Showing papers on "Climate change published in 1991"

To slow or not to slow : The economics of the greenhouse effect

Abstract: Over the last decade, scientists have studied extensively the greenhouse effect, which holds that the accumulation of carbon dioxide (CO2) and other greenhouse gases (GHGs) is expected to produce global warming and other significant climatic changes over the next century. Along with the scientific research have come growing alarm and calls for drastic curbs on the emissions of greenhouse gases, as for example the reports of the Intergovernmental Panel on Climate Change (IPCC [I990]) and the Second World Climate Conference (October I990). To date, these call to arms for forceful measures to slow greenhouse warming have been made without any serious attempt to weigh the costs and benefits of climatic change or alternative control strategies. The present study presents a simple approach for analyzing policies to slow climate change. We begin by summarizing the elements of an economic analysis of different approaches to controlling greenhouse warming. We then sketch a mathematical model of economic growth that links the economy, emissions, and climate changes and summarize the empirical evidence on the costs of reducing emissions and concentrations of greenhouse gases and on the damages from greenhouse warming, relying primarily on data for the United States. The different sections are then integrated to provide estimates of the efficient reduction of greenhouse gases, after which the final section summarizes the major results.

Amazonian Deforestation and Regional Climate Change

Abstract: Large-scale conversion of tropical forests into pastures or annual crops could lead to changes in the climate. We have used a coupled numerical model of the global atmosphere and biosphere (Center for Ocean-Land- Atmosphere GCM) to assess the effects of Amazonian deforestation on the regional and global climate. We found that when the Amazonian tropical forests were replaced by degraded grass (pasture) in the model, there was a significant increase in the mean surface temperature (about 2.5°C) and a decrease in the annual evapo-transpiration (30% reduction), precipitation (25% reduction), and runoff (20% reduction) in the region. The differences between the two simulations were greatest during the dry season. The deforested case was associated with larger diurnal fluctuations of surface temperature and vapor pressure deficit; such effects have been observed in existing deforested arms in Amazonia. The calculated reduction in precipitation was larger than the calculated decrease in evapotranspirat...

Approaches to the simulation of regional climate change: A review

Abstract: The increasing demand by the scientific community, policy makers, and the public for realistic projections of possible regional impacts of future climate changes has rendered the issue of regional climate simulation critically important. The problem of projecting regional climate changes can be identified as that of representing effects of atmospheric forcings on two different spatial scales: large-scale forcings, i.e., forcings which modify the general circulation and determine the sequence of weather events which characterize the climate regime of a given region (for example, greenhouse gas abundance), and mesoscale forcings, i.e., forcings which modify the local circulations, thereby regulating the regional distribution of climatic variables (for example, complex mountainous systems). General circulation models (GCMs) are the main tools available today for climate simulation. However, they are run and will likely be run for the next several years at resolutions which are too coarse to adequately describe mesoscale forcings and yield accurate regional climate detail. This paper presents a review of these approaches. They can be divided in three broad categories: (1) Purely empirical approaches, in which the forcings are not explicitly accounted for, but regional climate scenarios are constructed by using instrumental data records or paleoclimatic analogues; (2) semiempirical approaches, in which GCMs are used to describe the atmospheric response to large-scale forcings of relevance to climate changes, and empirical techniques account for the effect of mesoscale forcings; and (3) modeling approaches, in which mesoscale forcings are described by increasing the model resolution only over areas of interest. Since they are computationally inexpensive, empirical and semiempirical techniques have been so far more widely used. Their application to regional climate change projection is, however, limited by their own empiricism and by the availability of data sets of adequate quality. More recently, a nested GCM-limited area model methodology for regional climate simulation has been developed, with encouraging preliminary results. As it is physically, rather than empirically, based, the nested modeling framework has a wide range of applications.

Forcing mechanisms of the Indian Ocean monsoon

Abstract: Sediments in the Arabian Sea provide biological, biogeochemical and lithogenic evidence of past changes in the Indian Ocean summer monsoon winds. For the past 350,000 years, this system has been externally forced by cyclical changes in solar radiation, and internally phase-locked to the transport of latent heat from the southern subtropical Indian Ocean to the Tibetan Plateau. In contrast to the results of general circulation models, these geological data suggest that the climate change associated with variability in global ice volume is not a primary factor in determining the strength and timing of the monsoon winds.

Radiative forcing of climate

Abstract: An update of the scientific discussions presented in Chapter 2 of the Intergovernmental Panel on Climate Change (IPCC) report is presented. The update discusses the atmospheric radiative and chemical species of significance for climate change. There are two major objectives of the present update. The first is an extension of the discussion on the Global Warming Potentials (GWP's), including a reevaluation in view of the updates in the lifetimes of the radiatively active species. The second important objective is to underscore major developments in the radiative forcing of climate due to the observed stratospheric ozone losses occurring between 1979 and 1990.

Vegetation and climate change in eastern north america since the last glacial maximum

Abstract: Response surfaces describing the empirical dependence of surface pollen percentages of 13 taxa on three standard climatic variables (mean July temperature, mean January temperature, and mean annual precipitation) in eastern North America were used to infer past climates from palynological data. Inferred climates at 3000-yr intervals from 18 000 years ago to the present, based on six taxa (spruce, birch, northern pines, oak, southern pines, and prairie forbs), were used to generate time series of simulated isopoll maps for these taxa and seven others (hickory, fir, beech, hemlock, elm, alder, and sedge). The simulations captured the essential features of the observed isopoll maps for both sets of taxa, including differences in migration patterns during the past 10 000 yr that have previously been attributed to differential migration lag. These results establish that the continental-scale vegetation patterns have responded to continuous changes in climate from the last glacial maximum to the present, with lags < 1500 yr. The inferred climatic changes include seasonality changes consistent with orbitally controlled changes in inso- lation, and shifts in temperature and moisture gradients that are consistent with modelled climatic interactions of the insolation changes with the shrinking Laurentide ice sheet. These results pose new ecological questions about the processes by which vegetated land- scapes approach dynamic equilibrium with their changing environment.

On the Utility of Radiosonde Humidity Archives for climate studies

Abstract: This paper considers the use of upper-air data from radiosondes in long-term climate studies. The accuracy and precision of radiosonde humidity measurements, including temperature and pressure measurements used in calculating them, and their effects on the precision of reported and derived variables are estimated. Focusing on the U.S. radiosonde system, we outline the history of changes in instruments and reporting practices and attempt to assess the implications of such changes for studies of temporal variations in lower-tropospheric water vapor. Changes in biases in the data are highlighted, as these can lead to misinterpretation of climate change. We conclude that the upper-air data record for the United States is not homogeneous, especially before 1973. Because of problems with the humidity data in cold, dry conditions, the water vapor climatology in the upper troposphere, nominally above the 500-mb level, is not well known.

Reconstruction of Caribbean climate change over the past 10,500 years

Abstract: A high-resolution reconstruction of Caribbean climate is presented based on O-18/O-16 ratios in ostracod shells from Lake Miragoane, Haiti. The variations which are found can be largely explained by orbitally induced variations in seasonal insolation which modified the intensity of the annual cycle.

Climate change and wildfire in Canada

Abstract: This study investigates the impact of postulated greenhouse warming on the severity of the forest fire season in Canada. Using CO2 levels that are double those of the present (2 × CO2), simulation ...

The Cost of Slowing Climate Change: a Survey

Abstract: Policies to deal effectively and efficiently with the threat of greenhouse warming must balance the costs of slowing climate change against the potential damages. This survey discusses one half of this question, the costs of slowing climate change by reducing greenhouse gas (GHG) emissions. The analysis provides estimates of the cost of reducing chlorofluorocarbon and C02 emissions, and inquires into the costs of using forestry options to remove C02 from the atmosphere. A promising new approach, the use ofgeoengineering, is discussed qualitatively.

The Use of General Circulation Models to Predict Regional Climatic Change

Abstract: Equilibrium simulations using the best-available general circulation models to estimate the sensitivity of the climate to a doubling of the atmospheric carbon dioxide concentration are in broad general agreement that the global annual average surface air temperature would increase 2.5 to 4.5 K. However, at finer spatial scales, the range of changes in temperature and precipitation predicted by different computer models is much broader. Many shortcomings are also apparent in the model simulations of the present climate, indicating that further model improvements are needed to achieve reliable regional and seasonal projections of the future climatic conditions.

Element cycling in taiga forests : state-factor control

Abstract: ronment characterized by drastic seasonal fluctuations in day length and temperature, a short growing season, low soil temperatures, and permafrost (Van Cleve and Alexander 1981). The taiga is part of the circumpolar forest region near the latitudinal limit of tree growth. The taiga occupies large areas of Alaska, Canada, Scandinavia, and the Soviet Union (Van Cleve and Alexander 1981). With changing climate, ecological relationships within the taiga could assume global importance, because this region contains 20% of the world's stored carbon and is a large but unexplored source of methane and carbon dioxide, two gases implicated in causing climate change (Billings 1987, McBeath 1984, Reeburgh 1990). Flux rates of these gases are expected to change An understanding of taiga ecosystem controls is important for predicting global responses to climate change

Potential magnitude of future vegetation change in eastern north america: comparisons with the past.

Abstract: Increases in atmospheric trace gas concentrations could warm the global average temperature 1.5° to 4.5°C by the end of the next century. Application of climate-pollen response surfaces to three climate model simulations of doubled preindustrial atmospheric CO 2 levels shows that the change in the equilibrium distribution of natural vegetation over eastern North America over the next 200 to 500 years could be larger than the overall change during the past 7,000 to 10,000 years and equivalent to the change that took place over the 1,000- to 3,000-year period of most rapid deglaciation. Some plant ranges and abundance maxima could shift as much as 500 to 1000 km during the next 200 to 500 years; such changes would have dramatic impacts on silvicultural and natural ecosystems. Although unprecedented vegetation change is likely if climate changes as predicted, forecasting the exact timing and patterns of change will be difficult.

Solar total irradiance variations and the global sea surface temperature record

Abstract: The record of globally averaged sea surface temperature (SST) over the past 130 years shows a highly significant correlation with the envelope of the 11-year cycle of solar activity over the same period. This correlation could be explained by a variation in the sun's total irradiance (the solar “constant”) that is in phase with the solar-cycle envelope, supporting and updating an earlier conclusion by Eddy (1976) that such variations could have played a major role in climate change over the past millennium. Measurements of the total irradiance from spacecraft, rockets, and balloons over the past 25 years have provided evidence of long-term variations and have been used to develop a simple linear relationship between irradiance and the envelope of the sunspot cycle. This relationship has been used to force a one-dimensional model of the thermal structure of the ocean (Hoffert et al., 1980), consisting of a 100-m mixed layer coupled to a deep ocean and including a thermohaline circulation. The model was started in the mid-seventeenth century, at the time of the Maunder Minimum of solar activity, and mixed-layer temperatures were calculated at 6-month intervals up to the present. The total range of irradiance values during the period was about 1%, and the total range of SST was about 1°C. Cool periods, when temperatures were about 0.5°C below present-day values, were found in the early decades of both the nineteenth and twentieth centuries. There is direct evidence for the latter period from the historical SST record and some indirect evidence for the earlier cool period. While many aspects of the study are unavoidably simplistic, the results can be taken as indicating that solar variability has been an important contributor to global climate variations in recent decades. It has probably not been the only contributor, however, and in particular, the growing atmospheric burden of greenhouse gases may well have played an important role in the immediate past. This role is likely to become even more important in the near future.

Rapid changes in the range limits of scots pine 4000 years ago.

Abstract: Paleoecological data provide estimates of response rates to past climate changes. Fossil Pinus sylvestris stumps in far northern Scotland demonstrate former presence of pine trees where conventional pollen evidence of pine forests is lacking. Radiocarbon, dendrochronological, and fine temporal-resolution palynological data show that pine forests were present for about four centuries some 4000 years ago; the forests expanded and then retreated rapidly some 70 to 80 kilometers. Despite the rapidity of this response to climate change, it occurred at rates slower by an order of magnitude than those necessary to maintain equilibrium with forecast climate changes attributed to the greenhouse effect.

Ice-core record of oceanic emissions of dimethylsulphide during the last climate cycle

Abstract: THE Vostok ice core in Antarctica has provided one of the longest climate records, enabling the stable-isotope, major-ion and gas composition of the atmosphere to be reconstructed over many thousands of years. Here we present depth profiles along this core of methanesulphonate and non-seasalt sulphate (produced by the atmospheric oxidation of dimethylsulphide), which provide the first historical record of biogenic sulphur emissions from the Southern Hemisphere oceans over a complete glacial–interglacial cycle (160 kyr). Those measurements confirm and extend some previous observations made on a very limited data set from the Dome C ice core in Antarctica, which indicated increased oceanic emissions of dimethylsulphide during the later stages of the glacial period, compared with the present day1. The observed glacial–interglacial variations in methanesulphonate and non-seasalt sulphate confirm that the ocean–atmosphere sulphur cycle is extremely sensitive to climate change.

State‐of‐the‐Art of Models of Production‐Decomposition Linkages in Conifer and Grassland Ecosystems

Abstract: We review the state-of-the-art of models of forests and grasslands that could be used to predict the impact of a future climate change arising from increased atmospheric carbon dioxide concentration. Four levels of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in great detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationships between the plants and the soil system, but at the expense of requiring more ad ho formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. However, our conclusion is that, in spite of the gaps in knowledge, there are several models based on dominant processes that are well enough understood for the predictions of those models to be taken seriously.

The Radiative Effects of Clouds and their Impact on Climate

Abstract: Our knowledge of the direct role of clouds in long-term climate change is examined in an overview of key results published over the last 15 or 20 years, along with some relevant unpublished model studies. The focus is on 1) the impact of clouds on the incoming and outgoing radiation at the top of the atmosphere, and 2) the two-way interaction of clouds with other variables of the climate system—i.e., the cloud/climate feedback problem—as revealed by climate model simulations. A common framework is established for comparing results from different investigations. The total effect of clouds on radiative fluxes at the top of the atmosphere—specifically, the difference in flux between average conditions and cloud-free conditions, often called cloud forcing–has been derived from earth radiation budget measurements by several investigators using various data sources and methods. There is general agreement that the annual global mean effect of clouds is to cool the climate system, but there is significant disagre...

Increased ocean heat transports and warmer climate

Abstract: The impact of an increased ocean heat transport on climate is investigated in the framework of the GISS GMC model described by Hansen et al. (1983), using two scenarios: one starting from warmer polar temperatures/no sea ice and the other from the current ocean conditions. A 20-percent increase in cross-equatorial heat transport was sufficient to melt all sea ice; it resulted in a climate that was 2 C warmer for the global average, with values some 20-deg warmer at high altitudes and 1-deg warmer near the equator. It is suggested that the hydrological and dynamical changes associated with this different climate regime may be self-sustaining and, as such, would account for the high-latitude warmth of climates in the Mesozoic and Tertiary periods and the decadenal-scale climate fluctuations during the Holocene.

Positive water vapour feedback in climate models confirmed by satellite data

Abstract: It has recently been suggested that GCMs used to evaluate climate change overestimate the greenhouse effect due to increased concentrations of trace gases in the atmosphere Here, new satellite-generated water vapor data are used to compare summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence It is found that, as the hemispheres warm, increased convection leads to increased water vapor above 500 mbar in approximate quantitative agreement with results from current climate models The same conclusion is reached by comparing the tropical western and eastern Pacific regions Thus, water vapor feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations

Interpretation of snow-climate feedback as produced by 17 general circulation models.

Abstract: Snow feedback is expected to amplify global warming caused by increasing concentrations of atmospheric greenhouse gases. The conventional explanation is that a warmer Earth will have less snow cover, resulting in a darker planet that absorbs more solar radiation. An intercomparison of 17 general circulation models, for which perturbations of sea surface temperature were used as a surrogate climate change, suggests that this explanation is overly simplistic. The results instead indicate that additional amplification or moderation may be caused both by cloud interactions and longwave radiation. One measure of this net effect of snow feedback was found to differ markedly among the 17 climate models, ranging from weak negative feedback in some models to strong positive feedback in others.

Regional hydrologic and carbon balance responses of forests resulting from potential climate change

Abstract: The projected response of coniferous forests to a climatic change scenario of doubled atmospheric CO2, air temperature of +4 °C, and +10% precipitation was studied using a computer simulation model of forest ecosystem processes. A topographically complex forested region of Montana was simulated to study regional climate change induced forest responses. In general, increases of 10–20% in LAI, and 20–30% in evapotranspiration (ET) and photosynthesis (PSN) were projected. Snowpack duration decreased by 19–69 days depending on location, and growing season length increased proportionally. However, hydrologic outflow, primarily fed by snowmelt in this region, was projected to decrease by as much as 30%, which could virtually dry up rivers and irrigation water in the future.

Quaternary Ecology: A paleoecological perspective

Abstract: This book considers issues and problems in ecology which may be illuminated, if not solved, by considering paleoecology. The five central chapters include a discussion of application of Quaternary ecology to future global climate change, including global warming. Other areas presented include: population dispersal, invasions, expansions, and migrations; plant successions; ecotones; factors in community structure; ecosystem patterns and processes. Published case studies are numerous. The role played by continuing climatic change in vegetation change is acknowledged but not stressed.

Soil Carbon Isotope Evidence for Holocene Habitat Change in the Kenya Rift Valley

Abstract: In eastern Africa the altitude of the boundary between montane forest and lowland savanna grassland changed substantially in response to climate change during the later Holocene, but this is not clearly reflected in regional pollen records. The carbon-13 to carbon-12 ratios of tropical grasses are higher than those of most other plants, and this difference is preserved in soil organic carbon stable isotope ratios. Soil organic matter 13 C/ 12 C ratios in profiles along an altitude transect in the central Rift Valley of Kenya suggest that the forest-savanna boundary advanced more than 300 meters in altitude. This could have implications for understanding the effects of climate change on the configuration of floral zones, prehistoric hunter-gatherer land-use patterns, and the timing of the advent of Neolithic food production.

Plateau uplift and climatic change

Abstract: The earth of 40 million years ago was a warm, wet place. Forests abounded; grasslands and deserts were rare. Then the planet began to cool. Regional climate extremes developed. Many causes have been postulated, including continental drift and diminishing atmospheric carbon dioxide. The authors offer a new theory: continental uplift created huge plateaus that altered circulation of the atmosphere. The two largest masses of high, rocky terrain in the Northern Hemisphere today are the area encompassing the Tibetan Plateau and Himalaya Mountains and the broad region of the American West centered on the Colorado Plateau. Geologic evidence indicates that these regions rose substantially during the past 40 million years. The authors focused their research on these plateaus.