... and Oeschger 1987). Finally we used a combined 1oBe data set from Camp Century, Milcent, Sout... more ... and Oeschger 1987). Finally we used a combined 1oBe data set from Camp Century, Milcent, South pole and Dye 3 to calculate the !!.14C record over the last 4000 years (Fig. ... The differences may be due to local 10Be components and to climate-induced system effects. ...
The temperature on Earth varied largely in the Pleistocene from cold glacials to warmer than pres... more The temperature on Earth varied largely in the Pleistocene from cold glacials to warmer than present interglacials. To contribute to an understanding of the underlying causes of these changes we compile various environmental records (and model-based interpretations of some of them) in order to calculate the direct effect of various processes on Earth's radiative budget and, thus, on global annual
A Dynamic Global Vegetation model is used as part of a simplified Earth system model to simulate ... more A Dynamic Global Vegetation model is used as part of a simplified Earth system model to simulate the impact of human land use on Holocene atmospheric CO2 and the contemporary carbon cycle. We show that suggested upward revisions of Holocene land use reconstructions imply a smaller contemporary terrestrial carbon sink and that early agricultural activities did only marginally contribute to the late Holocene CO2 rise of 20 ppm measured on ice cores. Scenarios are used to test the robustness of the results. Simulated changes in atmospheric CO2 due to land use are less than 1 ppm before 0 AD and 22 ppm by 2004 AD when prescribing the HYDE 3.1 land use reconstruction over the past 12 000 years. Cumulative emissions are with 50 GtC by 1850 and 177 GtC by 2004 AD comparable to earlier estimates. In scenario H2, agricultural area from HYDE 3.1 is scaled by a factor of two before 1700 AD, thereby taking into account evidence that land area used per person was higher before than during early industrialisation. Then, the contemporary terrestrial carbon sink, required to close the atmospheric CO2 budget, is reduced by 0.5 GtC yr-1. CO2 changes due to land use change exceed natural interannual variability only after 1000 AD and are less than 4 ppmv until 1850 AD. Simulated CO2 change remains small even in scenarios where average land use per person is unrealistically increased by a factor of 4 to 8 above published estimates. Our results falsify the hypothesis that humans are responsible for the late Holocene CO2 increase and that anthropogenic land use prevented a new ice age.
Impulse-response-function (IRF) models are designed for applications requiring a large number of ... more Impulse-response-function (IRF) models are designed for applications requiring a large number of climate change simulations, such as multi-scenario climate impact studies or cost-benefit integrated-assessment studies. The models apply linear response theory to reproduce the characteristics of the climate response to external forcing computed with sophisticated state-of-the-art climate models like general circulation models of the physical ocean-atmosphere system and three-dimensional oceanic-plus-terrestrial carbon cycle models. Although highly computer efficient, IRF models are nonetheless capable of reproducing the full set of climate-change information generated by the complex models against which they are calibrated. While limited in principle to the linear response regime (less than about 3∘C global-mean temperature change), the applicability of the IRF model presented has been extended into the nonlinear domain through explicit treatment of the climate system's dominant nonlinearities: CO2 chemistry in ocean water, CO2 fertilization of land biota, and sublinear radiative forcing. The resultant nonlinear impulse-response model of the coupled carbon cycle-climate system (NICCS) computes the temporal evolution of spatial patterns of climate change for four climate variables of particular relevance for climate impact studies: near-surface temperature, cloud cover, precipitation, and sea level. The space-time response characteristics of the model are derived from an EOF analysis of a transient 850-year greenhouse warming simulation with the Hamburg atmosphere-ocean general circulation model ECHAM3-LSG and a similar response experiment with the Hamburg carbon cycle model HAMOCC. The model is applied to two long-term CO2 emission scenarios, demonstrating that the use of all currently estimated fossil fuel resources would carry the Earth's climate far beyond the range of climate change for which reliable quantitative predictions are possible today, and that even a freezing of emissions to present-day levels would cause a major global warming in the long term.
Epic3quaternary Climate from Pole to Pole Epica Open Science Conference Venice Italynovember 2008 10, 2008
The underlying causes for Earth s temperature variations during glacial cycles observed in the la... more The underlying causes for Earth s temperature variations during glacial cycles observed in the late Pleistocene are still not fully understood. To contribute to this understanding we here compile various climate records in order to calculate the direct effect of various processes on Earth s radiative budget and thus on global annual mean near surface temperature over the last 800,000 years. The importance of orbital variations, of the greenhouse gases CO2, CH4 and N2O, of the albedo of land ice sheets, sea ice area and vegetation, and of the ...
231Pa and 230Th are removed from the water column by a process of reversible scavenging which qui... more 231Pa and 230Th are removed from the water column by a process of reversible scavenging which quickly removes 230Th to the sediment. 231Pa is less efficiently scavenged onto particles than 230Th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment. This study combines particle fields (dust, opal, CaCO3, POC) derived from observations with the Bern3D intermediate complexity ocean model and an equilibrium-scavenging model for isotopes. The equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type. The model can explain many of the features of the global 231Pa and 230Th distribution. The success of such a simple model at representing the global pattern of 231Pa / 230Th activity ratio supports the use of this proxy in paleoceanographic studies. We use the model to address the controversy concerning which particle types are dominant in fractionating 231Pa / 230Th in the ocean. The lithogenic (dust) flux is found to be unimportant for 231Pa / 230Th fractionation- the ocean fractionation of 231Pa / 230Th is dominated by the distribution of the CaCO3 and opal flux. We also confirm that opal is a weak scavenger of 230Th.
In contrast to the detailed documentation of the evolution of atmospheric carbon dioxide (CO2) kn... more In contrast to the detailed documentation of the evolution of atmospheric carbon dioxide (CO2) knowledge about its underlying quantitative processes is scarce. The atmosphere is linked to the ocean and the biosphere by exchange of carbon. Oceanic and biospheric CO2 have distinctive carbon isotope ratios, accordingly, its precise measurement in ice cores allows constraining the individual contribution of different carbon
Information on how species distributions and ecosystem services are impacted by anthropogenic cli... more Information on how species distributions and ecosystem services are impacted by anthropogenic climate change is important for adaptation planning. Palaeo-data suggest that Abies alba formed forests under significantly warmer-than-present conditions in Europe and might be a native substitute for widespread drought-sensitive temperate and boreal tree species such as beech (Fagus sylvatica) and spruce (Picea abies) under future global warming conditions. Here, we combine pollen and macrofossil data, modern observations, and results from transient simulations with the LPX-Bern dynamic global vegetation model to assess past and future distributions of A. alba in Europe. LPX-Bern is forced with climate anomalies from a run over the past 20,000 years with the Community Earth System Model, modern climatology, and with 21(st) century multi-model ensemble results for the high-emission RCP8.5 and the stringent mitigation RCP2.6 pathway. The simulated distribution for present climate encompasses the modern range of A. alba, with the model exceeding the present distribution in Northwestern and Southern Europe. Mid-Holocene pollen data and model results agree for Southern Europe, suggesting that at present, human impacts suppress the distribution in Southern Europe. Pollen and model results both show range expansion starting during the Bølling-Allerød warm period, interrupted by the Younger Dryas cold, and resuming during the Holocene. The distribution of A. alba expands to the northeast in all future scenarios, whereas the potential (currently unrealized) range would be substantially reduced in Southern Europe under RCP8.5. A. alba maintains its current range in Central Europe despite competition by other thermophilous tree species. Our combined palaeoecological and model evidence suggest that A. alba may ensure important ecosystem services including stand and slope stability, infrastructure protection, and carbon sequestration under significantly warmer-than-present conditions in Central Europe. This article is protected by copyright. All rights reserved.
Natural methane (CH4) emissions from wet ecosystems are an important part of today's global C... more Natural methane (CH4) emissions from wet ecosystems are an important part of today's global CH4 budget. Climate affects the exchange of CH4 between ecosystems and the atmosphere by influencing CH4 production, oxidation, and transport in the soil. The net CH4 exchange depends on ecosystem hydrology, soil and vegetation characteristics. Here, the LPJ-WHyMe global dynamical vegetation model is used to simulate
An abrupt increase in the atmospheric 14C content at the beginning of the Younger Dryas, about 13... more An abrupt increase in the atmospheric 14C content at the beginning of the Younger Dryas, about 13,000 years ago, has been related to a slow-down of the global oceanic circulation. This has been well simulated by box models, but the amplitude and timing of such a 14C change could not be represented with dynamical models. We have forced a climate
... and Oeschger 1987). Finally we used a combined 1oBe data set from Camp Century, Milcent, Sout... more ... and Oeschger 1987). Finally we used a combined 1oBe data set from Camp Century, Milcent, South pole and Dye 3 to calculate the !!.14C record over the last 4000 years (Fig. ... The differences may be due to local 10Be components and to climate-induced system effects. ...
The temperature on Earth varied largely in the Pleistocene from cold glacials to warmer than pres... more The temperature on Earth varied largely in the Pleistocene from cold glacials to warmer than present interglacials. To contribute to an understanding of the underlying causes of these changes we compile various environmental records (and model-based interpretations of some of them) in order to calculate the direct effect of various processes on Earth's radiative budget and, thus, on global annual
A Dynamic Global Vegetation model is used as part of a simplified Earth system model to simulate ... more A Dynamic Global Vegetation model is used as part of a simplified Earth system model to simulate the impact of human land use on Holocene atmospheric CO2 and the contemporary carbon cycle. We show that suggested upward revisions of Holocene land use reconstructions imply a smaller contemporary terrestrial carbon sink and that early agricultural activities did only marginally contribute to the late Holocene CO2 rise of 20 ppm measured on ice cores. Scenarios are used to test the robustness of the results. Simulated changes in atmospheric CO2 due to land use are less than 1 ppm before 0 AD and 22 ppm by 2004 AD when prescribing the HYDE 3.1 land use reconstruction over the past 12 000 years. Cumulative emissions are with 50 GtC by 1850 and 177 GtC by 2004 AD comparable to earlier estimates. In scenario H2, agricultural area from HYDE 3.1 is scaled by a factor of two before 1700 AD, thereby taking into account evidence that land area used per person was higher before than during early industrialisation. Then, the contemporary terrestrial carbon sink, required to close the atmospheric CO2 budget, is reduced by 0.5 GtC yr-1. CO2 changes due to land use change exceed natural interannual variability only after 1000 AD and are less than 4 ppmv until 1850 AD. Simulated CO2 change remains small even in scenarios where average land use per person is unrealistically increased by a factor of 4 to 8 above published estimates. Our results falsify the hypothesis that humans are responsible for the late Holocene CO2 increase and that anthropogenic land use prevented a new ice age.
Impulse-response-function (IRF) models are designed for applications requiring a large number of ... more Impulse-response-function (IRF) models are designed for applications requiring a large number of climate change simulations, such as multi-scenario climate impact studies or cost-benefit integrated-assessment studies. The models apply linear response theory to reproduce the characteristics of the climate response to external forcing computed with sophisticated state-of-the-art climate models like general circulation models of the physical ocean-atmosphere system and three-dimensional oceanic-plus-terrestrial carbon cycle models. Although highly computer efficient, IRF models are nonetheless capable of reproducing the full set of climate-change information generated by the complex models against which they are calibrated. While limited in principle to the linear response regime (less than about 3∘C global-mean temperature change), the applicability of the IRF model presented has been extended into the nonlinear domain through explicit treatment of the climate system's dominant nonlinearities: CO2 chemistry in ocean water, CO2 fertilization of land biota, and sublinear radiative forcing. The resultant nonlinear impulse-response model of the coupled carbon cycle-climate system (NICCS) computes the temporal evolution of spatial patterns of climate change for four climate variables of particular relevance for climate impact studies: near-surface temperature, cloud cover, precipitation, and sea level. The space-time response characteristics of the model are derived from an EOF analysis of a transient 850-year greenhouse warming simulation with the Hamburg atmosphere-ocean general circulation model ECHAM3-LSG and a similar response experiment with the Hamburg carbon cycle model HAMOCC. The model is applied to two long-term CO2 emission scenarios, demonstrating that the use of all currently estimated fossil fuel resources would carry the Earth's climate far beyond the range of climate change for which reliable quantitative predictions are possible today, and that even a freezing of emissions to present-day levels would cause a major global warming in the long term.
Epic3quaternary Climate from Pole to Pole Epica Open Science Conference Venice Italynovember 2008 10, 2008
The underlying causes for Earth s temperature variations during glacial cycles observed in the la... more The underlying causes for Earth s temperature variations during glacial cycles observed in the late Pleistocene are still not fully understood. To contribute to this understanding we here compile various climate records in order to calculate the direct effect of various processes on Earth s radiative budget and thus on global annual mean near surface temperature over the last 800,000 years. The importance of orbital variations, of the greenhouse gases CO2, CH4 and N2O, of the albedo of land ice sheets, sea ice area and vegetation, and of the ...
231Pa and 230Th are removed from the water column by a process of reversible scavenging which qui... more 231Pa and 230Th are removed from the water column by a process of reversible scavenging which quickly removes 230Th to the sediment. 231Pa is less efficiently scavenged onto particles than 230Th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment. This study combines particle fields (dust, opal, CaCO3, POC) derived from observations with the Bern3D intermediate complexity ocean model and an equilibrium-scavenging model for isotopes. The equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type. The model can explain many of the features of the global 231Pa and 230Th distribution. The success of such a simple model at representing the global pattern of 231Pa / 230Th activity ratio supports the use of this proxy in paleoceanographic studies. We use the model to address the controversy concerning which particle types are dominant in fractionating 231Pa / 230Th in the ocean. The lithogenic (dust) flux is found to be unimportant for 231Pa / 230Th fractionation- the ocean fractionation of 231Pa / 230Th is dominated by the distribution of the CaCO3 and opal flux. We also confirm that opal is a weak scavenger of 230Th.
In contrast to the detailed documentation of the evolution of atmospheric carbon dioxide (CO2) kn... more In contrast to the detailed documentation of the evolution of atmospheric carbon dioxide (CO2) knowledge about its underlying quantitative processes is scarce. The atmosphere is linked to the ocean and the biosphere by exchange of carbon. Oceanic and biospheric CO2 have distinctive carbon isotope ratios, accordingly, its precise measurement in ice cores allows constraining the individual contribution of different carbon
Information on how species distributions and ecosystem services are impacted by anthropogenic cli... more Information on how species distributions and ecosystem services are impacted by anthropogenic climate change is important for adaptation planning. Palaeo-data suggest that Abies alba formed forests under significantly warmer-than-present conditions in Europe and might be a native substitute for widespread drought-sensitive temperate and boreal tree species such as beech (Fagus sylvatica) and spruce (Picea abies) under future global warming conditions. Here, we combine pollen and macrofossil data, modern observations, and results from transient simulations with the LPX-Bern dynamic global vegetation model to assess past and future distributions of A. alba in Europe. LPX-Bern is forced with climate anomalies from a run over the past 20,000 years with the Community Earth System Model, modern climatology, and with 21(st) century multi-model ensemble results for the high-emission RCP8.5 and the stringent mitigation RCP2.6 pathway. The simulated distribution for present climate encompasses the modern range of A. alba, with the model exceeding the present distribution in Northwestern and Southern Europe. Mid-Holocene pollen data and model results agree for Southern Europe, suggesting that at present, human impacts suppress the distribution in Southern Europe. Pollen and model results both show range expansion starting during the Bølling-Allerød warm period, interrupted by the Younger Dryas cold, and resuming during the Holocene. The distribution of A. alba expands to the northeast in all future scenarios, whereas the potential (currently unrealized) range would be substantially reduced in Southern Europe under RCP8.5. A. alba maintains its current range in Central Europe despite competition by other thermophilous tree species. Our combined palaeoecological and model evidence suggest that A. alba may ensure important ecosystem services including stand and slope stability, infrastructure protection, and carbon sequestration under significantly warmer-than-present conditions in Central Europe. This article is protected by copyright. All rights reserved.
Natural methane (CH4) emissions from wet ecosystems are an important part of today's global C... more Natural methane (CH4) emissions from wet ecosystems are an important part of today's global CH4 budget. Climate affects the exchange of CH4 between ecosystems and the atmosphere by influencing CH4 production, oxidation, and transport in the soil. The net CH4 exchange depends on ecosystem hydrology, soil and vegetation characteristics. Here, the LPJ-WHyMe global dynamical vegetation model is used to simulate
An abrupt increase in the atmospheric 14C content at the beginning of the Younger Dryas, about 13... more An abrupt increase in the atmospheric 14C content at the beginning of the Younger Dryas, about 13,000 years ago, has been related to a slow-down of the global oceanic circulation. This has been well simulated by box models, but the amplitude and timing of such a 14C change could not be represented with dynamical models. We have forced a climate
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