The impact of natural and anthropogenic forcings on climate and hydrology since 1550

A climate simulation of an ocean/atmosphere general circulation model driven with natural forcings alone (constant “pre-industrial” land-cover and well-mixed greenhouse gases, changing orbital, solar and volcanic forcing) has been carried out from 1492 to 2000. Another simulation driven with natural and anthropogenic forcings (changes in greenhouse gases, ozone, the direct and first indirect effect of anthropogenic sulphate aerosol and land-cover) from 1750 to 2000 has also been carried out. These simulations suggest that since 1550, in the absence of anthropogenic forcings, climate would have warmed by about 0.1 K. Simulated response is not in equilibrium with the external forcings suggesting that both climate sensitivity and the rate at which the ocean takes up heat determine the magnitude of the response to forcings since 1550. In the simulation with natural forcings climate sensitivity is similar to other simulations of HadCM3 driven with CO₂ alone. Climate sensitivity increases when anthropogenic forcings are included. The natural forcing used in our experiment increases decadal–centennial time-scale and large spatial scale climate variability, relative to internal variability, as diagnosed from a control simulation. Mean conditions in the natural simulation are cooler than in our control simulation reflecting the reduction in forcing. However, over certain regions there is significant warming, relative to control, due to an increase in forest cover. Comparing the simulation driven by anthropogenic and natural forcings with the natural-only simulation suggests that anthropogenic forcings have had a significant impact on, particularly tropical, climate since the early nineteenth century. Thus the entire instrumental temperature record may be “contaminated” by anthropogenic influences. Both the hydrological cycle and cryosphere are also affected by anthropogenic forcings. Changes in tree-cover appear to be responsible for some of the local and hydrological changes as well as an increase in northern hemisphere spring snow cover.

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A Plinian treatment of fallout from Hawaiian lava fountains

A new model is presented which simulates the dispersal and deposition of material from a Hawaiian eruption column. The model treats the Hawaiian column as a coarse-grained Plinian column and uses a modified version of the Wilson and Walker [Wilson, L., Walker, G.P.L., 1987. Explosive volcanic eruptions: VI. Ejecta dispersal in Plinian eruptions: the control of eruption conditions and atmospheric properties. Geophys. J. R. Astron. Soc. 89, 657–679.] Plinian pyroclast dispersal model to simulate the fall out of material during a Hawaiian eruption. The model results are found to be in good agreement with independent estimates of various parameters made for the 1959 Kilauea Iki eruption of Kilauea volcano. The close agreement between the model results and these independent estimates shows that, dynamically, Hawaiian eruptions are indistinguishable from Plinian eruptions. The major differences in the styles and deposits of these two types of eruptions are accounted for by differences in the mass fluxes and gas contents of the erupting magmas and, most fundamentally, by differences in the grainsize distribution of the erupted clasts. Plume heights predicted by the model are greater than those found for previous models of Hawaiian eruptions. This is because previous models did not allow for the progressive fall out of particles from the plume and, more importantly, made no correction for the velocity disequilibrium between gas and clasts when the grainsize distribution is coarse.     

Tectonic implications of new single zircon Pb-Pb evaporation data in the Lossogonoi and Longido ruby-districts,Mozambican metamorphic Belt of north-eastern Tanzania

Three single zircon Pb-Pb evaporation dating studies were performed on felsic orthogneisses and migmatites from the Longido and Lossogonoi ruby districts, Mozambique Belt of north-eastern Tanzania, in order to better constrain the geological setting of gemstone mineralizations. Igneous emplacement ages of protoliths ranging between 2636 and 2448 Ma document for the first time the presence of a Neoarchean to Lower Paleoproterozoic (Siderian) basement reworked in the Late Neoproterozoic Mozambique Belt of north-eastern Tanzania. This ancient crust of unknown dimension is well documented farther south, but also in south-eastern Kenya. A shearing event under high-grade amphibolite facies conditions, postdating the Pan-African metamorphic peak at 640 Ma and following nappes emplacement is demonstrated at ca. 610 Ma from metamorphic zircons of Lossogonoi district. In Lossogonoi district, ruby crystallizes during this last stage of deformation.     

Holistic, adaptive management of the terrestrial carbon cycle at local and regional scales

Actions to manage carbon dioxide (and other greenhouse gas) emissions at regional and local scales take place amid multiple requirements, participants, and agents. To address and solve tensions that emerge from diverse objectives and stakeholder needs, participatory decision processes and information tools are required. This paper explores how regional carbon budget information can contribute to the broader goal of holistic, adaptive regional development. We sketch the characteristics of a novel integrative framework for adaptive carbon management in the context of multiple criteria. An ex-post case study on carbon mitigation from Chiapas, Mexico, demonstrates challenges and trade-offs in a real-world setting.