Showing papers on "Carbon dioxide in Earth's atmosphere published in 1993"
TL;DR: The ocean is a significant sink for anthropogenic carbon dioxide, taking up about a third of the emissions arising from fossil fuel use and tropical deforestation as discussed by the authors, but there still appears to be a "missing sink" which may be located in the terrestrial biosphere.
Abstract: The ocean is a significant sink for anthropogenic carbon dioxide, taking up about a third of the emissions arising from fossil-fuel use and tropical deforestation. Increases in the atmospheric carbon dioxide concentration account for most of the remaining emissions, but there still appears to be a 'missing sink' which may be located in the terrestrial biosphere.
1,020 citations
TL;DR: This article found that the tundra on the North Slope of Alaska has indeed become a source of carbon dioxide to the atmosphere and that this change coincides with recent warming in the Arctic, whether this is due to increases in greenhouse gas concentrations in the atmosphere or to some other cause.
Abstract: ARCTIC tundra has been a net sink for carbon dioxide during historic and recent geological times1–4, and large amounts of carbon are stored in the soils of northern ecosystems. Many regions of the Arctic are warmer now than they have been in the past5–10, and this warming may cause the soil to change from a carbon dioxide sink to a source by lowering the water table11–12, thereby accelerating the rate of soil decomposition (CO2 source)3,13–15 so that this dominates over photosynthesis (CO2 sink). Here we present data indicating that the tundra on the North Slope of Alaska has indeed become a source of carbon dioxide to the atmosphere. This change coincides with recent warming in the Arctic, whether this is due to increases in greenhouse gas concentrations in the atmosphere or to some other cause. Our results suggest that tundra ecosystems may exert a positive feedback on atmospheric carbon dioxide and greenhouse warming.
926 citations
TL;DR: The eddy correlation method was used to measure the net ecosystem exchange of carbon dioxide continuously from April 1990 to December 1991 in a deciduous forest in central Massachusetts, and carbon uptake rates were notably larger than those assumed for temperate forests in global carbon studies.
Abstract: The eddy correlation method was used to measure the net ecosystem exchange of carbon dioxide continuously from April 1990 to December 1991 in a deciduous forest in central Massachusetts. The annual net uptake was 3.7 ± 0.7 metric tons of carbon per hectare per year. Ecosystem respiration, calculated from the relation between nighttime exchange and soil temperature, was 7.4 metric tons of carbon per hectare per year, implying gross ecosystem production of 11.1 metric tons of carbon per hectare per year. The observed rate of accumulation of carbon reflects recovery from agricultural development in the 1800s. Carbon uptake rates were notably larger than those assumed for temperate forests in global carbon studies. Carbon storage in temperate forests can play an important role in determining future concentrations of atmospheric carbon dioxide.
893 citations
TL;DR: In this article, the authors consider the long-term rates of river loading of organic carbon, organic burial, chemical reactivity of land-derived organic matter, and rates of community metabolism in the coastal zone, and estimate that coastal zone oxidizes about 7 × 1012 moles C/yr.
Abstract: Net organic metabolism (that is, the difference between primary production and respiration of organic matter) in the coastal ocean may be a significant term in the oceanic carbon budget. Historical change in the rate of this net metabolism determines the importance of the coastal ocean relative to anthropogenic perturbations of the global carbon cycle. Consideration of long-term rates of river loading of organic carbon, organic burial, chemical reactivity of land-derived organic matter, and rates of community metabolism in the coastal zone leads us to estimate that the coastal zone oxidizes about 7 × 1012 moles C/yr. The open ocean is apparently also a site of net organic oxidation (∼16 × 1012 moles C/yr). Thus organic metabolism in the ocean appears to be a source of CO2 release to the atmosphere rather than being a sink for atmospheric carbon dioxide. The small area of the coastal ocean accounts for about 30% of the net oceanic oxidation. Oxidation in the coastal zone (especially in bays and estuaries) takes on particular importance, because the input rate is likely to have been altered substantially by human activities on land.
674 citations
TL;DR: It is proposed that the global expansion of C4 biomass may be related to lower atmospheric carbon dioxide levels because C4 photosynthesis is favoured over C3 photosynthesis when there are low concentrations of carbon dioxide in the atmosphere.
Abstract: THE most common and the most primitive pathway of the three different photosynthetic pathways used by plants is the C3 pathway, or Calvin cycle, which is characterized by an initial CO2 carboxylation to form phosphoglyceric acid, a 3-carbon acid. The carbon isotope composition (δ13C) of C3 plants varies from about −23 to −35%l–3 and averages about −26%. Virtually all trees, most shrubs, herbs and forbs, and cool-season grasses and sedges use the C3 pathway. In the C4 pathway (Hatch–Slack cycle), CO2 initially combines with phosphoenol pyruvate to form the 4-carbon acids malate or aspartic acid, which are translocated to bundle sheath cells where CO2 is released and used in Calvin cycle reactions1–4. The carbon isotope composition of C4 plants ranges from about −10 to −14%, averaging about −13% for modern plants1–3. Warm-season grasses and sedges are the most abundant C4 plants, although C4 photosynthesis is found in about twenty families5. The third photosynthetic pathway, CAM, combines features of both C3 and C4 pathways. CAM plants, which include many succulents, have intermediate carbon isotope compositions and are also adapted to conditions of water and CO2 stress. The modern global ecosystem has a significant component of C4 plants, primarily in tropical savannas, temperate grasslands and semi-desert scrublands. Studies of palaeovegetation from palaeosols and palaeodiet from fossil tooth enamel indicate a rapid expansion of C4 biomass in both the Old World and the New World starting 7 to 5 million years ago. We propose that the global expansion of C4 biomass may be related to lower atmospheric carbon dioxide levels because C4 photosynthesis is favoured over C3 photosynthesis when there are low concentrations of carbon dioxide in the atmosphere.
654 citations
TL;DR: Evidence from stomatal frequencies of fossil Quercus petraea leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO2 concentrations during the last 10 million years.
Abstract: An increase in the atmospheric carbon dioxide (CO2) concentration results in a decrease in the number of leaf stomata. This relation is known both from historical observations of vegetation over the past 200 years and from experimental manipulations of microenvironments. Evidence from stomatal frequencies of fossil Quercus petraea leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO2 concentrations during the last 10 million years. The data suggest that late Neogene CO2 concentrations fluctuated between about 280 and 370 parts per million by volume.
274 citations
TL;DR: Holocene and glacial carbon isotope data of benthic foraminifera from shallow to mid-depth cores from the northeastern subpolar Atlantic show that this region was strongly stratified, with carbon- 13—enriched glacial North Atlantic intermediate water (GNAIW) overlying carbon-13—depleted Southern Ocean water (SOW).
Abstract: Holocene and glacial carbon isotope data of benthic foraminifera from shallow to mid-depth cores from the northeastern subpolar Atlantic show that this region was strongly stratified, with carbon-13—enriched glacial North Atlantic intermediate water (GNAIW) overlying carbon-13—depleted Southern Ocean water (SOW). The data suggest that GNAIW originated north of the polar front and define GNAIW end-member carbon isotope values for studies of water-mass mixing in the open Atlantic. Identical carbon isotope values in the core of GNAIW and below the subtropical thermocline are consistent with rapid cycling of GNAIW through the northern Atlantic. The high carbon isotope values below the thermocline indicate that enhanced nutrient leakage in response to increased ventilation may have extended into intermediate waters. Geochemical box models show that the atmospheric carbon dioxide response to nutrient leakage that results from an increase in ventilation rate may be greater than the response to nutrient redistribution by conversion of North Atlantic deep water into GNAIW. These results underscore the potential rule of Atlantic Ocean circulation changes in influencing past atmospheric carbon dioxide values.
249 citations
TL;DR: Observations showed a trend of increased interannual variability of Indian monsoon precipitation associated with warmer land and ocean temperatures in the monsoon region.
Abstract: Doubled atmospheric carbon dioxide concentration in a global coupled ocean-atmosphere climate model produced increased surface temperatures and evaporation and greater mean precipitation in the south Asian summer monsoon region. As a partial consequence, interannual variability of area-averaged monsoon rainfall was enhanced. Consistent with the climate sensitivity results from the model, observations showed a trend of increased interannual variability of Indian monsoon precipitation associated with warmer land and ocean temperatures in the monsoon region.
193 citations
TL;DR: In this paper, the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent Arrhenius activation energy of 18.4 kcal/mol (77.0 kJ/mol), much higher than most laboratory values.
Abstract: Estimation of the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent Arrhenius activation energy of 18.4 kcal/mol (77.0 kJ/mol), much higher than most laboratory values. This finding supports recent suggestions that hydrolytic weathering of silicate minerals may consume carbonic acid and thereby remove atmospheric carbon dioxide more rapidly with increasing temperature than previously thought. This result provides a stronger negative feedback on long-term greenhouse warming than has been assumed in most models of global carbon cycling. The present estimate was determined from the ratio of feldspar weathering rates (determined by geochemical mass balance) in the southern Blue Ridge Mountains of North Carolina, United States. Temperature (a function of elevation) is the only factor that differs between the two catchments; parent rock type, aspect, hillslope hydrology, and vegetation type and successional stage are the same in both.
173 citations
TL;DR: Observations from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity, which conflicts with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump.
Abstract: Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.
135 citations
State University of New York System1, Lawrence Livermore National Laboratory2, Bureau of Meteorology3, Colorado State University4, Goddard Institute for Space Studies5, Max Planck Society6, Russian Academy of Sciences7, National Center for Atmospheric Research8, Hadley Centre for Climate Prediction and Research9, European Centre for Medium-Range Weather Forecasts10, National Oceanic and Atmospheric Administration11
TL;DR: The largest contributor was the carbon dioxide radiation parameterizations of the models, which differed substantially among 15 atmospheric general circulation models.
Abstract: Global warming, caused by an increase in the concentrations of greenhouse gases, is the direct result of greenhouse gas-induced radiative forcing. When a doubling of atmospheric carbon dioxide is considered, this forcing differed substantially among 15 atmospheric general circulation models. Although there are several potential causes, the largest contributor was the carbon dioxide radiation parameterizations of the models.
TL;DR: In this paper, a minimum dynamical model of the late Cenozoic climatic changes, containing what are believed to be the main physical factors determining these changes: ice mass, bedrock depression, atmospheric carbon dioxide concentration, deep ocean thermohaline state, Milankovitch radiation forcing, and slow tectonically-induced carbon dioxide forcing, is presented.
Abstract: It has been noted that several distinct modes of glacial oscillation have existed during the past few million years, ranging from low-amplitude, high-frequency oscillations in the early Pliocene, through relatively high amplitude, predominantly near-40 ky period, oscillations in the late Pliocene and early Pleistocene, to the major near-100 ky period oscillations of the late Pleistocene. In addition to other plausible mechanisms suggested previously to explain aspects of this multirhythmic phenomenon, we now illustrate another possible contributor to this type of behavior based on the hypothesis that the slow-response climatic system is bistable and that two kinds of internal instability may be operative along with externally imposed forcing due to earth-orbital (Milankovitch) radiation changes and slow, tectonically-induced changes in atmospheric carbon dioxide. These two instabilities have been discussed previously: one is due to positive feedback in the global carbon cycle leading to near-100 ky free oscillations of the ice sheets, and the other is due to the potential for ice-calving catastrophes associated with bedrock variations that can lead to oscillations of a period near 40 ky, independent of obliquity forcing. Within the framework of a dynamical model containing the possibility for these two instabilities, as well as for stable modes, we show (1) how Milankovitch radiative changes or stochastic forcing influencing ice sheets can induce aperiodic (chaotic) transitions between the possible stable and unstable modes, and more significantly, (2) how progressive, long-term, tectonically-induced, changes in carbon dioxide, acting in concert with earth-orbital radiative variations in high Northern Hemisphere latitudes, can force systematic transitions between the modes. Such systematic changes can result in an ice mass chronology for the past 5 My that is qualitatively similar to the observed record of global ice mass. In essence, we have constructed a minimum dynamical model of the late Cenozoic climatic changes, containing what are believed to be the main physical factors determining these changes: ice mass, bedrock depression, atmospheric carbon dioxide concentration, deep ocean thermohaline state, Milankovitch radiation forcing, and slow tectonically-induced carbon dioxide forcing. This model forms the basis for a coherent theory for the complex climatic events of this long period.
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TL;DR: In 1896, the Nobel Prize-winning Swedish chemist Svante Arrhenius proposed that carbon dioxide going into the atmosphere from the burning of fossil fuels such as coal, oil, and natural gas was causing a change in the transparency of the atmosphere that might result in a warming outside the realm of previous human experience as mentioned in this paper.
Abstract: In 1896, the Nobel Prize-winning Swedish chemist Svante Arrhenius proposed that carbon dioxide going into the atmosphere from the burning of fossil fuels such as coal, oil, and natural gas was causing a change in the transparency of the atmosphere that might result in a warming outside the realm of previous human experience. The basic greenhouse theory had been introduced almost 70 years before by the French mathematician Jean-Baptiste-Joseph Fourier, who suggested that certain gases in the atmosphere could absorb radiation, thereby trapping it much as heat is trapped in a greenhouse. By the late 1850s, British physicist John Tyndall had analyzed the radiative properties of atmospheric gases, demonstrating that carbon dioxide was among those that strongly absorb radiation emitted from the Earth. Arrhenius' idea lapsed into obscurity, in part because scientists doubted that the carbon dioxide emitted by fossil fuel burning accumulated in the atmosphere. That's because the ocean plays an unusually important ...
TL;DR: A general circulation model with seasonally varying solar insolation and a mixed layer ocean is applied to assess the role of continental geometry and increased levels of carbon dioxide to explain the warmth of the Cretaceous period as discussed by the authors.
Abstract: A general circulation model (GENESIS) with seasonally varying solar insolation and a mixed layer ocean is applied to assess the role of continental geometry and increased levels of carbon dioxide to explain the warmth of the Cretaceous period. Model experiments suggest that the role of geography is negligible, in contrast to early model studies with mean annual solar insolation and a simple energy balance ocean. Higher atmospheric carbon dioxide (4 times present) resulted in a 5.5 degrees C globally averaged surface temperature increase, close to the lower limit required to explain the geologic record. Mid-Cretaceous carbon dioxide concentrations of 4-6 times the present day concentrations are a reasonable explanation of Cretaceous warmth if the GENESIS model provides an accurate estimate of climate sensitivity to geography and carbon dioxide.
TL;DR: The ozone hole was first discovered in 1985 and conclusive proof of its association with chlorofluorocarb ons (CFCs) was found in 1987 as mentioned in this paper, and the average thickness of the ozone layer in the northern mid-latitudes had decreased during the 1980s by as much as 5% (I, 2).
Abstract: Over the past five years there has been a renewed concern over the condition of the atmosphere and the global impact of air pollution. This concern has largely been sparked by the discovery of the ozone "hole" in the stratosphere, and the rediscovery of greenhouse warming_ The ozone hole was first discovered in 1985, and conclusive proof of its association with chlorofluorocarb ons (CFCs) was found in 1987. This was followed by estimates that the average thickness of the ozone layer in the northern mid-latitudes had decreased during the 1980s by as much as 5% (I, 2). The greenhouse effect is hardly a new discovery; the chemist Arrhenius suggested 100 years ago that increased carbon dioxide from fossil fuels could lead to increased greenhouse warming. However, the accelerated increase in atmospheric carbon dioxide and methane observed during the
TL;DR: In this article, the excess CO2 signal calculated from the carbonate data in the Atlantic, Pacific and Indian Oceans, including Norwegian, Greenland, Weddell, Bering, South China and the Red Seas indicate that the distribution of anthropogenic CO2 follows the large-scale movements of water masses such as vertical mixing in the northwest North Atlantic, upwelling, and Mode Water formation.
TL;DR: In this paper, the authors proposed that increasing sustainable development will not only improve the economic well-being of the people living in the tropics but also has a great potential to reduce atmospheric carbon dioxide concentrations through reduction of emissions and increase in area of land that serves as carbon sinks.
TL;DR: In this paper, the role of terrestrial feedback processes within the carbon cycle and their impact on the carbon budget was evaluated. But the authors only evaluated terrestrial feedbacks in terms of their potential influence on the global carbon cycle.
Abstract: Within the carbon cycle feedback, mechanisms that amplify or dampen the exchange of carbon dioxide between the different reservoirs to enhance concentrations of carbon dioxide and increase temperature from anthropogenic perturbations, play a crucial role. Quite a lot of these feedbacks are known, but most of them only potentially. This article evaluates the role of a number of these feedback processes within the carbon cycle. In order to assess their impact, some terrestrial feedbacks have been built into a coupled carbon cycle and climate model, as part of the integrated climate assessment model IMAGE. A number of simulation experiments have been performed with this coupled carbon cycle/climate model to compare historical atmospheric concentration values of carbon dioxide with simulated values. Also global biospheric and oceanic carbon fluxes were validated against other modelling estimates. Based on the assumptions of the IPCC's 1990 Business-as-Usual (BaU-1990) scenario, future projections of the carbon dioxide concentration have been made. A key principle in this is that we have used the modelled feedbacks in order to balance the past and present carbon budget. For atmospheric carbon dioxide, this results in substantially lower projections than the IPCC-estimates: the difference in 2100 is approximately 16% from the 1990 level. Furthermore, the IPCC's ‘best guess’ or ‘central estimate’ value of the CO 2 concentration in 2100 falls outside the uncertainty range estimated with our balanced modelling approach. Sensitivity experiments with the model have been performed to quantify to what extent the terrestrial feedback processes and oceanic fluxes influence the global carbon balance in the model. It is shown that a historical and present carbon balance can be obtained in many different ways, resulting in different biospheric fluxes and thus in considerably different atmospheric CO 2 projections. DOI: 10.1034/j.1600-0889.1993.t01-3-00001.x
01 Jan 1993
TL;DR: A currently popular question is whether the global warming, measured during the past century, and especially in the decade of the 1980s, is the warming expected to occur because of human-produced (anthropogenic) increases of atmospheric greenhouse gases (GHGs) as discussed by the authors.
Abstract: A currently popular question is whether the global warming, measured during the past century, and especially in the decade of the 1980s, is the warming expected to occur because of human-produced (anthropogenic) increases of atmospheric greenhouse gases (GHGs). These include not only CO2, but also methane, ozone, water vapor, and other radiatively active gases. The answer to this question has great political significance, serving as a basis for potential governmental actions.
01 Jan 1993
TL;DR: In this article, the relative roles of the ocean and land biota in the current global balance of atmospheric carbon dioxide are discussed. But the authors do not consider the role of the terrestrial biosphere.
Abstract: This volume is based on recent controversial findings regarding the relative roles of the ocean and land biota in the current global balance of atmospheric carbon dioxide. It reviews the multitude of known constraints on the present-day global carbon cycle as identified by research in the fields of meteorology, physical and biological oceanography, geology and terrestrial biosphere science. It is divided into three sections on emissions of carbon dioxide from fossil fuel use, the role of the terrestrial biosphere, and the role of the ocean and the contemporary global carbon cycle.
01 Jan 1993
TL;DR: Woodwell et al. as mentioned in this paper estimated that about 2100 Pg of organic carbon are held in the earth's terrestrial ecosystems: 550 Pg in living plants and 1500 pg in the organic matter of soils, and that changes in terrestrial ecosystems are important in affecting the atmospheric concentration of CO2.
Abstract: About 2100 Pg of organic C are held in the earth’s terrestrial ecosystems: 550 Pg in living plants and 1500 Pg in the organic matter of soils (Houghton et al. 1985b). Because this terrestrial reservoir of carbon is about 3 times greater than the atmospheric reservoir of carbon, and because the annual exchanges of carbon between terrestrial ecosystems and the atmosphere are large (100–120 PgC), changes in terrestrial ecosystems are important in affecting the atmospheric concentration of CO2. Attempts to estimate such changes have been underway for more than a decade (Woodwell and Pecan 1973, Bolin 1977, Woodwell and Houghton 1977, Woodwell et al. 1978).
TL;DR: This paper examined various possibilities and found that the evidence for a sink of sufficient magnitude on land is poor and it is unlikely that the land vegetation will act as a sink in the postulated warmer global climates of the future.
Abstract: Despite 20 years of intensive effort to understand the global carbon cycle, the budget for carbon dioxide in the atmosphere is unbalanced To explain why atmospheric CO2 is not increasing as rapidly as it should be, various workers have suggested that land vegetation acts as a sink for carbon dioxide Here, I examine various possibilities and find that the evidence for a sink of sufficient magnitude on land is poor Moreover, it is unlikely that the land vegetation will act as a sink in the postulated warmer global climates of the future In response to rapid human population growth, destruction of natural ecosystems in the tropics remains a large net source of CO2 for the atmosphere, which is only partially compensated by the potential for carbon storage in temperate and boreal regions Direct and inadvertent human effects on land vegetation might increase the magnitude of regional CO2 storage on land, but they are unlikely to play a significant role in moderating the potential rate of greenhouse warming in the future
01 Jan 1993
TL;DR: There has been a recent upsurge in interest in the reactivity of carbon dioxide for two primary reasons: carbon dioxide is the ultimate byproduct of all processes involving oxidation of carbon compounds and its increasing presence in the atmosphere since the beginning of the Industrial Revolution has given rise to widespread concern about possible consequences (the so- called "Greenhouse Effect").
Abstract: There has been a recent upsurge in interest in the reactivity of carbon dioxide for two primary reasons. Firstly, carbon dioxide is the ultimate by-product of all processes involving oxidation of carbon compounds and its increasing presence in the atmosphere since the beginning of the Industrial Revolution has given rise to widespread concern about possible consequences (the so- called "Greenhouse Effect"). Secondly, in view of the vastness of its supply, carbon dioxide represents a possible potential source for C₁ feedstocks for the manufacture of chemicals and fuels, alternative to the current predominant use of petroleum-derived sources. Carbon reserves in the form of atmospheric carbon dioxide, carbon dioxide in the hydrosphere and carbonates in the terrestrial environment substantially exceed those of the fossil fuels such as coal and petroleum.
01 Jan 1993
TL;DR: In this paper, the authors outline the scale of the discrepancies involved and offer hypotheses concerning previously underappreciated carbon fluxes that suggest new research directions and postulate global vegetation change at several time scales as a plausible reason for our inability to balance the global carbon cycle over long time periods.
Abstract: Over the past several decades, significant progress has been made in measuring and understanding the global carbon cycle and in developing methods for projecting future changes in atmospheric CO2 concentration During this time, a natural starting point was to check the balance sheet that accounts for all carbon as it exchanged between the major global carbon reservoirs While it is possible to achieve a balance for a single instant in time (for example, the year 1980: see Detweiler and Hall 1988; Houghton et al 1987), it is not possible with current information to balance carbon fluxes for decade-or-longer time periods The inability to account for all carbon exchanges indicates an insufficient knowledge of global carbon cycle processes In this chapter, I outline the scale of the discrepancies involved and offer hypotheses concerning previously underappreciated carbon fluxes that suggest new research directions These hypotheses postulate global vegetation change at several time scales as a plausible reason for our inability to “balance” the global carbon cycle over long time periods
01 Jan 1993
TL;DR: In this paper, the authors estimate that the CO2 sinks to remove 2.9-5.0 GtC/yr, an amount equal to 43% of the fossil fuel plus 100% of deforestation inputs.
Abstract: The atmospheric increase of carbon dioxide in the 1980s represents only ~57% of the release from fossil-fuel combustion. A balanced budget thus requires the CO2 sinks to remove 2.9–5.0 GtC/yr, an amount equal to 43% of the fossil fuel plus 100% of the deforestation inputs. Oceanic uptake estimated directly from data on air-sea differences in the partial pressures of CO2 is ~1.6 GtC/yr; uncertainties in this estimate due to inadequate sampling both in time and space are difficult to quantify. Ocean models yield oceanic sink strengths ~30% of the fossil-fuel inputs alone, implying a significant net terrestrial sink. Interhemispheric gradient of CO2 in the atmosphere points to a Northern Hemisphere mid-latitudes sink, whereas deconvolution of the historical records suggests that the sink has been operative for the past 50 years. Although isotopic data can potentially provide powerful constraints on the partitioning of the CO2 sink between land and sea, the conclusions are highly dependent on the δ13C value of the respired CO2. Understanding ecosystem dynamics with turnover times of 10–100 years is, thus, tantamount.
TL;DR: In this paper, two box models, one analytical and one numerical, are used to investigate systematically a broad range of oceanic circulation changes on the atmospheric carbon dioxide (CO2) concentration.
Abstract: Two box models, one analytical and one numerical, are used to investigate systematically a broad range of oceanic circulation changes on the atmospheric carbon dioxide (CO2) concentration. A number of oceanic carbon cycle models have failed to reproduce the 30% increase in CO2 partial pressure (pCO2) during the last deglaciation as reconstructed from polar ice cores. We apply therefore this approach of exploring the model's parameter space to examine the effect of long-lived dissolved organic matter on the system. The results from the two models complement each other, in terms of insight versus detail. Carbon is usually assumed to be transported from the surface into the deep ocean through the sedimentation of particulate matter. If there exists in the ocean a pool of dissolved organic matter (DOM) with a regeneration time comparable with the advection time, then the associated carbon can also be advected, resulting in a different distribution. Such a DOM reservoir acts as a smoother on the spatial distribution of nutrients in the sea, particularly in the equatorial intermediate waters. We establish the role of intermediate waters as one of the key components of the oceanic carbon cycle and show that DOM reduces the sensitivity of the carbon cycle to oceanic circulation pattern changes, mainly because of its smoothing effect. Consequently, the possible existence of DOM species with a time constant of the order of a century tends to reduce, rather than enhance, the glacial-interglacial difference in pCO2 levels due to changes in the thermohaline circulation.
01 Jan 1993
TL;DR: In this article, the processes that control atmospheric carbon dioxide can be analyzed in terms of biogeochemical cycles that transfer carbon between reservoirs, where the small atmospheric reservoir is closely linked to other small reservoirs, shallow sea and biota.
Abstract: The carbon dioxide content of the atmosphere affects life, climate, and the chemistry of oceans and sedimentary rocks. The processes that control atmospheric carbon dioxide can be analyzed in terms of biogeochemical cycles that transfer carbon between reservoirs. The small atmospheric reservoir is closely linked to other small reservoirs, shallow sea and biota. Transfer of carbon between these small reservoirs is rapid; residence times are short. The small reservoirs are connected by slower transfers to a much larger deep sea reservoir, and the coupled reservoirs of ocean, atmosphere, and biota are coupled, in turn, to very much larger reservoirs in sedimentary rocks. The exogenic reservoirs of sedimentary rocks, ocean, atmosphere, and life are coupled, in turn, by the very slow exchange of carbon with a large mantle reservoir. This hierarchy of interacting reservoirs controls atmospheric carbon dioxide on all time scales. Particular problems with restricted time scales can be analyzed in terms of a subset of the total system. Observations that illustrate interactions on different levels of the hierarchy include the seasonal change of carbon dioxide partial pressure, the glacial to interglacial change, and the evolving distribution of carbonate sediments.
01 May 1993
TL;DR: In this paper, a set of paleogeographic maps of Africa for the Last Glacial Maximum (LGM) and the Holocene Climatic Optimum (HCO) is compared.
Abstract: Comparison of a set of paleogeographic maps of Africa for the Last Glacial Maximum (LGM) and the Holocene Climatic Optimum (HCO) allows us to discuss the contribution of paleocontinental proxy-data in paleobiomass calculations and their accuracy. Maps show considerable shifts in the area covered by the main ecosystems. In this study we have quantified these areal changes, from the LGM to the HCO, in terms of variations in carbon storage. Each biome has been assigned a carbon density in living and soil organic matter. From desert to tropical forest the mean carbon densities vary from 0 to 20 kg m −2 for phytomass and from 0 to 13 kg m −2 for soil (peat excluded). During the world deglaciation Africa was a sink for 154 Gt (standard deviation 42 Gt) of atmospheric carbon. Since the HCO Africa has been a source of carbon. More recently human deforestation is responsible for a carbon flux towards the atmosphere which is ten times the mean annual flux due to vegetation change in response to climate change. Extended to a global scale this regional test shows that the paleoenvironmental approach is more appropriate for paleobiomass estimates than calculations based only on oceanic data.
01 Jan 1993
TL;DR: In this article, the authors present numerical simulations of atmospheric CO2 concentrations over the next few hundreds to hundreds of thousands of years for various patterns of fossil fuel consumption and land use.
Abstract: Atmospheric CO2 levels are currently increasing as a consequence of the burning of fossil fuels and deforestation of tropical lands. Here, we present numerical simulations of atmospheric CO2 concentrations over the next few hundreds to hundreds of thousands of years for various patterns of fossil-fuel consumption and land use. The computer model predicts that atmospheric CO2 concentrations could exceed 2000 ppm (parts per million) within the next few centuries if we consume most of the available fossil fuel and if the current trend toward deforestation continues. This prediction is relatively insensitive to the future rate of fossil-fuel-burning unless the consumption rate is several times lower than the present rate. Conserving existing forests or planting new ones might lower the peak CO2 level by a factor of 2 if CO2 fertilization of plant growth is effective in natural settings and if soil carbon storage does not decrease as the global climate warms. The model also predicts that most of the anthropogenic CO2 will be removed within the next 5000 to 10,000 years, but that more than a million years will pass before atmospheric CO2 returns to its original, reindustrial value.
01 Jan 1993
TL;DR: The human potential to rise its future atmospheric concentration seems to be very high, since the fossil carbon resources (coal, oil, natural gas) probably exceed 65 × 1012 tons (6,500 Gt) of carbon as discussed by the authors.
Abstract: Carbon dioxide is presently the most important anthropogenic greenhouse gas, and in contrast to the other greenhouse gases, the human potential to rise its future atmospheric concentration seems to be very high, since the fossil carbon resources (coal, oil, natural gas) probably exceed 65 × 1012 tons (6,500 Gt) of carbon The preindustrial CO2 concentration in the atmosphere of ca 280 μl-l1 will double within the next 5–6 decades The predicted global mean warming will then probably be 35 ±15 °C, according to climate models (Hansen et al 1988)