Posts Tagged 'globalmodeling'

Assessing carbon dioxide removal through global and regional ocean alkalization under high and low emission pathways

Atmospheric CO2 levels continue to rise, increasing the risk of severe impacts on the Earth system, and on the ecosystem services that it provides. Artificial Ocean Alkalization (AOA) is capable of reducing atmospheric CO2 concentrations, surface warming and addressing ocean acidification. Here we simulate global and regional responses to alkalinity addition (0.25 PmolAlk/year) using the CSIRO-Mk3L-COAL Earth System Model in the period 2020–2100, under high (RCP8.5) and low (RCP2.6) emissions. While regionally there are large changes associated with locations of AOA, globally we see only a very weak dependence on where and when AOA is applied. We see that under RCP2.6, while the carbon uptake associated with AOA is only ~ 60 % of the total under RCP8.5, the relative changes in temperature are larger, as are the changes in pH (1.4×) and aragonite saturation (1.7×). The results of this modelling study are significant as they demonstrate that AOA is more effective under lower emissions, and the higher the emissions the more AOA required to achieve the same reduction in global warming and ocean acidification. Finally, our simulations show AOA in the period 2020–2100 is capable of offsetting global warming and ameliorating ocean acidification increases due to low emissions, but regionally the response is more variable.

Continue reading ‘Assessing carbon dioxide removal through global and regional ocean alkalization under high and low emission pathways’

Simulated effect of carbon cycle feedback on climate response to solar geoengineering

Most modeling studies investigate climate effects of solar geoengineering under prescribed atmospheric CO2, thereby neglecting potential climate feedbacks from the carbon cycle. Here we use an Earth system model to investigate interactive feedbacks between solar geoengineering, global carbon cycle, and climate change. We design idealized sunshade geoengineering simulations to prevent global warming from exceeding 2°C above preindustrial under a CO2emission scenario with emission mitigation starting from middle of century. By year 2100, solar geoengineering reduces the burden of atmospheric CO2 by 47 PgC with enhanced carbon storage in the terrestrial biosphere. As a result of reduced atmospheric CO2, consideration of the carbon cycle feedback reduces required insolation reduction in 2100 from 2.0 to 1.7 W m−2. With higher climate sensitivity the effect from carbon cycle feedback becomes more important. Our study demonstrates the importance of carbon cycle feedback in climate response to solar geoengineering.

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Using fuzzy logic to determine the vulnerability of marine species to climate change

Marine species are being impacted by climate change and ocean acidification, although their level of vulnerability varies due to differences in species’ sensitivity, adaptive capacity and exposure to climate hazards. Due to limited data on the biological and ecological attributes of many marine species, as well as inherent uncertainties in the assessment process, climate change vulnerability assessments in the marine environment frequently focus on a limited number of taxa or geographic ranges. As climate change is already impacting marine biodiversity and fisheries, there is an urgent need to expand vulnerability assessment to cover a large number of species and areas. Here, we develop a modelling approach to synthesize data on species-specific estimates of exposure, and ecological and biological traits to undertake an assessment of vulnerability (sensitivity and adaptive capacity) and risk of impacts (combining exposure to hazards and vulnerability) of climate change (including ocean acidification) for global marine fishes and invertebrates. We use a fuzzy logic approach to accommodate the variability in data availability and uncertainties associated with inferring vulnerability levels from climate projections and species’ traits. Applying the approach to estimate the relative vulnerability and risk of impacts of climate change in 1074 exploited marine species globally, we estimated their index of vulnerability and risk of impacts to be on average 52 ± 19 SD and 66 ± 11 SD, scaling from 1 to 100, with 100 being the most vulnerable and highest risk, respectively, under the ‘business-as-usual’ greenhouse gas emission scenario (Representative Concentration Pathway 8.5). We identified 157 species to be highly vulnerable while 294 species are identified as being at high risk of impacts. Species that are most vulnerable tend to be large-bodied endemic species. This study suggests that the fuzzy logic framework can help estimate climate vulnerabilities and risks of exploited marine species using publicly and readily available information.

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The potential of 230Th for detection of ocean acidification impacts on pelagic carbonate production

Concentrations of dissolved 230Th in the ocean water column increase with depth due to scavenging and downward particle flux. Due to the 230Th scavenging process, any change in the calcium carbonate (CaCO3) fraction of the marine particle flux due to changes in biological CaCO3 hard shell production as a consequence of progressing ocean acidification would be reflected in the dissolved 230Th activity. Our prognostic simulations with a biogeochemical ocean general circulation model using different scenarios for the reduction of CaCO3production under ocean acidification and different greenhouse gas emission scenarios (RCPs 8.5 to 2.6) reveal the potential for deep 230Th measurements to detect reduced CaCO3 production at the sea surface. The time of emergence of an acidification induced signal on dissolved 230Th is of the same order of magnitude as for alkalinity measurements. Yet, deep ocean 230Th concentrations are less affected by seasonal and multiyear variability than surface alkalinity. Thus, deep ocean 230Th observations could be advantageous to guide monitoring and detection campaigns. Furthermore, given that the precision of 230Th measurements may potentially improve in the near future, earlier detection of ocean acidification impact signals would be possible. Our results indicate that the deep Pacific Ocean and the deep Southern Ocean are the most suitable regions for selected regular reoccupations of deep reaching 230Th stations.

Continue reading ‘The potential of 230Th for detection of ocean acidification impacts on pelagic carbonate production’

Climate, anchovy, and sardine

Anchovy and sardine populated productive ocean regions over hundreds of thousands of years under a naturally varying climate, and are now subject to climate change of equal or greater magnitude occurring over decades to centuries. We hypothesize that anchovy and sardine populations are limited in size by the supply of nitrogen from outside their habitats originating from upwelling, mixing, and rivers. Projections of the responses of anchovy and sardine to climate change rely on a range of model types and consideration of the effects of climate on lower trophic levels, the effects of fishing on higher trophic levels, and the traits of these two types of fish. Distribution, phenology, nutrient supply, plankton composition and production, habitat compression, fishing, and acclimation and adaptation may be affected by ocean warming, acidification, deoxygenation, and altered hydrology. Observations of populations and evaluation of model skill are essential to resolve the effects of climate change on these fish.

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Evaluation of the ocean ecosystem: Climate change modelling with backstop technologies

This paper discusses the economic impacts of climate change, including those on ecosystems, and whether a new backstop technology should be used under conditions of strict temperature targets. Using the dynamic integrated climate-economy (DICE) model, we developed a new model to calculate the optimal path by considering new backstop technologies, such as CO2 capture and storage (CCS). We identify the effects of parameter changes based on the resulting differences in CO2 leakage and sites, and we analyse the feasibility of CCS. In addition, we focus on ocean acidification and consider the impact on economic activity. As a result, when CCS is assumed to carry a risk of CO2 leakage and acidification is considered to result in a decrease in utility, we find that CCS can only delay the effects of climate change, but its use is necessary to achieve strict targets, such as a 1.5 °C limit. This observation suggests that if the target temperature is too tight, we might end up employing a technology that sacrifices the ecosystem too greatly.

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Drivers and implications of change in global ocean health over the past five years

Growing international and national focus on quantitatively measuring and improving ocean health has increased the need for comprehensive, scientific, and repeated indicators to track progress towards achieving policy and societal goals. The Ocean Health Index (OHI) is one of the few indicators available for this purpose. Here we present results from five years of annual global assessment for 220 countries and territories, evaluating potential drivers and consequences of changes and presenting lessons learned about the challenges of using composite indicators to measure sustainability goals. Globally scores have shown little change, as would be expected. However, individual countries have seen notable increases or declines due in particular to improvements in the harvest and management of wild-caught fisheries, the creation of marine protected areas (MPAs), and decreases in natural product harvest. Rapid loss of sea ice and the consequent reduction of coastal protection from that sea ice was also responsible for declines in overall ocean health in many Arctic and sub-Arctic countries. The OHI performed reasonably well at predicting near-term future scores for many of the ten goals measured, but data gaps and limitations hindered these predictions for many other goals. Ultimately, all indicators face the substantial challenge of informing policy for progress toward broad goals and objectives with insufficient monitoring and assessment data. If countries and the global community hope to achieve and maintain healthy oceans, we will need to dedicate significant resources to measuring what we are trying to manage.

Continue reading ‘Drivers and implications of change in global ocean health over the past five years’

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Ocean acidification in the IPCC AR5 WG II

OUP book