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This paper investigates patterns of daily evolutions of CO in the lower atmosphere at a rural site over 2 years. The first part is devoted to observation analysis using a clustering procedure. However, direct application of the average-linkage method yielded undesirable results. In order to improve this procedure, data were previously processed using three smoothing procedures: the kernel smoothing method, the elliptical procedure, and the second-order cylindrical model. These procedures successfully revealed that clusters were based on daily concentration and range. However, the unequal distribution of frequencies in the clusters proved to be a noticeable disadvantage. Four alternative and simpler schemes for grouping observations were proposed in the second part of this paper. The first, comprising groups following fixed values of daily range and mean concentration, provided a sharp contrast between spring, with a marked daily cycle linked to the biological peak, and summer with a smooth daily cycle and low concentration when the biological minimum was reached. The second scheme is based on isopleth analysis and considers observation groups of similar frequencies following an increasing order of mean concentration and daily range. As a result, seasonal evolution was less marked. Straight lines were the borders for groups in the third scheme, which was similar and simpler than the second. The final scheme divided observations by means of equations of daily range as a quadratic function of daily concentration. The groups formed may be linked to seasons, with the group prevailing in summer presenting a noticeable daily range. [ABSTRACT FROM AUTHOR]

The practice of using climate metrics to estimate carbon dioxide equivalent emissions has long been subject to scientific discussion. One strand of this literature has analysed whether the choice of metric affects the relative cost-effectiveness of options for climate change abatement, but there has been little discussion on the effect of metric choices on cost-effective abatement of near-term climate forcers (NTCFs). These NTCFs are air pollutants primarily regulated by policies outside the climate policy arena and their estimated carbon dioxide equivalent emissions are not typically considered in the evaluation of cost-effective abatement. However, the attention to NTCFs as climate forcers has increased during the last decade. The objective of this paper is to identify whether the relative cost-effectiveness of different NTCF abatement options is robust to climate metric choices. We assess nine plausible NTCF abatement options available in Sweden (with negligible effect on long-lived GHG emissions) and evaluate the robustness of the ranking of these, according to their estimated cost-effectiveness. Different metric designs are considered as well as climate impact uncertainty of NTCFs, with corresponding uncertainty in metric values. The results indicate that the choice of metric has little effect on the ranking of the options according to their cost-effectiveness, with options affecting NOx indicated as an exception. This suggests that the choice of metric utilised when calculating cost-effectiveness of NTCF abatement options is likely to have minor effect on which NTCF abatement options should be targeted for policy interventions (if NOx emissions are not significantly affected). [ABSTRACT FROM AUTHOR]

The Orbiting Carbon Observatory-2 (OCO-2) collects infrared spectra from which atmospheric properties are retrieved. OCO-2 operational data processing uses optimal estimation (OE), a state-of-the-art approach to inference of atmospheric properties from satellite measurements. One of the main advantages of the OE approach is computational efficiency, but it only characterizes the first two moments of the posterior distribution of interest. Here we obtain samples from the posterior using a Markov Chain Monte Carlo (MCMC) algorithm and compare this empirical estimate of the true posterior to the OE results. We focus on 600 simulated soundings that represent the variability of physical conditions encountered by OCO-2 between November 2014 and January 2016. We treat the two retrieval methods as ensemble and density probabilistic forecasts, where the MCMC yields an ensemble from the posterior and the OE retrieval result provide the first two moments of a normal distribution. To compare these methods, we apply both univariate and multivariate diagnostic tools and proper scoring rules. The general impression from our study is that when compared to MCMC, the OE retrieval performs reasonably well for the main quantity of interest, the column-averaged CO2 concentration XCO2, but not for the full state vector X which includes a profile of CO2 concentrations over 20 pressure levels, as well as several other atmospheric properties.Supplementary materials accompanying this paper appear on-line. [ABSTRACT FROM AUTHOR]

A review of the present status of the global warming science is presented in this paper. The term global warming is now popularly used to refer to the recent reported increase in the mean surface temperature of the earth; this increase being attributed to increasing human activity and in particular to the increased concentration of greenhouse gases (carbon dioxide, methane and nitrous oxide) in the atmosphere. Since the mid to late 1980s there has been an intense and often emotional debate on this topic. The various climate change reports (1996, 2001) prepared by the IPCC (Intergovernmental Panel on Climate Change), have provided the scientific framework that ultimately led to the Kyoto protocol on the reduction of greenhouse gas emissions (particularly carbon dioxide) due to the burning of fossil fuels. Numerous peer-reviewed studies reported in recent literature have attempted to verify several of the projections on climate change that have been detailed by the IPCC reports. The global warming debate as presented by the media usually focuses on the increasing mean temperature of the earth, associated extreme weather events and future climate projections of increasing frequency of extreme weather events worldwide. In reality, the climate change issue is considerably more complex than an increase in the earth’s mean temperature and in extreme weather events. Several recent studies have questioned many of the projections of climate change made by the IPCC reports and at present there is an emerging dissenting view of the global warming science which is at odds with the IPCC view of the cause and consequence of global warming. Our review suggests that the dissenting view offered by the skeptics or opponents of global warming appears substantially more credible than the supporting view put forth by the proponents of global warming. Further, the projections of future climate change over the next fifty to one hundred years is based on insufficiently verified climate models and are therefore not considered reliable at this point in time. [ABSTRACT FROM AUTHOR]

Researchers have proposed that a significant portion of the post-glacial rise in atmospheric CO could be due to the respiration of permafrost carbon stocks that formed over the course of glaciation. In this paper, we used the University of Victoria Earth System Climate Model v. 2.9 to simulate the deglacial and interglacial carbon cycle from the last glacial maximum to the present. The model's sensitivity to mid and high latitude terrestrial carbon storage is evaluated by including a 600 Pg C carbon pool parameterized to respire in concert with decreases in ice sheet surface area. The respiration of this stored carbon during the early stages of deglaciation had a large effect on the carbon cycle in these simulations, allowing atmospheric CO to increase by 40 ppmv in the model, with an additional 20 ppmv increase occurring in the case of a more realistic, prescribed CO radiative warming. These increases occurred prior to large-scale carbon uptake due to the reestablishment of boreal forests and peatlands in the proxy record (beginning in the early Holocene). Surprisingly, the large external carbon input to the atmosphere and oceans did not increase sediment dissolution and mean ocean alkalinity relative to a control simulation without the high latitude carbon reservoir. In addition, our simulations suggest that an early deglacial terrestrial carbon release may come closer to explaining some observed deglacial changes in deep-ocean carbonate concentrations than simulations without such a release. We conclude that the respiration of glacial soil carbon stores may have been an important contributor to the deglacial CO rise, particularly in the early stages of deglaciation. [ABSTRACT FROM AUTHOR]

This paper designs a comprehensive approach based on the engineering machine/ system concept, to model, analyze, and assess the level of carbon dioxide (CO) exchange between the atmosphere and terrestrial ecosystems, which is an important factor in understanding changes in global climate. The focus of this article is on spatial patterns and on the correlation between levels of CO fluxes and a variety of influencing factors in eco-environments. The engineering/machine concept used is a system protocol that includes the sequential activities of design, test, observe, and model. This concept is applied to explicitly include various influencing factors and interactions associated with CO fluxes. To formulate effective models of a large and complex climate system, this article introduces a modeling technique that will be referred to as stochastic filtering analysis of variance (SF-ANOVA). The CO flux data observed from some sites of AmeriFlux are used to illustrate and validate the analysis, prediction, and globalization capabilities of the proposed engineering approach and the SF-ANOVA technique. The SF-ANOVA modeling approach was compared to stepwise regression, ridge regression, and neural networks. The comparison indicated that the proposed approach is a valid and effective tool with similar accuracy and less complexity than the other procedures. [ABSTRACT FROM AUTHOR]

The interrelationship between the cryosphere and the climate is not always operating on Earth over a scale of billions or millions of years. Indeed, most of the time, the Earth is regulated at temperatures such that no ice sheet exists. Nevertheless, it is very fruitful to understand the conditions where and when ice sheets were triggered during the Earth's history. This paper deals with the paleoclimate and the cryosphere in the last 4.6 Ga and explains the different processes that make the climate of the first 4 billion years warm despite the weaker solar luminosity. We also describe the more recent evolution in the last 65 million years when a global decrease in atmospheric CO from around 4 PAL to 1 PAL was associated with a global cooling (1 PAL present atmospheric level = 280 ppm). It is in this context that the Quaternary occurred characterized by low atmospheric CO and the presence of two perennial ice sheets in Greenland and Antarctica. The last million years are certainly the most documented since direct and reliable CO measurements are available. They are characterized by a complex climate/cryosphere dynamics leading to oscillations between long glacial periods with four ice sheets and shorter ones with only two ice sheets (interglacial). We are currently living in one of those interglacials, generally associated with a CO level of 280 ppm. Presently, anthropogenic activities are seriously perturbing the carbon cycle and the atmospheric CO content and therefore the climate. The last but not least question raised in this paper is to investigate whether the anthropogenic perturbation may lead to a melting of the ice sheets. [ABSTRACT FROM AUTHOR]

It has been shown previously that the awareness and concern of the general public about global warming is not only a function of scientific information. Both psychological and sociological factors affect the willingness of laypeople to acknowledge the reality of global warming, and to support climate policies of their home countries. In this paper, I analyse a cross-national dataset of public concern about global warming, utilising data from 46 countries. Based on earlier results at the national and regional level, I expect concern to be negatively correlated to national measures of wealth and carbon dioxide emissions. I find that gross domestic product is indeed negatively correlated to the proportion of a population that regards global warming as a serious problem. There is also a marginally significant tendency that nations’ per capita carbon dioxide emissions are negatively correlated to public concern. These findings suggest that the willingness of a nation to contribute to reductions in greenhouse gas emissions decreases with its share of these emissions. This is in accordance with psychological findings, but poses a problem for political decision-makers. When communicating with the public, scientists ought to be aware of their responsibility to use a language that is understood by laypeople. [ABSTRACT FROM AUTHOR]

Fire is the major stand-renewing disturbance in the circumboreal forest. Weather and climate are the most important factors influencing fire activity and these factors are changing due to human-caused climate change. This paper discusses and synthesises the current state of fire and climate change research and the potential direction for future studies on fire and climate change. In the future, under a warmer climate, we expect more severe fire weather, more area burned, more ignitions and a longer fire season. Although there will be large spatial and temporal variation in the fire activity response to climate change. This field of research allows us to better understand the interactions and feedbacks between fire, climate, vegetation and humans and to identify vulnerable regions. Lastly, projections of fire activity for this century can be used to explore options for mitigation and adaptation. [ABSTRACT FROM AUTHOR]

The greenhouse gas emissions scenarios published by the IPCC in the Special Report on Emission Scenarios (SRES) continue to serve as a primary basis for assessing future climate change and possible response strategies. These scenarios were developed between 1996 and 1999 and sufficient time has now passed to make it worth examining their consistency with more recent data and projections. The comparison performed in this paper includes population, GDP, energy use, and emissions of CO2, non-CO2 gases and sulfur. We find the SRES scenarios to be largely consistent with historical data for the 1990-2000 period and with recent projections. Exceptions to this general observation include (1) in the long-term, relatively high population growth assumptions in some regions, particularly in the A2 scenario; (2) in the medium-term, relatively high economic growth assumptions in the LAM (Latin America, Africa and Middle East) region in the A1 scenario; (3) in the short-term, CO2 emissions projections in Al that are somewhat higher than the range of current scenarios; and (4) substantially higher sulfur emissions in some scenarios than in historical data and recent projections. In conclusion, given the relatively small inconsistencies for use as global scenarios there seems to be no immediate need for a large-scale IPCC-led update of the SRES scenarios that is solely based on the SRES scenario performance vis-a-vis data for the 1990-2000 period and/or more recent projections. Based on reported findings, individual research teams could make, and in some cases already have made, useful updates of the scenarios. [ABSTRACT FROM AUTHOR]

Summary Current predictions of the effects of climate change indicate that the Arctic may experience a larger than average increase in temperature with consequent changes to the length of the snow-free active summer period, winter snow depth and amount and frequency of summer precipitation being highly probable. This paper reports on measurements of carbon dioxide flux at a high arctic site at Ny-Ålesund (78° 56′ N, 11° 55′ E), Svalbard and the physical climate variables that largely control this flux. It is shown that during three important precipitation-free periods of the active summer period, namely post snowmelt, high summer, and early autumn, the net balance between CO2 flux from the soil (due to respiration of roots and soil organisms) and CO2 assimilation by the vegetation is controlled largely by soil temperature and solar radiation. A simple combined photosynthetic assimilation-soil respiration model is shown to be capable of simulating the net CO2 flux during mid-summer, but is less proficient in the post snowmelt period and in early autumn when the simple models’ inability to simulate the effects of emergent growth and ponding during the former and senescence, freezing temperatures and dew during the latter indicates the need for a more complex descriptive model. The net CO2 flux during the measurement periods progresses from a net CO2 source of 0.3 gC m-2 d-1 during late snowmelt to a mid summer net CO2 sink of -0.39 gC m-2 d-1, returning to a net CO2 source of 0.1 gC m-2 d-1 in the early autumn. Simple extrapolation of the data indicates that, during the active summer season in 1995, this site was a net sink of CO2 of approximately - 9 gC m-2. [ABSTRACT FROM AUTHOR]

In many East Asia regions, spring (from March to May) precipitation is an important restricting factor to vegetation growth, and atmospheric circulation system may influence spring precipitation patter. It is helpful to under the response of ecosystem to climate change by studying the influence of atmospheric circulation system on the coupling relationship between spring net primary productivity and precipitation. Driving CASA (Carnegie-Ames-Stanford Approach) NPP (Net Primary Productivity) model, we estimated spring NPP for East Asia area (70°E–1 70°E, 10°N–70°N) from 1982 to 1999, and by the method of singular value decomposition we further analyzed the coupling features of spring NPP with precipitation. The result showed that the response features of NPP to precipitation were mainly embodied within the leading six NPP-precipitation paired-modes. The interpretation rates of the leading six paired-modes to the covariance of NPP-precipitation were 42.91, 23.29, 9.96, 5.60, 5.04 and 3.95%, respectively, and total to 90.75%. The temporal correlation coefficients of the leading six paired-modes were 0.830, 0.889, 0.841, 0.747, 0.912 and 0.923, respectively, and all the correlations were significant at significant level of 0.001. In some high latitude regions, there was no obviously corresponding relationship between NPP and precipitation in the leading two paired-modes, and the reason of it may be that spring temperature was the main restricting factor to NPP. In middle and low latitude regions, the effect of precipitation on NPP was relatively more notable. Nine atmospheric circulation factors in spring affected the patterns of NPP and precipitation greatly, and the regions with interpretation rate over 50% shared 60.41 and 65.58% of the whole study area, respectively. [ABSTRACT FROM AUTHOR]

Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO2) and methane (CH4) are the most important, owing to their maximum contribution to the net radiative forcing of the Earth. India is undergoing rapid economic development, where fossil fuel emissions have increased drastically in the last three decades. Apart from the anthropogenic activities, the GHGs dynamics in India are governed by the biospheric process and monsoon circulation; however, these aspects are not well addressed yet. Towards this, we have measured CO2 and CH4 concentration at Sinhagad, located on the Western Ghats in peninsular India. The average concentrations of CO2 and CH4 observed during the study period are 406.05 ± 6.36 and 1.97 ± 0.07 ppm (µ ± 1σ), respectively. They also exhibit significant seasonal variabilities at this site. CH4 (CO2) attains its minimum concentration during monsoon (post-monsoon), whereas CO2 (CH4) reaches its maximum concentration during pre-monsoon (post-monsoon). CO2 poses significant diurnal variations in monsoon and post-monsoon. However, CH4 exhibits a dual-peak like pattern in pre-monsoon. The study suggests that the GHG dynamics in the western region of India are significantly influenced by monsoon circulation, especially during the summer season. [ABSTRACT FROM AUTHOR]

Future levels of climate change depend not only on carbon emissions but also on carbon uptake by the land and the ocean. Here we are using the Earth system model (ESM1) version of the Australian Community Climate and Earth System Simulator (ACCESS) to explore the potential and impact of removing carbon dioxide (CO2) from the atmosphere through the climate and carbon cycle reversibility experiment. This experiment builds on the standard Coupled Model Intercomparison Project (CMIP) experiment, increasing CO2 at 1% per year until 4xCO2 is reached. The atmospheric CO2 levels are then decreased at the same rate which brings the CO2 back to pre-industrial levels. We then continue to run the model with constant CO2 for another 350 years. Our analysis focuses on the response of the land carbon cycle. We find that carbon stores are largely reversible at the global scale over the timescale of changing CO2. However, carbon stores continue to decrease after CO2 returns to its initial value, and the land loses another 40 Pg of carbon (PgC) with the largest change in the tropics. It takes about 300 years beyond the period of changing CO2 for the carbon stores to recover. Interestingly, we saw strong regional variations in the strength of the land response to changing CO2. Australia showed the largest increase/decrease in biomass carbon (about 40%) and the largest variability in productivity, which was strongly correlated with rainfall. This highlights the importance of assessing the regional response to understanding the processes underlying the response and the sensitivity of these processes within each model. This understanding will benefit future multi-model analyses of this reversibility experiment. It also illustrates more generally the potential to use Earth system model experiments as part of the evaluation of proposed applications of carbon dioxide removal (CDR) technologies. As such, we recommend that these types of modelling experiments be included when mitigation policies are developed. [ABSTRACT FROM AUTHOR]

For aiming to keep global warming well-below 2 °C and pursue efforts to limit it to 1.5 °C, as set out in the Paris Agreement, a full-fledged assessment of negative emission technologies (NETs) that remove carbon dioxide from the atmosphere is crucial to inform science-based policy making. With the Paris Agreement in mind, we re-analyse available scenario evidence to understand the roles of NETs in 1.5 °C and 2 °C scenarios and, for the first time, link this to a systematic review of findings in the underlying literature. In line with previous research, we find that keeping warming below 1.5 °C requires a rapid large-scale deployment of NETs, while for 2 °C, we can still limit NET deployment substantially by ratcheting up near-term mitigation ambition. Most recent evidence stresses the importance of future socio-economic conditions in determining the flexibility of NET deployment and suggests opportunities for hedging technology risks by adopting portfolios of NETs. Importantly, our thematic review highlights that there is a much richer set of findings on NETs than commonly reflected upon both in scientific assessments and available reviews. In particular, beyond the common findings on NETs underpinned by dozens of studies around early scale-up, the changing shape of net emission pathways or greater flexibility in the timing of climate policies, there is a suite of "niche and emerging findings", e.g. around innovation needs and rapid technological change, termination of NETs at the end of the twenty-first century or the impacts of climate change on the effectiveness of NETs that have not been widely appreciated. Future research needs to explore the role of climate damages on NET uptake, better understand the geophysical constraints of NET deployment (e.g. water, geological storage, climate feedbacks), and provide a more systematic assessment of NET portfolios in the context of sustainable development goals. [ABSTRACT FROM AUTHOR]

The goal of the paper is to present and examine the method of classification of daily circulation patterns that allows (i) a fair comparison of groupings among different datasets (typically representing theobserved climate and that simulated by a general circulation model, GCM) and (ii) huge datasets, common in GCM studies based on daily values, to be classified. The circulation classification method is shownto be a useful tool in GCM validation and analysis of climate changeresponse, particularly in comparisons of (i) shapes of the mean typepatterns, (ii) the frequency and persistence of the types, (iii) theprobability of transitions from one type to another, and (iv) conditional surface temperature distributions. It is also shown that a simultaneous examination of multiple classifications is beneficial in eliminating subjectivity of any single classification and allowing a detailed inspection of differences between climates. The classification method is a modification of the T-mode principal component analysis (PCA). The T-mode refers to the input data matrix where gridpoint values are arranged in rows and daily patterns in columns. The classification procedure is applied to observed daily 500 hPa geopotential height patterns and those simulated by the control and $2\times {\rm CO}2$ ECHAM3 GCM runs. [ABSTRACT FROM AUTHOR]

In this paper a simple climate model is presented which is used to perform some sensitivity experiments. The atmospheric part is represented by a vertically and zonally averaged layer in which the surface air temperature, radiative fluxes at the surface and at the top of theatmosphere, the turbulent fluxes between atmosphere and surface and the snow cover are calculated. This atmospheric layer is coupled to atwo-dimensional advection-diffusion ocean model in which the zonal overturning pattern is prescribed. The ocean model evaluates the temperature distribution, the amount of sea-ice and the meridional and vertical heat fluxes. The present-day climate simulated by the model compares reasonably well with observations of the seasonal and latitudinal distribution of temperature, radiation, surface alebdo, sea-ice and snow cover and meridional energy fluxes. Then, the sensitivity of the model-simulated present-day climate to perturbations in the incident solar radiation at the top of the atmosphere is investigated. The temperature response displays large latitudinal and seasonal variations, which is in qualitative agreement with results obtained with other climate models. It is found that the seasonal variation of sea-ice cover (and hence, the effective oceanic heat capacity) is one of the most important elements determining seasonal variations in climate sensitivity. Differences in sensitivity between the seasonal and annualmean version of the model are discussed. Finally, the equilibrium response to perturbations in some selected model variables is presented; these variables include meridional diffusion coefficients, drag coefficient, sea-ice thickness, atmospheric CO{sub}2{end}-concentration and cloud optical thickness. [ABSTRACT FROM AUTHOR]

The climate impact of deforestation depends on the relative strength of several biogeochemical and biogeophysical effects. In addition to affecting the exchange of carbon dioxide (CO2) and moisture with the atmosphere and surface albedo, vegetation emits biogenic volatile organic compounds (BVOCs) that alter the formation of short-lived climate forcers (SLCFs), which include aerosol, ozone and methane. Here we show that a scenario of complete global deforestation results in a net positive radiative forcing (RF; 0.12 W m−2) from SLCFs, with the negative RF from decreases in ozone and methane concentrations partially offsetting the positive aerosol RF. Combining RFs due to CO2, surface albedo and SLCFs suggests that global deforestation could cause 0.8 K warming after 100 years, with SLCFs contributing 8% of the effect. However, deforestation as projected by the RCP8.5 scenario leads to zero net RF from SLCF, primarily due to nonlinearities in the aerosol indirect effect. [ABSTRACT FROM AUTHOR]

The emission of carbon dioxide (CO) from podzols (Albic Podzols (Arenic)) and the factors controlling its spatiotemporal variability in the forest ecosystems of the Pasvik Reserve in the Kola Subarctic are characterized. Relatively favorable climatic conditions beyond the polar circle in summer are responsible for intensive soil respiration. The type of forest affects the emission of CO from the soil surface. The lowest rate of the CO emission is typical of the soils under lichen pine forest (105-220 mg C/(m h) or 180 g C/m during the summertime). Higher rates are observed for the soils under green moss pine (170-385 mg C/(m h) or 360 g C/m during the summertime) and birch (190-410 mg C/(m h) or 470 g C/m during the summertime) forests. This may related to a higher contribution of root respiration (44, 88, and 67%, respectively). Soil respiration and the contribution of root respiration to it increase with an increase in the canopy density; mass of small roots; microbial biomass; depth of the stony layer; soil moistening; and the contents of available carbon, nitrogen, phosphorus, and potassium compounds. At the same time, they decrease with an increase in the portion of lichens in the ground cover. The seasonal dynamics are characterized by the CO emission maximums in the summer and fall and minimum in the spring. The daily dynamics are smoothed under conditions of the polar day. [ABSTRACT FROM AUTHOR]

Mountain fens found in western North America have sequestered atmospheric carbon dioxide (CO) for millennia, provide important habitat for wildlife, and serve as refugia for regionally-rare plant species typically found in boreal regions. It is unclear how Rocky Mountain fens are responding to a changing climate. It is possible that fens found at lower elevations may be particularly susceptible to changes because hydrological cycles that control water tables are likely to vary the most. In this study, we fit models of growing season ecosystem-atmosphere CO exchange to field-measured data among eight fen plant communities at four mountain fens along a climatic gradient in the Rocky Mountains of Colorado and Wyoming. Differences in growing season net ecosystem production (NEP) among study sites were not well correlated with monsoon precipitation, despite a twofold increase in summer rainfall between two study regions. Our results show that NEP was higher for fens located at high elevations compared to those found at lower elevations, with growing season estimates ranging from −342 to 256 g CO-C m. This was reflected in the negative correlation of growing season NEP with air temperature, and positive correlation with water table position, as the high elevation sites had the lowest air temperatures and highest water tables due to greater snowpack and later onset of melt. Our results suggest that sustainability of mountain fens occurring at the lower end of the known elevation range may be particularly susceptible to a changing climate, as these peatlands already experience lower snowpack, earlier snow melt, and warmer growing season air temperatures, which are all likely to be exacerbated under a future climate. [ABSTRACT FROM AUTHOR]

Climate stabilization efforts must integrate the actions of many socio-economic sectors to be successful in meeting climate stabilization goals, such as limiting atmospheric carbon dioxide (CO) concentration to be less than double the pre-industrial levels. Estimates of the costs and benefits of stabilization policies are often informed by Integrated Assessment Models (IAMs) of the climate and the economy. These IAMs are highly non-linear with many parameters that abstract globally integrated characteristics of environmental and socio-economic systems. Diagnostic analyses of IAMs can aid in identifying the interdependencies and parametric controls of modeled stabilization policies. Here we report a comprehensive variance-based sensitivity analysis of a doubled-CO stabilization policy scenario generated by the globally-aggregated Dynamic Integrated model of Climate and the Economy (DICE). We find that neglecting uncertainties considerably underestimates damage and mitigation costs associated with a doubled-CO stabilization goal. More than ninety percent of the states-of-the-world (SOWs) sampled in our analysis exceed the damages and abatement costs calculated for the reference case neglecting uncertainties (1.2 trillion 2005 USD, with worst case costs exceeding $60 trillion). We attribute the variance in these costs to uncertainties in the model parameters relating to climate sensitivity, global participation in abatement, and the cost of lower emission energy sources. [ABSTRACT FROM AUTHOR]

A cap is imposed on the carbon tax rate if the total tax revenue is not allowed to increase. Using recent data on the carbon-intensity of the economy and the overall tax take, I show that this cap constrains almost any climate policy in at least some countries. A larger number of countries, emitting a substantial share of global carbon dioxide, cannot fully participate if the carbon tax (or equivalent alternative regulation) is high enough to meet the 2 °C target. For that target, the carbon tax revenue in 2020 is greater than 10 % of total tax revenue in every country. [ABSTRACT FROM AUTHOR]

The ocean-atmosphere flux of carbon dioxide in subantarctic surface water (SASW) east of New Zealand has been determined using data from bi-monthly cruises on a time series transect for 8 years. The 60 km long transect extends from the coast (45.770°S 170.720°E) to a station at 45.833°S 171.500°E. Sea surface temperature, salinity, nutrient concentrations and pCO have been measured at a frequency of about once every 2 months from January 1998 until December 2005. Measured pCO exhibits a seasonal cycle with a maximum in late winter/spring, and a minimum in late summer/autumn, a mean 356 μatm, and an amplitude of 9 μatm. The magnitude of ΔpCO (the air-sea concentration gradient) has increased over the 8 years, primarily due to the increase in atmospheric CO concentration. The air-sea flux of CO was determined from wind speed data and ΔpCO. The uptake of atmospheric CO by SASW in the study area changed from + 1 and +82 mmol m in 1998 and 1999 respectively (ocean as source) to −870 and −510 mmol m in 2004 and 2005 (ocean as sink). These values are substantially less in magnitude than the value obtained from the Takahashi et al. (Deep-Sea Res II, ) flux climatology. [ABSTRACT FROM AUTHOR]

Climate reconstructions from data sensitive to past climates provide estimates of what these climates were like. Comparing these reconstructions with simulations from climate models allows to validate the models used for future climate prediction. It has been shown that for fossil pollen data, gaining estimates by inverting a vegetation model allows inclusion of past changes in carbon dioxide values. As a new generation of dynamic vegetation model is available we have developed an inversion method for one model, LPJ-GUESS. When this novel method is used with high-resolution sediment it allows us to bypass the classic assumptions of (1) climate and pollen independence between samples and (2) equilibrium between the vegetation, represented as pollen, and climate. Our dynamic inversion method is based on a statistical model to describe the links among climate, simulated vegetation and pollen samples. The inversion is realised thanks to a particle filter algorithm. We perform a validation on 30 modern European sites and then apply the method to the sediment core of Meerfelder Maar (Germany), which covers the Holocene at a temporal resolution of approximately one sample per 30 years. We demonstrate that reconstructed temperatures are constrained. The reconstructed precipitation is less well constrained, due to the dimension considered (one precipitation by season), and the low sensitivity of LPJ-GUESS to precipitation changes. [ABSTRACT FROM AUTHOR]

The response of ENSO frequency to the increasing CO2 concentration and associated mechanism are examined with outputs of four coupled climate models (GFDL/CM2.0, CNRM/CM3, IPSL/CM4 and INM/CM3.0) submitted to the IPCC Fourth Assessment Report (IPCC AR4). Results reveal a significant change of ENSO frequency as response to the increasing CO2 concentration. However, such a change exhibits an evident model dependence. The ENSO frequency tends to increase in GFDL/CM2.0 and CNRM/CM3 models and decreases in IPSL/CM4 and INM/CM3.0 models. The model dependence is found to be determined by how the model climatological background state of the tropical Pacific responds to the increasing CO2 concentration. It is demonstrated that the change of zonally- and vertically-averaged climatological background upper ocean temperature gradient between the equator and off-equator is crucially responsible for the ENSO frequency change. As response to the increasing CO2 concentration, the climatological background temperature gradient is increased in GFDL/CM2.0 and CNRM/CM3 models and decreased in IPSL/CM4 and INM/CM3.0 models. In terms of the recharge-discharge oscillator theory for ENSO, the increased (decreased) climatological background temperature gradient between the equator and off-equator induces a faster (slower) exchange of oceanic heat content between the equator and off-equator, thus giving rise to a shorter (longer) ENSO timescale and a higher (lower) ENSO frequency. [ABSTRACT FROM AUTHOR]

Introduces articles concerning surface fluxes in the March 2005 issue of "Theoretical and Applied Climatology". Observation on local temperature profiles in Antarctica; Description of a tool for the detection of coherent structures in complex terrain; Analysis of carbon dioxide flux measurements.

Eddy covariance measurements of the surface energy balance and carbon dioxide exchange above high-elevation (3,480 m above sea level) alpine tundra located near Niwot Ridge, Colorado, were compared to simultaneous measurements made over an adjacent subalpine forest over two summers and one winter, from June 9, 2007 to July 3, 2008. The surface energy balance closure at the alpine site averaged 71 and 91%, winter and summer, respectively, due to the high wind speeds, short turbulent flux footprint, and relatively flat ridge-top location of the measurement site. Throughout the year, the alpine site was cooler with higher relative humidity, and had a higher horizontal wind speed, especially in winter, compared to the forest site. Wind direction was persistently downslope at the alpine site (summer and winter, day and night), whereas upslope winds were common at the forest site during summer daytime periods. The latent and sensible heat fluxes were consistently larger in magnitude at the forest site, with the largest differences during summer. The horizontal advective flux of CO2 at the alpine site averaged 6% of the net ecosystem exchange ( NEE) during summer nights (5% during summer daytime), and was small in relation to the high wind speeds, relatively flat site, and weak sources of CO2 upwind of the site. The magnitudes and diurnal behavior of the alpine NEE calculated using three methods; eddy-covariance, friction velocity filter, and with advection and storage calculations, gave similar results. The period of net CO2 uptake (negative NEE) was 100 days at the alpine site with a net uptake of 16 g C m−2, compared to 208 days at the forest site with a net uptake of 108 g C m−2, with initiation of net uptake coinciding with air temperatures reaching +10°C. Winter respiration loss at the alpine site was 164 g C m−2 over 271 days, compared to 52 g C m−2 over 175 days at the forest site, with the initiation of net loss coinciding with air temperatures reaching −10°C at each site. [ABSTRACT FROM AUTHOR]

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering. Proxy records indicate, however, that the Earth’s atmospheric carbon dioxide concentrations did not fall below about 200–250 parts per million during this period. The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering. Here we investigate one possible negative feedback mechanism, occurring under relatively low carbon dioxide concentrations and in warm climates, that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals. We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period. These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink. Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate, our analysis indicates that the dynamic equilibrium between plants, climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years. [ABSTRACT FROM AUTHOR]

Focuses on the improvements in the responses to extreme weather among European countries. Efforts of governments to issue forecasts and heighten the alarmingly poor awareness of citizens both of their vulnerability and of what to do in the event of catastrophes; Initiative on protecting natural systems to mitigate the effects of peaks in rainfall and spells of high temperature; Challenge to convince citizens to do their bit to moderate the unimaginably enormous scale of mankind's carbon dioxide emissions.

The notion is pervasive in the climate science community and in the public at large that the climate impacts of fossil fuel CO2 release will only persist for a few centuries. This conclusion has no basis in theory or models of the atmosphere/ocean carbon cycle, which we review here. The largest fraction of the CO2 recovery will take place on time scales of centuries, as CO2 invades the ocean, but a significant fraction of the fossil fuel CO2, ranging in published models in the literature from 20–60%, remains airborne for a thousand years or longer. Ultimate recovery takes place on time scales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste. The glacial/interglacial climate cycles demonstrate that ice sheets and sea level respond dramatically to millennial-timescale changes in climate forcing. There are also potential positive feedbacks in the carbon cycle, including methane hydrates in the ocean, and peat frozen in permafrost, that are most sensitive to the long tail of the fossil fuel CO2 in the atmosphere. [ABSTRACT FROM AUTHOR]

Urban ecosystems are profoundly modified by human activities and thereby provide a unique “natural laboratory” to study potential ecosystem responses to anthropogenic environmental changes. Because urban environments are now affected by urban heat islands, carbon dioxide domes, and high-level nitrogen deposition, to some extent they portend the future of the global ecosystem. Urbanization in the metropolitan region of Phoenix, Arizona (USA) has resulted in pronounced changes in air temperature ( T air), atmospheric CO2 concentration, and nitrogen deposition (Ndep). In this study, we used a process-based ecosystem model to explore how the Larrea tridentata dominated Sonoran Desert ecosystem may respond to these urbanization-induced environmental changes. We found that water availability controls the magnitude and pattern of responses of the desert ecosystem to elevated CO2, air temperature, N deposition and their combinations. Urbanization effects were much stronger in wet years than normal and dry years. At the ecosystem level, aboveground net primary productivity (ANPP) and soil organic matter (SOM) both increased with increasing CO2 and Ndep individually and in combinations with changes in T air. Soil N (Nsoil) responded positively to increased N deposition and air temperature, but negatively to elevated CO2. Correspondingly, ANPP and SOM of the Larrea ecosystem decreased along the urban–suburban–wildland gradient, whereas Nsoil peaked in the suburban area. At the plant functional type (FT) level, ANPP generally responded positively to elevated CO2 and Ndep, but negatively to increased T air. C3 winter annuals showed a greater ANPP response to higher CO2 levels (>420 ppm) than shrubs, which could lead over the long term to changes in species composition, because competition among functional groups is strong for resources such as soil water and nutrients. Overall, the combined effects of the three environmental factors depended on rainfall variability and nonlinear interactions within and between plant functional types and environmental factors. We intend to use these simulation results as working hypotheses to guide our field experiments and observations. Experimental testing of these hypotheses through this process should improve our understanding of urban ecosystems under increasing environmental stresses. [ABSTRACT FROM AUTHOR]

Abstract General circulation models (GCMs) are unanimous in projecting warmer temperatures in an enhanced CO2 atmosphere, with amplification of this warming in higher latitudes. The Hudson Bay region, which is located in the Arctic and subarctic regions of Canada, should therefore be strongly influenced by global warming. In this study, we compare the response of Hudson Bay to a transient warming scenario provided by six-coupled atmosphere-ocean models. Our analysis focuses on surface temperature, precipitation, sea-ice coverage, and permafrost distribution. The results show that warming is expected to peak in winter over the ocean, because of a northward retreat of the sea-ice cover. Also, a secondary warming peak is observed in summer over land in the Canadian and Australian-coupled GCMs, which is associated with both a reduction in soil moisture conditions and changes in permafrost distribution. In addition, a relationship is identified between the retreat of the sea-ice cover and an enhancement of precipitation over both land and oceanic surfaces. The response of the sea-ice cover and permafrost layer to global warming varies considerably among models and thus large differences are observed in the projected regional increase in temperature and precipitation. In view of the important feedbacks that a retreat of the sea-ice cover and the distribution of permafrost are likely to play in the doubled and tripled CO2 climates of Hudson Bay, a good representation of these two parameters is necessary to provide realistic climate change scenarios. The use of higher resolution regional climate model is recommended to develop scenarios of climate change for the Hudson Bay region. [ABSTRACT FROM AUTHOR]

Response of the Atlantic thermohaline circulation (THC) to global warming is examined by using the climate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-toequator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmospheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic "conveyor belt" decelerating. [ABSTRACT FROM AUTHOR]

The range of possibilities for future climate evolution needs to be taken into account when planning climate change mitigation and adaptation strategies. This requires ensembles of multi-decadal simulations to assess both chaotic climate variability and model response uncertainty. Statistical estimates of model response uncertainty, based on observations of recent climate change, admit climate sensitivities-defined as the equilibrium response of global mean temperature to doubling levels of atmospheric carbon dioxide-substantially greater than 5?K. But such strong responses are not used in ranges for future climate change because they have not been seen in general circulation models. Here we present results from the‘climateprediction.net’experiment, the first multi-thousand-member grand ensemble of simulations using a general circulation model and thereby explicitly resolving regional details. We find model versions as realistic as other state-of-the-art climate models but with climate sensitivities ranging from less than 2?K to more than 11?K. Models with such extreme sensitivities are critical for the study of the full range of possible responses of the climate system to rising greenhouse gas levels, and for assessing the risks associated with specific targets for stabilizing these levels. [ABSTRACT FROM AUTHOR]

Catalytic activity of Ni/MgO-AN prepared from alcogel derived MgO was studied for the dry reforming of methane under atmospheric as well as high pressure (1.5 MPa). Different catalytic performances are observed in the atmospheric and high-pressure reactions; while the catalyst was highly active and extremely stable under atmospheric pressure it shows a self-stabilization process under high pressure. The self-stabilization process was characterized initially by a decrease in deactivation rate with increasing the reaction time-on-stream (TOS) up to ca. 12 h and then by a thereafter stabilization during the reaction. Characterizations of the coked catalyst with TPO, TEM, SEM, TPH and XRD techniques detected very little carbon deposits (ca. 0.2 wt% of the catalyst charge) on the used catalyst under atmospheric pressure. In contrast, large amount of whisker carbon deposit (ca. 100 wt% of the catalyst charge) were formed on the used catalyst under high pressure. In the high-pressure reaction, the activity decline during the initial stage was closely related to the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for ca. 12 h. The carbon deposits on the used catalyst in the high-pressure reaction contained two different components (a-carbon and ß-carbon) while the carbon deposits in the atmospheric pressure reaction were in the form of a-carbon. No notable sintering of metallic nickel was detected by XRD on the used catalyst in the reaction under atmospheric pressure whereas unavoidable sintering of metallic Ni particles happened within the very first hours of the high-pressure reaction. [ABSTRACT FROM AUTHOR]

In this study we apply new extensions of classical growth analysis to assess the interactive effects of elevated CO2 and differences in water availability on the leaf-nitrogen and transpiration productivities of velvet mesquite (Prosopis velutinaWoot.) seedlings. The models relate transpiration productivity (biomass gained per mass of water transpired per day) and leaf-nitrogen productivity (biomass gain per unit leaf N per day) to whole-plant relative growth rate (RGR) and to each other, allowing a comprehensive hierarchical analysis of how physiological and morphological responses to the treatments interact with each other to affect plant growth. Elevated CO2 led to highly significant increases in N and transpiration productivities but reduced leaf N per unit leaf area and transpiration per unit leaf area, resulting in no net effect of CO2 on the RGR of seedlings. In contrast, higher water availability led to an increase in leaf-tissue thickness or density without affecting leaf N concentration, resulting in a higher leaf N per unit leaf area and consequently a higher assimilatory capacity per unit leaf area. The net effect was a marginal increase in seedling RGR. Perhaps most important from an ecological perspective was a 41% reduction in whole-plant water use due to elevated CO2. These results demonstrate that even in the absence of CO2 effects on integrative measures of plant growth such as RGR, highly significant effects may be observed at the physiological and morphological level that effectively cancel each other out. The quantitative framework presented here enables some of these tradeoffs to be identified and related directly to each other and to plant growth. [ABSTRACT FROM AUTHOR]

An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO2 and H2O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO2 out of the control volume. From our measurements, a mean daily gain of 2.2 gC m-2 d-1 for the horizontal advection and a mean daily loss of 2.5 gC m-2d-1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studies. [ABSTRACT FROM AUTHOR]

Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity. [ABSTRACT FROM AUTHOR]

Sedimentary basins are suitable to different degrees for CO2 geological sequestration as a result of various intrinsic and extrinsic characteristics, of which the geothermal regime is one of the most important. Warm basins are less favorable for CO2 sequestration than cold basins because of reduced capacity in terms of CO2 mass, and because of higher CO2 buoyancy, which drives the upward CO2 migration. A set of 15 criteria, with several classes each, has been developed for the assessment and ranking of sedimentary basins in terms of their suitability for CO2 sequestration. Using a parametric normalization procedure, a basin's individual scores are summed to a total score using weights that express the relative importance of different criteria. The total score is ranked to determine the most suitable basin or region thereof for the geological sequestration of CO2. The method is extremely flexible in that it allows changes in the functions that express the importance of various classes for any given criterion, and in the weights that express the relative importance of various criteria. Examples of application are given for Canada's case and for the Alberta basin in Canada. [ABSTRACT FROM AUTHOR]

Summary The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69° N); fen, heathland, and snowbed willow ecosystems in northeastern Greenland (74° N); and a polar semidesert site in Svalbard (79° N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO2 fluxes. The seasonal periods important for the net CO2 fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3–5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2–5 weeks. The summer period lasts 6 weeks in NE Greenland but 10–14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GPmax, followed by the fen ecosystems. The polar semidesert ecosystem had the lowest GPmax. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2–5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland. [ABSTRACT FROM AUTHOR]

A firm understanding of the relationship between atmospheric carbon dioxide concentration and temperature is critical for interpreting past climate change and for predicting future climate change. A recent synthesis suggests that the increase in global-mean surface temperature in response to a doubling of the atmospheric carbon dioxide concentration, termed ‘climate sensitivity’, is between 1.5 and 6.2 °C (5–95 per cent likelihood range), but some evidence is inconsistent with this range. Moreover, most estimates of climate sensitivity are based on records of climate change over the past few decades to thousands of years, when carbon dioxide concentrations and global temperatures were similar to or lower than today, so such calculations tend to underestimate the magnitude of large climate-change events and may not be applicable to climate change under warmer conditions in the future. Here we estimate long-term equilibrium climate sensitivity by modelling carbon dioxide concentrations over the past 420 million years and comparing our calculations with a proxy record. Our estimates are broadly consistent with estimates based on short-term climate records, and indicate that a weak radiative forcing by carbon dioxide is highly unlikely on multi-million-year timescales. We conclude that a climate sensitivity greater than 1.5 °C has probably been a robust feature of the Earth’s climate system over the past 420 million years, regardless of temporal scaling. [ABSTRACT FROM AUTHOR]

Arising from M. T. Rosing, D. K. Bird, N. H. Sleep & C. J. Bjerrum 464, 744-747 (2010)Rosing and others recently proposed a new model for the early Earth's atmospheric composition. They suggest, on the basis of mineral assemblages in sedimentary rocks, that atmospheric CO2 and CH4 concentrations have been consistently overestimated. This proposal is intriguing, given that high concentrations of these gases are traditionally considered to be the solution to the 'faint young Sun paradox' of why the Earth did not freeze over in our Sun's youth when solar luminosity was greatly decreased. Rosing and others instead invoke a decreased planetary albedo during the Earth's early history. New insights into this problem, which has long captivated those interested in the Earth's early climate and biological history, are welcome. However, we believe that the arguments presented by Rosing and others for roughly modern values of the partial pressure of CO2 () are not robust. [ABSTRACT FROM AUTHOR]

It is expected that a change in climatic conditions due to global warming will directly impact agricultural production. Most climate change studies have been applied at very large scales, in which regions were represented by only one or two weather stations, which were mainly located at airports of major cities. The objective of this study was to determine the potential impact of climate change at a local level, taking into account weather data recorded at remote locations. Daily weather data for a 30-year period were obtained for more than 500 sites, representing the southeastern region of the USA. Climate change scenarios, using transient and equilibrium global circulation models (GCM), were defined, created and applied to the daily historical weather data. The modified temperature, precipitation and solar radiation databases corresponding to each of the climate change scenarios were used to run the CERES v.3.5 simulation model for maize and winter wheat and the CROPGRO v.3.5 model for soybean and peanut. The GCM scenarios projected a shorter duration of the crop-growing season. Underthe current level of CO2, the GCM scenarios projected a decrease of crop yields in the 2020s. When the direct effects of CO2 were assumed in the study, the scenarios resulted in an increase in soybean and peanut yield. Under equilibrium $2\times {\rm CO}2$, the GCM climate change scenarios projected a decreaseof maize and winter wheat yield. The indirect effects of climate change also tended to decrease soybean and peanut yield. However, when the direct effects of CO2 were included, most of the scenarios resulted in an increase in legume yields. Possible changes in sowing data, hybrids and cultivar selection, and fertilization were considered as adaptation options to mitigate the potential negative impact of potential warming. [ABSTRACT FROM AUTHOR]

Temperature and precipitation records from 1949 to 1998 were examined for 25 stations throughout the State of Alaska. Mean, maxima, and minima temperatures, diurnal temperature range, and total precipitation were analyzed for linear trends using least squares regressions. Annual and seasonal mean temperature increases were found throughout the entire state, and the majority were found to be statistically significant at the 95% level or better. The highest increases were found in winter in the Interior region (2.2 deg. C) for the 50 year period of record. Decreases in annual and seasonal mean diurnal temperature range were also found, of which only about half were statistically significant. A state-wide decrease in annual mean diurnal temperature range was found to be 0.3 deg. C, with substantially higher decreasesin the South/Southeastern region in winter. Increases were found in total precipitation for 3 of the 4 seasons throughout most of Alaska,while summer precipitation showed decreases at many stations. Few ofthe precipitation trends were found to be statistically significant,due to high interannual variability. Barrow, our only station in theArctic region, shows statistically significant decreases in annual and winter total precipitation. These findings are largely in agreement with existing literature, although they do contradict some of the precipitation trends predicted by the CO2-doubling GCM's. [ABSTRACT FROM AUTHOR]