Showing papers in "Climatic Change in 1998"

Climate Change and Forest Fire Potential in Russian and Canadian Boreal Forests

Abstract: In this study outputs from four current General Circulation Models (GCMs) were used to project forest fire danger levels in Canada and Russia under a warmer climate. Temperature and precipitation anomalies between 1 × CO2 and 2 × CO2 runs were combined with baseline observed weather data for both countries for the 1980–1989 period. Forecast seasonal fire weather severity was similar for the four GCMs, indicating large increases in the areal extent of extreme fire danger in both countries under a 2 × CO2 climate scenario. A monthly analysis, using the Canadian GCM, showed an earlier start to the fire season, and significant increases in the area experiencing high to extreme fire danger in both Canada and Russia, particularly during June and July. Climate change as forecast has serious implications for forest fire management in both countries. More severe fire weather, coupled with continued economic constraints and downsizing, mean more fire activity in the future is a virtual certainty. The likely response will be a restructuring of protection priorities to support more intensive protection of smaller, high-value areas, and a return to natural fire regimes over larger areas of both Canada and Russia, with resultant significant impacts on the carbon budget.

Climate warming, wildfire hazard, and wildfire occurrence in coastal eastern spain

Abstract: A climatic series (1941 to 1994) from a Mediterranean locality of NE Spain was used to calculate two wildfire hazard indices based on daily meteorological data. Both fire hazard indices increased over this period, as a consequence of increasing mean daily maximum temperature and decreasing minimum daily relative humidity. These trends were observed in both mean values of the indices and in the number of very high risk days. Annual data on the number of wildfires and burned area also show an increase from 1968 to 1994, and are significantly correlated with both fire hazard indices. Although other non-meteorological causes (e.g., human activities, fuel accumulation) have likely contributed to the observed increase of wildfires, an effect of climatic warming on wildfire occurrence is supported by this relationship.

Atmospheric moisture residence times and cycling: implications for rainfall rates and climate change

Abstract: New estimates of the moistening of the atmosphere through evaporation at the surface and of the drying through precipitation are computed. Overall, the e-folding residence time of atmospheric moisture is just over 8 days. New estimates are also made of how much moisture that precipitates out comes from horizontal transport versus local evaporation, referred to as ‘recycling’. The results depend greatly on the scale of the domain under consideration and global maps of the recycling for annual means are produced for 500 km scales for which global recycling is 9.6%, consisting of 8.9% over land and 9.9% over the oceans. Even for 1000 km scales, less than 20% of the annual precipitation typically comes from evaporation within the domain. While average overall atmospheric moisture depletion and restoration must balance, precipitation falls only a small fraction of the time. Thus precipitation rates are also examined. Over the United States, one hour intervals with 0.1 mm or more are used to show that the frequency of precipitation ranges from over 30% in the Northwest, to about 20% in the Southeast and less than 4% just east of the continental divide in winter, and from less than 2% in California to over 20% in the Southeast in summer. In midlatitudes precipitation typically falls about 10% of the time, and so rainfall rates, conditional on when rain is falling, are much larger than evaporation rates. The mismatches in the rates of rainfall versus evaporation imply that precipitating systems of all kinds feed mostly on the moisture already in the atmosphere. Over North America, much of the precipitation originates from moisture advected from the Gulf of Mexico and subtropical Atlantic or Pacific a day or so earlier. Increases in greenhouse gases in the atmosphere produce global warming through an increase in downwelling infrared radiation, and thus not only increase surface temperatures but also enhance the hydrological cycle, as much of the heating at the surface goes into evaporating surface moisture. Global temperature increases signify that the water-holding capacity of the atmosphere increases and, together with enhanced evaporation, this means that the actual atmospheric moisture should increase. It follows that naturally-occurring droughts are likely to be exacerbated by enhanced potential evapotranspiration. Further, globally there must be an increase in precipitation to balance the enhanced evaporation but the processes by which precipitation is altered locally are not well understood. Observations confirm that atmospheric moisture is increasing in many places, for example at a rate of about 5% per decade over the United States. Based on the above results, we argue that increased moisture content of the atmosphere therefore favors stronger rainfall or snowfall events, thus increasing risk of flooding, which is a pattern observed to be happening in many parts of the world. Moreover, because there is a disparity between the rates of increase of atmospheric moisture and precipitation, there are implied changes in the frequency of precipitation and/or efficiency of precipitation (related to how much moisture is left behind in a storm). However, an analysis of linear trends in the frequency of precipitation events for the United States corresponding to thresholds of 0.1 and 1 mm/h shows that the most notable statistically significant trends are for increases in the southern United States in winter and decreases in the Pacific Northwest from November through January, which may be related to changes in atmospheric circulation and storm tracks associated with El Nino–Southern Oscillation trends. It is suggested that as the physical constraints on precipitation apply only globally, more attention should be paid to rates in both observations and models as well as the frequency of occurrence.

Uncertainty in Predicting the Effect of Climatic Change on the Carbon Cycling of Canadian Peatlands

Abstract: Northern peatlands play an important role globally in the cycling of C, through the exchange of CO2 with the atmosphere, the emission of CH4, the production and export of dissolved organic carbon (DOC) and the storage of C. Under 2 × CO2 GCM scenarios, most Canadian peatlands will be exposed to increases in mean annual temperature ranging between 2 and 6° C and increases in mean annual precipitation of 0 to 15 %, with the most pronounced changes occurring during the winter. The increase in CO2 uptake by plants, through warmer temperatures and elevated atmospheric CO2, is likely to be offset by increased soil respiration rates in response to warmer soils and lowered water tables. CH4 emissions are likely to decrease in most peatlands because of lowered water tables, except where the peat surface adjusts to fluctuating water tables, and in permafrost, where the collapse of dry plateau and palsa will lead to increase CH4 emission. There likely will be little change in DOC production, but DOC export to water bodies will decrease as runoff decreases. The storage of C in peatlands is sensitive to all C cycle components and is difficult to predict. The challenge is to develop quantitative models capable of making these predictions for different peatlands. We present some qualitative responses, with levels of uncertainty. There will be, however, as much variation in response to climatic change within a peatland as there will be among peatland regions.

CO2 Mitigation by Agriculture: An Overview

Abstract: Agriculture currently contributes significantly to the increase of CO2 in the atmosphere, primarily through the conversion of native ecosystems to agricultural uses in the tropics. Yet there are major opportunities for mitigation of CO2 and other greenhouse gas emissions through changes in the use and management of agricultural lands. Agricultural mitigation options can be broadly divided into two categories: (I) strategies to maintain and increase stocks of organic C in soils (and biomass), and (ii) reductions in fossil C consumption, including reduced emissions by the agricultural sector itself and through agricultural production of biofuels to substitute for fossil fuels. Reducing the conversion of new land to agriculture in the tropics could substantially reduce CO2 emissions, but this option faces several difficult issues including population increase, land tenure and other socio-political factors in developing countries. The most significant opportunities for reducing tropical land conversions are in the humid tropics and in tropical wetlands. An important linkage is to improve the productivity and sustainability of existing agricultural lands in these regions. Globally, we estimate potential agricultural CO2 mitigation through soil C sequestration to be 0.4-0.9 Pg C y-1, through better management of existing agricultural soils, restoration of degraded lands, permanent "set-asides" of surplus agricultural lands in temperate developed countries and restoration of 10-20% of former wetlands now being used for agriculture. However, soils have a finite capacity to store additional C and therefore any increases in C stocks following changes in management would be largely realized within 50-100 years. Mitigation potential through reducing direct agricultural emissions is modest, 0.01-0.05 Pg C y-1. However, the potential to offset fossil C consumption through the use of biofuels produced by agriculture is substantial, 0.5-1.6 Pg C y-1, mainly through the production of dedicated biofuel crops with a smaller contribution (0.2-0.3 Pg C y-1) from crop residues. Many agricultural mitigation options represent "win-win" situations, in that there are important side benefits, in addition to CO2 mitigation, that could be achieved, e.g. improved soil fertility with higher soil organic matter, protection of lands poorly suited for permanent agriculture, cost saving for fossil fuel inputs and diversification of agricultural production (e.g. biofuels). However, the needs for global food production and farmer/societal acceptability suggest that mitigation technologies should conform to: (I) the enhancement of agricultural production levels in parts of the world where food production and population demand are in delicate balance and (ii) the accrual of additional benefits to the farmer (e.g., reduced labor, reduced or more efficient use of inputs) and society at large.

Deep Soil Moisture Storage and Transpiration in Forests and Pastures of Seasonally-Dry Amazonia

Abstract: To assess the impacts of land-use changes on plant-available water (PAW) and evapotranspiration (ET), volumetric water content (VWC) was measured to 8 m beneath three, adjacent ecosystems for four years (1991–1994). Estimates of PAW, ET, and deep drainage were generated for mature evergreen forest, adjacent pasture, and capoeira (second-growth forest on abandoned pasture land). PAW between 0 and 8 m depth for forest, pasture, and capoeira ranged from a low of 56, 400, and 138 mm at the end of the 1992 dry season to a high of 941, 1116, and 1021 mm during the 1994 wet season. We found significant differences in deep (4–8 m) stocks of PAW when comparing pasture with both forest types. In contrast, mature forest and capoeira PAW were not significantly different from one another at any depth during the experiment. In all three ecosystems available soil moisture from 4–8 m was depleted during the 1991 dry season by plant water uptake and was not recharged to 1991 levels until 1994 due to an intervening 2-year, El Nino Southern Oscillation event. Water balance estimates (based on measurements to 8 m) showed an average 10% decrease in ET from pasture compared to mature forest. Less than 15 years after pasture abandonment, ET in second-growth forest recovered to rates nearly equaling the mature forest rate. In seasonally dry environments annual and interannual cycles of deep soil moisture recharge and depletion influence rates of transpiration and drainage. These deep cycles are not currently incorporated in models of regional and global moisture flux.

Hydrology of Prairie Pothole Wetlands during Drought and Deluge: A 17-Year Study of the Cottonwood Lake Wetland Complex in North Dakota in the Perspective of Longer Term Measured and Proxy Hydrological Records

Abstract: From 1988 to 1992 the north-central plains of North America had a drought that was followed by a wet period that continues to the present (1997) Data on the hydrology of the Cottonwood Lake area (CWLA) collected for nearly 10 years before, and during, the recent dry and wet periods indicate that some prairie pothole wetlands served only a recharge function under all climate conditions Transpiration from groundwater around the perimeter of groundwater discharge wetlands drew water from the wetlands by the end of summer, even during very wet years Long-term records of a climate index (Palmer Drought Severity Index), stream discharge (Pembina River), and lake level (Devils Lake) were used to put the 17-year CWLA record into a longer term perspective In addition, proxy records of climate determined from fossils in the sediments of Devils Lake were also used These data, indicate that the drought of 1988-92 may have been the second Worst of the 20th century, but that droughts of that magnitude, and worse, were common during the past 500 years In contrast, the present wet period may be the wettest it has been during the past 130 years, or possibly the past 500 years

Assessing and mitigating N2O emissions from agricultural soils

Abstract: Agricultural cropping and animal production systems are important sources of atmospheric nitrous oxide (N2O). The assessment of the importance of N fertilization from synthetic fertilizer, animal wastes used as fertilizers and from N incorporated into the soil through biological N fixation, to global N2O emissions presented in this paper suggests that this source has been underestimated. We estimate that agricultural systems produce about one fourth of global N2O emissions. Methods of mitigating these emissions are presented which, if adopted globally could decrease annual N2O emissions from cropped soils by about 20%.

Uncertainty, Complexity and Concepts of Good Science in Climate Change Modelling: Are GCMs the Best Tools?

Abstract: In this paper we explore the dominant position of a particular style of scientific modelling in the provision of policy-relevant scientific knowledge on future climate change. We describe how the apical position of General Circulation Models (GCMs) appears to follow ‘logically’ both from conventional understandings of scientific representation and the use of knowledge, so acquired, in decision-making. We argue, however, that both of these particular understandings are contestable. In addition to questioning their current policy-usefulness, we draw upon existing analyses of GCMs which discuss model trade-offs, errors, and the effects of parameterisations, to raise questions about the validity of the conception of complexity in conventional accounts. An alternative approach to modelling, incorporating concepts of uncertainty, is discussed, and an illustrative example given for the case of the global carbon cycle. In then addressing the question of how GCMs have come to occupy their dominant position, we argue that the development of global climate change science and global environmental ‘management’ frameworks occurs concurrently and in a mutually supportive fashion, so uniting GCMs and environmental policy developments in certain industrialised nations and international organisations. The more basic questions about what kinds of commitments to theories of knowledge underpin different models of ‘complexity’ as a normative principle of ‘good science’ are concealed in this mutual reinforcement. Additionally, a rather technocratic policy orientation to climate change may be supported by such science, even though it involves political choices which deserve to be more widely debated.

Mitigating Agricultural Emissions of Methane

Abstract: Agricultural crop and animal production systems are important sources and sinks for atmospheric methane (CH4). The major CH4 sources from this sector are ruminant animals, flooded rice fields, animal waste and biomass burning which total about one third of all global emissions. This paper discusses the factors that influence CH4 production and emission from these sources and the aerobic soil sink for atmospheric CH4 and assesses the magnitude of each source. Potential methods of mitigating CH4 emissions from the major sources could lead to improved crop and animal productivity. The global impact of using the mitigation options suggested could potentially decrease agricultural CH4 emissions by about 30%.

Context and early origins of the intergovernmental panel on climate change

Abstract: Climate change is a problem which is global both in terms of causes and consequences. The uncertainties are large and likely to persist. Meanwhile, the political and economic stakes of both action and inaction are much higher than those in other transboundary concerns such as acid rain and ozone depletion. The public policy impact of scientific opinions on climate change, therefore, not only depends upon what is being said, but also, who is advancing those conclusions and how they were arrived at. This was the rationale behind the setting up of the Intergovernmental Panel on Climate Change (IPCC) in 1988. The paper examines the IPCC in the context of prior assessment efforts. It attempts to unravel the processes which caused the IPCC to be set up when it was and how it was, as opposed to different times and different forms.

Structural and Process History of the Intergovernmental Panel on Climate Change

Abstract: In the nine years since its establishment in 1988, the Intergovernmental Panel on Climate Change (IPCC) has attempted to walk the tightrope of being scientifically sound and politically acceptable. This paper investigates how the IPCC has evolved over two assessment cycles. It provides an in-depth examination of important characteristics of the IPCC process including the peer review mechanism, participation of developing countries, and its interactions with the intergovernmental negotiation process on climate change.

Vulnerabilities of Tropical Forests to Climate Change: The Significance of Resident Epiphytes

Abstract: Predictions about the impacts of climate change on tropical forests require information on the relative vulnerabilities and roles of the biological components of these unusually complex systems. Central to the structure and function of any ecosystem – and the subject of this paper – is its flora, the energetic base for co-occurring heterotrophs. Much data indicate that arboreal flora (the epiphytes), those plants anchored in the forest canopy without access to the ground, occupy unusually climate-defined ecospace compared with co-occurring types such as the supporting trees. This report also describes how the epiphytes influence adjacent biota and whole-system processes, specifically those concerned with energetics, hydrology, and mineral cycling. Second, a mechanistic explanation for the exceptionally climate-sensitive nature of arboreal flora is provided. Finally, points one and two are used to make the case that arboreal flora represent a weak link in the integrity of certain types of forest, especially cloud forest and other types at lower elevations well known for their extraordinarily diverse biota. These plants, more than most, should provide early indications of floristic response to climate change throughout much of the tropics, but particularly in montane regions.

Precambrian shield wetlands: Hydrologic control of the sources and export of dissolved organic matter

Abstract: Most Precambrian Shield forested catchments have some wetland component. Even small riparian wetlands are important modifiers of stream chemistry. Dissolved organic matter (DOM) is one of the most important products exported by wetlands in streams. Stratigraphic control of hydraulic conductivity generally leads to decreasing conductivity with depth. Thus important flowpaths occur in the uppermost organic rich layers and are reflected in chemical profiles of dissolved organic carbon (DOC). Accumulation of DOC in peat porewaters is the net effect of production, consumption and transport. DOC profiles vary with degree of interaction with the surrounding upland catchment and distance from the edge of the wetland as well as internal processes within the wetland. In wetlands, DOM production is offset by flushing resulting in decreasing DOC concentrations with increasing flows. Despite old carbon (2,000 to 3,000 years) at relatively shallow depths, 14C activity in DOC exported from wetlands is mostly modern (recent carbon), consistent with shallow flowpaths and export of DOM from shallow organic rich horizons. In contrast, the source area for DOM in upland catchments with developed B horizon soils increases with antecedent soil moisture conditions resulting in increasing DOC concentrations with higher stream flows. Activity of 14C in stream DOC from upland catchments span a range from low activities (older carbon) similar to B horizon soil water during dry moisture conditions to values slightly less than modern (more recent carbon) during high moisture conditions. The more modern carbon activities reflect the increased contribution of the organic rich litter and A horizon soil layers in the area immediately bordering the stream under wet antecedent moisture conditions. Reduced hydrologic export or loss of wetlands under drier climatic conditions may result in in larger fluctuations in stream DOC concentrations and reduced DOM loads to lakes.

Potential Effects of Global Warming on Waterfowl Populations Breeding in the Northern Great Plains

Abstract: The Prairie Pothole Region (PPR) of the Northern Great Plains is the most important breeding area for waterfowl in North America. Historically, the size of breeding duck populations in the PPR has been highly correlated with spring wetland conditions. We show that one indicator of climate conditions, the Palmer Drought Severity Index (PDSI), is strongly correlated with annual counts (from 1955 to 1996) of both May ponds (R2 = 0.72, p < 0.0001) and breeding duck populations (R2 = 0.69, p < 0.0001) in the Northcentral U.S., suggesting the utility of PDSI as an index for climatic factors important to wetlands and ducks. We then use this relationship to project future pond and duck numbers based on PDSI values generated from sensitivity analyses and two general circulation model (GCM) scenarios. We investigate the sensitivity of PDSI to fixed changes in temperature of 0°C, +1.5°C, +2.5°C, and +4.0°C in combination with fixed changes in precipitation of -10%, +0%, +7%, and +15%, changes spanning the range of typically-projected values for this region from human-induced climatic change. Most (11 of 12) increased temperature scenarios tested result in increased drought (due to greater evapotranspiration under warmer temperatures) and declining numbers of both wetlands and ducks. Assuming a doubling of CO2 by 2060, both the equilibrium and transient GCM scenarios we use suggest a major increase in drought conditions. Under these scenarios, Northcentral U.S. breeding duck populations would fluctuate around means of 2.1 or 2.7 million ducks based on the two GCMs, respectively, instead of the present long-term mean of 5.0 million. May pond numbers would fluctuate around means of 0.6 or 0.8 million ponds instead of the present mean of 1.3 million. The results suggest that the ecologically and economically important PPR could be significantly damaged by climate changes typically projected. We make several recommendations for policy and research to help mitigate potential effects.

Secular Climatic Oscillations as Indicated by Catastrophic Floods in the Spanish Mediterranean Coastal Area (14th–19th Centuries)

Abstract: Historical documentation describing events on the Mediterranean coast of the Iberian Peninsula allows us to reconstruct the record of catastrophic floods. Through this information, it is possible to identify and to date three climatic oscillations within the so-called ‘Little Ice Age’: 1570–1630, 1760–1800 and 1830–1870, which coincide with advances in some Alps glaciers.

A Gcm Study of the Impact of Greenhouse Gas Increase on the Frequency of Occurrence of Tropical Cyclones

Abstract: In order to make inferences on the possible future changes of tropical cyclogenesis frequency, we apply the diagnostic computation of the Yearly Genesis Parameter (YGP) proposed by Gray (1975) to the large-scale fields simulated by a GCM. The YGP is an empirical diagnostic of the frequency of Tropical Cyclones (TCs) based on six physical parameters computed from seasonal means of atmospheric and oceanic variables. In this paper, we apply the YGP diagnostic to the results of three climate simulations performed with the atmospheric General Circulation Model (GCM) of Meteo-France: ARPEGE-Climat. In a control simulation of the current climate, it is shown that the model has a realistic tropical climatology and that the computed YGP reproduces the geographical distribution of the tropical cyclogenesis frequency. The YGP is then applied to two simulations corresponding to two scenarios of doubled carbon dioxide concentration. The two experiments differ by the sea surface temperatures (SSTs) used as a lower boundary condition. In both simulations the YGP gives a large increase of total cyclogenesis frequency, but without extension of the area of possible cyclone genesis. The increase in YGP is due essentially to the contribution of the ocean thermal energy factor in the thermodynamical potential. The dynamical parameters, on the contrary, limit the cyclogenesis increase and are a major explanation of the difference between the two experiments. This is in agreement with the results of the previous similar study of Ryan et al. (1992) concerning the importance of large-scale atmospheric circulation modifications on tropical cyclone climatology. After discussing the observed relationships between ocean surface temperature and large-scale convection, and questioning the use of a fixed temperature threshold in the diagnosis of tropical cyclone frequency, we propose a modification to the YGP consisting in replacing the thermodynamical potential by a term proportional to the convective precipitation computed by the GCM. For the simulation of the present climate this modification affects only marginally the geographical distribution of tropical cyclone genesis, but for the doubled CO2 case, the modified YGP diagnoses a more limited increase in TC genesis in the Northern Hemisphere and a small reduction in the Southern Hemisphere, which seems in better agreement with other recent modelling studies with high resolution climate models (Bengtsson et al., 1996). We conclude that the modified YGP based on convective precipitation could serve as a useful diagnostic of tropical cyclone genesis, and should be tested in simulations with other GCMs.

Climate change and water resources in Britain.

Abstract: This paper explores the potential implications of climate change for the use and management of water resources in Britain. It is based on a review of simulations of changes in river flows, groundwater recharge and river water quality. These simulations imply, under feasible climate change scenarios, that annual, winter and summer runoff will decrease in southern Britain, groundwater recharge will be reduced and that water quality - as characterised by nitrate concentrations and dissolved oxygen contents - will deteriorate. In northern Britain, river flows are likely to increase throughout the year, particularly in winter. Climate change may lead to increased demands for water, over and above that increase which is forecast for non-climatic reasons, primarily due to increased use for garden watering. These increased pressures on the water resource base will impact not only upon the reliability of water supplies, but also upon navigation, aquatic ecosystems, recreation and power generation, and will have implications for water quality management. Flood risk is likely to increase, implying a reduction in standards of flood protection. The paper discusses adaptation options.

Responses of Tropical Trees to Rainfall Seasonality and Its Long-Term Changes

Abstract: Seasonality and physiognomy of tropical forests are mainly determined by the amount of annual rainfall and its seasonal distribution. Climatic change scenarios predict that global warming will result in reduced annual rainfall and longer dry seasons for some, but not all, tropical rainforests. Tropical trees can reduce the impact of seasonal drought by adaptive mechanisms such as leaf shedding or stem succulence and by utilization of soil water reserves, which enable the maintenance of an evergreen canopy during periods of low rainfall. Correlations between climate and responses of tropical trees are therefore poor and the responses of tropical rainforests to climatic changes are hard to predict. Predicted climate change is unlikely to affect the physiognomy of rainforests with high annual rainfall and low seasonality. Seasonal evergreen forests which depend on the use of soil water reserves will be replaced by more drought-tolerant semideciduous forests, once rainfall becomes insufficient to replenish soil water reserves regularly. As the limits of drought tolerance of tropical rainforests are not known, rate and extent of future changes cannot be predicted.

Possible Effects of Climate Change on Plant/Herbivore Interactions in Moist Tropical Forests

Abstract: The interactions between plants and herbivores are key determinants of community structure world wide. Their role is particularly important in lowland tropical rain forests where rates of herbivory are higher, plants are better defended chemically and physically, and herbivores have specialized diets. In contrast to the temperate zone, most of the herbivory in the tropics occurs on ephemeral young leaves (>70%), which requires herbivores to have finely tuned host-finding abilities. As a consequence of these tight ecological and evolutionary linkages, the interplay between plants and herbivores in the tropics may be more susceptible to perturbations of climate change.

Vulnerability of island tropical montane cloud forests to climate change, with special reference to east Maui, Hawaii

Abstract: Island tropical montane cloud forests may be among the most sensitive of the world’s ecosystems to global climate change. Measurements in and above a montane cloud forest on East Maui, Hawaii, document steep microclimatic gradients. Relatively small climate-driven shifts in patterns of atmospheric circulation are likely to trigger major local changes in rainfall, cloud cover, and humidity. Increased interannual variability in precipitation and hurricane incidence would provide additional stresses on island biota that are highly vulnerable to disturbance-related invasion of non-native species. Because of the exceptional sensitivity of these microclimates and forests to change, they may provide valuable ‘listening posts’ for detecting the onset of human-induced global climate change.

Tropical Forests under the Climates of the Last 30,000 Years

Abstract: Vegetational history can help us to predict future environments by providing data for testing AGCMs, for indicating the vegetational response to rapid warming and changing CO2 concentrations, and for mathematical modelling of vegetation. Most of the data are palynological, and there are well over 100 pollen diagrams from tropical regions. Maps are presented showing summarized pollen diagrams from the lowlands of South-East Asia and the West Pacific, Tropical Latin America and Tropical Africa. In all these regions there is some evidence suggesting that at the LGM lowland forests were somewhat restricted in area and included montane elements. This is consistent with cooler and drier climate at the LGM. From the montane and lowland areas of these three regions, the pollen evidence is summarized in altitudinal diagrams. These suggest considerable depression of altitudinal zones at the LGM, suggesting temperatures c. 5–10°C cooler than now. These results conflict with earlier oxygen isotope data from marine foraminifera, but do not conflict with more recent oxygen isotope measurements from tropical corals. It is also suggested that altitudinal movements may be partly controlled by CO2 concentration and ultraviolet light.

Regional Nested Model Simulations of Present Day and 2 × CO2 Climate over the Central Plains of the U.S.

Abstract: A nested regional climate model is used to generate a scenario of climate change over the MINK region (Missouri, Iowa, Nebraska, Kansas) due to doubling of carbon dioxide concentration (2 × CO2) for use in agricultural impact assessment studies. Five-year long present day (control) and 2 × CO2 simulations are completed at a horizontal grid point spacing of 50 km. Monthly and seasonal precipitation and surface air temperature over the MINK region are reproduced well by the model in the control run, except for an underestimation of both variables during the spring months. The performance of the nested model in the control run is greatly improved compared to a similar experiment performed with a previous version of the nested modeling system by Giorgi et al. (1994). The nested model generally improves the simulation of spatial precipitation patterns compared to the driving general circulation model (GCM), especially during the summer. Seasonal surface warming of 4 to 6 K and seasonal precipitation increases of 6 to 24% are simulated in 2 × CO2 conditions. The control run temperature biases are smaller than the simulated changes in all seasons, while the precipitation biases are of the same order of magnitude as the simulated changes. Although the large scale patterns of change in the driving GCM and nested RegCM model are similar, significant differences between the models, and substantial spatial variability, occur within the MINK region.

Potential impacts of climate change on tropical asian forests through an influence on phenology

Abstract: Changes in plant phenology will be one of the earliest responses to rapid global climate change and could potentially have serious consequences both for plants and for animals that depend on periodically available plant resources. Phenological patterns are most diverse and least understood in the tropics. In those parts of tropical Asia where low temperature or drought impose a seasonal rest period, regular annual cycles of growth and reproduction predominate at the individual, population, and community level. In aseasonal areas, individuals and populations show a range of sub- to supra-annual periodicities, with an overall supra-annual reproductive periodicity at the community level. There is no evidence for photoperiod control of phenology in the Asian tropics, and seasonal changes in temperature are a likely factor only near the northern margins. An opportunistic response to water availability is the simplest explanation for most observed patterns where water is seasonally limiting, while the great diversity of phenological patterns in the aseasonal tropics suggests an equal diversity of controls. The robustness of current phenological patterns to high interannual and spatial variability suggests that most plant species will not be seriously affected by the phenological consequences alone of climate change. However, some individual plant species may suffer, and the consequences of changes in plant phenology for flower-and fruit-dependent animals in fragmented forests could be serious.

The Temporal Climatic Variability in the ‘Río De La Plata’ Basin Displayed by the River Discharges

Abstract: Streamflows have a direct dependence on precipitation and these are directly linked to the climate. Then, in this paper the temporal climatic variability in the ‘Rio de la Plata’ Basin is analysed through the changes in the river's discharges. These are the reflection of the climatic inputs areally integrated, and in consequence, contain more information on climate variability than that provided by the scarce punctual records of precipitation and temperature. The time series of streamflows correspond to monthly and annual means in stations selected in the basin for the period 1931–1992. However, in the present paper, the period 1901–1992 was considered in all cases whenever possible. The following changes and tendencies in the flow series were detected: 1. An important change of tendency between 1970 and 1972, and another not so significant before that date were detected in 1917–1918 and 1943–1944. 2. The jumps in the means in several sub-periods were detected using different methods. They showed jumps mainly in the period 1970–1972 in the annual streamflows series. The jumps in the annual streamflow series consist of an abrupt change in climatic variables affecting temporarily the averages of such variables during a certain period of time (years). The results are consistent with the conclusions obtained by other authors for the same region, both in precipitation and in the general circulation of the atmosphere. Keeping in mind this analysis of the series of streamflows, indicators of normal variability of tendencies relative to natural regional causes were detected, although the local causes were not anthropogenically analysed, and so no other manifestations of randomless in the zone of the Basin under study because of the lacking of data.

Sea-Level Change: The Expected Economic Cost of Protection Or Abandonment in the United States

Abstract: Three distinct models from earlier work are combined to: (1) produce probabilistically weighted scenarios of greenhouse-gas-induced sea-level rise; (2) support estimates of the expected discounted value of the cost of sea-level rise to the developed coastline of the United States, and (3) develop reduced-form estimates of the functional relationship between those costs to anticipated sea-level rise, the cost of protection, and the anticipated rate of property-value appreciation. Four alternative representations of future sulfate emissions, each tied consistently to the forces that drive the initial trajectories of the greenhouse gases, are considered. Sea-level rise has a nonlinear effect on expected cost in all cases, but the estimated sensitivity falls short of being quadratic. The mean estimate for the expected discounted cost across the United States is approximately $2 billion (with a 3% real discount rate), but the range of uncertainty around that estimate is enormous; indeed, the 10th and 90th percentile estimates run from less than $0.2 billion up to more than $4.6 billion. In addition, the mean estimate is very sensitive to associated sulfate emissions; it is, specifically, diminished by nearly 25% when base-case sulfate emission trajectories are considered and by more than 55% when high-sulfate trajectories are allowed.

Ecological implications of changes in drought patterns: shifts in forest composition in Panama

Abstract: CO2 concentration is increasing, temperature is likely to rise, and precipitation patterns might change. Of these potential climatic shifts, it is precipitation that will have the most impact on tropical forests, and seasonal patterns of rainfall and drought will probably be more important than the total quantity of precipitation. Many tree species are limited in distribution by their inability to survive drought. In a 50 ha forest plot at Barro Colorado Island in Panama (BCI), nearly all tree and shrub species associated with moist microhabitats are declining in abundance due to a decline in rainfall and lengthening dry seasons. This information forms the basis for a simple, general prediction: drying trends can rapidly remove drought-sensitive species from a forest. If the drying trend continues at BCI, the invasion of drought-tolerant species would be anticipated, but computer models predict that it could take 500 or more years for tree species to invade and become established.

Biotic feedbacks in the warming of the earth

Abstract: A positive correlation exists between temperature and atmospheric concentrations of carbon dioxide and methane over the last 220,000 years of glacial history, including two glacial and three interglacial periods. A similar correlation exists for the Little Ice Age and for contemporary data. Although the dominant processes responsible may be different over the three time periods, a warming trend, once established, appears to be consistently reinforced through the further accumulation of heat-trapping gases in the atmosphere; a cooling trend is reinforced by a reduction in the release of heat-trapping gases. Over relatively short periods of years to decades, the correspondence between temperature and greenhouse gas concentrations may be due largely to changes in the metabolism of terrestrial ecosystems, whose respiration, including microbial respiration in soils, responds more sensitively, and with a greater total effect, to changes in temperature than does gross photosynthesis. Despite the importance of positive feedbacks and the recent rise in surface temperatures, terrestrial ecosystems seem to have been accumulating carbon over the last decades. The mechanisms responsible are thought to include increased nitrogen mobilization as a result of human activities, and two negative feedbacks: CO2 fertilization and the warming of the earth, itself, which is thought to lead to an accumulation of carbon on land through increased mineralization of nutrients and, as a result, increased plant growth. The relative importance of these mechanisms is unknown, but collectively they appear to have been more important over the last century than a positive feedback through warming-enhanced respiration. The recent rate of increase in temperature, however, leads to concern that we are entering a new phase in climate, one in which the enhanced greenhouse effect is emerging as the dominant influence on the temperature of the earth. Two observations support this concern. One is the negative correlation between temperature and global uptake of carbon by terrestrial ecosystems. The second is the positive correlation between temperature and the heat-trapping gas content of the atmosphere. While CO2 fertilization or nitrogen mobilization (either directly or through a warming-enhanced mineralization) may partially counter the effects of a warming-enhanced respiration, the effect of temperature on the metabolism of terrestrial ecosystems suggests that these processes will not entirely compensate for emissions of carbon resulting directly from industrial and land-use practices and indirectly from the warming itself. The magnitude of the positive feedback, releasing additional CO2, CH4, and N2O, is potentially large enough to affect the rate of warming significantly.

Possibilities for future carbon sequestration in Canadian agriculture in relation to land use changes

Abstract: Increasing carbon sequestration in agricultural soils in Canada is examined as a possible strategy in slowing or stopping the current increase in atmospheric CO2 concentrations. Estimates are provided on the amount of carbon that could be sequestered in soils in various regions in Canada by reducing summerfallow area, increased use of forage crops, improved erosion control, shifts from conventional to minimal and no-till, and more intensive use of fertilizers. The reduction of summerfallow by more intensive agriculture would increase the continuous cropland base by 8.1% in western Canada and 6.8% in all of Canada. Although increased organic carbon (OC) sequestration could be achieved in all agricultural regions, the greatest potential gains are in areas of Chernozemic soils. The best management options include reduction of summerfallow, conversion of fallow areas to hay or continuous cereals, fertilization to ensure nutrient balance, and adoption of soil conservation measures. The adoption of these options could sequester about 50-75% of the total agricultural emissions of CO2 in Canada for the next 30 years. However, increased sequestration of atmospheric carbon in the soil is possible for only a limited time. Increased efforts must be made to reduce emissions if long-term mitigation is to be achieved.

The value of improved enso prediction to u.s. agriculture

Abstract: The economic value of long-range weather prediction is measured by the increase in social welfare arising from the use of the prediction in economic decisionmaking. This paper describes a study of the economic value of ENSO prediction to U.S. agriculture. The interdisciplinary study involved the analysis of data and models from meteorology, plant science, and economics under a framework based on Bayesian decision analysis. The estimated annual value of perfect ENSO prediction to U.S. agriculture is $323 million.