The Role of China in Mitigating Climate Change

http://globalchange.mit.edu/research/publications/2265We explore short- and long-term implications of several energy scenarios of China’s role in efforts to mitigate global climate risk. The focus is on the impacts on China’s energy system and GDP growth, and on global climate indicators such as greenhouse gas concentrations, radiative forcing, and global temperature change. We employ the MIT Integrated Global System Model (IGSM) framework and its economic component, the MIT Emissions Prediction and Policy Analysis (EPPA) model. We demonstrate that China’s commitments for 2020, made during the UN climate meetings in Copenhagen and Cancun, are reachable at very modest cost. Alternative actions by China in the next 10 years do not yield any substantial changes in GHG concentrations or temperature due to inertia in the climate system. Consideration of the longer-term climate implications of the Copenhagen-type of commitments requires an assumption about policies after 2020, and the effects differ drastically depending on the case. Meeting a 2°C target is problematic unless radical GHG emission reductions are assumed in the short-term. Participation or non-participation of China in global climate architecture can lead by 2100 to a 200–280 ppm difference in atmospheric GHG concentration, which can result in a 1.1°C to 1.3°C change by the end of the century. We conclude that it is essential to engage China in GHG emissions mitigation policies, and alternative actions lead to substantial differences in climate, energy, and economic outcomes. Potential channels for engaging China can be air pollution control and involvement in sectoral trading with established emissions trading systems in developed countries

Regulatory Control of Vehicle and Power Plant Emissions: How Effective and at What Cost?

Passenger vehicles and power plants are major sources of greenhouse gas emissions. While economic analyses generally indicate that a broader market-based approach to greenhouse gas reduction would be less costly and more effective, regulatory approaches have found greater political success. Vehicle efficiency standards have a long history in the U.S and elsewhere, and the recent success of shale gas in the U.S. leads to a focus on coal–gas fuel switching as a way to reduce power sector emissions. We evaluate a global regulatory regime that replaces coal with natural gas in the electricity sector and imposes technically achievable improvements in the efficiency of personal transport vehicles. Its performance and cost are compared with other scenarios of future policy development including a no policy world, achievements under the Copenhagen accord, and a price-based policy to reduce global emissions by 50% by 2050. The assumed regulations applied globally achieve a global emissions reduction larger than projected for the Copenhagen agreements, but they do not prevent global GHG emissions from continuing to grow, and the reduction in emissions is achieved at a high cost compared to a price-based policy. Diagnosis of the reasons for the limited yet high-cost performance reveals influences including the partial coverage of emitting sectors, small or no influence on the demand for emissions-intensive products, leakage when a reduction in fossil use in the covered sectors lowers the price to others, and the partial coverage of GHGs.We thank BP for their support of this study. The MIT Integrated Global System Model (IGSM) and its economic component used in the analysis, the Emissions Prediction and Policy Analysis (EPPA model, are supported by a consortium of government, industry and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change, including U.S. Department of Energy, Office of Science (DE-FG02-94ER61937). For a complete list of sponsors see http://globalchange.mit.edu/sponsors/current.html

Early infant feeding and adiposity risk: from infancy to adulthood

Introduction: Systematic reviews suggest that a longer duration of breast-feeding is associated with a reduction in the risk of later overweight and obesity. Most studies examining breast-feeding in relation to adiposity have not used longitudinal analysis. In our study, we aimed to examine early infant feeding and adiposity risk in a longitudinal cohort from birth to young adulthood using new as well as published data. Methods: Data from the Western Australian Pregnancy Cohort (Raine) Study in Perth, W.A., Australia, were used to examine associations between breast-feeding and measures of adiposity at 1, 2, 3, 6, 8, 10, 14, 17, and 20 years. Results: Breast-feeding was measured in a number of ways. Longer breast-feeding (in months) was associated with reductions in weight z-scores between birth and 1 year (β = -0.027; p \u3c 0.001) in the adjusted analysis. At 3 years, breast-feeding for \u3c4 months increased the odds of infants experiencing early rapid growth (OR 2.05; 95% CI 1.43-2.94; p \u3c 0.001). From 1 to 8 years, children breast-fed for ≤4 months compared to ≥12 months had a significantly greater probability of exceeding the 95th percentile of weight. The age at which breast-feeding was stopped and a milk other than breast milk was introduced (introduction of formula milk) played a significant role in the trajectory of the BMI from birth to 14 years; the 4-month cutoff point was consistently associated with a higher BMI trajectory. Introduction of a milk other than breast milk before 6 months compared to at 6 months or later was a risk factor for being overweight or obese at 20 years of age (OR 1.47; 95% CI 1.12-1.93; p = 0.005). Discussion: Breast-feeding until 6 months of age and beyond should be encouraged and is recommended for protection against increased adiposity in childhood, adolescence, and young adulthood. Adverse long-term effects of early growth acceleration are fundamental in later overweight and obesity. Formula feeding stimulates a higher postnatal growth velocity, whereas breast-feeding promotes slower growth and a reduced likelihood of overweight and obesity. Biological mechanisms underlying the protective effect of breast-feeding against obesity are based on the unique composition and metabolic and physiological responses to human milk

The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI

We have surveyed Andromeda VI, a dwarf spheroidal galaxy companion to M31, for variable stars using F450W and F555W observations obtained with the Hubble Space Telescope. A total of 118 variables were found, with 111 being RR Lyrae, 6 anomalous Cepheids, and 1 variable we were unable to classify. We find that the Andromeda VI anomalous Cepheids have properties consistent with those of anomalous Cepheids in other dwarf spheroidal galaxies. We revise the existing period-luminosity relations for these variables. Further, using these and other available data, we show that there is no clear difference between fundamental and first-overtone anomalous Cepheids in a period-amplitude diagram at shorter periods, unlike the RR Lyrae. For the Andromeda VI RR Lyrae, we find that they lie close to the Oosterhoff type I Galactic globular clusters in the period-amplitude diagram, although the mean period of the RRab stars, = 0.588 d, is slightly longer than the typical Oosterhoff type I cluster. The mean V magnitude of the RR Lyrae in Andromeda VI is 25.29+/-0.03, resulting in a distance 815+/-25 kpc on the Lee, Demarque, & Zinn distance scale. This is consistent with the distance derived from the I magnitude of the tip of the red giant branch. Similarly, the properties of the RR Lyrae indicate a mean abundance for Andromeda VI which is consistent with that derived from the mean red giant branch color.Comment: 23 pages, including 13 figures and 6 tables, emulateapj5/apjfonts style. Accepted by the Astronomical Journal. We recommend the interested reader to download the preprint with full-resolution figures, which can be found at http://www.noao.edu/noao/staff/pritzl/M31dwarfs.htm

V2324Cyg - an F-type star with fast wind

For the first time high-resolution optical spectroscopy of the variable star V2324Cyg associated with the IR-source IRAS20572+4919 is made. More than 200 absorption features (mostly FeII, TiII, CrII, YII, BaII, and YII) are identified within the wavelength interval 4549-7880AA. The spectral type and rotation velocity of the star are found to be F0III and Vsini=69km/s, respectively. HI and NaID lines have complex PCyg-type profiles with an emission component. Neither systematic trend of radial velocity Vr with line depth Ro nor temporal variability of Vr have been found. We determined the average heliocentric radial velocity Vr=-16.8\pm 0.6km/s. The radial velocities inferred from the cores of the absorption components of the H$\beta$ and NaI wind lines vary from -140 to -225km/s (and the expansion velocities of the corresponding layers, from about 120 to 210km/s). The maximum expansion velocity is found for the blue component of the split H$\alpha$ absorption: 450km/s for December 12, 1995. The model atmospheres method is used to determine the star's parameters: Teff=7500K, log g=2.0, $\xi_t$=6.0km/s, and metallicity, which is equal to the solar value. The main peculiarity of the chemical abundances pattern is the overabundance of lithium and sodium. The results cast some doubt on the classification of V2324Cyg as a post-AGB star.Comment: 28 pages, 6 figure

Magnetic collimation of the relativistic jet in M87

We apply a two-zone MHD model to the jet of M87. The model consists of an inner relativistic outflow, which is surrounded by a non-relativistic outer disk-wind. The outer disk-wind collimates very well through magnetic self-collimation and confines the inner relativistic jet into a narrow region around the rotation axis. Further, we show by example, that such models reproduce very accurately the observed opening angle of the M87 jet over a large range from the kiloparsec scale down to the sub-parsec scale.Comment: 4 pages, 2 figures, accepted by A&A Letter

Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02

Observations of giant stars indicate that the frequency of giant planets is much higher for intermediate-mass stars than for solar-like stars. Up to now all known planets of giant stars orbit at relatively far distances from their host stars. It is not known whether intermediate-mass stars also had many close-in planets when they were on the main sequence, which were then engulfed when the star became a giant star. To understand the formation and evolution of planets it is therefore important to find out whether main-sequence stars of intermediate-mass have close-in planets or not. A survey for transiting planets of intermediate-mass stars would be ideal to solve this question, because the detection of transiting planets is not affected by the rapid rotation of these stars. As a first step for an efficient survey we need to identify intermediate-mass stars in the CoRoT-fields, which can then be used as an input list. To compile the input list we derived the spectral types of essentially all O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02 taken with the multi-object spectrograph AAOmega. We determined the spectral types by comparing the spectra with template spectra from a library. In total we identify 1856 A and B stars that have been observed with CoRoT. Given the number of planets that have been detected in these fields amongst late-type stars, we estimate that there are one to four transiting planets of intermediate-mass stars waiting to be discovered. Our survey not only allows us to carry out a dedicated planet search programme but is also essential for any types of studies of the light curves of early-type stars in the CoRoT database. We also show that it would be possible to extend the survey to all fields that CoRoT has observed using photometrically determined spectral types.Comment: 57 pages, 12 figures, accepted for publication in Astronomy and Astrophysic