Showing papers in "Climatic Change in 2003"

The Anthropogenic Greenhouse Era Began Thousands of Years Ago

Abstract: The anthropogenic era is generally thought to have begun 150 to 200 years ago, when the industrial revolution began producing CO2 and CH4 at rates sufficient to alter their compositions in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three arguments. (1) Cyclic variations in CO2 and CH4 driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene, but the CO2 trend began an anomalous increase 8000 years ago, and the CH4 trend did so 5000 years ago. (2) Published explanations for these mid- to late-Holocene gas increases based on natural forcing can be rejected based on paleocli- matic evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia, including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In recent millennia, the estimated warming caused by these early gas emissions reached a global-mean value of ∼0.8 ◦ C and roughly 2 ◦ C at high latitudes, large enough to have stopped a glaciation of northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of ∼10 ppm in the last 1000 years are too large to be explained by external (solar-volcanic) forcing, but they can be explained by outbreaks of bubonic plague that caused historically documented farm abandonment in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for the observed CO2 decreases. Plague-driven CO2 changes were also a significant causal factor in temperature changes during the Little Ice Age (1300-1900 AD).

Climatic Change in Mountain Regions: A Review of Possible Impacts

Abstract: This paper addresses a number of issues related to current and future climatic change and its impacts on mountain environments and economies, focusing on the `Mountain Regions' Chapter 13 of Agenda 21, a basis document presented at the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, and the International Year of the Mountains (IYM) 2002. The awareness that mountain regions are an important component of the earth's ecosystems, in terms of the resources and services that they provide to both mountain communities and lowland residents, has risen in the intervening decade. Based upon the themes outlined in the supporting documents for IYM, this paper will provide a succinct review of a number of sectors that warrant particular attention, according to IYM. These sectors include water resources, ecosystems and biological diversity, natural hazards, health issues, and tourism. A portfolio of research and policy options are discussed in the concluding section, as a summary of what the IYM and other concerned international networks consider to be the priority for mountain environmental protection, capacity building, and response strategies in the face of climatic change in the short to medium term future.

Recent Rapid Regional Climate Warming on the Antarctic Peninsula

Abstract: The Intergovernmental Panel on Climate Change (IPCC) confirmed that mean global warming was 0.6 ± 0.2 °C during the 20th century and cited anthropogenic increases in greenhouse gases as the likely cause of temperature rise in the last 50 years. But this mean value conceals the substantial complexity of observed climate change, which is seasonally- and diurnally-biased, decadally-variable and geographically patchy. In particular, over the last 50 years three high-latitude areas have undergone recent rapid regional (RRR) warming, which was substantially more rapid than the global mean. However, each RRR warming occupies a different climatic regime and may have an entirely different underlying cause. We discuss the significance of RRR warming in one area, the Antarctic Peninsula. Here warming was much more rapid than in the rest of Antarctica where it was not significantly different to the global mean. We highlight climate proxies that appear to show that RRR warming on the Antarctic Peninsula is unprecedented over the last two millennia, and so unlikely to be a natural mode of variability. So while the station records do not indicate a ubiquitous polar amplification of global warming, the RRR warming on the Antarctic Peninsula might be a regional amplification of such warming. This, however, remains unproven since we cannot yet be sure what mechanism leads to such an amplification. We discuss several possible candidate mechanisms: changing oceanographic or changing atmospheric circulation, or a regional air-sea-ice feedback amplifying greenhouse warming. We can show that atmospheric warming and reduction in sea-ice duration coincide in a small area on the west of the Antarctic Peninsula, but here we cannot yet distinguish cause and effect. Thus for the present we cannot determine which process is the probable cause of RRR warming on the Antarctic Peninsula and until the mechanism initiating and sustaining the RRR warming is understood, and is convincingly reproduced in climate models, we lack a sound basis for predicting climate change in this region over the coming century.

Climate dangers and atoll countries

Abstract: Climate change-induced sea-level rise, sea-surface warming, and increased frequency and intensity of extreme weather events puts the long-term ability of humans to inhabit atolls at risk. We argue that this risk constitutes a dangerous level of climatic change to atoll countries by potentially undermining their national sovereignty. We outline the novel challenges this presents to both climate change research and policy. For research, the challenge is to identify the critical thresholds of change beyond which atoll social-ecological systems may collapse. We explain how thresholds may be behaviorally driven as well as ecologically driven through the role of expectations in resource management. The challenge for the international policy process, centred on the UN Framework Convention on Climate Change (UNFCCC), is to recognize the particular vulnerability of atoll countries by operationalising international norms of justice, sovereignty, and human and national security in the regime.

Impact of secular climate change on the thermal structure of a large temperate central european lake

Abstract: Strong climate-related secular trends are apparent in a 52-yr long (1947–1998) uninterrupted series of monthly temperature profiles fromLake Zurich, a large, deep (136 m), temperate lake on the Swiss Plateau. Decadal mean water temperatures have undergone a secular increase at all depths, reflecting the high degree of regional warming that occurred in the European Alpine area during the 20th century. From the 1950s to the 1990s, high warming rates (∼ 0.24 K per decade) in the uppermost 20 m of the lake (i.e., the epi/metalimnion) combined with lower warming rates (∼ 0.13 K per decade) below 20 m (i.e., in the hypolimnion), have resulted in a20% increase in thermal stability and a consequent extension of 2–3 weeksin the stratification period. In common with many other parts of the world, 20th-century climate change on the Swiss Plateau has involved a steep secular increase in daily minimum (nighttime) air temperatures, but not in daily maximum (daytime) air temperatures. With respect to both secular change and decadal-scale variability, the temporal structure of the temperature of the surface mixed layer of Lake Zurich faithfully reflects that of the regional daily minimum air temperature, but not that of the daily maximum. The processes responsible for longer-term changes in the temperature structure of the lake therefore act during the night, presumably by suppressing nighttime convective cooling of the surface mixed layer. Application of a one-box heat exchange model suggests that the observed secular changes in thermal structure are due to shifts in the nighttime rate of emission of infrared radiation from the atmosphere and in the nighttime rates of latent and sensible heat exchange at the air-water interface. The increase in hypolimnetic temperatures is mainly a result of the increased prevalence of warm winters in Europe.

Preparing for Climatic Change: The Water, Salmon, and Forests of the Pacific Northwest

Abstract: The impacts of year-to-year and decade-to-decade climatic variations on some of the Pacific Northwest's key natural resources can be quantified to estimate sensitivity to regional climatic changes expected as part of anthropogenic global climatic change Warmer, drier years, often associated with El Nino events and/or the warm phase of the Pacific Decadal Oscillation, tend to be associated with below-average snowpack, streamflow, and flood risk, below-average salmon survival, below-average forest growth, and above-average risk of forest fire During the 20th century, the region experienced a warming of 08 °C Using output from eight climate models, we project a further warming of 05–25 °C (central estimate 15 °C) by the 2020s, 15–32°C (23 °C) by the 2040s, and an increase in precipitation except in summer The foremost impact of a warming climate will be the reduction of regional snowpack, which presently supplies water for ecosystems and human uses during the dry summers Our understanding of past climate also illustrates the responses of human management systems to climatic stresses, and suggests that a warming of the rate projected would pose significant challenges to the management of natural resources Resource managers and planners currently have few plans for adapting to or mitigating the ecological and economic effects of climatic change

U.S. Agriculture and Climate Change: New Results

Abstract: We examined the impacts on U.S. agriculture of transient climate change as simulated by 2 global general circulation models focusing on the decades of the 2030s and 2090s. We examined historical shifts in the location of crops and trends in the variability of U.S. average crop yields, finding that non-climatic forces have likely dominated the north and westward movement of crops and the trends in yield variability. For the simulated future climates we considered impacts on crops, grazing and pasture, livestock, pesticide use, irrigation water supply and demand, and the sensitivity to international trade assumptions, finding that the aggregate of these effects were positive for the U.S. consumer but negative, due to declining crop prices, for producers. We examined the effects of potential changes in El Nino/Southern Oscillation (ENSO) and impacts on yield variability of changes in mean climate conditions. Increased losses occurred with ENSO intensity and frequency increases that could not be completely offset even if the events could be perfectly forecasted. Effects on yield variability of changes in mean temperatures were mixed. We also considered case study interactions of climate, agriculture, and the environment focusing on climate effects on nutrient loading to the Chesapeake Bay and groundwater depletion of the Edward's Aquifer that provides water for municipalities and agriculture to the San Antonio, Texas area. While only case studies, these results suggest environmental targets such as pumping limits and changes in farm practices to limit nutrient run-off would need to be tightened if current environmental goals were to be achieved under the climate scenarios we examined

Pattern Scaling: An Examination of the Accuracy of the Technique for Describing Future Climates

Abstract: A fully probabilistic, or risk, assessment of future regional climate changeand its impacts involves more scenarios of radiative forcing than can besimulated by a general (GCM) or regional (RCM) circulation model Additionalscenarios may be created by scaling a spatial response pattern from a GCM bya global warming projection from a simple climate model I examine thistechnique, known as pattern scaling, using a particular GCM (HadCM2)Thecritical assumption is that there is a linear relationship between the scaler(annual global-mean temperature) and the response pattern Previous studieshave found this assumption to be broadly valid for annual temperature; Iextend this conclusion to precipitation and seasonal (JJA) climate However,slight non-linearities arise from the dependence of the climatic response onthe rate, not just the amount, of change in the scaler These non-linearitiesintroduce some significant errors into the estimates made by pattern scaling,but nonetheless the estimates accurately represent the modelled changes Aresponse pattern may be made more robust by lengthening the period from whichit is obtained, by anomalising it relative to the control simulation, and byusing least squares regression to obtain it The errors arising from patternscaling may be minimised by interpolating from a stronger to a weaker forcingscenario

How Long Have We Been in the Anthropocene Era

Abstract: With great interest we have read Ruddiman’s intriguing article which is in favor of placing the start of the Anthropocene at 5–8 millennia BP instead of the late quarter of the 18th century. He shows how land exploitation for agriculture and animal husbandry may have led to enhanced emissions of CO2 and CH4 to the atmosphere, thereby modifying the expected changes in the concentrations of these gases beyond those expected from variations in the Milankovich orbital parameters. Much of his argument depends on the correctness of their projected CH4 concentration curve from 7,000 years BP to pre-industrial times showing a decline to about 425 ppb, according to Milankovich, instead of the measured 700 ppb. It appears, however, strange that in Ruddiman’s analysis the proposed increase of CH4 due to anthropogenic activities stopped at about 1000 years BP, because ice core data showed almost constant mixing ratios of CH4 between 1000 years BP and about 200 years ago before the rapid rise of CH4 in the industrial period (IPCC, 2001). A major feature of Ruddiman’s argument is that natural atmospheric CH4 concentrations depend strongly on geological varying summer time insolations in the tropical northern hemisphere, controlling tropical wetlands and methane release from decaying organic matter under anaerobic conditions. The choice of the start of the anthropocene remains rather arbitrary. The records of atmospheric CO2, CH4, and N2O show a clear acceleration in trends since the end of the 18th century. For that reason, the start of the anthropocene was assigned to about that time, immediately following the invention of the steam engine in 1784 (Crutzen and Stoermer, 2000; Crutzen, 2002). The consequences of this innovation have been astounding, for instance, there has been a tenfold rise in human population to 6000 million, during the past three centuries, and a fourfold increase in the 20th century (Turner et al., 1990; McNeill, 2000). This expansion was made possible by medical advances and a major growth in agriculture and animal husbandry leading for instance to a current cattle population of 1400 million (globally averaged about one cow per average size family). Let us give a few more examples. In a few generations mankind is exhausting the fossil fuels that were generated over several hundred million years, resulting in large emissions of air pollutants. The release of SO2, globally about 160 Tg/year to the atmosphere by coal and oil burning, is at least two times larger than the sum of all natural emissions, occurring mainly as marine dimethyl-sulfide from the oceans (IPCC, 2001). The oxidation of SO2 to sulphuric and NOx to nitric acid has led to acidification of precipitation, causing forest damage and fish death in biologically sensitive lakes in regions, such

Plant phenological anomalies in germany and their relation to air temperature and nao

Abstract: This paper analyses long-term (1951–2000) phenological observations of20 plant seasonal phases recorded within the phenological network of the German Weather Service in relation to climate data and NAO. Phenological inter-annual variability and temporal trends were determined by using mean anomaly curves for Germany. For all phases, the mean trends derived by this method are similar to German averages of linear trends of single station records. Trend analysis using anomaly curves appears to be effective in relating seasonal phenological trends to climate or satellite data: Spring and summer phenological anomalies, such as leaf unfolding and flowering of different species, strongly correlate with temperature of the preceding months (R2 between 0.65 and 0.85, best one-variable model) andtheir onsets have advanced by 2.5 to 6.7 days per ° C warmer spring. Fruit ripening of Sambucus nigra and Aesculus hippocastanum, keyphenophases of early and mid autumn, correlate well with summer temperature (R2 0.74 and 0.84) and also advance by 6.5and 3.8 days per ° C (April–June). But the response of autumn colouringto warmer climate is more complex because two opposing factors influence autumn colouring dates. Higher spring and early summer temperatures advance leaf colouring, whereas warmer autumn temperatures delay leaf colouring. The percentage of variance explained by temperature (R2 0.22 to 0.51,best one-variable model) is less than for spring and summer phases. The length of the growing season is mainly increased by warmer springs (R2 0.48to 0.64, best one-variable model) and lengthened by 2.4 to 3.5 days/° C (February–April). The North Atlantic Oscillation Index (NAO) of January–March correlates with spring phenological anomalies(R2 0.37 to 0.56, best one-variable model), summer to mid autumn phases respond to NAO of February–March (R2 0.23 to 0.36) (both negativecorrelations). Leaf colouring is delayed by higher NAO of (August) September (R2 0.10to 0.18). NAO of January–February explains 0.41 to 0.44% of thevariance of the length of the growing season.

Metrics of Climate Change: Assessing Radiative Forcing and Emission Indices

Abstract: In this paper, we review existing and alternative metrics of climate change, with particular emphasis on radiative forcing and global warming potentials (GWPs), in terms of their scientific performance. Radiative forcing is assessed in terms of questions such as the utility of the concept, uncertainties and sensitivity to key assumptions. The assessment of emission indices focuses on the climate and other resulting impacts (end points) against which emissions are weighted; the extent to which (and how) time dependence is included, with regard to both emission control and impact; how cost issues are dealt with; and the sensitivity of the metrics to various assumptions. It is concluded that the radiative forcing concept is a robust and useful metric of the potential climatic impact of various agents and that there are prospects for improvement by weighing different forcings according to their effectiveness. We also find that although the GWP concept is associated with serious shortcomings, it retains advantages over any of the proposed alternatives in terms of political feasibility. Alternative metrics, however, make a significant contribution to addressing important issues, and this contribution should be taken into account in the further development of refined metrics of climate change.

20Th century climate change in the tropical Andes: Observations and model results

Abstract: Linear trend analysis of observational data combined with model diagnostics from an atmospheric general circulation model are employed to search for potential mechanisms related to the observed glacier retreat in the tropical Andes between 1950 and 1998. Observational evidence indicates that changes in precipitation amount or cloud cover over the last decades are minor in most regions and are therefore rather unlikely to have caused the observed retreat. The only exception is in southern Peru and western Bolivia where there is a general tendency toward slightly drier conditions. Near-surface temperature on the other hand has increased significantly throughout most of the tropical Andes. The temperature increase varies markedly between the eastern and western Andean slopes with a much larger temperature increase to the west. Simulations with the ECHAM-4 model, forced with observed global sea surface temperatures (SST) realistically reproduce the observed warming trend as well as the spatial trend pattern. Model results further suggest that a significant fraction of the observed warming can be traced to a concurrent rise in SST in the equatorial Pacific and that the markedly different trends in cloud cover to the east and west of the Andes contributed to the weaker warming east of the Andes in the model. The observed increase in relative humidity, derived from CRU 05 data, is also apparent in the model simulations, but on a regional scale the results between model and observations vary significantly. It is argued that changes in temperature and humidity are the primary cause for the observed glacier retreat during the 2nd half of the 20th century in the tropical Andes.

Uncertainty Analysis of Climate Change and Policy Response

Abstract: To aid climate policy decisions, accurate quantitative descriptions of the uncertainty in climate outcomes under various possible policies are needed. Here, we apply an earth systems model to describe the uncertainty in climate projections under two different policy scenarios. This study illustrates an internally consistent uncertainty analysis of one climate assessment modeling framework, propagating uncertainties in both economic and climate components, and constraining climate parameter uncertainties based on observation. We find that in the absence of greenhouse gas emissions restrictions, there is a one in forty chance that global mean surface temperature change will exceed 4.9 °C by the year 2100. A policy case with aggressive emissions reductions over time lowers the temperature change to a one in forty chance of exceeding 3.2 °C, thus reducing but not eliminating the chance of substantial warming.

Climate Variability and Change in High Elevation Regions: Past, Present and Future

Abstract: This special issue of Climatic Change contains a series of research and review articles, arising from papers that were presented and discussed at a workshop held in Davos, Switzerland on 25–28 June 2001. The workshop was titled ‘Climate Change at High Elevation Sites: Emerging Impacts’, and was convened to reprise an earlier conference on the same subject that was held in Wengen, Switzerland in 1995 (Diaz et al., 1997). The Davos meeting had as its main goals, a discussion of the following key issues: (1) reviewing recent climatic trends in high elevation regions of the world, (2) assessing the reliability of various biological indicators as indicators of climatic change, and (3) assessing whether physical impacts of climatic change in high elevation areas are becoming evident, and to discuss a range of monitoring strategies needed to observe and to understand the nature of any changes.

Global Warming and Potential Changes in Fish Habitat in U.S. Streams

Abstract: To project potential habitat changes of 57 fish species under global warming, their suitable thermal habitat at 764 stream gaging stations in the contiguous United States was studied. Global warming was specified by air temperature increases projected by the Canadian Centre of Climate Modelling General Circulation Model for a doubling of atmospheric CO2. The aquatic thermal regime at each gaging station was related to air temperature using a nonlinear stream temperature/air temperature relationship.Suitable fish thermal habitat was assumed to be constrained by both maximum temperature and minimum temperature tolerances. For cold water fishes with a 0 °C lower temperature constraint, the number of stations with suitable thermal habitat under a 2×CO2 climate scenario is projected to decrease by 36%, and for cool water fishes by 15%. These changes are associated with a northward shift of the range. For warm water fishes with a 2 °C lower temperature constraint, the potential number of stations with suitable thermal habitat is projected to increase by 31%.

Large-Scale Temperature Changes Across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years

Abstract: Long-term trends of temperature variations across the southern Andes (37-55 ◦ S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930-1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43 ◦ S are characterized by negative trends in mean annual temper- ature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46 ◦ S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45 ◦ S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes. Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% of the temperature variance over the interval 1930-1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930-1989, indicates that most of the explained variance is at periods >10 years in length. At periods >15 years, the squared coherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi- decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20th century have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900-1990 are 0.53 ◦ C and 0.86 ◦ C above the 1640-1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.

Tropical Glacier and Ice Core Evidence of Climate Change on Annual to Millennial Time Scales

Abstract: This paper examines the potential of the stable isotopic ratios, 18O/16O (δ 18Oice)and 2H/1H (δ Dice), preserved in mid to low latitude glaciers as a toolfor paleoclimate reconstruction. Ice cores are particularly valuable as they contain additional data, such as dust concentrations, aerosol chemistry, and accumulation rates, that can be combined with the isotopic information to assist with inferences about the regional climate conditions prevailing at the time of deposition. We use a collection of multi-proxy ice core histories to explore the δ 18O-climate relationship over the last 25,000 years that includes both Late Glacial Stage (LGS) and Holocene climate conditions. These results suggest that on centennial to millennial time scales atmospheric temperature is the principal control on the δ 18Oice of the snowfall that sustains these high mountainice fields.Decadally averaged δ 18Oice records from threeAndean and three Tibetan ice cores are composited to produce a low latitude δ 18Oice history for the last millennium. Comparison ofthis ice core composite with the Northern Hemisphere proxy record (1000–2000A.D.) reconstructed by Mann et al. (1999) and measured temperatures(1856–2000) reported by Jones et al. (1999) suggests the ice cores have captured the decadal scale variability in the global temperature trends. These ice cores show a 20th century isotopic enrichment that suggests a large scale warming is underway at low latitudes. The rate of this isotopically inferred warming is amplified at higher elevations over the Tibetan Plateau while amplification in the Andes is latitude dependent with enrichment (warming) increasing equatorward. In concert with this apparent warming, in situobservations reveal that tropical glaciers are currently disappearing. A brief overview of the loss of these tropical data archives over the last 30 years is presented along with evaluation of recent changes in mean δ18Oice composition. The isotopic composition of precipitation should be viewed not only as a powerful proxy indicator of climate change, but also as an additional parameter to aid our understanding of the linkages between changes in the hydrologic cycle and global climate.

Is the Uncertainty about Climate Change too Large for Expected Cost-Benefit Analysis?

Abstract: Cost-benefit analysis is only applicable if the variances of both costs and benefits are finite. In the case of climate change, the variances of the net present marginal costs and benefits of greenhouse gas emission reduction need to be finite. Finiteness is hard, if not impossible to prove. The opposite is easier to establish as one only needs to show that there is one, not impossible representation of the climate change with infinite variance. The paper shows that all relevant current variables of the FUND model have finite variances. However, there is a small chance that climate change reverses economic growth in some regions. In that case, the discount rate becomes negative and the net present marginal benefits of greenhouse gas emission reduction becomes very large. So large, that its variance is unbounded. One could interpret this as an indication that cost-benefit analysis is invalid. Alternatively, one could argue that the infinity is present in both the base case and the policy scenario, and therefore irrelevant; in that interpretation, cost-benefit analysis is a valid tool.

The Implications of Climate Change on Floods of the Ganges, Brahmaputra and Meghna Rivers in Bangladesh

Abstract: Climate change in the future would have implications for river discharges in Bangladesh. In this article, possible changes in the magnitude, extent and depth of floods of the Ganges, Brahmaputra and Meghna (GBM) rivers in Bangladesh were assessed using a sequence of empirical models and the MIKE11-GIS hydrodynamic model. Climate change scenarios were constructed from the results of four General Circulation Models (GCMs) –CSIRO9, UKTR, GFDL and LLNL, which demonstrate a range of uncertainties. Changes in magnitude, depth and extent of flood discharge vary considerably between the GCMs. Future changes in the peak discharge of the Ganges River are expected to be higher than those for the Brahmaputra River. Peak discharge of the Meghna River may also increase considerably. As a result, significant changes in the spatial extent and depths of inundation in Bangladesh may occur. Faster changes in inundation are expected at low temperature increases than of higher temperature changes. Changes in land inundation categories may introduce substantial changes in rice agriculture and cropping patterns in Bangladesh. Reduction of increased flood hazard due to climate change requires strengthening of flood management policies and adaptation measures in Bangladesh.

An issue of permanence: assessing the effectiveness of temporary carbon storage

Abstract: In this paper, we present a method to quantify the effectiveness of carbon mitigation options taking into account the `permanence' of the emissions reduction. While the issue of permanence is most commonly associated with a `leaky' carbon sequestration reservoir, we argue that this is an issue that applies to just about all carbon mitigation options. The appropriate formulation of this problem is to ask `what is the value of temporary storage?' Valuing temporary storage can be represented as a familiar economic problem, with explicitly stated assumptions about carbon prices and the discount rate. To illustrate the methodology, we calculate the sequestration effectiveness for injecting CO2 at various depths in the ocean. Analysis is performed for three limiting carbon price assumptions: constant carbon prices (assumes constant marginal damages), carbon prices rise at the discount rate (assumes efficient allocation of a cumulative emissions cap without a backstop technology), and carbon prices first rise at the discount rate but become constant after a given time (assumes introduction of a backstop technology). Our results show that the value of relatively deep ocean carbon sequestration can be nearly equivalent to permanent sequestration if marginal damages (i.e., carbon prices) remain constant or if there is a backstop technology that caps the abatement cost in the not too distant future. On the other hand, if climate damages are such as to require a fixed cumulative emissions limit and there is no backstop, then a storage option with even very slow leakage has limited value relative to a permanent storage option.

Climate change and people-caused forest fire occurrence in ontario

Abstract: Climate change that results from increasing levels of greenhouse gases in the atmosphere has the potential to increase temperature and alter rainfall patterns across the boreal forest region of Canada. Daily output from the Canadian Climate Centre coupled general circulation model (GCM) and the Hadley Centre's HadCM3 GCM provided simulated historic climate data and future climate scenarios for the forested area of the province of Ontario, Canada. These models project that in climates of increased greenhouse gases and aerosols, surface air temperatures will increase while seasonal precipitation amounts will remain relatively constant or increase slightly during the forest fire season. These projected changes in weather conditions are used to predict changes in the moisture content of forest fuel, which influences the incidence of people-caused forest fires. Poisson regression analysis methods are used to develop predictive models for the daily number of fires occurring in each of the ecoregions across the forest fire management region of Ontario. This people-caused fire prediction model, combined with GCM data, predicts the total number of people-caused fires in Ontario could increase by approximately 18% by 2020-2040 and 50% by the end of the 21st century.

Magnitude and frequency of flooding in the Tagus Basin (Central Spain) over the last Millennium

Abstract: A relational database using Access, and an interface based on a Geographical Information System (GIS) with ArcView program, were created to allow spatial-temporal analysis of documen- tary flood data collected for the Tagus basin (Central Spain). High flood frequencies were registered in the periods: AD 1160-1210 (3%), 1540-1640 (11%; peak at 1590-1610), 1730-1760 (5%), 1780-1810 (4%), 1870-1900 (19%), 1930-1950 (17%) and 1960-1980 (12%). Flood magnitudes of those documentary events were estimated at four sites (Aranjuez, Toledo, Talavera and Alcantara) along the Tagus River using HEC-RAS Computer program, matching the calculated water surface profiles with historical references of flood stage. The largest floods took place during the periods AD 1168-1211 (Toledo and Talavera), AD 1658-1706 (Talavera), AD 1870-1900, and AD 1930- 1950 (Aranjuez, Toledo, Talavera and Alcantara). The temporal distribution of flood magnitude and frequency is discussed within the context of climatic variability experienced by the Iberian Peninsula. Although flood producing mechanisms of Atlantic and Mediterranean basins of the Iberian Peninsula are related to different, independent atmospheric patterns, there is a clear coincidence between most periods showing high flood frequencies. These periods of high flooding seem to correspond to the initial and final decades of periods with climate deterioration described at the continental scale. This suggests that climatic variability over the last millennium has induced a response in hydrological extremes (positive or negative), irrespective of the flood-producing mechanism.

Using Specific Language to Describe Risk and Probability

Abstract: Good assessment of environmental issues, such as climate change, requires effective communication of the degree of uncertainty associated with numerous possible outcomes. One strategy that accomplishes this, while responding to people's difficulty understanding numeric probability estimates, is the use of specific language to describe probability ranges. This is the strategy adopted by the Intergovernmental Panel on Climate Change in their Third Assessment Report. There is a problem with this strategy, however, in that it uses words differently from the way lay readers of the assessment typically do. An experiment conducted with undergraduate science students confirms this. The IPCC strategy could result in miscommunication, leading readers to under-estimate the probability of high-magnitude possible outcomes.

Tree-Ring Reconstructed Winter Precipitation and Tropical Teleconnections in Durango, Mexico

Abstract: Earlywood width chronologies from Douglas-fir tree rings were used to reconstruct winter (November–March) precipitation for more than 600 years over Durango, Mexico. The tree-ring data were obtained from two sites of long-lived Douglas-fir in northern and southern Durango and the seasonal climatic precipitation data were regionally averaged from five weather stations well distributed across the state. The averaged earlywood chronology accounted for 56% of the variance in instrumental November–March precipitation 1942–1983. We validated the reconstruction against independent precipitation records. The worst winter drought of the 20th century in Durango occurred 1950–1965. However, the reconstruction indicates droughts more severe than any witnessed in the 20th century, e.g., the 1850s–1860s, and the megadrought in the mid- to late-16th century. Reconstructed winter precipitation 1540–1579 shows 33 of 40 years were dry. Persistent drought may be linked to extended La Nina episodes. The Tropical Rainfall Index (TRI) correlates well with instrumental and reconstructed winter precipitation (r = 0.49 and 0.55, respectively), reflecting the strong ENSO modulation of cool season climate over northern Mexico. The ENSO teleconnection varies through time, with TRI-reconstructed precipitation correlations ranging from 0.78 to 0.27 in five periods 1895–1993. The 1942–1983 winter observed and reconstructed Durango data correlate well with the corresponding seasonalization of the All-Mexico Rainfall Index (AMRI; r=0.68, P<0.0001 and r=0.70, P<0.001, respectively), indicating that both the observed and the reconstructed precipitation often reflect broad-scale precipitation anomalies across Mexico. New long Douglas-fir and baldcypress tree-ring chronologies are now available for central and southern Mexico near major population centers, allowing the exploration of relationships between drought, food scarcity, and social and political upheaval in Mexican history.

Recent trends in laurentian great lakes ice cover

Abstract: A 39-winter (1963-2001) record of annual maximum ice concentration (AMIC), the maximum fraction of lake surface area covered by ice each year, is analyzed for each Great Lake. Lake Erie has the largest median AMIC (94%) followed by Lakes Superior (80%), Huron (63%), Michigan (33%), and Ontario (21%). The frequency distribution of AMICs is negatively skewed for Lakes Superior and Erie and positively skewed for Lakes Michigan and Ontario. Temporal and spatial patterns of typical and extreme AMICs is presented within the context of long-term average air temperatures and lake bathymetry. The variation of spatially averaged ice concentration with discrete depth ranges are discussed for each lake for the upper and lower end of the typical range of AMIC values. In general, ice concentration decreases with increasing depth ranges for a given winter. A decrease in the gradient of ice concentration with depths was also observed with an increase in the AMIC from winter 1983 to winter 1984. A temporal trend in the AMICs supports the hypothesis of three ice cover regimes over the past 39 winters. Approximately 44% of the highest quartile (10 highest) AMICs for the Great Lakes occurred during the 6-winter period: 1977-1982 providing evidence of a higher ice cover regime during this period relative to the 14 winters before them (1963- 1976) and the 19 winters after them (1983-2001). Winter 1998 established new low AMIC extremes, and the AMIC averaged over the 1998-2001 winters is the lowest for the period of record on four of the five Great Lakes. These recent trends taken together are noteworthy as they may be harbingers of a period of even lower AMICs in the 21st Century.

Potential Soil C Sequestration on U.S. Agricultural Soils

Abstract: Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO2 increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (1012g) C yr− 1, over present rates of 17 Tg C yr−1(estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129Mha) would increase soil C sequestration by 47 Tg C yr−1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about37 Tg C yr−1. Elimination of summer fallow practices and conversionof highly erodible cropland to perennial grass cover could sequester around 20 and 28Tg C yr−1, respectively. The soil C sequestration potentialfrom including a winter cover crop on annual cropping systems was estimated at 40Tg C yr−1. All rates were estimated for a fifteen-yearprojection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr−1) represents about 5% of 1999total U.S. CO2 emissions or nearly double estimated CO2 emissionsfrom agricultural production (43 Tg C yr−1). For purposes ofstabilizing or reducing CO2 emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions(2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.

Modeling agriculture and land use in an integrated assessment framework

Abstract: The Agriculture and Land Use (AgLU) model is a top-downeconomic model with just enough structure to simulate globalland-use change and the resulting carbon emissions over one century.These simulations are done with and without a carbon policy representedby a positive carbon price. Increases in the carbon price createincentives for production of commercial biomass that affect thedistribution of other land types and, therefore, carbon emissionsfrom land-use change. Commercial biomass provides a link betweenthe agricultural and energy systems. The Integrated Assessmentof Climate Protection Strategies (ICLIPS) core model uses AgLUto provide estimates of carbon emissions from land-use changeas one component of total greenhouse gas emissions. Each majorland-use type is assigned an average carbon density used to calculatea total carbon stock; carbon emissions from land-use change arecalculated as the change in carbon stock between time periods.Significant carbon emissions from land-use change are presenteven in the reference scenario. An aggressive ICLIPS mitigationscenario results in carbon emissions from land-use change upto 800 million metric tons per year above the AgLU referencescenario.

Climate change in northern africa: the past is not the future

Abstract: By using a climate system model of intermediate complexity, we have simulated long- term natural climate changes occurring over the last 9000 years. The paleo-simulations in which the model is driven by orbital forcing only, i.e., by changes in insolation caused by changes in the Earth's orbit, are compared with sensitivity simulations in which various scenarios of increasing atmospheric CO2 concentration are prescribed. Focussing on climate and vegetation change in northern Africa, we recapture the strong greening of the Sahara in the early and mid-Holocene (some 9000-6000 years ago), and we show that some expansion of grassland into the Sahara is theoretically possible, if the atmospheric CO2 concentration increases well above pre-industrial values and if vegetation growth is not disturbed. Depending on the rate of CO2 increase, vegetation migration into the Sahara can be rapid, up to 1/10th of the Saharan area per decade, but could not exceed a coverage of 45%. In our model, vegetation expansion into today's Sahara is triggered by an increase in summer precipitation which is amplified by a positive feedback between vegetation and precipitation. This is valid for simulations with orbital forcing and greenhouse-gas forcing. However, we argue that the mid-Holocene climate optimum some 9000 to 6000 years ago with its marked reduction of deserts in northern Africa is not a direct analogue for future greenhouse-gas induced climate change, as previously hypothesized. Not only does the global pattern of climate change differ between the mid- Holocene model experiments and the greenhouse-gas sensitivity experiments, but the relative role of mechanisms which lead to a reduction of the Sahara also changes. Moreover, the amplitude of simulated vegetation cover changes in northern Africa is less than is estimated for mid-Holocene climate.

Indirect vs. Direct Effects of Anthropogenic Sulfate on the Climate of East Asia as Simulated with a Regional Coupled Climate-Chemistry/Aerosol Model

Abstract: We intercompare a series of multi-year simulations with a coupled regionalchemistry-climate model for east Asia to assess the relative importance ofdirect and indirect (Type I) effects of anthropogenic sulfate on the climateof the region. Both direct and indirect aerosol effects induce a negativeradiative forcing that results in a cooling of the surface and in a decrease of precipitation. Under present day sulfur emissions,the direct aerosol effects prevail during the cold season, while the indirecteffects dominate in the warm season (when cloudiness is maximum over the region). When both the direct and indirect effects are included, the surface cooling varies in the range of –0.1 to over –1 K throughout the region and extended areas ofstatistically significant cooling are found in all seasons except winter.The indirect effects largely dominate in inhibiting precipitation, especiallyduring the summer. When doubling the sulfur emissions, the direct effects aresubstantially strengthened, while the indirect effects are only marginally affected. This indicates that the indirect effects over the region might be asymptotically approaching their maximum efficiency. Overall, the indirect effects appear necessary to explain theobserved temperature record over some regions of China, at least in the warm season.A number of uncertainties need to be addressed, such as due to Type IIindirect effects, modeling of the relationship between aerosol concentration and cloud optical properties, and contribution of aerosols other than anthropogenic sulfate.

Burning Buried Sunshine: Human Consumption of Ancient Solar Energy

Abstract: Fossil fuels developed from ancient deposits of organic material, and thus can be thought of as a vast store of solar energy from which society meets >80% of its current energy needs. Here, using published biological, geochemical, and industrial data, I estimate the amount of photosyntheti- callyfixed and stored carbon that was required to form the coal, oil, and gas that we are burning today. Today's average U.S. Gallon (3.8 L) of gasoline required approximately 90 metric tons of ancient plant matter as precursor material. The fossil fuels burned in 1997 were created from organic matter containing 44 × 10 18 gC , which is>400 times the net primary productivity (NPP) of the planet's current biota. As stores of ancient solar energy decline, humans are likely to use an increasing share of modern solar resources. I conservatively estimate that replacing the energy humans derive from fossil fuels with energy from modern biomass would require 22% of terrestrial NPP, increasing the human appropriation of this resource by ∼50%.