Showing papers on "Climate change published in 1995"

Economics Of Climate Change

Abstract: Global climate change poses a threat to the well-being of humans and other living things through impacts on ecosystem functioning, biodiversity, capital productivity, and human health. Climate change economics attends to this issue by offering theoretical insights and empirical findings relevant to the design of policies to reduce, avoid, or adapt to climate change. This economic analysis has yielded new estimates of mitigation benefits, improved understanding of costs in the presence of various market distortions or imperfections, better tools for making policy choices under uncertainty, and alternate mechanisms for allowing flexibility in policy responses. These contributions have influenced the formulation and implementation of a range of climate change policies at the domestic and international levels.

Terrestrial ecosystems and the carbon cycle

Abstract: The terrestrial biosphere plays an important role in the global carbon cycle. In the 1994 Intergovernmental Panel Assessment on Climate Change (IPCC), an effort was made to improve the quantification of terrestrial exchanges and potential feedbacks from climate, changing CO2, and other factors; this paper presents the key results from that assessment, together with expanded discussion. The carbon cycle is the fluxes of carbon among four main reservoirs: fossil carbon, the atmosphere, the oceans, and the terrestrial biosphere. Emissions of fossil carbon during the 1980s averaged 5.5 Gt y−1. During the same period, the atmosphere gained 3.2 Gt C y−1 and the oceans are believed to have absorbed 2.0 Gt C y−1. The regrowing forests of the Northern Hemisphere may have absorbed 0.5 Gt C y−1 during this period. Meanwhile, tropical deforestation is thought to have released an average 1.6 Gt C y−1 over the 1980s. While the fluxes among the four pools should balance, the average 198Ds values lead to a ‘missing sink’ of 1.4 Gt C y−1 Several processes, including forest regrowth, CO2 fertilization of plant growth (c. 1.0 Gt C y−1), N deposition (c. 0.6 Gt C y−1), and their interactions, may account for the budget imbalance. However, it remains difficult to quantify the influences of these separate but interactive processes. Uncertainties in the individual numbers are large, and are themselves poorly quantified. This paper presents detail beyond the IPCC assessment on procedures used to approximate the flux uncertainties. Lack of knowledge about positive and negative feedbacks from the biosphere is a major limiting factor to credible simulations of future atmospheric CO2 concentrations. Analyses of the atmospheric gradients of CO2 and 13 CO2 concentrations provide increasingly strong evidence for terrestrial sinks, potentially distributed between Northern Hemisphere and tropical regions, but conclusive detection in direct biomass and soil measurements remains elusive. Current regional-to-global terrestrial ecosystem models with coupled carbon and nitrogen cycles represent the effects of CO2 fertilization differently, but all suggest longterm responses to CO2 that are substantially smaller than potential leaf- or laboratory whole plant-level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO2 concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere. Critical areas for future research are continued measurements and analyses of atmospheric data (CO2 and 13CO2) to serve as large-scale constraints, process studies of the scaling from the photosynthetic response to CO2 to whole-ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.

Climate change 1994 : radiative forcing of climate change and an evaluation of the IPCC IS92 emission scenarios

Abstract: Foreword Part I. Radiative Forcing of Climate Change: A Summary for Policy Makers: Preface to WGI Report Dedication 1. CO2 and the carbon cycle 2. Other trace gases and atmospheric chemistry 3. Aerosols 4. Radiative forcing 5. Trace gas radiative fircing indices Part II. An Evaluation of the IPCC IS92 Emission Scenarios: A Summary for Policymakers: Preface to WGIII Report 6. An evaluation of the IPCC IS92 emission scenarios Appendices.

Plio-Pleistocene African Climate

Abstract: Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.

Reconstruction of solar irradiance since 1610: Implications for climate change

Abstract: Solar total and ultraviolet (UV) irradiances are reconstructed annually from 1610 to the present. This epoch includes the Maunder Minimum of anomalously low solar activity (circa 1645-1715) and the subsequent increase to the high levels of the present Modern Maximum. In this reconstruction, the Schwabe (11-year) irradiance cycle and a longer term variability component are determined separately, based on contemporary solar and stellar monitoring. The correlation of reconstructed solar irradiance and Northern Hemisphere (NH) surface temperature is 0.86 in the pre-industrial period from 1610 to 1800, implying a predominant solar influence. Extending this correlation to the present suggests that solar forcing may have contributed about half of the observed 0.55°C surface warming since 1860 and one third of the warming since 1970.

Possible role of climate in the collapse of Classic Maya civilization

Abstract: THE Maya civilization developed around 3,000 years ago in Mesoamerica, and after flourishing during the so-called Classic period, it collapsed around 750–900 AD1. It has been specula ted2–6 that climate change may have played a part in this collapse. But efforts to reconstruct the last three millennia of Mesoamerican climate using palynological methods have met with equivocal success, because human-mediated deforestation has altered regional vegetation in ways that mimic climate shifts, making it difficult to discriminate between natural and anthropogenic changes7–15. Here we use temporal variations in oxygen isotope and sediment composition in a 4.9-m sediment core from Lake Chichancanab, Mexico, to reconstruct a continuous record of Holocene climate change for the central Yucatan peninsula. The interval between 1,300 and 1,100 yr BP (AD 800–1,000) was the driest of the middle to late Holocene epoch, and coincided with the collapse of Classic Maya civilization. This continuous climate proxy record thus provides evidence of climate deterioration in the Maya region during the terminal Classic period.

Impact of climate change

Abstract: U of M, Crookston assistant professor of biology Pamela Elf works with reptile species that have their sex determined by temperature while in the embryonic stage. Through her research, Elf is pin pointing exactly what makes reptiles male or female and how changes in the temperature outside aff ect reptile embryos. Her work can help determine the worldwide impact of global warming and climate change.

Climate Signal Detection Using Wavelet Transform: How to Make a Time Series Sing

Abstract: In this paper, the application of the wavelet transform (WT) to climate time series analyses is introduced. A tutorial description of the basic concept of WT, compared with similar concepts used in music, is also provided. Using an analogy between WT representation of a time series and a music score, the authors illustrate the importance of local versus global information in the time–frequency localization of climate signals. Examples of WT applied to climate data analysis are demonstrated using analytic signals as well as real climate time series. Results of WT applied to two climate time series—that is, a proxy paleoclimate time series with a 2.5-Myr deep-sea sediment record of δ18 O and a 140-yr monthly record of Northern Hemisphere surface temperature—are presented. The former shows the presence of a 40-kyr and a 100-kyr oscillation and an abrupt transition in the oscillation regime at 0.7 Myr before the present, consistent with previous studies. The latter possesses a myriad of oscillatory modes from...

Politics of climate change

Abstract: Sociólogo britânico nascido em Edmonton, norte de Londres, Anthony Giddens publicou mais de trinta livros a respeito de díspares temáticas, tais como: teoria sociológica clássica, nacionalidade e nacionalismo, estrutura de classes, divisão do trabalho, globalização, sexualidade e família. Educado na University of Hull e na London School of Economics, Anthony Giddens atuou como assessor do Primeiro Ministro britânico trabalhista, Tony Blair. Além disso, prestou consultoria para líderes políticos australianos, asiáticos e latino-americanos. O livro The politics of climate change foi publicado em inglês no ano de 2009, pela editora britânica Polity. A tradução para a língua portuguesa, intitulada “A política da mudança climática”, foi publicada em 2010, pela editora Zahar. O objetivo do livro é apresentar uma abordagem ampla e multissetorial acerca das políticas de mitigação e de adaptação The politics of climate change

Trends in high-frequency climate variability in the twentieth century

Abstract: HIGH-FREQUENCY climate variability is a fundamental aspect of climate. Understanding climate change demands attention to changes in climate variability and extremes1, but knowledge of the recent behaviour of these variables has been limited by the unavailability of long-term high-resolution data. Climate simulations incorporating increased greenhouse-gas concentrations2-9 indicate that a warmer climate could result in a decrease in high-frequency temperature variability (analogous to the decrease in variability observed from the poles to the tropics, and from winter to summer10) and an increase in the proportion of precipitation occurring in extreme events. Here we analyse high-frequency temperature and precipitation data from hundreds of sites spread over Australia, China, the former Soviet Union and the United States over the past 30 to 80 years. Day-to-day temperature variability is seen to have decreased in the Northern Hemisphere, and-at least within the United States-the proportion of total precipitation contributed by extreme, one-day events has increased significantly. We find that although the notion of a recent increase in interannual temperature variability is supported by data from the past few decades11, the longer data records indicate that this trend is an aberration.

Mechanisms of shrubland expansion: land use, climate or CO2?

Abstract: Encroachment of trees and shrubs into grasslands and the ‘thicketization’ of savannas has occurred worldwide over the past century. These changes in vegetation structure are potentially relevant to climatic change as they may be indicative of historical shifts in climate and as they may influence biophysical aspects of land surface-atmosphere interactions and alter carbon and nitrogen cycles. Traditional explanations offered to account for the historic displacement of grasses by woody plants in many arid and semi-arid ecosystems have centered around changes in climatic, livestock grazing and fire regimes. More recently, it has been suggested that the increase in atmospheric CO2 since the industrial revolution has been the driving force. In this paper we evaluate the CO2 enrichment hypotheses and argue that historic, positive correlations between woody plant expansion and atmospheric CO2 are not cause and effect.

Vegetation/ecosystem modeling and analysis project: Comparing biogeography and biogeochemistry models in a continental-scale study of terrestrial ecosystem responses to climate change and CO2 doubling

Abstract: VEMAP Members 1 Abstract. We compare the simulations of three biogeography models (BIOME2, Dynamic Global Phytogeography Model (DOLY), and Mapped Atmosphere-Plant Soil System (MAPSS)) and three biogeochemistry models (BIOME-BGC (BioGeochemistry Cycles), CENTURY, and Terrestrial Ecosystem Model (TEM)) for the conterminous United States under contemporary conditions of atmospheric CO2 and climate. We also compare the simulations of these models under doubled CO2 and a range of climate scenarios. For contemporary conditions, the biogeography models successfully simulate the geographic distribution of major vegetation types and have similar estimates of area for forests (42 to 46% of the conterminous United States), grasslands (17 to 27%), savannas (15 to 25%), and shrublands (14 to 18%). The biogeochemistry models estimate similar continental-scale net primary production (NPP; 3125 to 3772 x 10 2 gC yr ') and total carbon storage (108 to 118 5 x 10 gC) for contemporary conditions. Among the scenarios of doubled CO2 and associated equilibrium climates produced by the three general circulation models (Oregon State University (OSU), Geophysical Fluid Dynamics Laboratory (GFDL), and United Kingdom Meteorological Office (UKMO)), all three biogeography models show both gains and losses of total forest area depending on the scenario (between 38 and 53% of conterminous United States area). The only consistent gains in forest area with all three models (BIOME2, DOLY, and MAPSS) were under the GFDL scenario due to large increases in precipitation. MAPSS lost forest area under UKMO, DOLY under OSU, and BIOME2 under both UKMO and OSU. The variability in forest area estimates occurs because the hydrologic cycles of the biogeography models have different sensitivities to increases in temperature and CO2. However, in general, the biogeography models produced broadly similar results when incorporating both climate change and elevated CO2 concentrations. For these scenarios, the NPP estimated by the biogeochemistry models increases between 2% (BIOME-BGC with UKMO climate) and 35% (TEM with UKMO climate). Changes in total carbon storage range from losses of 33% (BIOME-BGC with UKMO climate) to gains of 16% (TEM with OSU climate). The CENTURY responses of NPP and carbon storage are positive and intermediate to the responses of BIOME-BGC and TEM. The variability in carbon cycle responses occurs because the hydrologic and nitrogen cycles of the biogeochemistry models have different sensitivities to increases in temperature and CO2. When the biogeochemistry models are run with the vegetation distributions of the biogeography models, NPP ranges from no response (BIOME-BGC with all three biogeography model vegetations for UKMO climate) to increases of 40% (TEM with MAPSS vegetation for OSU climate). The total carbon storage response ranges from a decrease of 39% (BIOME-BGC with MAPSS vegetation for UKMO climate) to an increase of 32% (TEM with MAPSS vegetation for OSU and GFDL climates). The UKMO responses of BIOME-BGC with MAPSS vegetation are primarily caused by decreases in forested area and temperature-induced water stress. The OSU and GFDL responses of TEM with MAPSS vegetations are primarily

Valuing Climate Change: The Economics of the Greenhouse

Abstract: Within only a few years, global warming has emerged from scientific speculation into an environmental threat of worldwide concern. Yet the scientific community remains uncertain as to the long-term trends and effects of climate change, and this uncertainty has been seized on as justification for inaction by an international community reluctant to bear the costs of policies to reduce greenhouse gas emissions. Valuing Climate Change presents concrete, economic evidence of the need for action. Fankhauser assesses the costs of a doubling of GHG emissions to be a significant percentage of gross world product; a figure which he then compares to the costs of reducing emissions. In his comparison, he looks at regional as well as global estimates of damage, and takes account of the non-climate change benefits of GHG reductions, such as a switch in the energy sector to cleaner technologies or renewable fuels, and the impacts on transport, with reduced congestion and improved air quality. It is clear that the stakes are high, and Fankhauser believes that tougher targets may be needed than those set out in the Framework Convention on Climate Change. He assesses the optimum policy responses to GHG reduction, the likely instruments for achieving it and the potential for international cooperation in dealing with the problems. This is a major contribution to the rapidly changing debate on global warming.

The Responses of Species to Climate Over Two Centuries: An Analysis of the Marsham Phenological Record, 1736-1947

Abstract: 1 The Marsham phenological data have been 'rediscovered' several times. This unique data set, spanning two centuries, consists of first dates of observation, or 'indications of spring', for 27 phenological events which relate to over 20 species of plants and animals. 2 This paper extends the 1926 appraisal of the data from 1736 to 1925 by adding the 22 years up to 1947, when publication of the record ceased. 3 The Marsham data are examined in relation to Manley's central England monthly temperature data and Craddock's annual rainfall data and are further examined for unexplained trends over time. 4 Most of the phenological variables were significantly related to climatic variables or changed through time. 5 An appraisal of the historical response of flora and fauna to climate was made and allowed us to predict changes in species performance due to climate change in the future. If commonly used climate scenarios are accurate we predict that most or all of the indications of spring noted in the Marsham record will occur earlier in the calendar year.

Climate change and northern fish populations

Abstract: This title provides a summary of 57 studies and six poster sessions related to evidence of climate change, and its effects on freshwater and marine aquatic environments, and on the dynamics of fish populations and fisheries. Numerous examples of the relationships between fish abundance trends and the environment are included. Most investigations are from the North Pacific Ocean, but studies done in the North Atlantic Ocean, the Bering Sea, the Yellow Sea, and selected freshwater lakes are also included. The effect of climate change on cod, pollock, salmon, herring, Dungeness crab, Japanese sardine, and Californian anchovy (among others) is discussed.

Potential impact of global climate change on malaria risk.

Abstract: The biological activity and geographic distribution of the malarial parasite and its vector are sensitive to climatic influences, especially temperature and precipitation. We have incorporated General Circulation Model-based scenarios of anthropogenic global climate change in an integrated linked-system model for predicting changes in malaria epidemic potential in the next century. The concept of the disability-adjusted life years is included to arrive at a single measure of the effect of anthropogenic climate change on the health impact of malaria. Assessment of the potential impact of global climate change on the incidence of malaria suggests a widespread increase of risk due to expansion of the areas suitable for malaria transmission. This predicted increase is most pronounced at the borders of endemic malaria areas and at higher altitudes within malarial areas. The incidence of infection is sensitive to climate changes in areas of Southeast Asia, South America, and parts of Africa where the disease is less endemic; in these regions the numbers of years of healthy life lost may increase significantly. However, the simulated changes in malaria risk must be interpreted on the basis of local environmental conditions, the effects of socioeconomic developments, and malaria control programs or capabilities.

The damage costs of climate change toward more comprehensive calculations

Abstract: It is argued that estimating the damage costs of a certain benchmark climate change is not sufficient. What is needed are cost functions and confidence intervals. Although these are contained in the integrated models and their technical manuals, this paper brings them into the open in order to stimulate discussion. After briefly reviewing the benchmark climate change damage costs, region-specific cost functions are presented which distinguish tangible from intangible losses and the losses due to a changing climate from those due to a changed climate. Furthermore, cost functions are assumed to be quadratic, as an approximation of the unknown but presumably convex functions. Results from the damage module of the integrated climate economy modelFUND are presented. Next, uncertainties are incorporated and expected damages are calculated. It is shown that because of convex loss functions and right-skewed uncertainties, the risk premium is substantial, calling for more action than analysis based on best-guess estimates. The final section explores some needs for further scientific research.

Mission to planet Earth: Role of clouds and radiation in climate

Abstract: The role of clouds in modifying the earth's radiation balance is well recognized as a key uncertainty in predicting any potential future climate change. This statement is true whether the climate change of interest is caused by changing emissions of greenhouse gases and sulfates, deforestation, ozone depletion, volcanic eruptions, or changes in the solar constant. This paper presents an overview of the role of the National Aeronautics and Space Administration's Earth Observing System (EOS) satellite data in understanding the role of clouds in the global climate system. The paper gives a brief summary of the cloud/radiation problem, and discusses the critical observations needed to support further investigations. The planned EOS data products are summarized, including the critical advances over current satellite cloud and radiation budget data. Key advances include simultaneous observation of radiation budget and cloud properties, additional information on cloud particle size and phase, improved detection ...

Subjective judgments by climate experts.

Abstract: Structured interviews using `expert elicitation` methods drawn from decision analysis were conducted with 16 leading U.S. climate scientists. We obtained quantitative, probabilistic judgments about a number of key climate variables and about the nature of the climate system. We also obtained judgments about the relative contributions of various factors to the uncertainty in climate sensitivity. We found strong support for the importance of convection/water vapor feedback and of cloud optical properties. A variety of questions were posed to elicit judgments about future research needs and the possible sources and magnitude of future surprises. The results reveal a rich diversity of expert opinion and, aside from climate sensitivity, a greater degree of disagreement than is often conveyed in scientific consensus documents. Research can make valuable contributions, but we interpret our results to mean that overall uncertainty about the geophysics of climate change is not likely to be reduced dramatically in the next few decades. 22 refs., 5 figs., 2 tabs.

Modelling present and potential future ranges of some European higher plants using climate response surfaces : The ecologist and environmental history : a British perspective

Abstract: It is hypothesized that the principal features of higher plant distributions at continental scales are determined by the macroclimate. Bioclimate data have been computed on a 50 km grid across Europe. Along with published maps of higher plant distributions based upon the same grid, these data have been used to derive climate response surfaces that model the relationship between a species' distribution and the present climate. Eight species representative of a variety of phytogeographic patterns have been investigated. The results support the hypothesis that the European distributions of all eight species are principally determined by macroclimate and illustrate the nature of the climatic constraints upon each species. Simulated future distributions in equilibrium with 2 x CO 2 climate scenarios derived from two alternative GCMs show that all of the species are likely to experience major shifts in their potential range if such climatic changes take place. Some species may suffer substantial range and population reductions and others may face the threat of extinction. The rate of the forecast climate changes is such that few, if any, species may be able to maintain their ranges in equilibrium with the changing climate. In consequence, the transient impacts upon ecosystems will be varied but often may lead to a period of dominance by opportunist, early-successional species. Our simulations of potential ranges take no account of such factors as photoperiod or the direct effects of CO2, both of which may substantially alter the realized future equilibrium.

Application of inventory data for estimating characteristics of and regional climate-change effects on mountain glaciers: a pilot study with the European Alps

Abstract: A parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate-change effects on mountain glaciers For past and potential climate scenarios, glacier changes for assumed mass-balance changes are calculated as step functions between steady-state conditions for time intervals that approximately correspond to the characteristic dynamic response time (a few decades) of the glaciers In order to test the procedure, a pilot study was carried out in the European Alps where detailed glacier inventories had been compiled around the mid-1970s Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s; strongly negative mass balances are likely to have caused a loss of about 10–20% of this total volume during the decade 1980–90 Backward calculation of glacier-length changes using a mean annual mass balance of 025m wea−1 since the end of the “Little Ice Age” around 1850 AD gives considerable scatter but satisfactory overall results as compared with long-term observations The total loss of Alpine surface ice mass since 1850 can be estimated at about half the original value An acceleration of this development, with annual mass losses of around 1 m a−1 or more as anticipated from IPCC scenario A for the coming century, could eliminate major parts of the presently existing Alpine ice volume within decades

A coupled atmosphere‐ocean model for transient climate change studies

Abstract: A new coupled atmosphere‐ocean model has been developed for climate predictions at decade to century scales. The atmospheric model is similar to that of Hansen et al. (1983) except that the atmospheric dynamic equations for mass and momentum are solved using Arakawa and Lamb's (1977) C grid scheme and the advection of potential enthalpy and water vapour uses the linear upstream scheme (Russell and Lerner, 1981). The new global ocean model conserves mass, allows for divergent flow, has a free surface and uses the linear upstream scheme for the advection of potential enthalpy and salt. Both models run at 4° × 5° resolution, with 9 vertical layers for the atmosphere and 13 layers for the ocean. Twelve straits are included, allowing for subgrid‐scale water flow. Runoff from land is routed into appropriate ocean basins. Atmospheric and oceanic surface fluxes are of opposite sign and are applied synchronously. Flux adjustments are not used. Except for partial strength alternating binomial filters (Shap...

Impact of climate change on grassland production and soil carbon worldwide

Abstract: The impact of climate change and increasing atmospheric CO2 was modelled for 31 temperate and tropical grassland sites, using the CENTURY model. Climate change increased net primary production, except in cold desert steppe regions, and CO2 increased production everywhere. Climate change caused soil carbon to decrease overall, with a loss of 4 Pg from global grasslands after 50 years. Combined climate change and elevated CO2 increased production and reduced global grassland C losses to 2 Pg, with tropical savannas becoming small sinks for soil C. Detection of statistically significant change in plant production would require a 16% change in measured plant production because of high year to year variability in plant production. Most of the predicted changes in plant production are less than 10%.

World Agriculture and Climate Change: Economic Adaptations

Abstract: Recent studies suggest that global increases in temperature and changes in precipitation patterns during the next century will affect world agriculture. Because farmer adaptations, however, these changes are not likely to imperil world food production. Nevertheless, world production of all goods and services may decline if climate change is severe enough or if cropland expansion is hindered. Impacts are not equally distributed around the world. Agricultural production may increase in polar and alpine areas, but decrease in tropical and some other areas. In the United States, soil moisture losses may reduce agricultural production in the Corn Belt or Southeast.

Chapter 10 - Climatic effects of changing atmospheric aerosol levels

Abstract: This chapter discusses the various sources of atmospheric aerosols, their potential change in the future, and the effects that aerosols have on climate through perturbation of the radiation balance and through modification of cloud properties. Tremendous amounts of dust are mobilized by high winds in the desert regions of the globe, especially the Sahara, Gobi, and the Australian deserts. The dust plumes originating from these large deserts are the most conspicuous features in maps of the global distribution of atmospheric haze obtained from satellite data. The size of the desert regions and the intensity of the winds over them obviously have a great influence on the amounts of dust mobilized, and on the heights to which it is lofted. Changing mineral aerosol burdens have also been associated with climatic change in the past. Analysis of the mineral aerosol content of Antarctic ice cores shows elevated levels of soil dust during the ice ages, when large areas on the continental shelves were open to erosion by intense winds over the southern Hemisphere continents.

Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia

Abstract: IN the current debate on the magnitude of modern-day climate change, there is a growing appreciation of the importance of long, high-resolution proxies of past climate1–3. Such records provide an indication of natural (pre-anthropogenic) climate variability, either singly at specific geographical locations or in combination on continental and perhaps even hemispheric scales4. There are, however, relatively few records that are well dated, of high resolution and of verifiable fidelity in terms of climate response, and conspicuously few that extend over a thousand years or more5. Here we report a tree-ring-based reconstruction of mean summer temperatures over the northern Urals since AD 914. This record shows that the mean temperature of the twentieth century (1901–90) is higher than during any similar period since AD 914.

Coastal megacities and climate change

Abstract: Rapid urbanization is projected to produce 20 coastal megacities (population exceeding 8 million) by 2010. This is mainly a developing world phenomenon: in 1990, there were seven coastal megacities in Asia (excluding those in Japan) and two in South America, rising by 2010 to 12 in Asia (including Istanbul), three in South America and one in Africa. All coastal locations, including megacities, are at risk to the impacts of accelerated global sea-level rise and other coastal implications of climate change, such as changing storm frequency. Further, many of the coastal megacities are built on geologically young sedimentary strata that are prone to subsidence given excessive groundwater withdrawal. At least eight of the projected 20 coastal megacities have experienced a local orrelative rise in sea level which often greatly exceeds any likely global sea-level rise scenario for the next century. The implications of climate change for each coastal megacity vary significantly, so each city requires independent assessment. In contrast to historical precedent, a proactive perspective towards coastal hazards and changing levels of risk with time is recommended. Low-cost measures to maintain or increase future flexibility of response to climate change need to be identified and implemented as part of an integrated approach to coastal management.