Showing papers on "Climate change published in 1999"

Climate change and global water resources

Abstract: By 2025, it is estimated that around 5 billion people, out of a total population of around 8 billion, will be living in countries experiencing water stress (using more than 20% of their available resources). Climate change has the potential to impose additional pressures in some regions. This paper describes an assessment of the implications of climate change for global hydrological regimes and water resources. It uses climate change scenarios developed from Hadley Centre climate simulations (HadCM2 and HadCM3), and simulates global river #ows at a spatial resolution of 0.5]0.53 using a macro-scale hydrological model. Changes in national water resources are calculated, including both internally generated runo! and upstream imports, and compared with national water use estimates developed for the United Nations Comprehensive Assessment of the Freshwater Resources of the World. Although there is variation between scenarios, the results suggest that average annual runo! will increase in high latitudes, in equatorial Africa and Asia, and southeast Asia, and will decrease in mid-latitudes and most subtropical regions. The HadCM3 scenario produces changes in runo! which are often similar to those from the HadCM2 scenarios * but there are important regional di!erences. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover. This has implications for the timing of stream#ow in such regions, with a shift from spring snow melt to winter runo!. Under the HadCM2 ensemble mean scenario, the number of people living in countries with water stress would increase by 53 million by 2025 (relative to those who would be a!ected in the absence of climate change). Under the HadCM3 scenario, the number of people living in countries with water stress would rise by 113 million. However, by 2050 there would be a net reduction in populations in stressed countries under HadCM2 (of around 69 million), but an increase of 56 million under HadCM3. The study also showed that di!erent indications of the impact of climate change on water resource stresses could be obtained using di!erent projections of future water use. The paper emphasises the large range between estimates of ‘impacta, and also discusses the problems associated with the scale of analysis and the de"nition of indices of water resource impact. ( 1999 Elsevier Science Ltd. All rights reserved.

Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland

Abstract: Climate fluctuations during the past millennium are relatively well documented1 On a longer timescale, there is growing evidence of millennial-scale variability of Holocene climate, at periodicities of ∼2,500 and 950 years (possibly caused by changes in solar flux)2,3 and ∼1,500 years (maybe related to an internal oscillation of the climate system)4,5,6 But the involvement of deep water masses in these Holocene climate changes has yet to be established Here we use sediment grain-size data from the Iceland basin to reconstruct past changes in the speed of deep-water flow The study site is under the influence of Iceland–Scotland Overflow Water (ISOW), the flow of which is an important component of the ‘thermohaline’ circulation that modulates European climate Flow changes coincide with some known climate events (the Little Ice Age and the Mediaeval Warm Period), and extend over the entire Holocene epoch with aquasi-periodicity of ∼1,500 years The grain-size data indicate afaster ISOW flow when the climate of northern Europe is warmer However, a second mode of operation is observed in the early Holocene, when warm climate intervals are associated with slower ISOW flow At that time the melting remnant of land-based, glacial-age ice may have provided a sufficient source of fresh water to the ocean to reduce ISOW flow south of Iceland

GISS analysis of surface temperature change

Abstract: We describe the current GISS analysis of surface temperature change based primarily on meteorological station measurements. The global surface temperature in 1998 was the warmest in the period of instrumental data. The rate of temperature change is higher in the past 25 years than at any previous time in the period of instrumental data. The warmth of 1998 is too large and pervasive to be fully accounted for by the recent El Nino, suggesting that global temperature may have moved to a higher level, analogous to the increase that occurred in the late 1970s. The warming in the United States over the past 50 years is smaller than in most of the world, and over that period there is a slight cooling trend in the Eastern United States and the neighboring Atlantic ocean. The spatial and temporal patterns of the temperature change suggest that more than one mechanism is involved in this regional cooling.

Dust sources and deposition during the last glacial maximum and current climate: A comparison of model results with paleodata from ice cores and marine sediments

Abstract: Mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean. Ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2–20 times greater during glacial periods, raising the possibility that mineral aerosols might have contributed to climate change on glacial-interglacial time scales. To address this question, we have used linked terrestrial biosphere, dust source, and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum (LGM) climates. We obtain a 2.5-fold higher dust loading in the entire atmosphere and a twenty-fold higher loading in high latitudes, in LGM relative to present. Comparisons to a compilation of atmospheric dust deposition flux estimates for LGM and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations; differences suggest where further improvements in the simple dust model could be made. The simulated increase in high-latitude dustiness depends on the expansion of unvegetated areas, especially in the high latitudes and in central Asia, caused by a combination of increased aridity and low atmospheric [CO2]. The existence of these dust source areas at the LGM is supported by pollen data and loess distribution in the northern continents. These results point to a role for vegetation feedbacks, including climate effects and physiological effects of low [CO2], in modulating the atmospheric distribution of dust.

Conceptual Framework for Changes of Extremes of the Hydrological Cycle with Climate Change

Abstract: A physically based conceptual framework is put forward that explains why an increase in heavy precipitation events should be a primary manifestation of the climate change that accompanies increases in greenhouse gases in the atmosphere. Increased concentrations of greenhouse gases in the atmosphere increase downwelling infrared radiation, and this global heating at the surface not only acts to increase temperatures but also increases evaporation which enhances the atmospheric moisture content. Consequently all weather systems, ranging from individual clouds and thunderstorms to extratropical cyclones, which feed on the available moisture through storm-scale moisture convergence, are likely to produce correspondingly enhanced precipitation rates. Increases in heavy rainfall at the expense of more moderate rainfall are the conseqUence along with increased runoff and risk of flooding. However, because of constraints in the surface energy budget, there are also implications for the frequency and/or efficiency of precipitation. It follows that increased attention should be given to trends in atmospheric moisture content, and datasets on hourly precipitation rates and frequency need to be developed and analyzed as well as total accumulation.

Climate change and plant disease management

Abstract: ▪ Abstract Research on impacts of climate change on plant diseases has been limited, with most work concentrating on the effects of a single atmospheric constituent or meteorological variable on the host, pathogen, or the interaction of the two under controlled conditions. Results indicate that climate change could alter stages and rates of development of the pathogen, modify host resistance, and result in changes in the physiology of host-pathogen interactions. The most likely consequences are shifts in the geographical distribution of host and pathogen and altered crop losses, caused in part by changes in the efficacy of control strategies. Recent developments in experimental and modeling techniques offer considerable promise for developing an improved capability for climate change impact assessment and mitigation. Compared with major technological, environmental, and socioeconomic changes affecting agricultural production during the next century, climate change may be less important; it will, however, ...

Signature of recent climate change in frequencies of natural atmospheric circulation regimes

Abstract: A crucial question in the global-warming debate concerns the extent to which recent climate change is caused by anthropogenic forcing or is a manifestation of natural climate variability1. It is commonly thought that the climate response to anthropogenic forcing should be distinct from the patterns of natural climate variability. But, on the basis of studies of nonlinear chaotic models with preferred states or ‘regimes’, it has been argued2,3 that the spatial patterns of the response to anthropogenic forcing may in fact project principally onto modes of natural climate variability. Here we use atmospheric circulation data from the Northern Hemisphere to show that recent climate change can be interpreted in terms of changes in the frequency of occurrence of natural atmospheric circulation regimes. We conclude that recent Northern Hemisphere warming may be more directly related to the thermal structure of these circulation regimes than to any anthropogenic forcing pattern itself. Conversely, the fact that observed climate change projects onto natural patterns cannot be used as evidence of no anthropogenic effect on climate. These results may help explain possible differences between trends in surface temperature and satellite-based temperature in the free atmosphere4,5,6.

Climate change and world food security: a new assessment

Abstract: Building on previous work quantitative estimates of climate change impacts on global food production have been made for the UK Hadley Centre's HadCM2 greenhouse gas only ensemble experiment and the more recent HadCM3 experiment (Hulme et al., 1999). The consequences for world food prices and the number of people at risk of hunger as defined by the Food and Agriculture Organisation (FAO, 1988) have also been assessed. Climate change is expected to increase yields at high and mid-latitudes, and lead to decreases at lower latitudes. This pattern becomes more pronounced as time progresses. The food system may be expected to accommodate such regional variations at the global level, with production, prices and the risk of hunger being relatively unaffected by the additional stress of climate change. By the 2080s the additional number of people at risk of hunger due to climate change is about 80 million people (±10 million depending on which of the four HadCM2 ensemble members is selected). However, some regions (particularly the arid and sub-humid tropics) will be adversely affected. A particular example is Africa, which is expected to experience marked reductions in yield, decreases in production, and increases in the risk of hunger as a result of climate change. The continent can expect to have between 55 and 65 million extra people at risk of hunger by the 2080s under the HadCM2 climate scenario. Under the HadCM3 climate scenario the effect is even more severe, producing an estimated additional 70+ million people at risk of hunger in Africa.

Climate change related to egg-laying trends

Abstract: Analysis of 20 species of UK breeding birds over a 25-year period found a long-term trend towards earlier egg-laying1. Further studies have correlated such trends with spring temperatures (one species)2 or the North Atlantic Oscillation (three species)3. We have studied a data set spanning 57 years and find that laying date is related to temperature or rainfall for 31 of 36 species (86%), and that 53% of species show long-term trends in laying date over time, of which 37% can be statistically accounted for by changes in climate. These data provide evidence for the large-scale impact of rising temperatures on wildlife. Our analysis of a UKCIP98 national-level climate scenario4 predicts that average laying dates will be even earlier for 75% of species by the year 2080.

Simulation of an abrupt change in Saharan vegetation in the mid-Holocene

Abstract: Climate variability during the present inter- glacial, the Holocene, has been rather smooth in compar- ison with the last glacial. Nevertheless, there were some rather abrupt climate changes. One of these changes, the desertication of the Saharan and Arabian region some 4 - 6 thousand years ago, was presumably quite important for human society. It could have been the stimulus leading to the foundation of civilizations along the Nile, Euphrat and Tigris rivers. Here we argue that Saharan and Arabian de- sertication was triggered by subtle variations in the Earth's orbit which were strongly amplied by atmosphere- vegeta- tion feedbacks in the subtropics. The timing of this tran- sition, however, was mainly governed by a global interplay between atmosphere, ocean, sea ice, and vegetation.

Simulation of recent northern winter climate trends by greenhouse-gas forcing

Abstract: The temperature of air at the Earth's surface has risen during the past century1, but the fraction of the warming that can be attributed to anthropogenic greenhouse gases remains controversial. The strongest warming trends have been over Northern Hemisphere land masses during winter, and are closely related to changes in atmospheric circulation. These circulation changes are manifested by a gradual reduction in high-latitude sea-level pressure, and an increase in mid-latitude sea-level pressure associated with one phase of the Arctic Oscillation (a hemisphere-scale version of the North Atlantic Oscillation)2. Here we use several different climate-model versions to demonstrate that the observed sea-level-pressure trends, including their magnitude, can be simulated by realistic increases in greenhouse-gas concentrations. Thus, although the warming appears through a naturally occurring mode of atmospheric variability, it may be anthropogenically induced and may continue to rise. The Arctic Oscillation trend is captured only in climate models that include a realistic representation of the stratosphere, while changes in ozone concentrations are not necessary to simulate the observed climate trends. The proper representation of stratospheric dynamics appears to be important to the attribution of climate change, at least on a broad regional scale.

Genetic responses to climate in pinus contorta: niche breadth, climate change, and reforestation

Abstract: Fundamental plant–environment relationships were revealed by analyses of 20-yr height and survival of 118 populations representing two subspecies of Pinus contorta growing in common gardens at 60 environmentally disparate test sites in British Columbia. The approach involved (1) preparing models that described the general climate of British Columbia, (2) developing population-specific response functions driven by predicted climate variables, (3) developing general transfer functions that predict performance from the climatic distances over which populations were transferred, and (4) interpreting the results in terms of niche breadth, effects of climate change on adaptedness of populations, and reforestation in a changing environment. Polynomial regression models used physiographic descriptors to predict seven climate variables from normalized records of 513 weather stations. Values of R2 ranged over 0.80–0.97 for thermal variables and 0.54–0.61 for precipitation variables. Validations with independent data from 45 stations were strong and suggested that the models were generally free of bias within the limits of the original data. Response functions describing the height or survival of each population were developed from quadratic regressions using predicted climate variables for each test site. Mean annual temperature and mean temperature in the coldest month were the most effective variables for predicting population height, while the ratio of summer temperature to summer moisture was the best predictor of survival. Validation of the response functions with independent data from two additional test sites produced values of R2 between actual and predicted values that were as high as 0.93 for height and 0.73 for survival. The results demonstrated that natural populations have different climatic optima but tend to occupy suboptimal environments. Nevertheless, the general transfer functions showed that optimal growth and survival of the species as a whole is associated with the null transfer distance. These seemingly anomalous results suggest that the same processes thought to determine the distribution of species control the distribution of genotypes within species: (1) environmental selection to produce a broad fundamental niche, and (2) density-dependent selection to produce a relatively narrow realized niche within which most populations are relegated to suboptimal environments. Consequently, the steep geographic clines typical of P. contorta seem to be driven more by density-dependent selection than by environmental selection. Asymmetric gene flow from the center of distribution toward the periphery is viewed as a primary regulator that provides the fuel for both environmental and density-dependent selection and thereby indirectly perpetuates suboptimality. The response functions predict that small changes in climate will greatly affect growth and survival of forest tree populations and, therefore, that maintaining contemporary forest productivities during global warming will require a wholesale redistribution of genotypes across the landscape. The response functions also provide the climatic bases to current reforestation guidelines and quantify the adjustments necessary for maintaining adaptedness in planted trees during periods of small (∼1°C) temporal temperature shifts.

New estimates of the damage costs of climate change. Part II: Dynamic estimates

Abstract: Monetised estimates of the impact of climate change are derived. Impacts areexpressed as functions of climate change and `vulnerability'. Vulnerabilityis measured by a series of indicators, such as per capita income, populationabove 65, and economic structure. Impacts are estimated for nine worldregions, for the period 2000–2200, for agriculture, forestry, waterresources, energy consumption, sea level rise, ecosystems, fatal vector-borne diseases, and fatal cardiovascular and respiratory disorders.Uncertainties are large, often including sign switches. In the short term,the estimated sensitivity of a sector to climate change is found to be thecrucial parameter. In the longer term, the change in the vulnerability of thesector is often more important for the total impact. Impacts can be negativeor positive, depending on the time, region, and sector one is looking at.Negative impacts tend to dominate in the later years and in the poorerregions.

Climate change and trophic interactions.

Abstract: With confirmation of anthropogenically induced climate change, the spotlight is on biologists to predict and detect effects on populations. The complexity of interactions within and between the biotic and abiotic components involved makes this a tough challenge, and most studies have consequently considered effects of only single climate variables on single species. However, some have gone further, and recently published long-term datasets now offer opportunities that complement new experimental approaches that span trophic levels. With these datasets, predicting relative shifts in temporal and spatial associations could be among the most tractable problems.

Transient climate change simulations with a coupled atmosphere–ocean GCM including the tropospheric sulfur cycle

Abstract: The time-dependent climate response to changing concentrations of greenhouse gases and sulfate aerosols is studied using a coupled general circulation model of the atmosphere and the ocean (ECHAM4/OPYC3). The concentrations of the well-mixed greenhouse gases like CO2, CH4, N2O, and CFCs are prescribed for the past (1860–1990) and projected into the future according to International Panel on Climate Change (IPCC) scenario IS92a. In addition, the space–time distribution of tropospheric ozone is prescribed, and the tropospheric sulfur cycle is calculated within the coupled model using sulfur emissions of the past and projected into the future (IS92a). The radiative impact of the aerosols is considered via both the direct and the indirect (i.e., through cloud albedo) effect. It is shown that the simulated trend in sulfate deposition since the end of the last century is broadly consistent with ice core measurements, and the calculated radiative forcings from preindustrial to present time are within th...

Effects of climate change on hydrology and water resources in the columbia river basin

Abstract: As part of the National Assessment of Climate Change, the implications of future climate predictions derived from four global climate models (GCMs) were used to evaluate possible future changes to Pacific Northwest climate, the surface water response of the Columbia River basin, and the ability of the Columbia River reservoir system to meet regional water resources objectives. Two representative GCM simulations from the Hadley Centre (HC) and Max Planck Institute (MPI) were selected from a group of GCM simulations made available via the National Assessment for climate change. From these simulations, quasi-stationary, decadal mean temperature and precipitation changes were used to perturb historical records of precipitation and temperature data to create inferred conditions for 2025, 2045, and 2095. These perturbed records, which represent future climate in the experiments, were used to drive a macro-scale hydrology model of the Columbia River at 1/8 degree resolution. The altered streamflows simulated for each scenario were, in turn, used to drive a reservoir model, from which the ability of the system to meet water resources objectives was determined relative to a simulated hydrologic base case (current climate). Although the two GCM simulations showed somewhat different seasonal patterns for temperature change, in general the simulations show reasonably consistent basin average increases in temperature of about 1.8–2.1°C for 2025, and about 2.3–2.9°C for 2045. The HC simulations predict an annual average temperature increase of about 4.5°C for 2095. Changes in basin averaged winter precipitation range from -1 percent to + 20 percent for the HC and MPI scenarios, and summer precipitation is also variously affected. These changes in climate result in significant increases in winter runoff volumes due to increased winter precipitation and warmer winter temperatures, with resulting reductions in snowpack. Average March 1 basin average snow water equivalents are 75 to 85 percent of the base case for 2025, and 55 to 65 percent of the base case by 2045. By 2045 the reduced snowpack and earlier snow melt, coupled with higher evapotranspiration in early summer, would lead to earlier spring peak flows and reduced runoff volumes from April-September ranging from about 75 percent to 90 percent of the base case. Annual runoff volumes range from 85 percent to 110 percent of the base case in the simulations for 2045. These changes in streamflow create increased competition for water during the spring, summer, and early fall between non-firm energy production, irrigation, instream flow, and recreation. Flood control effectiveness is moderately reduced for most of the scenarios examined, and desirable navigation conditions on the Snake are generally enhanced or unchanged. Current levels of winter-dominated firm energy production are only significantly impacted for the MPI 2045 simulations.

Geomorphic limits to climate-induced increases in topographic relief

Abstract: Recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross-disciplinary investigation and debate on the question of whether tectonics have driven long-term climate change or vice versa. It has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision. Because isostasy acts to compensate mean elevations, the debate hinges on the question of whether climate change can significantly increase topographic relief or, more precisely, increase the volume of ‘missing mass’ between summits and ridges. Here we show that, in tectonically active mountain ranges, geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change. Thus, although climate change may cause significant increases in denudation rates, potentially establishing an important feedback between surficial and crustal processes, neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift.

Northern Hemisphere Ice-Sheet Influences on Global Climate Change

Abstract: Large ice sheets actively interact with the rest of the climate system by amplifying, pacing, and potentially driving global climate change over several time scales. Direct and indirect influences of ice sheets on climate cause changes in ocean surface temperatures, ocean circulation, continental water balance, vegetation, and land-surface albedo, which in turn cause additional feedbacks in the climate system and help to synchronize global climate change. The effect of the underlying geological substrate on ice-sheet dynamics may be the missing link in understanding the ice sheet–climate interactions that are integral to the middle Pleistocene transition; the 100,000-year climate cycle; high-amplitude, millennial-scale climate variability; and low–aspect ratio ice sheets of the Last Glacial Maximum.

The Arctic and Antarctic oscillations and their projected changes under global warming

Abstract: The Arctic Oscillation (AO) and the Antarctic Oscillation (AAO) are the leading modes of high-latitude variability in each hemisphere as characterized by the first EOF of mean sea-level pressure. Observations suggest a recent positive trend in the AO and it is speculated that this may be related to global warming. The CCCma coupled general circulation model control simulation exhibits a robust and realistic AO and AAO. Climate change simulations for the period 1900–2100, with forcing due to greenhouse gases and aerosols, exhibit positive trends in both the AO and the AAO. The model simulates essentially unchanged AO/AAO variations superimposed on a forced climate change pattern. The results do not suggest that a simulated trend in the AO/AAO necessarily depends on stratospheric involvement nor that forced climate change will be expressed as a change in the occurence of one phase of the AO/AAO over another. This pattern of climate change projects exclusively on the AAO pattern in the southern hemisphere but not in the northern hemisphere where other EOFs are involved. The extent to which this forced climate change pattern and the unforced modes of variation are determined by the same mechanisms and feedbacks remains an open question.

From GCMs to river flow: a review of downscaling methods and hydrologic modelling approaches

Abstract: The scientific literature of the past decade contains a large number of reports detailing the development of downscaling methods and the use of hydrologic models to assess the potential effects of climate change on a variety of water resource issues. This article reviews the current state of methodologies for simulating hydrological responses to global climate change. Emphasis is given to recent advances in climatic downscaling and the problems related to the practical application of appropriate models in impact studies. Following a discussion of the advantages and deficiencies of the various approaches, challenges for the future study of the hydrological impacts of climate change are identified.

The effect of climate change on hydrological regimes in Europe: a continental perspective

Abstract: This paper outlines the effects of climate change by the 2050s on hydrological regimes at the continental scale in Europe, at a spatial resolution of 0.5×0.5°. Hydrological regimes are simulated using a macro-scale hydrological model, operating at a daily time step, and four climate change scenarios are used. There are differences between the four scenarios, but each indicates a general reduction in annual runoff in southern Europe (south of around 50°N), and an increase in the north. In maritime areas there is little difference in the timing of flows, but the range through the year tends to increase with lower flows during summer. The most significant changes in flow regime, however, occur where snowfall becomes less important due to higher temperatures, and therefore both winter runoff increases and spring flow decreases: these changes occur across a large part of eastern Europe. In western maritime Europe low flows reduce, but further east minimum flows will increase as flows during the present low flow season – winter – rise. “Drought” was indexed as the maximum total deficit volume below the flow exceeded 95% of the time: this was found to increase in intensity across most of western Europe, but decrease in the east and north. The study attempted to quantify several sources of uncertainty, and showed that the effects of model uncertainty on the estimated change in runoff were generally small compared to the differences between scenarios and the assumed change in global temperature by 2050.

Closing the global N2O budget: A retrospective analysis 1500–1994

Abstract: We present new estimates of global nitrous oxide (N2O) emissions for the period 1500–1994 based on revised Intergovernmental Panel on Climate Change guidelines [Intergovernmental Panel on Climate Change (IPCC), 1997; Mosier et al., 1998]. Use of these estimates as input to a simple atmospheric box model resulted in a closed N2O budget over time, showing that increases in atmospheric N2O can be primarily attributed to changes in food production systems. We hypothesize that before the ninetheenth century conversion of natural land to agriculture had no net effect on N2O. During the twentieth century a fast expansion of agricultural land coupled with intensification of land use may have caused a net increase in N2O. In our base scenario the total N2O emissions increased from 11 Tg N yr−1 in 1850 to 15 Tg N yr−1 in 1970 and to 18 Tg N yr−1 in 1994.

Climate‐related change in an intertidal community over short and long time scales

Abstract: Changes in the abundance of macroinvertebrate species documented in a rocky intertidal community between surveys in 1931-1933 and 1993-1996 are consistent with the predicted effects of recent climate warming. We resampled 57 0.84-M2 plots of an intertidal transect first surveyed by W. G. Hewatt at Hopkins Marine Station (HMS), Pacific Grove, California, between 1931 and 1933. Replicating precisely the location of the plots and methodology used by Hewatt, we documented changes in the abundances of 46 invertebrate species, indicating that this intertidal community changed significantly during the 60 yr between surveys. Changes in abundance were related to geographic ranges of species. Most southern species (10 of 11) increased in abundance, whereas most northern species (5 of 7) decreased. Cosmopolitan species showed no clear trend, with 12 increasing and 16 decreasing. Although Hewatt did not record algal species as thoroughly as inver- tebrates, we were able to document a massive decline in cover of Pelvetia compressa, a cosmopolitan fucoid alga that is typically more common in the southern part of its range. Shoreline ocean temperature, taken daily at HMS, warmed by 0.790C during this 60-yr period, with average summer temperatures up to 1.940C warmer in the 13 yr preceding our study than in the 13 yr preceding Hewatt's. The hypothesis that-climatic warming drove the observed range-related community shifts is supported further by historical records and data from other investigators. Several alternative hypotheses to explain changes in the invertebrate community at HMS, including habitat changes, anthropogenic effects, indirect biological interactions, El Nifio-Southern Oscillation (ENSO) events, and upwelling are considered to be less important than climate change. Changes in species' abundances over a short period (3 yr) were relatively small compared to large species shifts over 60 yr and were unrelated to geographic range of the species, indicating that short-term population fluctuations play a relatively minor role in the long-term community changes that we observed.

Orbital controls on the El Niño/Southern Oscillation and the tropical climate

Abstract: The global synchroneity of glacial-interglacial events is one of the major problems in understanding the link between Milankovitch forcing and the climate of the late Quaternary. In this study we isolate a part of the climate system, the tropical Pacific, and test its sensitivity to changes in solar forcing associated with changes in the Earth's orbital parameters. We use a simplified coupled ocean-atmosphere model that is run for the past 150,000 years and forced with Milankovitch changes in the solar insolation. This system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant. The mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the El Nifio/Southern Oscillation (ENSO). Changes in the ENSO behavior result in a mean tropical climate change. The hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to Milankovitch forcing.

Climate change impacts and adaptation assessment in Bangladesh

Abstract: Bangladesh is likely to be one of the most vulnerable countries in the world to climate change. This paper discusses the possible impacts of climate change in Bangladesh through tropical cyclones, storm surges, coastal erosion and back water effect. The possible increase in cyclone fre- quency in the Bay of Bengal, lying south of Bangladesh, due to climate change is looked at by analyz- ing the cyclone data for 119 yr. Both qualitative and quantitative discussions are made on cyclone intensity increase for a sea surface temperature rise of 2 and 4°C. Different scenarios of storm surges under different climate change conditions are developed by using a numerical model of storm surges for the Bay of Bengal. Possible loss of land through beach erosion due to sea level rise on the eastern coast of Bangladesh is examined. Some discussions are also made on the impacts of back water effect due to sea level rise on flood situations in the country. Finally, a few remarks are made on the adapta- tion options for Bangladesh in the event of climate change.

Assessment of coastal vulnerability to climate change

Abstract: The UNEP Handbook on Methods for Climate Change Impact Assessment and Adaptation Strategies provides an elaboration of the IPCC Technical Guidelines for Assessing Climate Change Impacts and Adaptations. This paper presents the concepts and ideas that underpin the chapter Coastal Zones of the UNEP Handbook. Particular emphasis is given to the conceptual framework, which is centered around the concept of vulnerability. Further, the IPCC Common Methodology for Assessing Coastal Vulnerability to Sea-Level Rise is evaluated and compared with the Technical Guidelines. One notable difference between the 2 approaches concerns the use of scenarios. In the Common Methodology scenarios are prescribed, while the Technical Guidelines allow users maximum freedom in selecting and developing scenarios. Finally, the paper discusses 3 levels of increasingly complex assessment in coastal zones. As more experience is acquired, coastal databases improve and better analytical tools and techniques are developed, more comprehensive and integrated assessments will become feasible.

Climate change and future populations at risk of malaria

Abstract: Global estimates of the potential impact of climate change on malaria transmission were calculated based on future climate scenarios produced by the HadCM2 and the more recent HadCM3 global climate models developed by the UK Hadley Centre. This assessment uses an improved version of the MIASMA malaria model, which incorporates knowledge about the current distributions and characteristics of the main mosquito species of malaria. The greatest proportional changes in potential transmission are forecast to occur in temperate zones, in areas where vectors are present but it is currently too cold for transmission. Within the current vector distribution limits, only a limited expansion of areas suitable for malaria transmission is forecast, such areas include: central Asia, North America and northern Europe. On a global level, the numbers of additional people at risk of malaria in 2080 due to climate change is estimated to be 300 and 150 million for P. falciparum and P. vivax types of malaria, respectively, under the HadCM3 climate change scenario. Under the HadCM2 ensemble projections, estimates of additional people at risk in 2080 range from 260 to 320 million for P. falciparum and from 100 to 200 million for P. vivax. Climate change will have an important impact on the length of the transmission season in many areas, and this has implications for the burden of disease. Possible decreases in rainfall indicate some areas that currently experience year-round transmission may experience only seasonal transmission in the future. Estimates of future populations at risk of malaria differ significantly between regions and between climate scenarios.

The Interpretation of Short Climate Records, with Comments on the North Atlantic and Southern Oscillations

Abstract: This pedagogical note reminds the reader that the interpretation of climate records is dependent upon understanding the behavior of stochastic processes. In particular, before concluding that one is seeing evidence for trends, shifts in the mean, or changes in oscillation periods, one must rule out the purely random fluctuations expected from stationary time series. The example of the North Atlantic oscillation (NAO) is mainly used here: the spectral density is nearly white (frequency power law ≈ s-0.2) with slight broadband features near 8 and 2.5 yr. By generating synthetic but stationary time series, one can see exhibited many of the features sometimes exciting attention as being of causal climate significance. Such a display does not disprove the hypothesis of climate change, but it provides a simple null hypothesis for what is seen. In addition, it is shown that the linear predictive skill for the NAO index must be very slight (less than 3% of the variance). A brief comparison with the South...