Showing papers in "Climatic Change in 1996"

Robust estimation of background noise and signal detection in climatic time series

Abstract: We present a new technique for isolating climate signals in time series with a characteristic ‘red’ noise background which arises from temporal persistence. This background is estimated by a ‘robust’ procedure that, unlike conventional techniques, is largely unbiased by the presence of signals immersed in the noise. Making use of multiple-taper spectral analysis methods, the technique further provides for a distinction between purely harmonic (periodic) signals, and broader-band (‘quasiperiodic’) signals. The effectiveness of our signal detection procedure is demonstrated with synthetic examples that simulate a variety of possible periodic and quasiperiodic signals immersed in red noise. We apply our methodology to historical climate and paleoclimate time series examples. Analysis of a ≈ 3 million year sediment core reveals significant periodic components at known astronomical forcing periodicities and a significant quasiperiodic 100 year peak. Analysis of a roughly 1500 year tree-ring reconstruction of Scandinavian summer temperatures suggests significant quasiperiodic signals on a near-century timescale, an interdecadal 16–18 year timescale, within the interannual El Nino/Southern Oscillation (ENSO) band, and on a quasibiennial timescale. Analysis of the 144 year record of Great Salt Lake monthly volume change reveals a significant broad band of significant interdecadal variability, ENSO-timescale peaks, an annual cycle and its harmonics. Focusing in detail on the historical estimated global-average surface temperature record, we find a highly significant secular trend relative to the estimated red noise background, and weakly significant quasiperiodic signals within the ENSO band. Decadal and quasibiennial signals are marginally significant in this series.

The effect of changes in daily and interannual climatic variability on CERES-Wheat: A sensitivity study

Abstract: We investigate the effect of changes in daily and interannual variability of temperature and precipitation on yields simulated by the CERES-Wheat model at two locations in the central Great Plains. Changes in variability were effected by adjusting parameters of the Richardson daily weather generator. Two types of changes in precipitation were created: one with both intensity and frequency changed; and another with change only in persistence. In both types mean total monthly precipitation is held constant. Changes in daily (and interannual) variability of temperature result in substantial changes in the mean and variability of simulated wheat yields. With a doubling of temperature variability, large reductions in mean yield and increases in variability of yield result primarily from crop failures due to winter kill at both locations. Reduced temperature variability has little effect. Changes in daily precipitation variability also resulted in substantial changes in mean and variability of yield. Interesting interactions of the precipitation variability changes with the contrasting base climates are found at the two locations. At one site where soil moisture is not limiting, mean yield decreased and variability of yield increased with increasing precipitation variability, whereas mean yields increased at the other location, where soil moisture is limiting. Yield changes were similar for the two different types of precipitation variability change investigated. Compared to an earlier study for the same locations wherein variability changes were effected by altering observed time series, and the focus was on interannual variability, the present results for yield changes are much more substantial. This study demonstrates the importance of taking into account change in daily (and interannual) variability of climate when analyzing the effect of climate change on crop yields.

Agricultural adaptation to climatic variation

Abstract: Assumptions underlying impact assessments of climatic change for agriculture are explored conceptually and empirically. Variability in climatic conditions, the relevance of human decision-making, and the role of non-climatic forces are reviewed and captured in a model of agricultural adaptation to climate. An empirical analysis of farmers' decisions in light of variations in climate and other forces is based on a survey of 120 farm operators in southwestern Ontario. Many farmers were affected by variable climatic conditions over a six-year-period, and some undertook strategic adaptations in their farm operations. Frequency of dry years was the key climatic stimulus to farming adaptations. However, only 20 percent of farmers were sufficiently influenced by climatic conditions to respond with conscious changes in their farm operations.

The economic cost of greenhouse-induced sea-level rise for developed property in the United States

Abstract: Estimates of the true economic cost that might be attributed to greenhouse-induced sea-level rise on the developed coastline of the United States are offered for the range of trajectories that is now thought to be most likely. Along a 50-cm sea level rise trajectory (through 2100), for example, transient costs in 2065 (a year frequently anticipated for doubling of greenhouse-gas concentrations) are estimated to be roughly $70 million (undiscounted, but measured in constant 1990$). More generally and carefully cast in the appropriate context of protection decisions for developed property, the results reported here are nearly an order of magnitude lower than estimates published prior to 1994. They are based upon a calculus that reflects rising values for coastal property as the future unfolds, but also includes the cost-reducing potential of natural, market-based adaptation in anticipation of the threat of rising seas and/or the efficiency of discrete decisions to protect or not to protect small tracts of property that will be made when necessary and on the (then current) basis of their individual economic merit.

Ethics and intentional climate change

Abstract: In recent years the idea of geoengineering climate has begun to attract increasing attention. Although there was some discussion of manipulating regional climates throughout the 1970s and 1980s, the discussion was largely dormant. What has reawakened the conversation is the possibility that Earth may be undergoing a greenhouse-induced global warming, and the paucity of serious measures that have been taken to prevent it. In this paper I assess the ethical acceptability of ICC, based on my impressions of the conversation that is now taking place. Rather than offering a dispassionate analysis, I argue for a point of view. I propose a set of conditions that must be satisfied for an ICC project to be morally permissible and conclude that these conditions are not now satisfied. However, research on ICC should go forward so long as certain other conditions are met. I do not intend this to be the last word on the subject, but rather the first word. My hope is that others will be stimulated to think through the ethics of ICC.

Climate change, tree species distributions and forest dynamics: A case study in the mixed conifer/northern hardwoods zone of northern Europe

Abstract: Three bioclimate variables (growing degree days after budburst, temperature of the coldest month and a moisture index) are used in a model (STASH) to predict potential range limits of north European tree species. CO2-induced climate warming scenarios cause major changes in these limits. The dominant conifers of the mixed conifer/northern hardwoods zone, Picea abies and Pinus sylvestris, retreat from the south and west while Fagus sylvatica and other temperate hardwoods spread to the north. A gap model (FORSKA 2) is used to simulate the associated transient responses of a forest reserve within this zone. In both dry Pinus- and moist Picea- dominated forest communities, Picea continues to increase while Pinus sooner or later declines. These changes are continuing successional (non-climatic) responses to the cessation of disturbance 150 years ago. Climate warming speeds up the succession, and allows Fagus to establish and increase. The eventual decline of Picea however is delayed due to the persistence of old-growth stands. Picea forests subject to continuing disturbance show a more rapid shift to dominance by Fagus and other temperate hardwoods. Delayed immigration of new species, including Fagus, would favour earlysuccessional species such as Betula pendula and Quercus spp. in a forest with reduced biomass and diversity. The results emphasise the complex and sometimes counter-intuitive nature of transient responses, and the importance of considering disturbance history and potential migration rates when predicting the impacts of rapid climate change on forests.

Siberian CO2 efflux in winter as a CO2 source and cause of seasonality in atmospheric CO2

Abstract: Over three years, we found a consistent CO2 efflux from forest tundra of the Russian North throughout the year, including a large (89 g C m−2 yr−1) efflux during winter. Our results provide one explanation for the observations that the highest atmospheric CO2 concentration and greatest seasonal amplitude occur at high latitudes rather than over the mid-latitudes, where fossil fuel sources are large, and where high summer productivity offset by winter respiration should give large seasonal oscillations in atmospheric CO2. Winter respiration probably contributed substantially to the boreal winter CO2 efflux. Respiration is an exothermic process that produces enough heat to warm soils and promote further decomposition. We suggest that, as a result of this positive feedback, small changes in surface heat flux, associated with human activities in the North or with regional or global warming, could release large quantities of organic carbon that are presently stored in permafrost.

Learning from integrated assessment of climate change

Abstract: The objective of integrated assessment of climate change is to put available knowledge together in order to evaluate what has been learned, policy implications, and research needs. This paper summarizes insights gained from five years of integrated assessment activity at Carnegie Mellon. After an introduction, in Section 2 we ask: who are the climate decision makers? We conclude that they are a diffuse and often divergent group spread all over the world whose decisions are primarily driven by local non-climate considerations. Insights are illustrated with results from the ICAM-2 model. In Section 3 we ask: what is the climate problem? In addition to the conventional answer, we note that in a democracy the problem is whatever voters and their elected representatives think it is. Results from studies of public understanding are reported. Several other specific issues that define the problem, including the treatment of aerosols and alternative indices for comparing greenhouse gases, are discussed. In Section 4 we discuss studies of climate impacts, focusing on coastal zones, the terrestrial biosphere and human health. Particular attention is placed on the roles of adaptation, value change, and technological innovation. In Section 5 selected policy issues are discussed. We conclude by noting that equity has received too little attention in past work. We argue that many conventional tools for policy analysis are not adequate to deal with climate problems. Values that change, and mixed levels of uncertainty, pose particularly important challenges for the future.

Impact of temperature and precipitation variability on crop model predictions

Abstract: Future climate changes, as well as differences in climates from one location to another, may involve changes in climatic variability as well as changes in means. In this study, a synthetic weather generator is used to systematically change the within-year variability of temperature and precipitation (and therefore also the interannual variability), without altering long-term mean values. For precipitation, both the magnitude and the qualitative nature of the variability are manipulated. The synthetic daily weather series serve as input to four crop simulation models. Crop growth is simulated for two locations and three soil types. Results indicate that average predicted yield decreases with increasing temperature variability where growing-season temperatures are below the optimum specified in the crop model for photosynethsis or biomass accumulation. However, increasing within-year variability of temperature has little impact on year-to-year variability of yield. The influence of changed precipitation variability on yield was mediated by the nature of the soil. The response on a droughtier soil was greatest when precipitation amounts were altered while keeping occurrence patterns unchanged. When increasing variability of precipitation was achieved through fewer but larger rain events, average yield on a soil with a large plant-available water capacity was more affected. This second difference is attributed to the manner in which plant water uptake is simulated. Failure to account for within-season changes in temperature and precipitation variability may cause serious errors in predicting crop-yield responses to future climate change when air temperatures deviate from crop optima and when soil water is likely to be depleted at depth.

Detection of changes in streamflow and floods resulting from climate fluctuations and land use-drainage changes

Abstract: Detection of effects of changing climate on the hydrologic responses of rivers can be further complicated by changes in land use, drainage, and water use. To discern effects of human-caused changes in a basin and those due to precipitation over time, a comparison was made of annual mean flows and peakflows in Midwestern basins that experienced increases in annual precipitation and heavy rain events during 1940–1990. Two pairs of basins, one pair in a rural area and one pair in an urbanized area, were selected for in-pair comparisons, with one basin in each pair experiencing more land use and drainage changes during 1940–1990 than the other basin. All basins experienced significant upward trends in annual precipitation and annual mean flows. Human-produced changes affecting runoff in both rural basins accounted for about two-thirds of the fluctuations in the mean flows, and precipitation changes accounted for the other third. However, much of the change in peakflows in the rural basin undergoing sizable changes in drainage was due to these changes (85%) versus 75% in the rural basin without comparable shifts in drainage. The mean and peak flows of the two urban basins showed considerably more response to precipitation shifts than those of the two rural basins. The urbanized area doubled within one urban basin during 1940–1990, and these land use changes explained much more of the increase in mean flows and peakflows there than in the urban basin with less change in land use. By 1990 precipitation accounted for 69% of the upward trend in mean flows since 1941 in the heavily developed urban basin, as compared to 37% of the trend in the less settled urban basin. For purposes of assessing climate change, the precipitation changes over fifty years in all basins produced marked uptrends in basin streamflow, but the magnitude of the precipitation effect was masked by the land use and drainage changes. The results illustrate the need for careful analysis of natural basin characteristics (soils and basin shape), land use and drainage changes, and of various precipitation conditions if the influence of shifting precipitation on hydrologic conditions is to be detected, accurately measured, and correctly interpreted. For such studies the paired basin comparison techniques appears to be a valuable approach.

When we don't know the costs or the benefits: Adaptive strategies for abating climate change

Abstract: Most quantitative studies of climate-change policy attempt to predict the greenhouse-gas reduction plan that will have the optimum balance of long-term costs and benefits. We find that the large uncertainties associated with the climate-change problem can make the policy prescriptions of this traditional approach unreliable. In this study, we construct a large uncertainty space that includes the possibility of large and/or abrupt climate changes and/or of technology breakthroughs that radically reduce projected abatement costs. We use computational experiments on a linked system of climate and economic models to compare the performance of a simple adaptive strategy - one that can make midcourse corrections based on observations of the climate and economic systems - and two commonly advocated ‘best-estimate’ policies based on different expectations about the longterm consequences of climate change. We find that the ‘Do-a-Little’ and ‘Emissions-Stabilization’ best-estimate policies perform well in the respective regions of the uncertainty space where their estimates are valid, but can fail severely in those regions where their estimates are wrong. In contrast, the adaptive strategy can make midcourse corrections and avoid significant errors. While its success is no surprise, the adaptive-strategy approach provides an analytic framework to examine important policy and research issues that will likely arise as society adapts to climate change, which cannot be easily addressed in studies using best-estimate approaches.

Assessing integrated assessments

Abstract: Integrated assessment of global environmental change is a relatively new field that is beginning to define itself and its forms of practice. As yet, the field has not grappled directly with issues of quality control and assessment of quality, and this work is a first attempt in that direction. We argue that if integrated assessment is to be successful in the long run, then building and maintaining credibility via quality control procedures is a necessary condition for realizing its potential. We highlight a number of pitfalls in the practice of integrated assessment, and discuss their causes. We buttress our concerns using examples from both within climate change integrated assessment, and from the history of other similar endeavors. We also provide a number of suggestions that we hope will serve to alleviate some of these pitfalls. For instance, tools, methods, and assumptions from disciplines form archetypes for components in integrated assessment models, and we need to apply greater scrutiny to these archetypes. Further, tools which may be reasonable to use in particular disciplinary, geographical, or temporal contexts may be unsuited to the broader contexts inherent in integrated assessment studies of global environmental change.

Climate change and snow-cover duration in the Australian Alps

Abstract: This study uses a model of snow-cover duration, an observed climate data set for the Australian alpine area, and a set of regional climate-change scenarios to assess quantitatively how changes in climate may affect snow cover in the Australian Alps. To begin, a regional interannual climate data set of high spatial resolution is prepared for input to the snow model and the resulting simulated interannual and spatial variations in snow-cover duration are assessed and compared with observations. The model provides a reasonable simulation of the sensitivities of snow-cover duration to changes in temperature and precipitation in the Australian Alps, although its performance is poorer at sites highly marginal for snow cover. (In a separate comparison, the model also performs well for sites in the European Alps.) The input climate data are then modified in line with scenarios of regional climate change based on the results of five global climate models run in enhanced greenhouse experiments. The scenarios are for the years 2030 and 2070 and allow for uncertainty associated with projecting future emissions of greenhouse gases and with estimating the sensitivity of the global climate system to enhanced greenhouse forcing. Attention focuses on the climate changes most favourable (‘best-case scenario’) and least favourable (‘worst-case scenario’) for snow cover amongst the range of climate changes in the scenarios. Under the best case scenario for 2030, simulated average snow-cover duration and the frequency of years of more than 60 days cover decline at all sites considered. However, at the higher sites (e.g., more than 1700 m) the effect is not very marked. For the worst case scenario, a much more dramatic decline in snow conditions is simulated. At higher sites, simulated average snow cover duration roughly halves by 2030 and approaches zero by 2070. At lower sites (around 1400 m), near zero average values are simulated by 2030 (compared to durations of around 60 days for current climate). These simulated changes, ranging between the best and worst case, are likely to be indicative of how climate change will affect natural snow-cover duration in the Australian Alps. However, note that the model does not allow directly for changes in the frequency and intensity of snow-bearing circulation systems, nor do the climate-change scenarios allow possible changes in interannual variability (particularly that due to the El Nino-Southern Oscillation) and local topographical effects not resolved by global climate models. The simulated changes in snow cover are worthy of further consideration in terms of their implications for the ski industry and tourism, water resources and hydroelectric power, and land-use management and planning.

Use of conditional stochastic models to generate climate change scenarios

Abstract: Stochastic models have been proposed as one technique for generating scenarios of future climate change. One particular daily stochastic weather generator, termed Richardson's Model or WGEN, has received much attention. Because it is expressed in a conditional form convenient for simulation (e.g., temperature is modeled conditional on precipitation occurrence), some of its statistical characteristics are unclear. In the present paper, the theoretical statistical properties of a simplified version of Richardson's model are derived. These results establish that when its parameters are varied, certain unanticipated effects can be produced. For instance, modifying the probability of daily precipitation occurrence not only changes the mean of daily temperature, but its variance and autocorrelation as well. A prescription for how best to adjust these model parameters to obtain the desired climate changes is provided. Such precautions apply to conditional stochastic models more generally.

The economic diplomacy of geoengineering

Abstract: ‘Geoengineering’ is a new term, still seeking a definition. It seems to imply something global, intentional, and unnatural. For the radiation balance, geoengineering may be fifty years in the future; today's means may be out of date then, and the future means are not yet known. It might immensely simplify greenhouse policy, transforming it from an exceedingly complicated regulatory regime to a problem in international cost sharing, a problem that we are familiar with. Putting things in the stratosphere or in orbit can probably be done by ‘exo-national’ programs, not depending on the behavior of populations, not requiring national regulations or incentives, not dependent on universal participation. It will involve merely deciding what to do, how much to do, and who is to pay for it.

The risk of sea level rise

Abstract: The United Nations Framework Convention on Climate Change requires nations to implement measures for adapting to rising sea level and other effects of changing climate. To decide upon an appropriate response, coastal planners and engineers must weigh the cost of these measures against the likely cost of failing to prepare, which depends on the probability of the sea rising a particular amount. This study estimates such a probability distribution, using models employed by previous assessments, as well as the subjective assessments of twenty climate and glaciology reviewers about the values of particular model coefficients. The reviewer assumptions imply a 50 percent chance that the average global temperature will rise 2 °C, as well as a 5 percent chance that temperatures will rise 4.7 °C by 2100. The resulting impact of climate change on sea level has a 50 percent chance of exceeding 34 cm and a 1% chance of exceeding one meter by the year 2100, as well as a 3 percent chance of a 2 meter rise and a 1 percent chance of a 4 meter rise by the year 2200. The models and assumptions employed by this study suggest that greenhouse gases have contributed 0.5 mm/yr to sea level over the last century. Tidal gauges suggest that sea level is rising about 1.8 mm/yr worldwide, and 2.5–3.0 mm/yr along most of the U.S. Coast. It is reasonable to expect that sea level in most locations will continue to rise more rapidly than the contribution from climate change alone. We provide a set of ‘normalized’ projections which express the extent to which climate change is likely to accelerate the rate of sea level rise. Those projections suggest that there is a 65 percent chance that sea level will rise 1 mm/yr more rapidly in the next 30 years than it has been rising in the last century. Assuming that nonclimatic factors do not change, there is a 50 percent chance that global sea level will rise 45 cm, and a 1 percent chance of a 112 cm rise by the year 2100; the corresponding estimates for New York City are 55 and 122 cm. Climate change impact assessments concerning agriculture, forests, water resources, and other noncoastal resources should also employ probability-based projections of regional climate change. Results from general circulation models usually provide neither the most likely scenario nor the full range of possible outcomes; probabilistic projections do convey this information. Moreover, probabilistic projections can make use of all the available knowledge, including the views of skeptics; the opinions of those who study ice cores, fossils, and other empirical evidence; and the insights of climate modelers, which may be as useful as the model results themselves.

Geoengineering: could - or should - we do it?

Abstract: Schemes to modify large-scale environment systems or to control climate have been seriously proposed for over 50 years, some to (1) increase temperatures in high latitudes, (2) increase precipitation, (3) decrease sea ice, (4) create irrigation opportunities or to offset potential global warming by spreading dust in the stratosphere to reflect away an equivalent amount of solar energy. These and other proposed geoengineering schemes are briefly reviewed from a historical perspective. More recently, many such schemes to advertently modify climate have been proposed as cheaper methods to counteract inadvertent climatic modifications than conventional mitigation techniques such as carbon taxes or pollutant emissions regulations. Whereas proponents argue cost effectiveness, critics of geoengineering argue that there is too much uncertainty to either (1) be confident that any geoengineering scheme would work as planned, or (2) that the many decades of international political stability and cooperation needed for the continuous maintenance of such schemes to offset century long inadvertent efforts is problematic. Moreover, there is potential for transboundary conflicts should negative climatic events occur during geoengineering activities since, given all the large uncertainties, it could not be assured to victims of such events that the schemes were entirely unrelated to their damages. Nevertheless, although I believe it would be irresponsible to implement any large-scale geoengineering scheme until scientific, legal and management uncertainties are substantially narrowed, I do agree that, given the potential for large inadvertent climatic changes now being built into the earth system, more systematic study of the potential for geoengineering is probably needed.

A comparison of forest gap models : Model structure and behaviour

Abstract: Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models.

Effects of summer precipitation on urban transportation

Abstract: Potential shifts in summer precipitation due to an enhanced greenhouse effect indicate the possibility of more rain days and heavier rains in the Midwest, and this study assessed the effects of such changes on transportation in Chicago using a 3-year period of data Traffic accidents in the metropolitan area doubled on rainy days, with 30% more accidents in more densely populated urban areas than in suburban-rural areas During rain events accident severity (number of injuries) was 55% higher in suburban and rural areas where less dense but higher speed traffic flows exist than in the city, however Rain days during dry months produced more accidents and injuries than during normal or wet months Three times as many accidents occurred during heavy rain periods (> 128 mm) as during nonrain conditions Rain had a negligible influence on weekday traffic volume on busy highways but there was a 9% decrease in traffic volume on rainy weekends A 3–5% decrease in ridership of public transportation occurred on rainy days, with most decreases during midday Nationally, 27% of all fatality-producing aircraft accidents occurred during rainy weather conditions, as did 57% of the 30-min flight delays at Chicago's O'Hare Airport Results suggest that given continued transportation use patterns extend into the future, a future climate with more summer rain days, somewhat higher rain rates, and more storms would mean more total vehicular accidents, more total injuries in vehicular accidents, decreased ridership on public transportation systems, and more aircraft accidents and delays A drier climate would likely experience fewer moderate to heavy rain events but results show that rain events during drier conditions produced a greater frequency of accidents and injuries per event than during wetter conditions

Temperature depression in the lowland tropics in glacial times

Abstract: Equatorial air temperatures at low elevations in the New World tropics are shown by pollen and other data to have been significantly lowered in long intervals of the last glaciation. These new data show that long recognized evidence for cooling at high elevations in the tropics were symptomatic of general tropical cooling and that they did not require appeal to altered lapse rates or other special mechanisms to be made to conform with conclusions that equatorial sea surface temperatures (SSTs) were scarcely changed in glacial times. The new data should be read in conjunction with recent findings that Caribbean (SSTs) were lowered in the order of 5 ° C, contrary to previous interpretations. Thus these accumulating data show that low latitudes as well as high were cooled in glaciations. In part the earlier failure to find evidence of low elevation cooling in the lowland tropics resulted from the data being masked by strong signals for aridity given by old lake levels in parts of Africa and elsewhere. Global circulation models used to predict future effects of greenhouse warming must also be able to simulate the significant cooling of the large tropical land masses at glacial times with reduced greenhouse gas concentrations. Plants and animals of the Amazon forest and similar ecosystems are able to survive in wide ranges of temperatures, CO2 concentrations, and disturbance, though associations change constantly.

The great dry fog of 1783

Abstract: A persistent dry haze hung over Europe during the second half of 1783. Spawned by the Laki basalt fissure eruption in southern Iceland, this fog evoked much contemporary written commentary, from which the course of events is here reconstructed in a quantitative way. It was the densest European dry fog since the late Middle Ages, and it lay primarily in the troposphere. Spreading broadly toward the south and east, it nevertheless remained mostly confined to the North Atlantic, western Eurasia, and the Arctic. Previously it was believed by many to have risen to the middle stratosphere and to have blanketed much of North America. Composed of sulfuric-acid aerosols, its total mass reached about 200 megatons, as determined from its observed optical thickness. Several authors have pointed out that it may have been responsible for the cold winter of 1783–84, which caused much economic and social distress in many parts of the Northern Hemisphere. As the earliest dry fog to be studied scientifically, it remains the paradigm even today and poses an interesting challenge to climate modelers.

Linkages — an individual-based forest ecosystem model

Abstract: Carbon storage and flow through forest ecosystems are major components of the global carbon cycle. The cycle of carbon is intimately coupled with the cycle of nitrogen and the flow of water through forests. The supply of water for tree growth is determined by climate and soil physical properties. The rate at which nitrogen mineralization occurs depends on climate and the type of carbon compounds with which the nitrogen is associated. Species composition, which is also affected by climate, can greatly influence the composition of carbon compounds and subsequently nitrogen availability. Climate change can therefore have a direct effect on forest ecosystem production and carbon storage through temperature and water limitations, and an indirect effect through the nitrogen cycle by affecting species composition. Model simulations of these interactions show that climate change initiates a complex set of direct and indirect responses that are sensitive to the exact nature of the project climate changes. We show results using four different climate-change projections for a location in northeastern Minnesota. Modeled forest responses to each of these climate projections is different indicating that uncertainties in the climate projections may be amplified further as a result of shifts in balance between positive and negative ecosystem feedbacks.

Estimates of indirect global warming potentials for CH4, CO and NOX

Abstract: Emissions may affect climate indirectly through chemical interactions in the atmosphere, but quantifications of such effects are difficult and uncertain due to incomplete knowledge and inadequate methods. A preliminary assessment of the climatic impact of changes in tropospheric O3 and CH4 in response to various emissions is given. For a 10% increase in the CH4 emissions the relative increase in concentration has been estimated to be 37% larger. The radiative forcing from enhanced levels of tropospheric O3 is estimated to 37% of the forcing from changes in CH4. Inclusion of indirect effects approximately doubles the climatic impact of CH4 emissions. Emissions of NOx increase tropospheric O3, while the levels of CH4 are reduced. For emissions of NOx from aircraft, the positive effects via O3 changes are significantly larger than the negative through changes in CH4. For NOx emitted from surface sources, the effects through changes in O3 and CH4 are estimated to be of similar magnitude and large uncertainty is connected to the sign of the net effect. Emissions of CO have positive indirect effects on climate through enhanced levels of tropospheric o3 and increased lifetime of CH4. These results form the basis for estimates of global warming potentials for sustained step increases in emissions.

When is it appropriate to combine expert judgments

Abstract: Rather than seeking improved methodologies, difficulty in combining expert opinion should serve as a warning flag that causes us to seek alternative modes of policy analysis. These alternatives are usually more appropriate for the real audience for our analyses. Policy analysis of climate change is too often framed in terms that amount to preparing the tools with which a benevolent world dictator could do cost-benefit analysis. This tends to overemphasize end-to-end analysis that must rely on the combined opinions of experts. This framing is unrealistic and encourages omission of important aspects of the climate problem such as its heterogeneity. Rejecting this framing in favor of alternate, less all encompassing, forms of policy analysis permits more robust results, and reduces the emphasis on combining expert opinion. While the opinions expressed here are my own, I thank Hadi Dowlatabadi, M. Granger Morgan, Ted Parson, and James Risbey for their perceptive comments.

Modeling carbon stores in oregon and washington forest products: 1900-1992

Abstract: A new model, FORPROD, for estimating the carbon stored in forest products, considers both the manufacture of the raw logs into products and the fate of the products during use and disposal. Data for historical patterns of harvest, manufacturing efficiencies, and product use and disposal were used for estimating the accumulation of carbon in Oregon and Washington forest products from 1900 to 1992. Pools examined were long- and short-term structures, paper supplies, mulch, open dumps, and landfills. The analysis indicated that of the 1,692 Tg of carbon harvested during the selected period, only 396 Tg, or 23%, is currently stored. Long-term structures and landfills contain the largest fraction of that store, holding 74% and 20%, respectively. Landfills currently have the highest rates of accumulation, but total landfill stores are relatively low because they have been used only in the last 40 years. Most carbon release has occurred during manufacturing, 45% to 60% lost to the atmosphere, depending upon the year. Sensitivity analyses of the effects of recycling, landfill decomposition, and replacement rates of long-term structures indicate that changing these parameters by a factor of two changes the estimated fraction of total carbon stored less than 2%.

Public expectation as an element of human perception of climate change

Abstract: Human expectations regarding weather and climate sometimes lead to perceptions of climate change which are not supported by observational evidence. This paper analyses two very characteristic complaints about current climate in Switzerland, i.e., the lack of snow in winter and the lack of sunshine in summer, through a statistical investigation of climatological data. As one major problem of public perception of climate in mid-latitude regions is linked to the strong variability of the climatic parameters, the paper suggests means of presenting climatic data which include a measure of this variability. Such presentations would help overcome the common confusion between the terms 'weather' and 'climate', and stress the fact that short-term extreme events are not necessarily indicative of a long-term shift in climate.

Rainfall and foliar dynamics in tropical Southern Africa: Potential impacts of global climatic change on savanna vegetation

Abstract: Foliar dynamics in tropical southern Africa are examined using meteorological satellite observations (NOAA-AVHRR) collected from 1981–1990, processed as monthly Normalized Difference Vegetation Index (NDVI) images, and resampled to 7.6 km resolution. Time series of NDVI and raingauge data are presented and analyzed using a variety of statistics. The analysis of time series from individual locations revealed positive correlations between NDVI and rainfall at semiarid locations where rainfall tended to be highly variable; whereas the relationships between these variables was insignificant in more mesic sites where the climate tended to be more predictable. In addition, there appeared to be an annual rainfall threshold of approximately 600 mm beyond which relationships between rainfall and NDVI were insignificant at the monthly time scale. Relationships between rainfall and NDVI were stronger at annual time scale, which suggests that factors other than contemporaneous rainfall account for photosynthetic activity in any given growing season. Using a rainfall surface and NDVI imagery, a large area of ‘early’ greening behavior is identified, which corresponded approximately to the distribution of mesic, plateau woodlands. These so-called, ‘miombo’ woodlands may be especially vulnerable if the arrival of spring rainfall were to undergo a positive shift in phase.

Winter severity in europe: the fourteenth century

Abstract: The fourteenth century is known to include a period of winter cooling in Central and Western Europe, but its timing and magnitude are not clearly established. An attempt to obtain a coherent picture from verified documentary evidence yielded 2133 records from a region covering Central Europe and Northern Italy, mostly originating from the ‘Monumenta Germaniae Historica’. Temperatures were assessed using semi-quantitative indices on the basis of proxy information on snow-cover, ice and untimely activity of vegetation. Results: A run of cold winters from 1303 to 1328 was followed by a run of ‘average’ winters up to 1354. Then winter temperatures were extremely variable up to 1375. For the rest of the century they fluctuated somewhat below the average of the twentieth century. The pattern in the first five decades is compared to that in the Late Maunder Minimum (1675–1715). The possible role of forcing factors (variations in solar output, North Atlantic Deep Water formation) is briefly discussed.