Simulations are run until the year 3000 A.D. and extend substantially farther into the future than conceptually similar simulations with atmosphere-ocean general circulation models (AOGCMs) coupled to carbon cycle models. In this paper the following are investigated: 1) the climate change commitment in response to stabilized greenhouse gases and stabilized total radiative forcing, 2) the climate change commitment in response to earlier CO 2 emissions, and 3) emission trajectories for profiles leading to the stabilization of atmospheric CO 2 and their uncertainties due to carbon cycle processes. Results over the twenty-first century compare reasonably well with results from AOGCMs, and the suite of EMICs proves well suited to complement more complex models. Substantial climate change commitments for sea level rise and global mean surface temperature increase after a stabilization of atmospheric greenhouse gases and radiative forcing in the year 2100 are identified. The additional warming by the year 3000 is 0.6-1.6 K for the low-CO 2 IPCC Special Report on Emissions Scenarios (SRES) B1 scenario and 1.3-2.2 K for the high-CO 2 SRES A2 scenario. Correspondingly, the post-2100 thermal expansion commitment is 0.3-1.1 m for SRES B1 and 0.5-2.2 m for SRES A2. Sea level continues to rise due to thermal expansion for several centuries after CO 2 stabilization. In contrast, surface temperature changes slow down after a century. The meridional overturning circulation is weakened in all EMICs, but recovers to nearly initial values in all but one of the models after centuries for the scenarios considered. Emissions during the twenty-first century continue to impact atmospheric CO 2 and climate even at year 3000. All models find that most of the anthropogenic carbon emissions are eventually taken up by the ocean (49%-62%) in year 3000, and that a substantial fraction (15%-28%) is still airborne even 900 yr after carbon emissions have ceased. Future stabilization of atmospheric CO 2 and climate change requires a substantial reduction of CO 2 emissions below present levels in all EMICs. This reduction needs to be substantially larger if carbon cycle-climate feedbacks are accounted for or if terrestrial CO 2 fertilization is not operating. Large differences among EMICs are identified in both the response to increasing atmospheric CO 2 and the response to climate change. This highlights the need for improved representations of carbon cycle processes in these models apart from the sensitivity to climate change. Sensitivity simulations with one single EMIC indicate that both carbon cycle and climate sensitivity related uncertainties on projected allowable emissions are substantial.n Current affiliation: IBP, ETH Zürich, Zürich, Switzerland.
The Chagos Archipelago was designated a no-take marine protected area (MPA) in 2010; it covers 550 000 km2, with more than 60 000 km2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs.It contains 25–50% of the Indian Ocean reef area remaining in excellent condition, as well as the world’s largest contiguous undamaged reef area. It has suffered from warming episodes, but after the most severe mortality event of 1998, coral cover was restored after 10 years.Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless of whether the latter are fished or protected.Coral diseases are extremely low, and no invasive marine species are known.Genetically, Chagos marine species are part of the Western Indian Ocean, and Chagos serves as a ‘stepping-stone’ in the ocean.The no-take MPA extends to the 200 nm boundary, and. includes 86 unfished seamounts and 243 deep knolls as well as encompassing important pelagic species.On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in plantation times, but several smaller islands are in relatively undamaged state.There are now 10 ‘important bird areas’, coconut crab density is high and numbers of green and hawksbill turtles are recovering.Diego Garcia atoll contains a military facility; this atoll contains one Ramsar site and several ‘strict nature reserves’. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strict environmental regulations are enforced.Shoreline erosion is significant in many places. Its economic cost in the inhabited part of Diego Garcia is very high, but all islands are vulnerable.Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of the archipelago for this purpose.
We present a new similarity index, taxonomic similarity (∆ S ), which can be used to measure β-diversity. ∆ S utilises species presence/absence data, and incorporates both higher taxon richness and evenness concepts. It is derived from the average taxonomic distance (relatedness) of any 2 species from different sites. Therefore ∆ S is analogous to taxonomic distinctness recently developed for biodiversity assessment at α-and γ-(landscape or seascape) scales. ∆ S is a new index, although its derivation uses a concept similar to the 'optimal taxonomic mapping statistic' developed independently for quantifying structural redundancy in marine macrobenthos. Using echinoderm data, we show that ∆ S exhibits smoother behaviour and is less influenced by species richness, and hence sampling effort, than the widely used Jaccard coefficient of species similarity. We also believe ∆ S to be a more intuitive and comprehensive measure of similarity than Jaccard and other conventional indices based solely on species held in common. Taxonomic similarity between sites is computed for echinoderms examined over 3 different spatial scales: local/small-scale (<10 km), intermediate-scale (10 to 100s km) and province/oceanic-scale (100s to 1000s km). Taxonomic similarity between sites increases progressively with spatial scale, with significantly lower values and higher β-diversity at small spatial scales. The same pattern is evident for species similarity, using the Jaccard coefficient. Possible explanations for this pattern centre on: (1) the large-scale oceanic area examined (Indo-West Pacific), representing a metapopulation of echinoderms for the 2 other, smaller areas examined within (Pula Wé, Sumatra and Lakshadweeps); (2) greater biophysical instability and unpredictability at small spatial scales. Compared with larger spatial scales, these may be characterised by greater likelihood and influence of species migrations and extinctions on a site's total species composition. Hence, species composition may be highly changeable at small scales, leading to high β-diversity. These findings are based on 1 set of comparative data for 1 faunal group. Any wider conclusions drawn would be premature, although corals may also show greater β-diversity at small spatial scales. The extent to which patterns observed are evident for other marine species groups is not well known.KEY WORDS: Biodiversity · β-diversity · Taxonomic similarity · Echinoderms · Indo-West PacificResale or republication not permitted without written consent of the publisher
Effects of atmospheric dynamics and ocean resolution on bi-stability of the thermohaline circulation examined using the Grid ENabled Integrated Earth system modelling (GENIE) framework AbstractWe have used the Grid ENabled Integrated Earth system modelling (GENIE) framework to undertake a systematic search for bi-stability of the ocean thermohaline circulation (THC) for different surface grids and resolutions of 3-D ocean (GOLDSTEIN) under a 3-D dynamical atmosphere model (IGCM). A total of 407,000 years were simulated over a three month period using Grid computing. We find bi-stability of the THC despite significant, quasi-periodic variability in its strength driven by variability in the dynamical atmosphere. The position and width of the hysteresis loop depends on the choice of surface grid (longitude-latitude or equal area), but is less sensitive to changes in ocean resolution. For the same ocean resolution, the region of bi-stability is broader with the IGCM than with a simple energy-moisture balance atmosphere model (EMBM).
Global and smaller-scale assessments of biodiversity typically use only 'species' measures. Using a broader set of concepts, we show that different biodiversity elements can exhibit contrasting patterns within the same environment. The Arabian Gulf, estuaries and hydrothermal vents are stressful environments having low species richness yet high β(turnover)-diversity, and around vents taxonomic distinctness is also marked. Similarly, in the Atlantic, β-diversity of starfishes declines from the coasts to the deep sea, contrasting with patterns of species richness and taxonomic distinctness. Thus, environments can, unexpectedly, be both 'hotspots' and 'coldspots' of biodiversity. These results have major implications for international conservation programmes which use biodiversity as a major criterion for identifying priority regions. Unpicking and prioritizing biodiversity's different threads will help environmental organisations better define and target hotspot regions. Current applications of complementarity could theoretically be expanded from a regional to a global perspective, to determine areas in which biodiversity representation is maximal but concepts are not applicable to assemblage properties (e.g. taxonomic distinctness).
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