Combination Of Climate Change Research Articles

Human impacts, climate change, and aquatic ecosystem response during the past 2000 yr at Lake Wandakara, Uganda

Analyses of carbon and hydrogen isotope ratios of terrestrial leaf waxes and the carbon and nitrogen abundance, ratio, and isotopic composition of bulk sediments from Lake Wandakara, a crater lake in western Uganda, East Africa, document human and climatic controls on the aquatic system and on the surrounding terrestrial vegetation during the past two millennia. Our data indicate that Wandakara was a relatively stable, productive lake surrounded by C 3 vegetation from AD 70 to 1000. Abrupt changes in the δ 13C of terrestrial leaf waxes indicate a series of abrupt shifts in the relative abundance of C 3 and C 4 vegetation caused by a combination of climate change and human activities around Wandakara beginning at AD 1000. Abrupt shifts in bulk sediment organic geochemistry, particularly C/N ratios and δ 15N, indicate that human activities at this time caused permanent changes in the limnology of Lake Wandakara, including eutrophication. Our results suggest that the biogeochemistry of Lake Wandakara was more sensitive to shifting human impacts than to climate variations during the past millennium, highlighting the importance of understanding the intensity of pre-colonial human impacts on Africa's aquatic ecosystems.

The effects of climate change and urbanization on the runoff of the Rock Creek basin in the Portland metropolitan area, Oregon, USA

AbstractClimate changes brought on by increasing greenhouse gases in the atmosphere are expected to have a significant effect on the Pacific Northwest hydrology during the 21st century. Many climate model simulations project higher mean annual temperatures and temporal redistribution of precipitation. This is of particular concern for highly urbanized basins where runoff changes are more vulnerable to changes in climate. The Rock Creek basin, located in the Portland metropolitan area, has been experiencing rapid urban growth throughout the last 30 years, making it an ideal study area for assessing the effect of climate and land cover changes on runoff. A combination of climate change and land cover change scenarios for 2040 with the semi‐distributed AVSWAT (ArcView Soil and Water Assessment Tool) hydrological model was used to determine changes in mean runoff depths in the 2040s (2030–2059) from the baseline period (1973–2002) at the monthly, seasonal, and annual scales. Statistically downscaled climate change simulation results from the ECHAM5 general circulation model (GCM) found that the region would experience an increase of 1·2 °C in the average annual temperature and a 2% increase in average annual precipitation from the baseline period. AVSWAT simulation shows a 2·7% increase in mean annual runoff but a 1·6% decrease in summer runoff. Projected climate change plus low‐density, sprawled urban development for 2040 produced the greatest change to mean annual runoff depth (+5·5%), while climate change plus higher‐density urban development for 2040 resulted in the smallest change (+5·2%), when compared with the climate and land cover of the baseline period. This has significant implications for water resource managers attempting to implement adaptive water resource policies to future changes resulting from climate and urbanization. Copyright © 2008 John Wiley & Sons, Ltd.

Climate Change, Humans, and the Extinction of the Woolly Mammoth

Woolly mammoths inhabited Eurasia and North America from late Middle Pleistocene (300 ky BP [300,000 years before present]), surviving through different climatic cycles until they vanished in the Holocene (3.6 ky BP). The debate about why the Late Quaternary extinctions occurred has centred upon environmental and human-induced effects, or a combination of both. However, testing these two hypotheses—climatic and anthropogenic—has been hampered by the difficulty of generating quantitative estimates of the relationship between the contraction of the mammoth's geographical range and each of the two hypotheses. We combined climate envelope models and a population model with explicit treatment of woolly mammoth–human interactions to measure the extent to which a combination of climate changes and increased human pressures might have led to the extinction of the species in Eurasia. Climate conditions for woolly mammoths were measured across different time periods: 126 ky BP, 42 ky BP, 30 ky BP, 21 ky BP, and 6 ky BP. We show that suitable climate conditions for the mammoth reduced drastically between the Late Pleistocene and the Holocene, and 90% of its geographical range disappeared between 42 ky BP and 6 ky BP, with the remaining suitable areas in the mid-Holocene being mainly restricted to Arctic Siberia, which is where the latest records of woolly mammoths in continental Asia have been found. Results of the population models also show that the collapse of the climatic niche of the mammoth caused a significant drop in their population size, making woolly mammoths more vulnerable to the increasing hunting pressure from human populations. The coincidence of the disappearance of climatically suitable areas for woolly mammoths and the increase in anthropogenic impacts in the Holocene, the coup de grâce, likely set the place and time for the extinction of the woolly mammoth.

Holocene coastal environmental changes on the periphery of an area of glacio‐isostatic uplift: an example from Scapa Bay, Orkney, UK

AbstractThe first detailed investigation of a deep, coastal, sedimentary basin in Orkney reveals a complex Holocene history of back‐barrier morphodynamics. At Scapa Bay, the sea flooded a freshwater marsh after ca. 9400 yr BP at ca. −5.4 m OD. Before ca. 7800 BP, abundant sediment from nearby cliffs was mobilised inland into a series of gravel barriers across the valley mouth. By ca. 7500 BP, direct marine influence was restricted in the back‐barrier area, although saltmarsh persisted until ca. 5900 BP. By then, at least four gravel ridges had enclosed the backing lagoon, where freshwater inputs became dominant. As terrestrial sediments filled the basin, another freshwater marsh developed. The multiple barrier complex demonstrates progradation resulting from continuous sediment supply in a sheltered embayment. The progressively rising height of the barrier crests seawards probably resulted from a combination of factors such as barrier morphodynamics, increased storminess and long‐term rising relative sea levels. The dominant vegetation surrounding Scapa Bay changed from open grassland to scrub ca. 9400 BP, then to deciduous woodland ca. 7800 BP, and to dwarf‐shrub heath ca. 2600 BP, the latter probably a response to a combination of climate change and human activity. Copyright © 2007 John Wiley & Sons, Ltd.

GEOCHEMISTRY OF THE RIVER RHINE AND THE UPPER DANUBE:<br>RECENT TRENDS AND LITHOLOGICAL INFLUENCE ON BASELINES

Human pressure is now severe on most of the rivers worldwide. The long term fluxes of dissolved geogenic and biogenic matter are changing dramatically, causing notable changes in aquatic bioactivity. Typical patterns of anthropogenic pressure that influence eutrophication, salinization and chemical contamination are discussed. The heavily influenced rivers Rhine and upper Danube will be used as examples, also considering their geological settings. In the past decade sewage treatment reduced nitrate and orthophosphate loads in both basins. This influenced bioactivity in the rivers, causing less silica depletion due to diatom blooms in the Rhine. Therefore a notable increase in minima concentrations of dissolved silica can be observed. In the upper Danube, however, an increase in orthophosphate concentration since 2003 is noticeable; breaking the former decreasing trend, despite treatment efforts. The hydrochemistry of major ions in both basins is strongly influenced by the ratios of carbonate, siliciclastic sediment and igneous or metamorphic rock outcrops. In addition Mesozoic evaporites and salt mining were responsible for extremely high levels of Cl, Na and SO4 in the Rhine, peaking in the 70s and 80s at concentrations of 350, 180 and 140 mg/l, respectively. Water basin management efforts cut former high levels to less than a half. Heavy metals and persistent organic pollutant concentrations are declining in the Rhine as well. A combination of climate change and anthropogenic water inputs resulted in an increase of water temperature of the Rhine by 3.5 °C during the past 50 years. In the upper Danube such a trend in water temperature can not be observed.

Multiple exposures and dynamic vulnerability: Evidence from the grape industry in the Okanagan Valley, Canada

This paper assesses the vulnerability of grape growers and winery operators in the Okanagan Valley, British Columbia to climate variability and change, in the context of other sources of risk. Through interviews and focus groups, producers identified the climatic and non-climatic risks relevant to them and the strategies employed to manage these risks. The results show that the presence of multiple exposures affects the way in which producers are vulnerable to climate change. Producers are vulnerable to conditions that not only affect crop yield, but also affect their ability to compete in or sell to the market. Their sensitivity to these conditions is influenced in part by institutional factors such as trade liberalization and a “markup-free delivery” policy. Producers’ ability to adapt or cope with these risks varies depending on such factors as the availability of resources and technology, and access to government programmes. Producers will likely face challenges associated with the supply of water for irrigation due to a combination of climatic changes and changing demographics in the Okanagan Valley, which in turn affect their ability to adapt to climatic conditions. Finally, adaptations made by producers can change the nature of the operation and its vulnerability, demonstrating the dynamic nature of vulnerability.

Habitat loss confounds climate change impacts

Biological reserves are set aside to conserve species in dynamic, human-dominated landscapes; however, most reserve systems protect only small, potentially biased samples of environmental conditions across the range of individual species or habitat types. Such biases can result in counter-intuitive distributions of environmental conditions under combinations of climate change and habitat loss. This study outlines the potential range of interactions and presents a case study investigating vernal pool wetlands in California, USA. The results indicate that future distributions of environmental conditions will be determined as much by land-use decisions as by atmospheric emissions.

Habitat Loss Confounds Climate Change Impacts

Biological reserves are set aside to conserve species in dynamic, human-dominated landscapes; however, most reserve systems protect only small, potentially biased samples of environmental conditions across the range of individual species or habitat types. Such biases can result in counter-intuitive distributions of environmental conditions under combinations of climate change and habitat loss. This study outlines the potential range of interactions and presents a case study investigating vernal pool wetlands in California, USA. The results indicate that future distributions of environmental conditions will be determined as much by land-use decisions as by atmospheric emissions.

Tree diversity change in remaining primary mixed-broadleaved Korean pine forest under climate change and human activities

Studying biodiversity change in existing typical ecosystems of the world under possible global climate change and local human activities is important for diversity conservation. An adapted forest dynamics model is used to simulate tree diversity change of the remaining primary mixed-broadleaved Korean pine forest (RPMKPF) in northeast China under global climate change and local human activities for the next 50 years. Human activities include logging, which removes all big trees (DBH > 50 cm), removing all individuals of each single species and all species of each functional type (shade tolerant, shade intolerant and medium type tree species). As results for RPMKPF, the α index of tree diversity decreases under climate change, but it increases significantly under a combination of climate change and logging. Removing all individuals of each single species significantly affects the tree diversity of the ecosystem. After the removal of shade tolerant species, both α and βc indices of tree diversity experience a significant change. The α index decreases significantly under climate change when shade intolerant or medium type tree species are removed, but the βc index does not change significantly. The results of this study have implications for tree diversity management in RPMKPF under climate change and human activities.

Within-type variability of 700 hPa winter circulation patterns over the Lake Superior basin

A correlation-based map-pattern classification technique was applied to 25 winters of daily 700 hPa maps to group them into discrete types, which were then examined to determine their association with surface air temperatures over the Lake Superior basin. The focus of this study was to identify and to remove sources of within-type variability of temperature. Within-type variability was considerable. Its source turned out to be a combination of climate change and small-scale circulation features that were present in the data but were not captured by the map pattern classification. These small-scale features, identified using composite difference maps for cold and warm days of each map type, consisted of height anomalies centered to the east of Lake Superior. Viewing these differences as anomalous components of the mean 700 hPa height pattern-which when added to or subtracted from the pattern create subtle but important modifications-provided insight into the differences in the shape of the 700 hPa steering current for different surface weather systems. To incorporate these features into the classification, daily relative vorticity patterns were computed and discriminant analysis was used to create cold, average, and warm subtypes for each of the first five map types. Replacing the first five map types by their subtypes in the regression models increased the explained variance by 20- 30%. Collapsing warm and cold types did not increase the explained variance as much as it stabilized the models. The creation of cold and warm subtypes also removed a warming trend (significant for two of the map types) by translating the warming trend into a change in the frequency of the subtypes. The analysis used four different floating grids or windows. Classifications for windows centered east of the lake generated better results than those to the west.

Water Management in the Egyptian Delta: Problems of Wastage and Inefficiency

WATER HAS LONG BEEN A FIJNDAMENTAL constraint on development for most countries in the Middle East and North Africa. To overcome these constraints such societies have traditionally developed successful techniques to harness the productive force of water through a combination of social and technical arrangements which allow a high degree of productive efficiency. However, a combination of climatic changes and failure of social systems to respond to

Increased UV-B penetration in a lake owing to drought-induced acidification

CLIMATE change, acid deposition and increasing solar ultraviolet irradiance1 have all combined to produce marked effects on lake waters and their ecosystems. Schindler et al.2 have shown that both climate warming and lake acidification have led to decreases in dissolved organic carbon concentrations in North American boreal lakes, resulting in a markedly increased exposure of the upper water column to solar ultraviolet radiation. Here we report ten years of observations of rainfall and lake chemistry at Swan Lake, Canada, that suggest that a fall in dissolved organic carbon concentrations can also occur by a different combination of climate change and acidification. In this boreal fresh water, a drought decreased lakewater levels, thus exposing to the atmosphere littoral sediments containing reduced sulphur from the previous atmospheric deposition of industrial sulphur dioxide into the lake and its catchment. This exposure caused a reoxidation of sediment sulphur, resulting in a remobilization of acid into the lake water, and thus a decrease in dissolved organic carbon concentrations sufficient to increase by three-fold the depth to which ultraviolet radiation can penetrate.

Controls of Plant and Soil Carbon in a Semihumid Temperate Grassland

A modeling study evaluated the importance of photosynthetic pathways (C3, C4, or both) and management strategies to the foliage productivity and soil carbon characteristics of a semihumid temperate grassland subjected to various combinations of climate change. Model values for plant and soil characteristics were obtained at sites near Manhattan, Kansas, and the Manhattan climate record provided the nominal climatic drivers. Model runs used both actual monthly temperature and precipitation data for a 100—yr interval and average weather conditions generated from this record. Monthly temperatures were increased 2°C, left unchanged, or decreased 2°C; annual precipitation was increased 6 cm, left unchanged, or decreased 6 cm. All possible combinations of temperature and precipitation were then used in 100—yr simulations. Regardless of the specific climate scenario, plant production was lowest for C3 grasses and highest for the mixed C3—C4 community. The nominal seasonal pattern of precipitation favored an active C3 plant community in early to late spring, prior to the emergence of the C4 vegetation. However, the higher growth and water use efficiencies of C4 vegetation during summer contributed to the maximization response of the grasslands containing both C3 and C4 grasses. An analysis of variance of annual average values observed from 100—yr simulations was used to evaluate the relative importance of climate, photosynthetic pathways, and management activities (annually burned, burned every 4 yr, unburned, or lightly grazed) to plant production and soil carbon values. Photosynthetic pathway and precipitation were identified as the most significant single variables affecting foliage production; the interaction between photosynthetic and temperature was the most significant interaction term. Management treatments were by far the most important variables affecting soil carbon values, but 2°C warming did produce substantial soil carbon losses from C3 grasslands. Enhanced carbon fixation by the C4 and C3—C4 plant communities negated the losses of soil carbon caused by enhanced soil respiration at warmer temperatures.

Effects of CO2-induoed climatic changes on soowpack and streamflow

Abstract Atmospheric concentrations of carbon dioxide (CO2) may double during the next century, causing changes in the Earth's climate. Warming of up to 4°C, slight cooling, and 10% changes in precipitation have been projected. Researchers have studied the possible impacts these changes may have on various aspects of the hydrological cycle, but little emphasis has been placed on snow accumulation and melt. In this study, the effects of climatic change on streamflow from a snowmelt-dominated basin in southwestern Montana, USA, are investigated. The National Weather Service River Forecast System model (NWSRFS) was first calibrated using data for the 1973–1984 period. Daily temperature and precipitation values were then changed, and the model ran again to assess the effects on snowpack and streamflow of some possible climatic changes. Results indicate that streamflow may vary by from −22 to +45% depending on the combination of climatic changes imposed.