Some thoughts on the value added from a new round of climate change damage estimates

This paper offers some thoughts on the value added of new economic estimates of climate change damages. We begin with a warning to beware of analyses that are so narrow that they miss a good deal of the important economic ramifications of the full suite of manifestations of climate change. Our second set of comments focuses attention on one of the most visible products of integrated assessment modeling—estimates of the social cost of carbon which we take as one example of aggregate economic indicators that have been designed to summarize climate risk in policy deliberations. Our point is that these estimates are so sensitive to a wide range of parameters that improved understanding of economic damages across many (if not all) climate sensitive sectors may offer only limited value added. Having cast some doubt on the ability of improved estimates of economic damages to increase the value of economic damage estimates in integrated assessment modeling designed to inform climate policy deliberations, we offer an alternative approach—describing implicitly a research agenda that could (a) effectively inform mitigation decisions while, at the same time, (b) providing economic estimates for aggregate indicators like the social cost of carbon.     

1/f noise in the UV solar spectral irradiance

The investigation of the intrinsic properties of the solar spectral irradiance as a function of the ultraviolet (UV) wavelength is attempted by exploiting rare observations performed at the Villard St. Pancrace station of the Lille University of Sciences and Technology ranging from 278 to 400 nm with a step of 0.05 nm every half an hour from nearly sunrise to sunset. To achieve this goal, the modern method of the detrended fluctuation analysis was applied on the solar spectral irradiance values versus wavelength. This analysis revealed that the solar incident flux at the top of the atmosphere and the solar spectral irradiance at the ground during two overcast sky days fluctuate with the UV wavelength exhibiting persistent long-range power-law behavior. More interestingly, the exponent of the power-law relationship between the fluctuations of the solar spectral irradiance versus UV wavelength at both the top of the atmosphere and the ground is consistently close to unity (of 1/f-type) throughout the day. This 1/f behavior has been detected in many complex dynamical systems, but despite much effort to derive a theory for its widespread occurrence in nature, it remains unexplained so far. According to the above-mentioned findings we speculate that the 1/f property of the incident solar UV flux at the top of the atmosphere could probably drive both the 1/f behavior depicted in the atmospheric components and the solar UV irradiance at the Earth's surface. The latter could influence the UV-sensitive biological ecosystems, giving rise to a 1/f-type variability in the biosphere, which has already been proven by recent observational data. We finally propose that Wien approximation could be multiplied by a 1/f function of wavelength (e.g., of the type of the fractional Brownian motion) in order to reproduce the aforementioned 1/f feature of the solar UV flux.     

Marginal mixing theories

Abstract

Mixing near the sloping boundaries of oceans or lakes may be a significant mechanism of diapycnal transport. The basic physics of this is reviewed, with emphasis on the reduction of the effectiveness of the process due to both reduced stratification and the restratifying secondary circulation driven by buoyancy forces. This re stratification is shown to reduce the effectiveness of intermittent mixing events as well as steady mixing. It is argued that for boundary mixing to be effective in the abyssal ocean it must extend sufficiently far from the boundary that the stratification can be maintained; this may be true for breaking bottom‐reflected internal waves. The alongslope flow implied by steady‐state boundary mixing theories is downwelling‐favourable and has a magnitude related to the thickness and other properties of the boundary layer. Mixing near a boundary may thus tend to drive a downwelling‐favourable mean circulation in the interior. If the interior circulation is imposed by other forces, the bottom boundary layer may evolve to a steady state if the interior flow is downwelling‐favourable, but if it is upwelling‐favourable initially a steady state seems unlikely and the downwelling‐favourable alongslope flow induced by the boundary mixing will tend to diffuse slowly into the interior. The nature of the solution in all these cases is sensitive to the Burger number, N² sin² θ/f², where θ is the bottom slope, and to the eddy Prandtl number.     

Does the Agulhas Current amplify global temperatures during super‐interglacials?

Future projections of climate suggest our planet is moving into a ‘super‐interglacial’. Here we report a global synthesis of ice, marine and terrestrial data from a recent palaeoclimate equivalent, the Last Interglacial (ca. 130–116 ka ago). Our analysis suggests global temperatures were on average ～1.5°C higher than today (relative to the AD 1961–1990 period). Intriguingly, we identify several Indian Ocean Last Interglacial sequences that suggest persistent early warming, consistent with leakage of warm, saline waters from the Agulhas Current into the Atlantic, intensifying meridional ocean circulation and increasing global temperatures. This mechanism may have played a significant positive feedback role during super‐interglacials and could become increasingly important in the future. These results provide an important insight into a future 2°C climate stabilisation scenario. Copyright © 2010 John Wiley & Sons, Ltd.     

A re-assessment of the nearest neighbour alignment of the X-ray isophotes of galaxy clusters

Alignment is defined as the tendency of the distribution of pointing angles between the major axes of clusters and their nearest neighbours to be more concentrated towards small values for small nearest neighbour distances, whereas the distribution is expected to be uniform over all angles at larger distances. Conflicting pronouncements on the reality of this effect have been published in the astronomy literature. A re-assessment of the evidence for alignment is presented, based on three recently published X-ray data sets. We find that whereas there is evidence for alignment, it is not as convincing as previously claimed. In particular, the scale to which the effect has been claimed to extend seems to have been severely overstated.     

Observations of Hipparcos short-period red giant stars

Optical UBV(RI) _C and infrared JHK photometry is presented of a small sample of giant stars with short periods in the Hipparcos catalogue. Observations were limited, but were sufficient to rule out most of the Hipparcos periods. Radial velocity measurement were also made for a few stars, over six successive nights. Low-level variability was detected in a few stars. It is argued that in most cases the brightness variations are primarily due to temperature changes. These findings show that high-overtone pulsations in M giant stars occur, if at all, in a far more limited number of stars than proposed in the authors' previous discussion of the Hipparcos data alone.     

3D MHD Simulations of Laboratory Plasma Jets

Jets and outflows are thought to be an integral part of accretion phenomena and are associated with a large variety of objects. In these systems, the interaction of magnetic fields with an accretion disk and/or a magnetized central object is thought to be responsible for the acceleration and collimation of plasma into jets and wider angle flows. In this paper we present three-dimensional MHD simulations of magnetically driven, radiatively cooled laboratory jets that are produced on the MAGPIE experimental facility. The general outflow structure comprises an expanding magnetic cavity which is collimated by the pressure of an extended plasma background medium, and a magnetically confined jet which develops within the magnetic cavity. Although this structure is intrinsically transient and instabilities in the jet and disruption of the magnetic cavity ultimately lead to its break-up, a well collimated, “knotty” jet still emerges from the system; such clumpy morphology is reminiscent of that observed in many astrophysical jets. The possible introduction in the experiments of angular momentum and axial magnetic field will also be discussed.