Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.     

Assessing housing growth when census boundaries change

The US Census provides the primary source of spatially explicit social data, but changing block boundaries complicate analyses of housing growth over time. We compared procedures for reconciling housing density data between 1990 and 2000 census block boundaries in order to assess the sensitivity of analytical methods to estimates of housing growth in Oregon. Estimates of housing growth varied substantially and were sensitive to the method of interpolation. With no processing and areal‐weighted interpolation, more than 35% of the landscape changed; 75–80% of this change was due to decline in housing density. This decline was implausible, however, because housing structures generally persist over time. Based on aggregated boundaries, 11% of the landscape changed, but only 4% experienced a decline in housing density. Nevertheless, the housing density change map was almost twice as coarse spatially as the 2000 housing density data. We also applied a dasymetric approach to redistribute 1990 housing data into 2000 census boundaries under the assumption that the distribution of housing in 2000 reflected the same distribution as in 1990. The dasymetric approach resulted in conservative change estimates at a fine resolution. All methods involved some type of trade‐off (e.g. analytical difficulty, data resolution, magnitude or bias in direction of change). However, our dasymetric procedure is a novel approach for assessing housing growth over changing census boundaries that may be particularly useful because it accounts for the uniquely persistent nature of housing over time.     

内华达北中部新月谷—独立金矿区线性构造带的证据

内华达北中部的新月谷-独立金矿区线性构造(CVIL)是一个呈20°～30°走向、具多期变形、侵入及热液活动的构造带,该带从独立金矿区向南至科特兹矿山附近延伸达90 km,经过科特兹-派普来恩、卡林及独立三个主要的沉积岩型金矿区,含有罗伯茨山异地岩(可能是奥陶系Vinini组)的强烈构造岩,NE向的断层,白垩或第三纪的NE向的岩墙.变形带的组构具混杂岩的特点,但混杂岩中也显示有与晚三叠世和晚侏罗世之间形成的褶皱展布方向一致的定向组构.此外,沿CVIL带局部出现有第三纪的碧玉状岩石、角砾岩、方解石脉及脱钙蚀变作用.CVIL构造带南北两端成群出现的沉积岩型金矿床具有与卡林矿带金矿床相同的矿物特征.上述二个矿区都有NE向的断层,穿越罗伯茨山异地岩上盘中的构造窗和构造高地.CVIL可能是形成某些金矿床的主要热液通道.     

Skilled migration and cumulative disadvantage: the case of highly qualified Asian Indian immigrant women in the US

The research on skilled international migration focuses primarily on the experiences of male migrants. Little work has been done on female migrants, especially those who migrated as dependents of highly skilled males. This paper presents some data on Asian Indian women in the US, and argues that these women suffer from cumulative disadvantage. The paper emphasizes that it is necessary to adopt a complex model involving the interaction of gendered/racialised immigration laws, workplace and household experiences in order to understand the experiences of these women.     

Measurement and prediction of sediment production from unpaved roads,St John,US Virgin Islands

Excess delivery of land‐based sediments is an important control on the overall condition of nearshore coral reef ecosystems. Unpaved roads have been identified as a dominant sediment source on St John in the US Virgin Islands. An improved understanding of road sediment production rates is needed to guide future development and erosion control efforts. The main objectives of this study were to: (1) measure sediment production rates at the road segment scale; (2) evaluate the importance of precipitation, slope, contributing area, traffic, and grading on road sediment production; (3) develop an empirical road erosion predictive model; and (4) compare our measured erosion rates to other published data. Sediment production from 21 road segments was monitored with sediment traps from July 1998 to November 2001. The selected road segments had varying slopes, contributing areas, and traffic loads. Precipitation was measured by four recording rain gauges. Sediment production was related to total precipitation and road segment slope. After normalizing by precipitation and slope, the mean sediment production rate for roads that had been graded within the last two years was 0·96 kg m^?2 cm^?1 m m^?1 or approximately 11 kg m^?2 a^?1 for a typical road with a 10 per cent slope and an annual rainfall of 115 cm a^?1. The mean erosion rate for ungraded roads was 42 per cent lower, or 0·56 kg m^?2 cm^?1 m m^?1. The normalized mean sediment production rate for road segments that had been abandoned for over fifteen years was only about 10 per cent of the mean value for ungraded roads. Sediment production was not related to traffic loads. Multiple regression analysis led to the development of an empirical model based on precipitation, slope to the 1·5 power, and a categorical grading variable. The measured and predicted erosion rates indicate that roads are capable of increasing hillslope‐scale sediment production rates by up to four orders of magnitude relative to undisturbed conditions. The values from St John are at the high end of reported road erosion rates, a finding that is consistent with the high rainfall erosivities and steep slopes of many of the unpaved roads on St John. Other than paving, the most practical methods to reduce current erosion rates are to minimize the frequency of grading and improve road drainage. Copyright © 2005 John Wiley & Sons, Ltd.     

全球地质学复兴：我们正进入“人类幻”——第32届国际地质大会环境地质述评

概要介绍了第32届国际地质大会的议题概况。7个大会报告中与环境地质问题相关的竟有6个，反映以人类与地球相互作用为中心的研究已成为地质学家们不得不关注的主题。重点介绍了环境地质方面的几个重要议题：气候与地质环境、地质灾害风险评估、城市化与城市地质、地下水资源与环境、地质环境标识。阐明了关于全球地质学复兴的几点思考：人类活动已成为一种地质营力、地质工作者应成为管理地球的主力军、重在预测人类的未来、地质环境与地球环境、地球系统与地球问题。     

Attenuation characteristics of ground motions in northern China

Four recently developed attenuation models are calibrated by using a very limited amount of strong motion data recorded in China. The research shows that the attenuation characteristics of the earthquake shaking in northern China are similar to those in the western US. The supporting evidence includes Q factors, preliminary results of kappa values, stress drop, shear wave velocity profile in the shallow earth crust, areas enclosed by the isoseismals of Modified Mercalli Intensity V. From these comparisons of different attenuation models, it is recommended that the Crouse and McGuire spectral attenuation model could possibly be used for northern China. Funded by: The Hong Kong Polytechnic University, and partly supported by NSFC (Grant No.59678048)     

The effectiveness of climate clubs under Donald Trump

On 1 June 2017, President Trump announced that the US intends to leave the Paris Agreement if no alternative terms acceptable to his administration can be agreed upon. In this article, an agent-based model of bottom-up climate mitigation clubs is used to derive the impact that lack of US participation may have on the membership of such clubs and their emissions coverage. We systematically analyse the prospects for climate mitigation clubs, depending on which of three conceivable roles the US takes on: as a leader (for benchmarking), as a follower (i.e. willing to join climate mitigation clubs initiated by others if this is in its best interest) or as an outsider (i.e. staying outside of any climate mitigation club no matter what). We investigate these prospects for three types of incentives for becoming a member: club goods, conditional commitments and side-payments. Our results show that lack of US leadership significantly constrains climate clubs’ potential. Lack of US willingness to follow others’ lead is an additional, but smaller constraint. Only in a few cases will US withdrawal entail widespread departures by other countries. We conclude that climate mitigation clubs can function without the participation of an important GHG emitter, given that other major emitters show leadership, although these clubs will rarely cover more than 50% of global emissions.

Key policy insights

• The US switching from being a leader to being a follower substantially reduces the emissions coverage of climate mitigation clubs.

• The US switching from being a follower to being an outsider sometimes reduces coverage further, but has a smaller impact than the switch from leader to follower.

• The switch from follower to outsider only occasionally results in widespread departures by other countries; in a few instances it even entices others to join.

• Climate mitigation clubs can function even without the participation of the US, provided that other major emitters show leadership; however, such clubs will typically be unable to cover more than 50% of global emissions.

• Climate mitigation clubs may complement the Paris Agreement and can also serve as an alternative in case Paris fails.