Showing papers on "Carbon dioxide in Earth's atmosphere published in 2010"
TL;DR: Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants.
Abstract: Climate change, rising atmospheric carbon dioxide, excess nutrient inputs, and pollution in its many forms are fundamentally altering the chemistry of the ocean, often on a global scale and, in some cases, at rates greatly exceeding those in the historical and recent geological record. Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants. Most of these perturbations, tied either directly or indirectly to human fossil fuel combustion, fertilizer use, and industrial activity, are projected to grow in coming decades, resulting in increasing negative impacts on ocean biota and marine resources.
714 citations
TL;DR: In this paper, a reconstruction of atmospheric carbon dioxide levels 4.5 million years ago suggests that Earth-system climate sensitivity is significantly higher than that estimated from global climate models, which includes only fast feedback mechanisms such as changes in clouds and sea ice.
Abstract: Earth-system climate sensitivity includes the effects of long-term feedbacks such as changes in continental ice-sheet extent and terrestrial ecosystems. A reconstruction of atmospheric carbon dioxide levels 4.5 million years ago suggests that Earth-system climate sensitivity is significantly higher than that estimated from global climate models, which includes only fast feedback mechanisms such as changes in clouds and sea ice. Climate sensitivity—the mean global temperature response to a doubling of atmospheric CO2 concentrations through radiative forcing and associated feedbacks—is estimated at 1.5–4.5 ∘C (ref. 1). However, this value incorporates only relatively rapid feedbacks such as changes in atmospheric water vapour concentrations, and the distributions of sea ice, clouds and aerosols2. Earth-system climate sensitivity, by contrast, additionally includes the effects of long-term feedbacks such as changes in continental ice-sheet extent, terrestrial ecosystems and the production of greenhouse gases other than CO2. Here we reconstruct atmospheric carbon dioxide concentrations for the early and middle Pliocene, when temperatures were about 3–4 ∘C warmer than preindustrial values3,4,5, to estimate Earth-system climate sensitivity from a fully equilibrated state of the planet. We demonstrate that only a relatively small rise in atmospheric CO2 levels was associated with substantial global warming about 4.5 million years ago, and that CO2 levels at peak temperatures were between about 365 and 415 ppm. We conclude that the Earth-system climate sensitivity has been significantly higher over the past five million years than estimated from fast feedbacks alone.
543 citations
TL;DR: Evidence is presented that carbon dioxide inhibition of nitrate assimilation is a major determinant of plant responses to rising atmospheric concentrations of carbon dioxide, and that the relative availability of soil ammonium and nitrate to most plants will become increasingly important in determining their productivity as well as their quality as food.
Abstract: The concentration of carbon dioxide in Earth's atmosphere may double by the end of the 21st century. The response of higher plants to a carbon dioxide doubling often includes a decline in their nitrogen status, but the reasons for this decline have been uncertain. We used five independent methods with wheat and Arabidopsis to show that atmospheric carbon dioxide enrichment inhibited the assimilation of nitrate into organic nitrogen compounds. This inhibition may be largely responsible for carbon dioxide acclimation, the decrease in photosynthesis and growth of plants conducting C(3) carbon fixation after long exposures (days to years) to carbon dioxide enrichment. These results suggest that the relative availability of soil ammonium and nitrate to most plants will become increasingly important in determining their productivity as well as their quality as food.
498 citations
TL;DR: Radiocarbon data from the Southern Ocean indicate that the deep water circulating around Antarctica was about twice as old relative to the atmosphere as it is today, a condition considered indicative of carbon dioxide accumulation and storage.
Abstract: Past glacial-interglacial increases in the concentration of atmospheric carbon dioxide (CO2) are thought to arise from the rapid release of CO2 sequestered in the deep sea, primarily via the Southern Ocean. Here, we present radiocarbon evidence from the Atlantic sector of the Southern Ocean that strongly supports this hypothesis. We show that during the last glacial period, deep water circulating around Antarctica was more than two times older than today relative to the atmosphere. During deglaciation, the dissipation of this old and presumably CO2-enriched deep water played an important role in the pulsed rise of atmospheric CO2 through its variable influence on the upwelling branch of the Antarctic overturning circulation.
447 citations
TL;DR: In this paper, a coupled atmosphere-ocean general circulation model was used to simulate the climate of the mid-Pliocene warm period (about three million years ago) and analyse the forcings and feedbacks that contributed to relatively warm temperatures.
Abstract: Quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is one of the cornerstones of climate research Components of the Earth’s climate system that vary over long timescales, such as ice sheets and vegetation, could have an important effect on this temperature sensitivity, but have often been neglected Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30–50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity We conclude that targets for the long-term stabilization of atmospheric greenhouse-gas concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system
267 citations
TL;DR: It is hypothesized that a lower albedo on the Earth, owing to considerably less continental area and to the lack of biologically induced cloud condensation nuclei, made an important contribution to moderating surface temperature in the Archaean eon, thus alleviating the need for extreme greenhouse-gas concentrations to satisfy the faint early Sun paradox.
Abstract: The faint early or 'young' Sun paradox, raised by Carl Sagan and George Mullen in 1972, points out that solar luminosity during the Archaean was about 70% of today's, so it would the theory goes have been too cold for liquid oceans to survive on Earth. Yet the geological record shows that liquid water was present. This is usually explained as the consequence of a greenhouse effect due to a high concentration of atmospheric carbon dioxide and/or methane. Minik Rosing et al. suggest that there is no need to invoke greenhouse warming and no climate paradox. They demonstrate that the mineralogy of Archaean sediments is inconsistent with high greenhouse gas concentrations and the metabolic constraints of the methanogens of the time. They hypothesize that the low albedo of the early Earth, with little in the way of continents, and a preponderance of dark heat-absorbing ocean, together with a lack of biologically induced cloud condensation nuclei, were sufficient to maintain temperatures above freezing.
244 citations
TL;DR: It appears that vast amounts of CO2 were injected into the atmosphere, and a sea surface temperature increase of as much a 6°C accompanied the atmospheric CO2 rise, suggesting that elevated pCO2 played a major role in global warming during the MECO.
Abstract: The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.
181 citations
TL;DR: Carbonate and organic matter carbon-isotope data are presented that demonstrate no decoupling from approximately 820 to 760 million years ago and complete decoupled between the Sturtian and Marinoan glacial events of the Cryogenian Period (approximately 720 to 635 million years old).
Abstract: Global carbon cycle perturbations throughout Earth history are frequently linked to changing paleogeography, glaciation, ocean oxygenation, and biological innovation. A pronounced carbonate carbon-isotope excursion during the Ediacaran Period (635 to 542 million years ago), accompanied by invariant or decoupled organic carbon-isotope values, has been explained with a model that relies on a large oceanic reservoir of organic carbon. We present carbonate and organic matter carbon-isotope data that demonstrate no decoupling from approximately 820 to 760 million years ago and complete decoupling between the Sturtian and Marinoan glacial events of the Cryogenian Period (approximately 720 to 635 million years ago). Growth of the organic carbon pool may be related to iron-rich and sulfate-poor deep-ocean conditions facilitated by an increase in the Fe:S ratio of the riverine flux after Sturtian glacial removal of a long-lived continental regolith.
168 citations
TL;DR: In this article, the authors measured the relationship between net ecosystem exchange of carbon and climate factors using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years.
Abstract: Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate–carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ~ 16 °C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.
167 citations
TL;DR: This paper found a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which they attributed to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow-leaf assemblage.
Abstract: An episode of climate warming 200 Myr ago was associated with catastrophic environmental changes. Experimental and palaeontological data suggest that a climate-driven shift to more flammable leaf shapes contributed to increased fire activity in East Greenland at this time. One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers1 have been linked to a marked increase in atmospheric carbon dioxide levels2, probably resulting from massive volcanism in the Central Atlantic Magmatic Province3,4. Future climate change predictions suggest that fire activity may increase5, in part because higher global temperatures are thought to increase storminess6,7. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow-leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad-leaved morphologies. We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.
161 citations
TL;DR: The authors analyzed the parallel evolution of CO2 and its stable carbon isotopic ratio in the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core to bring additional constraints.
Abstract: The causes of the ∼80 ppmv increase of atmospheric carbon dioxide (CO2) during the last glacial-interglacial climatic transition remain debated. We analyzed the parallel evolution of CO2 and its stable carbon isotopic ratio (δ13CO2) in the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core to bring additional constraints. Agreeing well but largely improving the Taylor Dome ice core record of lower resolution, our δ13CO2 record is characterized by a W shape, with two negative δ13CO2 excursions of 0.5‰ during Heinrich 1 and Younger Dryas events, bracketing a positive δ13CO2 peak during the Bolling/Allerod warm period. The comparison with marine records and the outputs of two C cycle box models suggest that changes in Southern Ocean ventilation drove most of the CO2 increase, with additional contributions from marine productivity changes on the initial CO2 rise and δ13CO2 decline and from rapid vegetation buildup during the CO2 plateau of the Bolling/Allerod.
TL;DR: In this article, the authors developed constraints on the rate of carbon drawdown based on rates of carbon isotope change in well-dated marine and terrestrial sediments spanning the PETM.
Abstract: The Palaeocene–Eocene Thermal Maximum warm event about 56 million years ago was caused by the release of large amounts of carbon to the ocean and atmosphere. Estimates of the rate of recovery from the event suggest that about 2,000 Pg of the carbon released was sequestered as organic carbon. The Palaeocene–Eocene Thermal Maximum (PETM), an approximately 170,000-year-long period of global warming about 56 million years ago, has been attributed to the release of thousands of petagrams of reduced carbon into the ocean, atmosphere and biosphere1,2. However, the fate of this excess carbon at the end of the event is poorly constrained: drawdown of atmospheric carbon dioxide has been attributed to an increase in the weathering of silicates or to increased rates of organic carbon burial1,3,4,5. Here we develop constraints on the rate of carbon drawdown based on rates of carbon isotope change in well-dated marine and terrestrial sediments spanning the event. We find that the rate of recovery is an order of magnitude more rapid than that expected for carbon drawdown by silicate weathering alone. Unless existing estimates of carbon stocks and cycling during this time are widely inaccurate, our results imply that more than 2,000 Pg of carbon were sequestered as organic carbon over 30,000–40,000 years at the end of the PETM. We suggest that the accelerated sequestration of organic carbon could reflect the regrowth of carbon stocks in the biosphere or shallow lithosphere that were released at the onset of the event.
TL;DR: In this article, the authors examined carbon cycling in the Mississippi River using stable isotopes of inorganic carbon and dissolved oxygen, and they estimated that the flux of CO2 to the atmosphere (1 × 1013 g C yr−1) approximately equaled the flow of alkalinity to the Gulf of Mexico.
Abstract: [1] We examined carbon cycling in the Mississippi River using stable isotopes of inorganic carbon and dissolved oxygen. Eighteen sites were sampled along the river and its tributaries over 1 year. We estimate using a conservative approach that the flux of CO2 to the atmosphere (1 × 1013 g C yr−1) approximately equaled the flux of alkalinity to the Gulf of Mexico (9.7 × 1012 g C yr−1) and greatly exceeded the flux of dissolved organic carbon (1.5 × 1012 g C yr−1). Though only a first-order estimate, our work shows that the atmospheric flux of CO2 is significant and should not be ignored when examining the carbon budget of the Mississippi River. As expected, because of the large area covered by the Mississippi watershed, the isotopic composition of dissolved inorganic carbon, δ13CDIC, varied widely. In the Ohio and upper and lower Mississippi basins, δ13CDIC indicates that the source of inorganic carbon in the rivers is primarily from carbonate dissolution by soil CO2. Dissolved inorganic carbon in the Missouri River was enriched in 13C, and the isotopic composition of dissolved oxygen in this river suggests that this results from an excess of aquatic photosynthesis over respiration.
TL;DR: Insect damage richness appears to be more sensitive to past climate change than to plant diversity, although plant diversity in the authors' samples only ranges from 6 to 25 dicot species, and increased insect herbivory is likely to be a net long-term effect of anthropogenic warming.
Abstract: Paleoecological studies enhance our understanding of biotic response to climate change because they consider timescales not accessible through laboratory or ecological studies. From 60 to 51 million years ago (Ma), global temperatures gradually warmed to the greatest sustained highs of the last 65 million years. Superimposed on this gradual warming is a transient spike of high temperature and pCO2 (partial pressure of carbon dioxide in the atmosphere; the Paleocene-Eocene Thermal Maximum 55.8 Ma) and a subsequent short-term cooling event (∼54 Ma). The highly resolved continental fossil record of the Bighorn Basin, Wyoming, USA, spans this interval and is therefore uniquely suited to examine the long-term effects of temperature change on the two dominant groups in terrestrial ecosystems, plants and insect herbivores. We sampled insect damage on fossil angiosperm leaves at nine well-dated localities that range in age from 52.7 to 59 Ma. A total of 9071 leaves belonging to 107 species were examined for the presence or absence of 71 insect-feeding damage types. Damage richness, frequency, and composition were analyzed on the bulk floras and individual host species. Overall, there was a strong positive correlation between changes in damage richness and changes in estimated temperature, a weak positive relationship for damage frequency and temperature, and no significant correlation for floral diversity. Thus, insect damage richness appears to be more sensitive to past climate change than to plant diversity, although plant diversity in our samples only ranges from 6 to 25 dicot species. The close tracking of the richness of herbivore damage, a presumed proxy for actual insect herbivore richness, to both warming and cooling over a finely divided, extended time interval has profound importance for interpreting the evolution of insects and plant–insect associations in the context of deep time. Our results also indicate that increased insect herbivory is likely to be a net long-term effect of anthropogenic warming.
TL;DR: The rise in atmospheric carbon dioxide at the end of the Last Glacial Maximum has been attributed to the release of carbon dioxide from the deep Southern Ocean as discussed by the authors, however, reconstructions of the radiocarbon signature of Chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release.
Abstract: The rise in atmospheric carbon dioxide at the end of the Last Glacial Maximum has been attributed to the release of carbon dioxide from the deep Southern Ocean. However, reconstructions of the radiocarbon signature of Chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release.
TL;DR: In this article, the authors used an Earth system model to investigate the response of the coupled climate-carbon system to an instantaneous removal of all anthropogenic CO2 from the atmosphere.
Abstract: Carbon capture from ambient air has been proposed as a mitigation strategy to counteract anthropogenic climate change. We use an Earth system model to investigate the response of the coupled climate–carbon system to an instantaneous removal of all anthropogenic CO2 from the atmosphere. In our extreme and idealized simulations, anthropogenic CO2 emissions are halted and all anthropogenic CO2 is removed from the atmosphere at year 2050 under the IPCC A2 CO2 emission scenario when the model-simulated atmospheric CO2 reaches 511 ppm and surface temperature reaches 1.8 °C above the pre-industrial level. In our simulations a one-time removal of all anthropogenic CO2 in the atmosphere reduces surface air temperature by 0.8 °C within a few years, but 1 °C surface warming above pre-industrial levels lasts for several centuries. In other words, a one-time removal of 100% excess CO2 from the atmosphere offsets less than 50% of the warming experienced at the time of removal. To maintain atmospheric CO2 and temperature at low levels, not only does anthropogenic CO2 in the atmosphere need to be removed, but anthropogenic CO2 stored in the ocean and land needs to be removed as well when it outgasses to the atmosphere. In our simulation to maintain atmospheric CO2 concentrations at pre-industrial levels for centuries, an additional amount of CO2 equal to the original CO2 captured would need to be removed over the subsequent 80 years.
TL;DR: In this paper, the main and interactive effects of elevated CO2 and nitrogen addition on soil respiration were assessed by growing tree seedlings in ten large open-top chambers under CO2 (ambient CO2) and nitrogen (100 kg N ha−1 yr−1) treatments.
Abstract: . Global climate change in the real world always exhibits simultaneous changes in multiple factors. Prediction of ecosystem responses to multi-factor global changes in a future world strongly relies on our understanding of their interactions. However, it is still unclear how nitrogen (N) deposition and elevated atmospheric carbon dioxide concentration [CO2] would interactively influence forest floor soil respiration in subtropical China. We assessed the main and interactive effects of elevated [CO2] and N addition on soil respiration by growing tree seedlings in ten large open-top chambers under CO2 (ambient CO2 and 700 μmol mol−1) and nitrogen (ambient and 100 kg N ha−1 yr−1) treatments. Soil respiration, soil temperature and soil moisture were measured for 30 months, as well as above-ground biomass, root biomass and soil organic matter (SOM). Results showed that soil respiration displayed strong seasonal patterns with higher values observed in the wet season (April–September) and lower values in the dry season (October–March) in all treatments. Significant exponential relationships between soil respiration rates and soil temperatures, as well as significant linear relationships between soil respiration rates and soil moistures (below 15%) were found. Both CO2 and N treatments significantly affected soil respiration, and there was significant interaction between elevated [CO2] and N addition (p
TL;DR: Two papers in this issue contribute to understanding the land-atmosphere exchange by elegantly analyzing rich data sets on CO2 fluxes from a global network of monitoring sites.
Abstract: One key to accurately predicting future levels of atmospheric carbon dioxide (CO2) is understanding how land and atmosphere exchange CO2. Each year, photosynthesizing land plants remove (fix) one in eight molecules of atmospheric CO2, and respiring land plants and soil organisms return a similar number. This exchange determines whether terrestrial ecosystems are a net carbon sink or source. Two papers in this issue contribute to understanding the land-atmosphere exchange by elegantly analyzing rich data sets on CO2 fluxes from a global network of monitoring sites. On page 834, Beer et al. ( 1 ) estimate total annual terrestrial gross primary production (GPP) in an approach more solidly based on data than previous simple approximations. On page 838, Mahecha et al. ( 2 ) assess how ecosystem respiration (R) is related to temperature over short (week-to-month) and long (annual) time scales, and find a potentially important but difficult-to-interpret relationship.
TL;DR: In this paper, the authors evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide.
Abstract: . The accelerated rate of increase in atmospheric carbon dioxide and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic signatures of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, CANT. CT at constant salinity, NCT, increased at a rate of 0.85 μmol kg−1 yr−1 in the mixed layer, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr−1, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg−1 yr−1 at 300, 600, and 1000 m, respectively. The general processes controlling the vertical variations of alkalinity and the inorganic carbon distribution were computed by considering the pre-formed values, the production/decomposition of organic matter and the formation/dissolution of carbonates. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, increasing to 35% at 3685 m. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented as a reference site to follow CANT changes in the Northeast Atlantic Sub-tropical gyre.
TL;DR: In this paper, coupled carbon-climate model simulations suggest that artificial upwelling may, under most optimistic assumptions, be able to sequester atmospheric CO2 at a rate of about 0.9 PgC/yr.
Abstract: Recent suggestions to reduce the accumulation of anthropogenic carbon dioxide in the atmosphere have included ocean fertilization by artificial upwelling. Our coupled carbon-climate model simulations suggest that artificial upwelling may, under most optimistic assumptions, be able to sequester atmospheric CO2 at a rate of about 0.9 PgC/yr. However, the model predicts that about 80% of the carbon sequestered is stored on land, as a result of reduced respiration at lower air temperatures brought about by upwelling of cold waters. This remote and distributed carbon sequestration would make monitoring and verification particularly challenging. A second caveat predicted by our simulations is that whenever artificial upwelling is stopped, simulated surface temperatures and atmospheric CO2 concentrations rise quickly and for decades to centuries to levels even somewhat higher than experienced in a world that never engaged in artificial upwelling.
TL;DR: On page 1330 of this issue, Davis et al. (6) offer new insights into just how difficult it will be to say farewell to fossil fuels.
Abstract: One concrete goal adopted by some policy-makers is to reduce the risks associated with climate change by preventing the mean global temperature from rising by more than 2°C above preindustrial levels ( 1 ). Climate models indicate that achieving this goal will require limiting atmospheric carbon dioxide (CO2) concentrations to less than 450 parts per million (ppm), a level that implies substantial reductions in emissions from burning fossil fuels ( 2 , 3 ). So far, however, efforts to curb emissions through regulation and international agreement haven't worked ( 4 ); emissions are rising faster than ever, and programs to scale up “carbon neutral” energy sources are moving slowly at best ( 5 ). On page 1330 of this issue, Davis et al. ( 6 ) offer new insights into just how difficult it will be to say farewell to fossil fuels.
Pierre-and-Marie-Curie University1, Hobart Corporation2, Lamont–Doherty Earth Observatory3, Bjerknes Centre for Climate Research4, University of Gothenburg5, Cooperative Institute for Marine and Atmospheric Studies6, Atlantic Oceanographic and Meteorological Laboratory7, University of Iceland8, Centre national de la recherche scientifique9
TL;DR: In this paper, the authors describe the evolution of the surface ocean CO2 fugacity (fCO2oc) over the period 1993-2008 in the North Atlantic subpolar gyre (NASPG).
Abstract: [1] Recent studies based on ocean and atmospheric carbon dioxide (CO2) observations, suggesting that the ocean carbon uptake has been reduced, may help explain the increase in the fraction of anthropogenic CO2 emissions that remain in the atmosphere. Is it a response to climate change or a signal of ocean natural variability or both? Regional process analyses are needed to follow the ocean carbon uptake and to enable better attributions of the observed changes. Here, we describe the evolution of the surface ocean CO2 fugacity (fCO2oc) over the period 1993–2008 in the North Atlantic subpolar gyre (NASPG). This analysis is based primarily on observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) conducted at different seasons in the NASPG between Iceland and Canada. The fCO2oc trends based on DIC and TA data are also compared with direct fCO2 measurements obtained between 2003 and 2007 in the same region. During winters 1993–2003, the fCO2oc growth rate was 3.7 (±0.6) μatm yr−1, higher than in the atmosphere, 1.8 (±0.1) μatm yr−1. This translates to a reduction of the ocean carbon uptake primarily explained by sea surface warming, up to 0.24 (±0.04) °C yr−1. This warming is a consequence of advection of warm water northward from the North Atlantic into the Irminger basin, which occurred as the North Atlantic Oscillation (NAO) index moved into a negative phase in winter 1995/1996. In winter 2001–2008, the fCO2oc rise was particularly fast, between 5.8 (±1.1) and 7.2 (±1.3) μatm yr−1 depending on the region, more than twice the atmospheric growth rate of 2.1 (±0.2) μatm yr−1, and in the winter of 2007–2008 the area was supersaturated with CO2. As opposed to the 1990s, this appears to be almost entirely due to changes in seawater carbonate chemistry, the combination of increasing DIC and decreasing of TA. The rapid fCO2oc increase was not only driven by regional uptake of anthropogenic CO2 but was also likely controlled by a recent increase in convective processes-vertical mixing in the NASPG and cannot be directly associated with NAO variability. The fCO2oc increase observed in 2001–2008 leads to a significant drop in pH of −0.069 (±0.007) decade−1.
TL;DR: In this paper, a coupled carbon-climate model with the marine biology's response to iron addition calibrated against data from natural iron fertilization experiments was used to examine biogeochemical side effects of a hypothetical large-scale Southern Ocean Iron Fertilization (OIF) that need to be considered when attempting to account for possible OIF-induced carbon offsets.
Abstract: . Recent suggestions to slow down the increase in atmospheric carbon dioxide have included ocean fertilization by addition of the micronutrient iron to Southern Ocean surface waters, where a number of natural and artificial iron fertilization experiments have shown that low ambient iron concentrations limit phytoplankton growth. Using a coupled carbon-climate model with the marine biology's response to iron addition calibrated against data from natural iron fertilization experiments, we examine biogeochemical side effects of a hypothetical large-scale Southern Ocean Iron Fertilization (OIF) that need to be considered when attempting to account for possible OIF-induced carbon offsets. In agreement with earlier studies our model simulates an OIF-induced increase in local air-sea CO2 fluxes by about 73 GtC over a 100-year period, which amounts to about 48% of the OIF-induced increase in organic carbon export out of the fertilized area. Offsetting CO2 return fluxes outside the region and after stopping the fertilization at 1, 7, 10, 50, and 100 years are quantified for a typical accounting period of 100 years. For continuous Southern Ocean iron fertilization, the CO2 return flux outside the fertilized area cancels about 20% of the fertilization-induced CO2 air-sea flux within the fertilized area on a 100-yr timescale. This "leakage" effect has a radiative impact more than twice as large as the simulated enhancement of marine N2O emissions. Other side effects not yet discussed in terms of accounting schemes include a decrease in Southern Ocean oxygen levels and a simultaneous shrinking of tropical suboxic areas, and accelerated ocean acidification in the entire water column in the Southern Ocean at the expense of reduced globally-averaged surface-water acidification. A prudent approach to account for the OIF-induced carbon sequestration would account for global air-sea CO2 fluxes rather than for local fluxes into the fertilized area only. However, according to our model, this would underestimate the potential for offsetting CO2 emissions by about 20% on a 100 year accounting timescale. We suggest that a fair accounting scheme applicable to both terrestrial and marine carbon sequestration has to be based on emission offsets rather than on changes in individual carbon pools.
TL;DR: A review of the recent literature on ocean acidification can be found in this paper, where the potential effects of increasing atmospheric carbon dioxide levels on marine biogeochemistry are discussed and discussed in detail.
Abstract: During recent decades, Earth system research has provided overwhelming evidence that climate change, with disastrous consequences, will result from unbridled anthropogenic emissions of greenhouse gases. It is well accepted among climate scientists that these emissions, especially of CO2, may force the planet to warm by up to seven degrees C by the end of the century. During recent years, however, a second comparably dangerous consequence of steadily increasing atmospheric carbon dioxide levels has received growing attention, namely the acidification of the oceans. Here we discuss its potential effects on marine biogeochemistry and review the recent literature on this issue. Calcifying organisms such as corals, pteropods, coccolithophorides and foraminifera are among the species that will suffer most from unabated ocean acidification.
TL;DR: Cubasch et al. as mentioned in this paper predicted that continued combustion of fossil fuels would lead to a doubling of carbon dioxide in the atmosphere and associated climate warming, despite this warning, we are now faced with the predicted doubling of atmospheric carbon dioxide and global temperature increase of 1.3°C by the end of this century if no policy changes are made.
Abstract: More than a century ago Svante Arrhenius predicted that continued combustion of fossil fuels would lead to a doubling of carbon dioxide in the atmosphere and associated climate warming (Arrhenius 1896). Despite this warning, we are now faced with the predicted doubling of atmospheric carbon dioxide and global temperature increase of 1.3°C by the end of this century if no policy changes are made (Cubasch et al. 2001). Furthermore, not only are we faced with rising global temperature but also shifting weather patterns, ocean acidification, and the potential loss of many species on earth (Intergovernmental Panel on Climate Change (IPCC) 2001). These factors will all have a marked impact on land use, land cover, soil quality, and productivity.
TL;DR: In this paper, a record of Cryogenian interglacial ocean pH, based on boron (B) isotopes in marine carbonates, is presented, indicating a largely constant ocean pH and no critically elevated p CO 2 throughout the older postglacial and interglaciation periods.
Abstract: The Neoproterozoic Earth underwent at least two severe glaciations, each extending to low paleomagnetic latitudes and punctuating warmer climates. The two widespread older and younger Cryogenian glacial deposits in Namibia are directly overlain by cap carbonates deposited under inferred periods of high atmospheric carbon dioxide concentrations. Oceanic uptake of carbon dioxide decreases ocean pH; here we present a record of Cryogenian interglacial ocean pH, based on boron (B) isotopes in marine carbonates. Our data suggest a largely constant ocean pH and no critically elevated p CO 2 throughout the older postglacial and interglacial periods. In contrast, a marked ocean acidification event marks the younger deglaciation period and is compatible with elevated postglacial p CO 2 concentration. Our data are consistent with the presence of two panglacial climate states in the Cryogenian, but indicate that each had its own distinct environmental conditions.
TL;DR: In this issue of PNAS, Breecker and colleagues break important new ground for resolving this conflict over the linkages between paleo-CO2 and other parts of the Earth system.
Abstract: Global temperatures have covaried with atmospheric carbon dioxide (CO2) over the last 450 million years of Earth’s history (1). Critically, ancient greenhouse periods provide some of the most pertinent information for anticipating how the Earth will respond to the current anthropogenic loading of greenhouse gases. Paleo-CO2 can be inferred either by proxy or by the modeling of the long-term carbon cycle. For much of the geologic past, estimates of CO2 are consistent across methods (1). One exception is the paleosol carbonate proxy, whose CO2 estimates are often more than twice as high as coeval estimates from other methods (1). This discrepancy has led some to question the validity of the other methods and has hindered attempts to understand the linkages between paleo-CO2 and other parts of the Earth system. In this issue of PNAS, Breecker and colleagues (2) break important new ground for resolving this conflict.
TL;DR: In this paper, the transient response of global-mean precipitation to an increase in atmospheric carbon dioxide levels was investigated in 13 fully coupled atmosphere-ocean general circulation models (AOGCMs) and compared to a period of stabilization.
Abstract: The transient response of global-mean precipitation to an increase in atmospheric carbon dioxide levels of 1% yr − 1 is investigated in 13 fully coupled atmosphere–ocean general circulation models (AOGCMs) and compared to a period of stabilization. During the period of stabilization, when carbon dioxide levels are held constant at twice their unperturbed level and the climate left to warm, precipitation increases at a rate of ~ 2.4% per unit of global-mean surface-air-temperature change in the AOGCMs. However, when carbon dioxide levels are increasing, precipitation increases at a smaller rate of ~ 1.5% per unit of global-mean surface-air-temperature change. This difference can be understood by decomposing the precipitation response into an increase from the response to the global surface-temperature increase (and the climate feedbacks it induces), and a fast atmospheric response to the carbon dioxide radiative forcing that acts to decrease precipitation. According to the multi-model mean, stabilizing atmospheric levels of carbon dioxide would lead to a greater rate of precipitation change per unit of global surface-temperature change.
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11 Nov 2010
TL;DR: In this paper, the authors study the risk, process, and dynamics of potential Amazon dieback and its implications, and assist in understanding the risk and process of the potential Amazon ecosystem dieback.
Abstract: The Amazon basin is a key component of the global carbon cycle. The old-growth rainforests in the basin represent storage of ~ 120 petagrams of carbon (Pg C) in their biomass. Annually, these tropical forests process approximately 18 Pg C through respiration and photosynthesis. This is more than twice the rate of global anthropogenic fossil fuel emissions. The basin is also the largest global repository of biodiversity and produces about 20 percent of the world's flow of fresh water into the oceans. Despite the large carbon dioxide (CO2) efflux from recent deforestation, the Amazon rainforest ecosystem is still considered to be a net carbon sinks of 0.8-1.1 Pg C per year because growth on average exceeds mortality (Phillips et al. 2008). However, current climate trends and human-induced deforestation may be transforming forest structure and behavior (Phillips et al. 2009). Increasing temperatures may accelerate respiration rates and thus carbon emissions from soils (Malhi and Grace 2000). High probabilities for modification in rainfall patterns (Malhi et al. 2008) and prolonged drought stress may lead to reductions in biomass density. Resulting changes in evapo-transpiration and therefore convective precipitation could further accelerate drought conditions and destabilize the tropical ecosystem as a whole, causing a reduction in its biomass carrying capacity or dieback. In turn, changes in the structure of the Amazon and its associated water cycle will have implications for the many endemic species it contains and result in changes at a continental scale. Clearly, with much at stake, if climate-induced damage alters the state of the Amazon ecosystem, there is a need to better understand its risk, process, and dynamics. The objective of this study is to assist in understanding the risk, process, and dynamics of potential Amazon dieback and its implications.
TL;DR: A statistical model is developed for estimating SOC sequestration potential in cropland and suggested that soils with high clay content and low pH in the cold, humid regions possess a larger carbon sequestration Potential than other soils.
Abstract: Agroecosystems have a critical role in the terrestrial carbon cycling process. Soil organic carbon (SOC) in cropland is of great importance for mitigating atmospheric carbon dioxide increases and for global food security. With an understanding of soil carbon saturation, we analyzed the datasets from 95 global long-term agricultural experiments distributed across a vast area spanning wide ranges of temperate, subtropical and tropical climates. We then developed a statistical model for estimating SOC sequestration potential in cropland. The model is driven by air temperature, precipitation, soil clay content and pH, and explains 58% of the variation in the observed soil carbon saturation (n=76). Model validation using independent data observed in China yielded a correlation coefficient R2 of 0.74 (n=19, P<0.001). Model sensitivity analysis suggested that soils with high clay content and low pH in the cold, humid regions possess a larger carbon sequestration potential than other soils. As a case study, we estimated the SOC sequestration potential by applying the model in Henan Province. Model estimations suggested that carbon (C) density at the saturation state would reach an average of 32 t C ha−1 in the top 0–20 cm soil depth. Using SOC density in the 1990s as a reference, cropland soils in Henan Province are expected to sequester an additional 100 Tg C in the future.