Alteration of Residual Circulation Due to Large-Scale Infrastructure in a Coastal Plain Estuary

Large-scale human-built infrastructure is shown to alter the salinity and subtidal residual flow in a realistic numerical simulation of hydrodynamic circulation in a coastal plain estuary (Tampa Bay). Two model scenarios are considered. The first uses a modern bathymetry and boundary conditions from the years 2001–2003. The second is identical to the first except that the bathymetry is based on depth soundings from the pre-construction year 1879. Differences between the models' output can only result from changes in bay morphology, in particular built infrastructure such as bridges, causeways, and dredging of the shipping channel. Thirty-day means of model output are calculated to remove the dominant tidal signals and allow examination of the subtidal dynamics. Infrastructure is found to steepen the mean axial salinity gradient $ \partial \overline{s}/ dx $ by ~40% when there is low freshwater input but flatten $ \partial \overline{s}/ dx $ by ~25% under more typical conditions during moderate freshwater inflow to the estuary. Deepening of the shipping channel also increases the magnitude of the residual Eulerian circulation, allowing for larger up-estuary salt transport. Local bathymetry and morphology are important. Some regions within the estuary show little change in residual circulation due to infrastructure. In others, the residual circulation can vary by a factor of 4 or more. Major features of the circulation and changes due to infrastructure can be partially accounted for with linear theory.     

Spectral distribution of solar radiation in Athens

Summary A 25-year (1966–1990) record of measurements of the broadband direct solar irradiances performed in Athens, has been utilized to determine the radiant energy distribution in several spectral bands. Using these data the year-to-year trend of the time sequences of the mean values of the irradiation ratios in the various spectral intervals, viz. blue, green/orange, red, and photosynthetically active radiation (PAR) and the total direct irradiance for the whole spectrum, are evaluated.From this trend the following can be concluded: the blue spectral band (0.380–0.525 m) decreased from the beginning of the examined period until the mid-seventies and then increased gradually; the red band (0.630–0.710 m) shows similar trend but opposite in sense. The PAR band (0.380–0.710 m) decreased slightly until 1985 and then increases. In the green/orange band (0.525–0.630 m) the trend can be considered as nearly constant throughout the examined period. This trend of the irradiation ratios is related to the aerosol and gaseous pollutant content of the atmosphere, which probably reflects the urbanization, industrialization and heavy traffic conditions of the Athens area, during the last three decades.With 2 Figures     

Global and regional coupled climate sensitivity to the parameterization of rainfall interception

A coupled land?Catmosphere model is used to explore the impact of seven commonly used canopy rainfall interception schemes on the simulated climate. Multiple 30-year simulations are conducted for each of the seven methods and results are analyzed in terms of the mean climatology and the probability density functions (PDFs) of key variables based on daily data. Results show that the method used for canopy interception strongly affects how rainfall is partitioned between canopy evaporation and throughfall. However, the impact on total evaporation is much smaller, and the impact on rainfall and air temperature is negligible. Similarly, the PDFs of canopy evaporation and transpiration for six selected regions are strongly affected by the method used for canopy interception, but the impact on total evaporation, temperature and precipitation is negligible. Our results show that the parameterization of rainfall interception is important to the surface hydrometeorology, but the seven interception parameterizations examined here do not cause a statistically significant impact on the climate of the coupled model. We suggest that broad scale climatological differences between coupled climate models are not likely the result of how interception is parameterized. This conclusion is inconsistent with inferences derived from earlier uncoupled simulations, or simulations using very simplified climate models.     

Satellite monitoring of global land cover changes and their impact on climate

Land cover is a crucial, spatially and temporally varying component of global carbon and climate systems. Therefore accurate estimation and monitoring of land cover changes is important in global change research. Although, land cover has dramatically changed over the last few centuries, until now there has been no consistent way of quantifying the changes globally.In this study we used long-term climate, soils data along with coarse resolution satellite observations to quantify the magnitude and spatial extent of global land cover changes due to anthropogenic processes. Differences between potential leaf area index, derived from climate-soil-leaf area equilibrium and actual leaf area index obtained from satellite data were used to estimate changes in land cover.Forest clearing for agriculture and irrigated farming in arid and semi-arid lands are found to be two major sources of climatically important land cover changes. Satellite derived Spectral Vegetation indices (SV I) and surface temperatures (T s) show strong impact of land cover changes on climatic processes. Irrigated agriculture in dry areas increased energy absorption and evapotranspiration (ET) compared to natural vegetation. On the other hand, forest clearing for crops decreased energy absorption andET. A land cover classification and monitoring system is proposed using satellite derivedSV I andT s that simultaneously characterize energy absorption and exchange processes. This completely remote sensing based approach is useful for monitoring land cover changes as well as their impacts on climate. Monitoring the spatio-temporal dynamics of land cover is possible with current operational satellites, and could be substantially improved with the Earth Observing System (EOS) era satellite sensors.     

The eruptive history of the Mascota volcanic field,western Mexico: Age and volume constraints on the origin of andesite among a diverse suite of lamprophyric and calc-alkaline lavas

The Mascota volcanic field is located in the Jalisco Block of western Mexico, where the Rivera Plate subducts beneath the North American Plate. It spans an area of ∼ 2000 km² and contains ∼ 87 small cones and lava flows of minette, absarokite, basic hornblende lamprophyre, basaltic andesite, and andesite. There are no contemporary dacite or rhyolite lavas. New ⁴⁰Ar/³⁹Ar ages are presented for 35 samples, which are combined with nine dates from the literature to document the eruptive history of this volcanic field. The oldest lavas (2.4 to 0.5 Ma) are found in the southern part of the field area, whereas the youngest lavas (predominantly < 0.5 Ma) are found in the northern portion. On the basis of these ages, field mapping, and the use of ortho aerial photographs and digital elevation models, it is estimated that a combined volume of 6.8 ± 3.1 km³ erupted in the last 2.4 Myr, which leads to an average eruption rate of ∼ 0.003 km³/kyr, and an average volume per eruptive unit of < 0.1 km³. The dominant lava type is andesite (2.1 ± 0.9 km³), followed by absarokite (1.6 ± 0.8 km³), basaltic andesite (1.2 ± 0.5 km³), basic hornblende lamprophyre (1.0 ± 0.4 km³), and minette (0.9 ± 0.5 km³). Thus, the medium-K andesite and basaltic andesite comprise approximately half (49%) of the erupted magma, with twice as much andesite as basaltic andesite, and they occur in close spatial and temporal association with the highly potassic, lamprophyric lavas. There is no time progression to the type of magma erupted. A wide variety of evidence indicate that the high-MgO (8–9 wt.% ) basaltic andesites (52–53% wt.% SiO₂) were formed by H₂O flux melting of the asthenopheric arc mantle wedge, whereas the mafic minettes and absarokites were formed by partial melting (induced by thermal erosion) of depleted lithospheric mantle containing phlogopite-bearing veins. There is only limited differentiation of the potassic magmas, with none more evolved than 55.4 wt.% SiO₂ and 4.4 wt.% MgO. This may be attributable to rapid crystallization of the mantle-derived melts in the deep crust, owing to their low volumes. Thus, the andesites (58–63 wt.% SiO₂) are notable for being both the most voluminous and the most evolved of all lava types in the Mascota volcanic field, which is not consistent with their extraction from extensively crystallized (60–70%), low-volume intrusions. Instead, the evidence supports the origin of the andesites by partial melting of amphibolitized, mafic lower crust, driven by the emplacement of the minettes, absarokites, and the high-Mg basaltic andesites.     

The long-term policy context for solar radiation management

We examine the potential role of “solar radiation management” or “sunlight reduction methods” (SRM) in limiting future climate change, focusing on the interplay between SRM deployment and mitigation in the context of uncertainty in climate response. We use a straightforward scenario analysis to show that the policy and physical context determine the potential need, amount, and timing of SRM. SRM techniques, along with a substantial emission reduction policy, would be needed to meet stated policy goals, such as limiting climate change to 2 °C above pre-industrial levels, if the climate sensitivity is high. The SRM levels examined by current modeling studies are much higher than the levels required under an assumption of a consistent long-term policy. We introduce a degree-year metric, which quantifies the magnitude of SRM that would be needed to keep global temperatures under a given threshold.     

The role of technology for achieving climate policy objectives: overview of the EMF 27 study on global technology and climate policy strategies

This article presents the synthesis of results from the Stanford Energy Modeling Forum Study 27, an inter-comparison of 18 energy-economy and integrated assessment models. The study investigated the importance of individual mitigation options such as energy intensity improvements, carbon capture and storage (CCS), nuclear power, solar and wind power and bioenergy for climate mitigation. Limiting the atmospheric greenhouse gas concentration to 450 or 550 ppm CO₂ equivalent by 2100 would require a decarbonization of the global energy system in the 21^st century. Robust characteristics of the energy transformation are increased energy intensity improvements and the electrification of energy end use coupled with a fast decarbonization of the electricity sector. Non-electric energy end use is hardest to decarbonize, particularly in the transport sector. Technology is a key element of climate mitigation. Versatile technologies such as CCS and bioenergy are found to be most important, due in part to their combined ability to produce negative emissions. The importance of individual low-carbon electricity technologies is more limited due to the many alternatives in the sector. The scale of the energy transformation is larger for the 450 ppm than for the 550 ppm CO₂e target. As a result, the achievability and the costs of the 450 ppm target are more sensitive to variations in technology availability.     

Relative humidity history on the Batang–Litang Plateau of western China since 1755 reconstructed from tree-ring δ18O and δD

We measured the annual variation in the stable isotopes of oxygen (δ¹⁸O) and hydrogen (δD) in tree rings of Abies georgei on the Batang–Litang Plateau of western China. Although correlations between tree-ring δ¹⁸O and δD are relatively weak in semi-arid regions, we found a strong correlation between the δ¹⁸O and δD time series from 1755 to 2009 under the wetter environment. Tree-ring δ¹⁸O and δD time series are both significantly and negatively correlated with moisture conditions from June to August, including relative humidity and total precipitation, respectively, from 1960 to 2009. Considering the difference in low-frequency domain between the two isotopes, the relative humidity histories from June to August, reconstructed separately from the tree-ring δ¹⁸O and δD data with instrumental climate data, reveal a persistent drying trend since 1850s, especially since the early 1970s. There is an obvious offset of reconstructed relative humidity from tree-ring δ¹⁸O and δD in the period 1755–1820, despite the strong similarity in their 21-year moving averages. The decreased relative humidity since the 1850s may be associated with the thermal contrast between the sea surface temperature of the Indian Ocean and the Qinghai-Tibetan Plateau, which determines the strength of moisture transfer via the Indian summer monsoon.     

Climate change at the ecosystem scale: a 50-year record in New Hampshire

Observing the full range of climate change impacts at the local scale is difficult. Predicted rates of change are often small relative to interannual variability, and few locations have sufficiently comprehensive long-term records of environmental variables to enable researchers to observe the fine-scale patterns that may be important to understanding the influence of climate change on biological systems at the taxon, community, and ecosystem levels. We examined a 50-year meteorological and hydrological record from the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, an intensively monitored Long-Term Ecological Research site. Of the examined climate metrics, trends in temperature were the most significant (ranging from 0.7 to 1.3 °C increase over 40–50 year records at 4 temperature stations), while analysis of precipitation and hydrologic data yielded mixed results. Regional records show generally similar trends over the same time period, though longer-term (70–102 year) trends are less dramatic. Taken together, the results from HBEF and the regional records indicate that the climate has warmed detectably over 50 years, with important consequences for hydrological processes. Understanding effects on ecosystems will require a diversity of metrics and concurrent ecological observations at a range of sites, as well as a recognition that ecosystems have existed in a directionally changing climate for decades, and are not necessarily in equilibrium with the current climate.     

Integrated estimates of global terrestrial carbon sequestration

Assessing the contribution of terrestrial carbon sequestration to climate change mitigation requires integration across scientific and disciplinary boundaries. A comprehensive analysis incorporating ecologic, geographic and economic data was used to develop terrestrial carbon sequestration estimates for agricultural soil carbon, reforestation and pasture management. These estimates were applied in the MiniCAM integrated assessment model to evaluate mitigation strategies within policy and technology scenarios aimed at achieving atmospheric greenhouse gas stabilization by 2100. Terrestrial sequestration reaches a peak rate of 0.5–0.7 GtC yr⁻¹ in mid-century with contributions from agricultural soils (0.21 GtC yr⁻¹), reforestation (0.31 GtC yr⁻¹) and pasture (0.15 GtC yr⁻¹). Sequestration rates vary over time and with different technology and policy scenarios. The combined contribution of terrestrial sequestration over the next century ranges from 23 to 41 GtC.