Increasing CO2 Levels Research Articles

Effects of increased CO2 levels on monsoons

Increased atmospheric carbon dioxide concentration provided warmer atmospheric temperature and higher atmospheric water vapor content, but not necessarily more precipitation. A set of experiments performed with a state-of-the-art coupled general circulation model forced with increased atmospheric CO2 concentration (2, 4 and 16 times the present-day mean value) were analyzed and compared with a control experiment to evaluate the effect of increased CO2 levels on monsoons. Generally, the monsoon precipitation responses to CO2 forcing are largest if extreme concentrations of carbon dioxide are used, but they are not necessarly proportional to the forcing applied. In fact, despite a common response in terms of an atmospheric water vapor increase to the atmospheric warming, two out of the six monsoons studied simulate less or equal summer mean precipitation in the 16×CO2 experiment compared to the intermediate sensitivity experiments. The precipitation differences between CO2 sensitivity experiments and CTRL have been investigated specifying the contribution of thermodynamic and purely dynamic processes. As a general rule, the differences depending on the atmospheric moisture content changes (thermodynamic component) are large and positive, and they tend to be damped by the dynamic component associated with the changes in the vertical velocity. However, differences are observed among monsoons in terms of the role played by other terms (like moisture advection and evaporation) in shaping the precipitation changes in warmer climates. The precipitation increase, even if weak, occurs despite a weakening of the mean circulation in the monsoon regions (“precipitation-wind paradox”). In particular, the tropical east-west Walker circulation is reduced, as found from velocity potential analysis. The meridional component of the monsoon circulation is changed as well, with larger (smaller) meridional (vertical) scales.

Factors influencing the acid–base (pH) balance in the Baltic Sea: a sensitivity analysis

Using calculations based on the marine carbon system and on modelling, the sensitivity of Baltic Sea surface pH was examined. Transient long-term calculations demonstrated that the marine carbon system adjusts to lateral boundary conditions within some decades, as does salinity. Climate changes in temperature or salinity will only marginally affect the acid–base (pH) balance. Wetter or dryer climate will also play a minor role in the pH balance. The direct effect on seawater pH of acid precipitation over the Baltic Sea surface was demonstrated to be small. Acidification due to river transport of dissolved organic carbon (DOC) into the marine system seems marginal although mineralization of terrestrial DOC may cause extra marine acidification, but the effect has yet to be quantified. Increased nutrient load may increase the amplitude in the pH seasonal cycle and increase the acidification during winter time. Fossil fuel burning is likely to have both a direct and indirect effect through increased CO2 levels, altering seawater pH as well as changing the river chemistry. This may severely threaten some species in the Baltic Sea, particularly in the Northern Baltic.

Climate change and its impact on vegetation

Climate change will affect on vegetation directly because of increased atmospheric CO2 concentration and greenhouse gases and indirectly through stratospheric ozone layer depletion. Increased CO2 level could increase photosynthesis and water use efficiency. However, high temperature and greenhouse gases will modify rainfall, evaporation runoff and soil moisture storage and will adversely affect growth and productivity. The increased amount of ultraviolet (UV) radiation due to depletion of stratospheric ozone layer will exert its deleterious effect on growth and productivity by destruction of chlorophyll and reducing photosynthetic rate.

Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab <i>Hyas araneus</i>

Abstract. Future scenarios for the oceans project combined developments of CO2 accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO2 concentrations on thermal tolerance of the cold-eurythermal spider crab Hyas araneus from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO2), CO2 levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO2 (PeO2) were measured during progressive short term cooling from 10 to 0°C and during warming from 10 to 25°C. An increase of PeO2 occurred during cooling, the highest values being reached at 0°C under all three CO2 levels. Heart rate increased during warming until a critical temperature (Tc) was reached. The putative Tc under normocapnia was presumably >25°C, from where it fell to 23.5°C under 710 ppm and then 21.1°C under 3000 ppm. At the same time, thermal sensitivity, as seen in the Q10 values of heart rate, rose with increasing CO2 concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO2 levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.

A Low Carbon Built Environment

There are many technical challenges and opportunities ahead as sustainability in the built environment becomes a major economic force in relation to both building construction and energy supply. Climate change, the depletion of fossil fuel energy sources, and the security of future energy supplies are becoming a major concern for all countries. Materials and water are also becoming short in supply. All these issues are a clear indication that we are living in unsustainable ways. Many countries are developing at a rapid pace and the global rate of building construction is unprecedented, generally with little attention given to the impact that the construction and operation of these building will have on the environment, both locally and from a global perspective. In 2007, the Intergovernmental Panel on Climate Change (IPCC) reported a 90% certainty that global warming is caused by human activity associated with greenhouse gas emissions. The increased CO2 level in the global atmosphere is now a major concern. The reports states that if we are to avoid catastrophic climate change, average temperature rises must be maintained within 28C which equates to carbon dioxide (CO2) levels in the atmosphere staying below 450 ppm. Perhaps the most alarming aspect of this is that we must take action within 10 years from 2007. That means we have only 8 years, not just to plan, but to act on the sustainability issues concerning the built environment. In the longer term the planet needs to achieve carbon neutrality. If we take the view of climate change modellers that we have a finite amount of CO2 that we can put into the atmosphere before the 28C limit is exceeded then we must budget this over a period of time. We might take the view that the carbon neutrality target is to be achieved by the end of this century and that the amount of emissions must be agreed globally, with some countries allowed to continue to increase their emissions, whilst other more developed countries begin to reduce sooner. At some stage all countries would emit the same per capita and then reduce to zero carbon. This is called the contraction and convergence principle. So what role should the built environment play in this? In a global context the built environment is said to be responsible for about 50% of emissions and 70% if we include transportation associated with mobility within the built environment. It is convenient to divide the built environment into new build, existing buildings and supporting infrastructures (for transport, water/sewage, waste and energy supply). Probably the easiest sector to deal with first is new build. As they are likely to be around for some time it is important that they perform well in relation to CO2 emissions. Many governments worldwide are developing policies to reduce CO2 emissions. In the UK, the government has set a target for all new houses to be ‘‘zero carbon’’ by 2016, and in some regions of the UK, for example Wales, the regional government has set a target for all new buildings to be zero carbonby2011.Thedefinitionofazerocarbonbuilding in its simplest form is that it has a reduced energy demand for thermal energy and power and that the supply is from renewable energy sources, integrated into the building,

Late Cretaceous seasonal ocean variability from the Arctic

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65-99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized. Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre, or those indicated for the Mediterranean sapropels. With increased CO(2) levels and warming currently driving increased stratification in the global ocean, this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean, rather than recent suggestions of a 15 degrees C mean annual temperature at this time.

Effects of essential oil treatment, gas atmosphere, and storage temperature on Listeria monocytogenes in a model vegetable system.

Natural antimicrobials such as plant essential oils (EOs) may be useful for controlling pathogenic bacteria on fresh-cut vegetables. The antilisterial properties of EOs (thyme, oregano, and rosemary), in combination with different storage atmospheres (air, 5% CO2-2% O2-93% N2, and 20% CO2-1% O2-79% N2) and temperatures (4 and 80C), were examined using a gas flow-through system combined with a vegetable agar model. The antimicrobial effects of the EOs varied depending on the oil, the Listeria strain and species, the method of application, and the storage conditions tested. Using the disk diffusion assay, the antilisterial effectiveness of the oils was in the following order: thyme EO > oregano EO > rosemary EO. Volatiles released from the EOs resulted in very small antilisterial effects, indicating that the oils needed to be in direct contact with cultures in order to be effective. There were strain and species effects, with L. innocua NCTC 11288 exhibiting the strongest resistance to EOs, and L. monocytogenes NCTC 7973 being the most sensitive strain. In addition, the effectiveness of the EOs was influenced by storage atmosphere and temperature. Use of EOs in combination with a gas atmosphere of 20% CO2-1% O2-79% N2 had the greatest antilisterial effect, suggesting that high CO2 atmospheres enhanced the antilisterial properties of EOs. Lowering the storage temperature from 8 to 4OC improved the antilisterial activity of thyme oil. It is concluded that thyme and oregano EOs display strong inhibitory effects against Listeria and that increasing CO2 levels and lowering storage temperatures further enhance these antilisterial effects.

Effects of varying combustion conditions on PCDD/F emissions and formation during MSW incineration

Process, combustion and fuel parameters were varied to elucidate factors that substantially affect the formation and emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) arising from municipal solid waste (MSW) incineration. The combustion conditions were varied by changing the: freeboard temperatures; quench time in the post-combustion zone; fuel load; chlorine and copper levels in the fuel; and the water, sulfur dioxide, carbon monoxide and oxygen levels in the combustion gases. The study was performed using a 5kW laboratory-scale fluidized-bed reactor and PCDD/Fs were sampled at a point at 300°C in the post-combustion zone. The results showed that increasing the SO2 level (from 0 to 130ppm) substantially reduced the PCDD/F emissions, by up to 60%. In contrast, increasing the CO levels (due to transient combustion conditions), raising the Cl level (from 0.7% to 1.7%) and reducing the freeboard temperature (from 800°C to 660°C) all substantially increased the emission levels (more than 3-fold). Changes in PCDD/F profiles associated with increases in Cl, SO2 or CO levels and increasing the freeboard temperature (from 800°C to 950°C) indicate that the PCDFs were mainly formed by chlorination. In addition, increasing the Cl level increased the chlorination activity in the formation of PCDDs. Increasing the SO2 level appeared to be less effective in reducing the amount of PCDDs formed via the precursor pathway. While increased CO levels induced PCDD formation via the precursor pathway, although this was found to depend on the O2 level in the flue gas.

Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon

The boreal forests of North America are undergoing major changes because of the direct effects of global warming and increased CO2 levels. Plant production in the boreal forest is nutrient limited, and we examined how long-term fertilization affected growth of white spruce Picea glauca in the face of these major changes. We conducted a large-scale experiment by fertilizing two 1 km 2 stands of white spruce in the southwestern Yukon with commercial NPK fertilizer from 1987 to 1994. Tree growth was measured by the width of annual increments in 60 trees from each of 2 con- trol and of 2 matched fertilized 1 km 2 sites for the period from 1977 to 1997 in a before, during, and after experimental design. Ring widths increased in both control and fertilized trees over this period as summer temperatures increased. Ring widths in fertilized trees increased from 9 to 48% over con- trol trees during the years in which fertilizer was added, but immediately fell back to control levels from 1995 to 1997 at 1 site as soon as fertilization was stopped. In the long term, nitrogen in these forests may become tied up in shrubs, grasses, herbs, and fungi and not be available to the trees. There are 2 other possible explanations for this lack of sustained tree growth: first, the conversion of nitrogen into a form not readily available to spruce and, second, a spruce bark beetle outbreak that hit the southwestern Yukon during and after 1994 and affected 1 study site much more than the other.

Response of marine viral populations to a nutrient induced phytoplankton bloom at different pCO<sub>2</sub> levels

Abstract. During the PeECE III mesocosm experiment in 2005 we investigated how the virioplankton community responded to increased levels of nutrients (N and P) and CO2. We applied a combination of flow cytometry, Pulsed Field Gel Electrophoresis and degenerate PCR primers to categorize and quantify individual viral populations, and to investigate their temporal dynamics. Species specific and degenerate primers enabled us to identify two specific large dsDNA viruses, EhV and CeV, infecting the haptophytes Emiliania huxleyi and Crysochromulina ericina, respectively. Some of the viral populations detected and enumerated by flow cytometry did not respond to altered CO2-levels, but the abundance of EhV and an unidentified dsDNA virus decreased with increasing CO2 levels. Our results thus indicate that CO2 conditions, or the related change in pH, may affect the marine pelagic food web at the viral level. Our results also demonstrate that in order to unravel ecological problems as how CO2 and nutrient levels affect the relationship between marine algal viruses and their hosts, we need to continue the effort to develop molecular markers used to identify both hosts and viruses.

A Continuum Model for Metabolic Gas Exchange in Pear Fruit

Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres.

Conserving narrow range endemic insects in the face of climate change: options for some Australian butterflies

Many insects in the southern hemisphere are regarded as ‘point endemics’ or ‘narrow range endemics’, known from single sites or small, strictly circumscribed areas. Failure to find them elsewhere during extensive targeted searches suggests strongly that such distributions are initially ‘real’ (reflecting long isolation and speciation) rather than the remnant consequences of extensive anthropogenic changes. The latter may further fragment the already small range. Not unexpectedly, such species commonly arouse conservation attention. However, recovery plans or less focused conservation management agendas commonly can pay little constructive heed to ramifications of future climate changes, not least because those ramifications can only be inferred within rather broad limits and require a certain amount of ‘crystal ball-gazing’. In addition, the factors causing the current narrow distributions of the insects can usually only be suggested, most commonly in terms of supply of critical resources as a key component of suitable habitat. In practice, conservation of narrow range species has concentrated almost wholly on urgent short-term issues of site and resource security with—should it be considered at all—little heed to the changing suitability of the site(s) as climates change. This approach alone may prove inadequate and is based on the largely unproven presumption that the species may still be able to persist on those sites. Alternatives may be possible for some taxa, in helping to cater for likely future range changes by (1) acknowledging and plotting environmental gradients and preparing new sites to support those species within the species’ dispersal capability, and (2) securing sites within more distant but potentially suitable areas to receive translocations in the future. Any change in distribution of the species necessitates change of both scope and detail of management, as the spatial and temporal distributions of its resources change. There is at least suggestion that the entire present range of some such taxa may be rendered unsuitable, predominantly by changes in temperature and precipitation patterns, and possibly within only a few decades. Additionally, increasing CO2 levels may influence plant metabolism and affect food availability. Whereas increasing connectivity between occupied sites is a common recommendation in insect species management, it is not as frequently acknowledged that this may not always serve for the longer term. It is, nevertheless, a valid ‘insurance tactic’ to guard against increased risk of destructive fires, already recognized as a threat to many such taxa in Australia and likely to increase in the future with projected global warming. As Dennis (1993) discussed, three aspects of climate change relate strongly to butterfly biology: the absolute rise in regional temperatures and consequent changes in other attributes, particularly precipitation; the rate at which such changes occur; and the frequency and magnitude of ‘extreme weather events’. Consequences to species are extinction, adaptation in situ, or movement elsewhere, with the last of these gaining particular attention for conservation. However, the options available to plan for the future of narrow range endemic insects in the face of range alterations imposed by climate change will vary with the kind of distribution, as well as the level of ecological specialization, with extreme specialization curtailing the alternative ‘outlets of escape’ (Dennis 1993) within an occupied site. Several different scenarios or distribution patterns are evident in narrowly distributed Australian butterflies. They manifest one of about five basic patterns, T. R. New (&) Department of Zoology, La Trobe University, Bundoora, VIC 3086, Australia e-mail: T.New@latrobe.edu.au

Evidence for major environmental perturbation prior to and during the Toarcian (Early Jurassic) oceanic anoxic event from the Lusitanian Basin, Portugal

The timing and causal relationships between the pronounced negative C isotope excursion and paleoenvironmental perturbations associated with the Toarcian oceanic anoxic event (Early Jurassic) remain unclear, particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main C isotope anomaly. Here we present a new quantification of Late Pliensbachian–Early Toarcian calcareous nannofossils abundance and size from the Peniche reference section (Portugal) together with O and C isotope records of well‐preserved brachiopod shells from the same section. The brachiopod shell δ13C curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions, close to the Pliensbachian‐Toarcian boundary (∼−2‰) and during the Toarcian oceanic anoxic event (∼−3.5‰). Our results indicate that both C isotope negative excursions were characteristic of benthic and shallow‐water environments, suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs. Coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of Mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures, probably as a result of increased CO2 levels and enhanced greenhouse conditions. CO2‐induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems, as evidenced by synchronous drops of platform‐derived carbonate accumulation and drastic reductions in size (>3 μm) of the main pelagic carbonate producer Schizosphaerella. We suggest that the Early Toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the Karoo‐Ferrar province.

Aerosol-cloud-climate interactions in the climate model CAM-Oslo

A new aerosol module is integrated on-line in the atmospheric GCM CAM-Oslo coupled to a slab ocean for equilibrium climate response studies. The response to an anthropogenic change in aerosols since pre-industrial times is compared with that of a future 63% increased CO2 level. The aerosol module calculates concentrations of sea-salt, mineral dust, sulphate, black carbon (BC) and particulate organic matter (POM). Look-up tables, constructed from first principles, are used to obtain optical parameters and cloud droplet numbers (CDNC) for any given aerosol composition. Anthropogenic aerosols thus produce a global near-surface cooling of 1.94Kand a 5.5% precipitation decrease, including amplifications by positive cloud feedbacks. In comparison, the CO2 increase gives a warming of 1.98 K and a 3.8% precipitation increase, causing slightly reduced sulphate, BC, POM and sea-salt burdens. A minor increase in mineral dust is ascribed to reduced subtropical precipitation downwind of Sahara over the Atlantic Ocean. The modelled indirect effects are probably overestimated, mainly due to neglected natural aerosol components and the diagnostic scheme for CDNC. Adding 15cm−3 to CDNC everywhere reduces the indirect forcing from −2.34 to −1.36 Wm−2, whilst solving a prognostic equation for CDNC reduces it from −2.34 to −1.44 Wm−2.

Hierarchical saturation of soil carbon pools near a natural CO2 spring

AbstractSoil has been identified as a possible carbon (C) sink to mitigate increasing atmospheric CO2 concentration. However, several recent studies have suggested that the potential of soil to sequester C is limited and that soil may become saturated with C under increasing CO2 levels. To test this concept of soil C saturation, we studied a gley and organic soil at a grassland site near a natural CO2 spring. Total and aggregate‐associated soil organic C (SOC) concentration showed a significant increase with atmospheric CO2 concentration. An asymptotic function showed a better fit of SOC and aggregation with CO2 level than a linear model. There was a shift in allocation of total C from smaller size fractions to the largest aggregate fraction with increasing CO2 concentration. Litter inputs appeared to be positively related to CO2 concentration. Based on modeled function parameters and the observed shift in the allocation of the soil C from small to large aggregate‐size classes, we postulate that there is a hierarchy in C saturation across different SOC pools. We conclude that the asymptotic response of SOC concentration at higher CO2 levels indicates saturation of soil C pools, likely because of a limit to physical protection of SOC.

Semi‐arid grazing systems and climate change: a survey of present modelling potential and future needs

Summary Sustainable land use under climate change requires detailed knowledge of the system dynamics. This applies particularly for the management of domestic livestock in semi‐arid and arid grazing systems, where the risk of degradation is high and likely climate change may have a strong impact. A suitable way to assess potential future trends of these complex systems is through the application of simulation models. We reviewed 41 models published between 1995 and 2005 simulating semi‐arid and arid livestock grazing systems. The models were categorized according to the model aim and type, their temporal and spatial scale, and several indicators of model complexity. Additionally, we developed a list of model requirements for adequately simulating the effects of climate change. Based on these requirements, we evaluated the potential of current models to simulate impacts of climate change and determine important shortcomings. Three general model types could be distinguished, namely state and transition, difference and differential equation, and rule‐based models. Over time, we found that the number of models aiming to improve management strategies increased, while there were fewer models that aimed to understand system dynamics. This was accompanied by a trend to simplify model descriptions of hydrological relationships. Important shortcomings of current models included the impact of increased CO2 levels on plant productivity and the ability to resolve changes in intra‐annual precipitation patterns. The consideration of both external drivers is crucial under climate change, hence sustainable long‐term decision making is currently lacking important information. Synthesis and applications. Sustainable livestock management in semi‐arid and arid systems requires knowledge about effects of future climate change to adjust livestock density adequately. Producers’ experiences from current weather conditions are not necessarily transferable to future conditions, thus models could help to support management. However, an analysis of current models has shown that few existing models are able to assess the impacts of the predicted climate change. Therefore, we call for the development of new dynamic grazing models that provide land managers with the necessary tools to face the threat of future climate changes.

Effects of Soluble Gas Stabilisation, Modified Atmosphere, Gas to Product Volume Ratio and Storage on the Microbiological and Sensory Characteristics of Ready-to-Eat Shrimp (Pandalus borealis)

The effects of storage time, modified atmospheres (30% or 60% CO2), soluble gas stabilisation and gas to product volume ( g/ p) ratio were investigated on the microbiological and sensory characteristics of cooked, peeled and brined ready-to-eat (RTE) deep-water shrimps ( Pandalus borealis). Soluble gas stabilisation (SGS) treatment prior to packaging (2h) increased the CO2 content in the packaged shrimp and counteracted package collapse, even at low g/ p ratios (0.66). SGS treatment reduced significantly (P 0.01) the aerobic plate count and psychrotrophic count. The increase of CO2 levels during modified atmosphere (MA) packaging and the application of SGS significantly enhanced (P 0.01) the sensory quality of the shrimps. The exudates in the packages (%) were significantly reduced (P 0.01) when applying SGS treatment. Therefore, SGS treatment in combination with MA packaging can be used successfully on RTE shrimps to reduce the package volume and to improve the microbiological and sensory characteristics.

Exhaled CO, a predictor of lung function?

Smoking is associated with an accelerated loss of lung function and inhalation accelerates the decline further. Exhaled CO reflects the exposure of smoke to the lungs. To investigate whether self-reported inhalation and type of cigarette influenced the level of exhaled CO and whether CO could provide additional information to usual measures of smoking regarding prediction of present lung function and decline in lung function over an extended period of time. Cigarette smokers from the Copenhagen City Heart Study with valid measures of lung function and exhaled CO; in total 3738 subjects, 2096 women and 1642 men. Subjects not inhaling had slightly lower exhaled CO values than those inhaling, but substantially higher values than non-smokers (P<0.001). Smokers of plain cigarettes had slightly lower CO values than smokers of filter cigarettes (P<0.001). Increasing CO levels were correlated to a lower FEV(1)%pred and to an accelerated decline in lung function. However, in multiple linear regression analyses these correlations were not significant. Inhalation and type of cigarette affects exhaled CO levels. CO measures have no predictive value regarding neither present lung function nor decline in lung function with time in a population survey setting.

How close are we to a predictive science of the biosphere?

In just 20 years, the field of biosphere-atmosphere interactions has gone from a nascent discipline to a central area of modern climate change research. The development of terrestrial biosphere models that predict the responses of ecosystems to climate and increasing CO2 levels has highlighted several mechanisms by which changes in ecosystem composition and function might alter regional and global climate. However, results from empirical studies suggest that ecosystem responses can differ markedly from the predictions of terrestrial biosphere models. As I discuss here, the challenge now is to connect terrestrial biosphere models to empirical ecosystem measurements. Only by systematically evaluating the predictions of terrestrial biosphere models against suites of ecosystem observations and experiments measurements will a true predictive science of the biosphere be achieved.

Nitrogen limitation constrains sustainability of ecosystem response to CO2

Enhanced plant biomass accumulation in response to elevated atmospheric CO2 concentration could dampen the future rate of increase in CO2 levels and associated climate warming. However, it is unknown whether CO2-induced stimulation of plant growth and biomass accumulation will be sustained or whether limited nitrogen (N) availability constrains greater plant growth in a CO2-enriched world. Here we show, after a six-year field study of perennial grassland species grown under ambient and elevated levels of CO2 and N, that low availability of N progressively suppresses the positive response of plant biomass to elevated CO2. Initially, the stimulation of total plant biomass by elevated CO2 was no greater at enriched than at ambient N supply. After four to six years, however, elevated CO2 stimulated plant biomass much less under ambient than enriched N supply. This response was consistent with the temporally divergent effects of elevated CO2 on soil and plant N dynamics at differing levels of N supply. Our results indicate that variability in availability of soil N and deposition of atmospheric N are both likely to influence the response of plant biomass accumulation to elevated atmospheric CO2. Given that limitations to productivity resulting from the insufficient availability of N are widespread in both unmanaged and managed vegetation, soil N supply is probably an important constraint on global terrestrial responses to elevated CO2.