on resource selection by moose. Undisturbed forest had moderately strong positive selection at both scales, illustrating the importance of maintaining undisturbed forest habitat for moose

Public attitudes toward hospital service

Thesis (M.S.)--Boston Universit

Kink Chains from Instantons on a Torus

We describe how the procedure of calculating approximate solitons from instanton holonomies may be extended to the case of soliton crystals. It is shown how sine-Gordon kink chains may be obtained from CP1 instantons on a torus. These kink chains turn out to be remarkably accurate approximations to the true solutions. Some remarks on the relevance of this work to Skyrme crystals are also made.Comment: latex 17 pages, DAMTP 94-7

The Surgery of the Thoracic Duct:

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Numerical Simulations of Dynamos Generated in Spherical Couette Flows

We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculiar regime where dynamo action may be obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner core might explain the decrease of the dynamo threshold. For lower $E$ ($E=10^{-4}$) this internal shear layer becomes unstable, leading to small scales fluctuations, and the favorable dynamo regime is lost. We also model the effect of ferromagnetic boundary conditions. Their presence have only a small impact on the dynamo onset but clearly enhance the saturated magnetic field in the ferromagnetic parts. Implications for experimental studies are discussed

Semi-relativistic charge-current density operator

The charge-current density and two-photon operators consistent with a single-particle semi-relativistic Hamiltonian are derived within a suitable functional derivative formalism which preserves gauge invariance. An application to electron scattering is presented and results are compared with a fully relativistic case and the non-relativistic cases corrected through fourth order in M^{-1}.Comment: 20 pages, 3 postscript figures, typos correcte