Revision of the global carbon budget due to changing air-sea oxygen fluxes

Carbon budgets inferred from measurements of the atmospheric oxygen to nitrogen ratio (O2/N2) are revised considering sea-to-air fluxes of O2 and N2 in response to global warming and volcanic eruptions. Observational estimates of changes in ocean heat content are combined with a model-derived relationship between changes in atmospheric O2/N2 due to oceanic outgassing and heat fluxes to estimate ocean O2 outgassing. The inferred terrestrial carbon sink for the 1990s is reduced by a factor of two compared with the most recent estimate by the Intergovernmental Panel on Climate Change (IPCC). This also improves the agreement between calculated ocean carbon uptake rates and estimates from global carbon cycle models, which indicate a higher ocean carbon uptake during the 1990s than the 1980s. The simulated decrease in oceanic O2 concentrations is in qualitative agreement with observed trends in oceanic O2 concentrations

Decoupling marine export production from new production

We investigate the relationship between annually integrated new and export production for the central Californian marine upwelling system using an eddy-resolving coupled physical-ecosystem-biogeochemical model. We find that when averaged over the annual cycle lateral transport leads to a substantial spatial decoupling of export from new production, with a length-scale of decoupling on the order of 300 km. The decoupling is largely caused by mean horizontal fluxes induced by persistent meso- and submesoscale circulation structures and to a lesser degree by the mean lateral offshore transport induced by Ekman transport. This indicates that the concept of numerically equal new and export production has to be used with great care, particularly in dynamic oceanic environments

Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model

© 2009 The Authors. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 6 (2009): 515-533, doi:10.5194/bg-6-515-2009Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm), and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185% (ΔpH=−0.45). Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally within a decade and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.This work was funded by the European Union projects CARBOOCEAN (511176-2) and EUROCEANS (511106-2) and is a contribution to the “European Project on Ocean Acidification” (EPOCA) which received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 211384. Additional support was received from the Swiss National Science Foundation and SCD acknowledges support from the US National Science Foundation (NSF) grant ATM-0628582

Model sensitivity in the effect of Antarctic sea ice and stratification on atmospheric pCO2

Several recent papers have demonstrated a decrease in atmospheric pCO2 resulting from barriers to communication between the deep sea and the atmosphere in the Southern Ocean. Stephens and Keeling [2000] decreased pCO2 by increasing Antarctic sea ice in a seven-box model of the world ocean, and Toggweiler [1999] showed a similar response to Southern Ocean stratification. In box models the pCO2 of the atmosphere is controlled by the region of the surface ocean that fills the deep sea [Archer et al., 2000a]. By severing the Southern Ocean link between the deep sea and the atmosphere, atmospheric pCO2 in these models is controlled elsewhere and typically declines, although the models range widely in their responses. “Continuum models,” such as three-dimensional (3-D) and 2-D general circulation models, control pCO2 in a more distributed way and do not exhibit box model sensitivity to high-latitude sea ice or presumably stratification. There is still uncertainty about the high-latitude sensitivity of the real ocean. Until these model sensitivities can be resolved, glacial pCO2 hypotheses and interpretations based on Southern Ocean barrier mechanisms (see above mentioned references plus Elderfield and Rickaby [2000], Francois et al. [1998], Gildor and Tziperman [2001], Sigman and Boyle [2000], and Watson et al. [2000]) are walking on thin ice

Uncertainty and risk in climate projections for the 21st century: comparing mitigation to non-intervention scenarios

Probabilistic climate projections based on two SRES scenarios, an IMAGE reference scenario and five IMAGE mitigation scenarios (all of them multi-gas scenarios) using the Bern2.5D climate model are calculated. Probability distributions of climate model parameters that are constrained by observations are employed as input for the climate model. The sensitivity of the resulting distributions with respect to prior assumptions on climate sensitivity is then assessed. Due to system inertia, prior assumptions on climate sensitivity play a minor role in the case of temperature projections for the first half of the 21st century, but these assumptions have a considerable influence on the distributions of the projected temperature increase in the year 2100. Upper and lower probabilities for exceeding 2°C by the year 2100 are calculated for the different scenarios. Only the most stringent mitigation measures lead to low probabilities for exceeding the 2°C threshold. This finding is robust with respect to our prior assumptions on climate sensitivity. Further, probability distributions of total present-value damages over the period 2000-2100 for the different scenarios are calculated assuming a wide range of damage cost functions, and the sensitivity of these distributions with respect to the assumed discount rate is investigated. Absolute values of damage costs depend heavily on the chosen damage cost function and discount rate. Nevertheless, some robust conclusions are possibl

Trends in marine dissolved oxygen: Implications for ocean circulation changes and the carbon budget

Recent measurements and model studies have consistently identified a decreasing trend in the concentration of dissolved O2 in the ocean over the last several decades. This trend has important implications for our understanding of anthropogenic climate change. First, the observed oceanic oxygen changes may be a signal of the beginning of a reorganization of large-scale ocean circulation in response to anthropogenic radiative forcing. Second, the repartitioning of oxygen between the ocean and the atmosphere requires a revision of the current atmospheric carbon budget and the estimates of the terrestrial and oceanic carbon sinks as calculated by the Intergovernmental Panel on Climate Change (IPCC) from measurements of atmospheric O2/N2

Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Special Report of the Intergovernmental Panel on Climate Change

This Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) has been jointly coordinated by Working Groups I (WGI) and II (WGII) of the Intergovernmental Panel on Climate Change (IPCC). The report focuses on the relationship between climate change and extreme weather and climate events, the impacts of such events, and the strategies to manage the associated risks. The IPCC was jointly established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), in particular to assess in a comprehensive, objective, and transparent manner all the relevant scientific, technical, and socioeconomic information to contribute in understanding the scientific basis of risk of human-induced climate change, the potential impacts, and the adaptation and mitigation options. Beginning in 1990, the IPCC has produced a series of Assessment Reports, Special Reports, Technical Papers, methodologies, and other key documents which have since become the standard references for policymakers and scientists.This Special Report, in particular, contributes to frame the challenge of dealing with extreme weather and climate events as an issue in decisionmaking under uncertainty, analyzing response in the context of risk management. The report consists of nine chapters, covering risk management; observed and projected changes in extreme weather and climate events; exposure and vulnerability to as well as losses resulting from such events; adaptation options from the local to the international scale; the role of sustainable development in modulating risks; and insights from specific case studies

The IPCC AR5 guidance note on consistent treatment of uncertainties: A common approach across the working groups

Evaluation and communication of the relative degree of certainty in assessment findings are key cross-cutting issues for the three Working Groups of the Intergovernmental Panel on Climate Change. A goal for the Fifth Assessment Report, which is currently under development, is the application of a common framework with associated calibrated uncertainty language that can be used to characterize findings of the assessment process. A guidance note for authors of the Fifth Assessment Report has been developed that describes this common approach and language, building upon the guidance employed in past Assessment Reports. Here, we introduce the main features of this guidance note, with a focus on how it has been designed for use by author teams. We also provide perspectives on considerations and challenges relevant to the application of this guidance in the contribution of each Working Group to the Fifth Assessment Report. Despite the wide spectrum of disciplines encompassed by the three Working Groups, we expect that the framework of the new uncertainties guidance will enable consistent communication of the degree of certainty in their policy-relevant assessment findings