19 results on '"Stocker, TF"'
Search Results
2. Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation.
- Author
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Schilt A, Brook EJ, Bauska TK, Baggenstos D, Fischer H, Joos F, Petrenko VV, Schaefer H, Schmitt J, Severinghaus JP, Spahni R, and Stocker TF
- Subjects
- Antarctic Regions, Global Warming, History, Ancient, Nitrogen Isotopes analysis, Nitrous Oxide analysis, Nitrous Oxide history, Oxygen Isotopes analysis, Rain, Temperature, Time Factors, Aquatic Organisms metabolism, Atmosphere chemistry, Ice Cover, Nitrous Oxide metabolism
- Abstract
Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming.
- Published
- 2014
- Full Text
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3. Climate policy: Rethink IPCC reports.
- Author
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Stocker TF and Plattner GK
- Subjects
- Electronic Data Processing standards, International Cooperation, Organizations economics, Organizations standards, Organizations trends, Time, Climate Change, Organizations organization & administration, Publications standards
- Published
- 2014
- Full Text
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4. Allowable carbon emissions lowered by multiple climate targets.
- Author
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Steinacher M, Joos F, and Stocker TF
- Subjects
- Atmosphere chemistry, Bayes Theorem, Carbon Cycle, Climate, Feedback, Forecasting, Fossil Fuels, Greenhouse Effect statistics & numerical data, Temperature, Time Factors, Uncertainty, Carbon Dioxide analysis, Climate Change statistics & numerical data, Models, Theoretical
- Abstract
Climate targets are designed to inform policies that would limit the magnitude and impacts of climate change caused by anthropogenic emissions of greenhouse gases and other substances. The target that is currently recognized by most world governments places a limit of two degrees Celsius on the global mean warming since preindustrial times. This would require large sustained reductions in carbon dioxide emissions during the twenty-first century and beyond. Such a global temperature target, however, is not sufficient to control many other quantities, such as transient sea level rise, ocean acidification and net primary production on land. Here, using an Earth system model of intermediate complexity (EMIC) in an observation-informed Bayesian approach, we show that allowable carbon emissions are substantially reduced when multiple climate targets are set. We take into account uncertainties in physical and carbon cycle model parameters, radiative efficiencies, climate sensitivity and carbon cycle feedbacks along with a large set of observational constraints. Within this framework, we explore a broad range of economically feasible greenhouse gas scenarios from the integrated assessment community to determine the likelihood of meeting a combination of specific global and regional targets under various assumptions. For any given likelihood of meeting a set of such targets, the allowable cumulative emissions are greatly reduced from those inferred from the temperature target alone. Therefore, temperature targets alone are unable to comprehensively limit the risks from anthropogenic emissions.
- Published
- 2013
- Full Text
- View/download PDF
5. IPCC: cherish it, tweak it or scrap it?
- Author
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Hulme M, Zorita E, Stocker TF, Price J, and Christy JR
- Subjects
- Access to Information, Advisory Committees statistics & numerical data, Internationality, Volunteers, Advisory Committees organization & administration, Advisory Committees trends, Ecology methods, Ecology organization & administration, Global Warming
- Published
- 2010
- Full Text
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6. Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core.
- Author
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Elsig J, Schmitt J, Leuenberger D, Schneider R, Eyer M, Leuenberger M, Joos F, Fischer H, and Stocker TF
- Subjects
- Air analysis, Animals, Antarctic Regions, Anthozoa growth & development, Anthozoa metabolism, Atmosphere chemistry, Carbon Dioxide analysis, Carbon Isotopes, Climate, Ecosystem, History, Ancient, Time Factors, Carbon analysis, Carbon metabolism, Carbon Dioxide metabolism, Ice Cover chemistry
- Abstract
Reconstructions of atmospheric CO(2) concentrations based on Antarctic ice cores reveal significant changes during the Holocene epoch, but the processes responsible for these changes in CO(2) concentrations have not been unambiguously identified. Distinct characteristics in the carbon isotope signatures of the major carbon reservoirs (ocean, biosphere, sediments and atmosphere) constrain variations in the CO(2) fluxes between those reservoirs. Here we present a highly resolved atmospheric delta(13)C record for the past 11,000 years from measurements on atmospheric CO(2) trapped in an Antarctic ice core. From mass-balance inverse model calculations performed with a simplified carbon cycle model, we show that the decrease in atmospheric CO(2) of about 5 parts per million by volume (p.p.m.v.). The increase in delta(13)C of about 0.25 per thousand during the early Holocene is most probably the result of a combination of carbon uptake of about 290 gigatonnes of carbon by the land biosphere and carbon release from the ocean in response to carbonate compensation of the terrestrial uptake during the termination of the last ice age. The 20 p.p.m.v. increase of atmospheric CO(2) and the small decrease in delta(13)C of about 0.05 per thousand during the later Holocene can mostly be explained by contributions from carbonate compensation of earlier land-biosphere uptake and coral reef formation, with only a minor contribution from a small decrease of the land-biosphere carbon inventory.
- Published
- 2009
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7. Palaeoclimate: Greenhouse-gas fingerprints.
- Author
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Stocker TF and Schilt A
- Subjects
- Carbon Dioxide analysis, Ecosystem, History, Ancient, Nitrous Oxide analysis, Phytoplankton metabolism, Greenhouse Effect, Ice Cover chemistry, Seawater chemistry, Water Movements
- Published
- 2008
- Full Text
- View/download PDF
8. High-resolution carbon dioxide concentration record 650,000-800,000 years before present.
- Author
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Lüthi D, Le Floch M, Bereiter B, Blunier T, Barnola JM, Siegenthaler U, Raynaud D, Jouzel J, Fischer H, Kawamura K, and Stocker TF
- Abstract
Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. Here we present results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data and the present work, we find that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. We report the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172-300 p.p.m.v.
- Published
- 2008
- Full Text
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9. Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.
- Author
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Loulergue L, Schilt A, Spahni R, Masson-Delmotte V, Blunier T, Lemieux B, Barnola JM, Raynaud D, Stocker TF, and Chappellaz J
- Subjects
- Greenhouse Effect, History, Ancient, Ice Cover, Temperature, Time Factors, Tropical Climate, Wetlands, Atmosphere chemistry, Methane analysis
- Abstract
Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between approximately 350 and approximately 800 parts per 10(9) by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of approximately 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is approximately 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by approximately 100,000 yr glacial-interglacial cycles up to approximately 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.
- Published
- 2008
- Full Text
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10. Changing boreal methane sources and constant biomass burning during the last termination.
- Author
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Fischer H, Behrens M, Bock M, Richter U, Schmitt J, Loulergue L, Chappellaz J, Spahni R, Blunier T, Leuenberger M, and Stocker TF
- Subjects
- Atmosphere chemistry, Carbon analysis, Carbon Isotopes, Cold Climate, Greenland, History, Ancient, Hydrogen analysis, Methane metabolism, Monte Carlo Method, Wetlands, Biomass, Fires statistics & numerical data, Ice Cover, Methane analysis, Methane chemistry, Temperature, Trees metabolism
- Abstract
Past atmospheric methane concentrations show strong fluctuations in parallel to rapid glacial climate changes in the Northern Hemisphere superimposed on a glacial-interglacial doubling of methane concentrations. The processes driving the observed fluctuations remain uncertain but can be constrained using methane isotopic information from ice cores. Here we present an ice core record of carbon isotopic ratios in methane over the entire last glacial-interglacial transition. Our data show that the carbon in atmospheric methane was isotopically much heavier in cold climate periods. With the help of a box model constrained by the present data and previously published results, we are able to estimate the magnitude of past individual methane emission sources and the atmospheric lifetime of methane. We find that methane emissions due to biomass burning were about 45 Tg methane per year, and that these remained roughly constant throughout the glacial termination. The atmospheric lifetime of methane is reduced during cold climate periods. We also show that boreal wetlands are an important source of methane during warm events, but their methane emissions are essentially shut down during cold climate conditions.
- Published
- 2008
- Full Text
- View/download PDF
11. Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core.
- Author
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Lambert F, Delmonte B, Petit JR, Bigler M, Kaufmann PR, Hutterli MA, Stocker TF, Ruth U, Steffensen JP, and Maggi V
- Abstract
Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation; it can also be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed approximately 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.
- Published
- 2008
- Full Text
- View/download PDF
12. Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles.
- Author
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Wolff EW, Fischer H, Fundel F, Ruth U, Twarloh B, Littot GC, Mulvaney R, Röthlisberger R, de Angelis M, Boutron CF, Hansson M, Jonsell U, Hutterli MA, Lambert F, Kaufmann P, Stauffer B, Stocker TF, Steffensen JP, Bigler M, Siggaard-Andersen ML, Udisti R, Becagli S, Castellano E, Severi M, Wagenbach D, Barbante C, Gabrielli P, and Gaspari V
- Subjects
- Calcium analysis, Climate, Marine Biology, Mesylates analysis, Oceans and Seas, Periodicity, Sodium analysis, South America, Environment, Ice, Iron analysis
- Abstract
Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.
- Published
- 2006
- Full Text
- View/download PDF
13. Climate change: water cycle shifts gear.
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Stocker TF and Raible CC
- Published
- 2005
- Full Text
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14. Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation.
- Author
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Knutti R, Flückiger J, Stocker TF, and Timmermann A
- Abstract
The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3.
- Published
- 2004
- Full Text
- View/download PDF
15. Climate change: models change their tune.
- Author
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Stocker TF
- Published
- 2004
- Full Text
- View/download PDF
16. Eight glacial cycles from an Antarctic ice core.
- Author
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Augustin L, Barbante C, Barnes PR, Barnola JM, Bigler M, Castellano E, Cattani O, Chappellaz J, Dahl-Jensen D, Delmonte B, Dreyfus G, Durand G, Falourd S, Fischer H, Flückiger J, Hansson ME, Huybrechts P, Jugie G, Johnsen SJ, Jouzel J, Kaufmann P, Kipfstuhl J, Lambert F, Lipenkov VY, Littot GC, Longinelli A, Lorrain R, Maggi V, Masson-Delmotte V, Miller H, Mulvaney R, Oerlemans J, Oerter H, Orombelli G, Parrenin F, Peel DA, Petit JR, Raynaud D, Ritz C, Ruth U, Schwander J, Siegenthaler U, Souchez R, Stauffer B, Steffensen JP, Stenni B, Stocker TF, Tabacco IE, Udisti R, Van De Wal RS, Van Den Broeke M, Weiss J, Wilhelms F, Winther JG, Wolff EW, and Zucchelli M
- Abstract
The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long--28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.
- Published
- 2004
- Full Text
- View/download PDF
17. Global change: south dials north.
- Author
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Stocker TF
- Published
- 2003
- Full Text
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18. Constraints on radiative forcing and future climate change from observations and climate model ensembles.
- Author
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Knutti R, Stocker TF, Joos F, and Plattner GK
- Abstract
The assessment of uncertainties in global warming projections is often based on expert judgement, because a number of key variables in climate change are poorly quantified. In particular, the sensitivity of climate to changing greenhouse-gas concentrations in the atmosphere and the radiative forcing effects by aerosols are not well constrained, leading to large uncertainties in global warming simulations. Here we present a Monte Carlo approach to produce probabilistic climate projections, using a climate model of reduced complexity. The uncertainties in the input parameters and in the model itself are taken into account, and past observations of oceanic and atmospheric warming are used to constrain the range of realistic model responses. We obtain a probability density function for the present-day total radiative forcing, giving 1.4 to 2.4 W m-2 for the 5-95 per cent confidence range, narrowing the global-mean indirect aerosol effect to the range of 0 to -1.2 W m-2. Ensemble simulations for two illustrative emission scenarios suggest a 40 per cent probability that global-mean surface temperature increase will exceed the range predicted by the Intergovernmental Panel on Climate Change (IPCC), but only a 5 per cent probability that warming will fall below that range.
- Published
- 2002
- Full Text
- View/download PDF
19. The role of the thermohaline circulation in abrupt climate change.
- Author
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Clark PU, Pisias NG, Stocker TF, and Weaver AJ
- Abstract
The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean-atmosphere system. But it remains difficult to assess the likelihood of future changes in the thermohaline circulation, mainly owing to poorly constrained model parameterizations and uncertainties in the response of the climate system to greenhouse warming. Analyses of past abrupt climate changes help to solve these problems. Data and models both suggest that abrupt climate change during the last glaciation originated through changes in the Atlantic thermohaline circulation in response to small changes in the hydrological cycle. Atmospheric and oceanic responses to these changes were then transmitted globally through a number of feedbacks. The palaeoclimate data and the model results also indicate that the stability of the thermohaline circulation depends on the mean climate state.
- Published
- 2002
- Full Text
- View/download PDF
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