SST and circulation trend biases cause an underestimation of European precipitation trends

Clear precipitation trends have been observed in Europe over the past century. In winter, precipitation has increased in north-western Europe. In summer, there has been an increase along many coasts in the same area. Over the second half of the past century precipitation also decreased in southern Europe in winter. An investigation of precipitation trends in two multi-model ensembles including both global and regional climate models shows that these models fail to reproduce the observed trends. In many regions the model spread does not cover the trend in the observations. In contrast, regional climate model (RCM) experiments with observed boundary conditions reproduce the observed precipitation trends much better. The observed trends are largely compatible with the range of uncertainties spanned by the ensemble, indicating that the boundary conditions of RCMs are responsible for large parts of the trend biases. We find that the main factor in setting the trend in winter is atmospheric circulation, for summer sea surface temperature (SST) is important in setting precipitation trends along the North Sea and Atlantic coasts. The causes of the large trends in atmospheric circulation and summer SST are not known. For SST there may be a connection with the well-known ocean circulation biases in low-resolution ocean models. A quantitative understanding of the causes of these trends is needed so that climate model based projections of future climate can be corrected for these precipitation trend biases.     

Probabilistic projections of transient climate change

This paper describes a Bayesian methodology for prediction of multivariate probability distribution functions (PDFs) for transient regional climate change. The approach is based upon PDFs for the equilibrium response to doubled carbon dioxide, derived from a comprehensive sampling of uncertainties in modelling of surface and atmospheric processes, and constrained by multiannual mean observations of recent climate. These PDFs are sampled and scaled by global mean temperature predicted by a Simple Climate Model (SCM), in order to emulate corresponding transient responses. The sampled projections are then reweighted, based upon the likelihood that they correctly replicate observed historical changes in surface temperature, and combined to provide PDFs for 20 year averages of regional temperature and precipitation changes to the end of the twenty-first century, for the A1B emissions scenario. The PDFs also account for modelling uncertainties associated with aerosol forcing, ocean heat uptake and the terrestrial carbon cycle, sampled using SCM configurations calibrated to the response of perturbed physics ensembles generated using the Hadley Centre climate model HadCM3, and other international climate model simulations. Weighting the projections using observational metrics of recent mean climate is found to be as effective at constraining the future transient response as metrics based on historical trends. The spread in global temperature response due to modelling uncertainty in the carbon cycle feedbacks is determined to be about 65–80 % of the spread arising from uncertainties in modelling atmospheric, oceanic and aerosol processes of the climate system. Early twenty-first century aerosol forcing is found to be extremely unlikely to be less than ?1.7 W m^?2. Our technique provides a rigorous and formal method of combining several lines of evidence used in the previous IPCC expert assessment of the Transient Climate Response. The 10th, 50th and 90th percentiles of our observationally constrained PDF for the Transient Climate Response are 1.6, 2.0 and 2.4 °C respectively, compared with the 10–90 % range of 1.0–3.0 °C assessed by the IPCC.     

The Prestige crisis: operational oceanography applied to oil recovery, by the Basque fishing fleet

On 19th November 2002, the oil tanker Prestige (containing 77,000 tonnes of heavy fuel no. 2 (M100)) sank in 3500 m of water, off the coast of northwestern Spain. Intermittent discharge of oil from the stricken tanker, combined with large-scale sea surface dispersion, created a tracking and recovery problem. Initially, conventional oil recovery approaches were adopted, close to the wreck. With time and distance from the source, the oil dispersed dramatically and became less viscous. Consequently, a unique monitoring, prediction and data dissemination system was established, based upon the principles of 'operational oceanography'; this utilised in situ tracked buoys and numerical (spill trajectory) modelling outputs, in combination with remote sensing (satellite sensors and visual observation). Overall, wind effects on the surface waters were found to be the most important mechanism controlling the smaller oil slick movements. The recovery operation involved up to 180 fishing boats, 9-30 m in length. Such labour-intensive recovery of the oil (21,000 tonnes, representing an unprecedented ratio of 6.6 tonnes at sea, per tonne recovered on land) continued over a 10 month period. The overall recovery at sea, by the fishing vessels, represented 63% of the total oil recovered at sea; this compares to only 37% recovered by specialised 'counter- pollution' vessels.     

Climate predictability on interannual to decadal time scales: the initial value problem

Any initial value forecast of climate will be subject to errors originating from poorly known initial conditions, model imperfections, and by "chaos" in the sense that, even if the initial conditions were perfectly known, infinitesimal errors can amplify and spoil the forecast at some lead time. Here the latter source of error is examined using a "perfect model" approach whereby small perturbations are made to a coupled atmosphere-ocean general circulation model and the spread of nearby model trajectories, on time and space scales appropriate to seasonal-decadal climate variability, is measured to assess the lead time at which the error saturates. The study therefore represents an estimate of the upper limit of the predictability of climate (appropriate to the initial value problem) given a perfect model and near perfect knowledge of the initial conditions. It is found that, on average, surface air temperature anomalies are potentially predictable on seasonal to interannual time scales in the tropical regions and are potentially predictable on decadal time scales over the ocean in the North Atlantic. For mid-latitude surface air temperature anomalies over land, model trajectories rapidly diverge and there is little sign of any potential predictability on time scales greater than a season or so. For mean sea level pressure anomalies, there is potential predictability on seasonal time scales in the tropics, and for some global scale annual-decadal anomalies, although not those associated with the North Atlantic Oscillation. For precipitation, the only potential for predictability is for seasonal time anomalies associated with the El-Niño Southern Oscillation. For the majority of the highly populated regions of the world, climate predictability on interannual to decadal time scales based in the initial value approach is likely to be severely limited by chaotic error growth. It is found however that there can be cases in which the potential predictability can be higher than average indicating that there is perhaps some utility in making initial value forecasts of climate in those regions which show low predictability on average.     

Dextral transpression and late Eocene magmatism in the trans-Himalayan Ladakh Batholith (North India): implications for tectono-magmatic evolution of the Indo-Eurasian collisional arc

The trans-Himalayan Ladakh batholith is a result of arc magmatism caused by the northward subduction of the Tethyan oceanic lithosphere below the edge of the Eurasian plate. The batholith dominantly consists of calc-alkaline I-type granitoids which are ferromagnetic in nature with the presence of magnetite as the principal carrier of magnetic susceptibility. The mesoscopic and magnetic fabric are concordant and generally vary from WNW–ESE to ENE–WSW for different intrusions of ferromagnetic granites in different parts of the batholith. Strike of magnetic fabric is roughly parallel with the regional trend of the Ladakh batholith in the present study area and is orthogonal to the direction of India-Eurasia collision. In Khardungla and Changla section, the magnetic fabric is distributed in a sigmoidal manner. It is inferred that this sigmoidal pattern is caused by shearing due to transpression induced by oblique convergence between the two plates. U–Pb zircon geochronology of a rhyolite from the southern parts of the batholith gives a crystallization age of 71.7 ± 0.6 Ma, coeval with ~68 Ma magmatism in the northern parts of the batholith. The central part of the batholith is characterized by S-type two-mica granites, which gives much younger age of magmatism at 35.5 ± 0.5 Ma. The magnetic fabric of these two-mica granites is at a high angle to the regional trend of the batholith. It is proposed that these two-mica granites were emplaced well after the cessation of subduction and arc magmatism, along fractures that developed perpendicular to the regional strike of the batholith due to shearing.