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Kolstad E.W.,University of Bergen | Kolstad E.W.,Bjerknes Center for Climate Research | Johansson K.A.,University of Bergen
Environmental Health Perspectives | Year: 2011

Background: Climate change is expected to have large impacts on health at low latitudes where droughts and malnutrition, diarrhea, and malaria are projected to increase. Objectives: The main objective of this study was to indicate a method to assess a range of plausible health impacts of climate change while handling uncertainties in a unambiguous manner. We illustrate this method by quantifying the impacts of projected regional warming on diarrhea in this century. Methods: We combined a range of linear regression coefficients to compute projections of future climate change-induced increases in diarrhea using the results from five empirical studies and a 19-member climate model ensemble for which future greenhouse gas emissions were prescribed. Six geographical regions were analyzed. Results: The model ensemble projected temperature increases of up to 4°C over land in the tropics and subtropics by the end of this century. The associated mean projected increases of relative risk of diarrhea in the six study regions were 8-11% (with SDs of 3-5%) by 2010-2039 and 22-29% (SDs of 9-12%) by 2070-2099. Conclusions: Even our most conservative estimates indicate substantial impacts from climate change on the incidence of diarrhea. Nevertheless, our main conclusion is that large uncertainties are associated with future projections of diarrhea and climate change. We believe that these uncertainties can be attributed primarily to the sparsity of empirical climate-health data. Our results therefore highlight the need for empirical data in the cross section between climate and human health. Source

Wettstein J.J.,Bjerknes Center for Climate Research | Wallace J.M.,University of Washington
Journal of the Atmospheric Sciences | Year: 2010

Month-to-month storm-track variability is investigated via EOF analyses performed on ERA-40 monthlyaveraged high-pass filtered daily 850-hPa meridional heat flux and the variances of 300-hPa meridional wind and 500-hPa height. The analysis is performed both in hemispheric and sectoral domains of the Northern and Southern Hemispheres. Patterns characterized as "pulsing" and "latitudinal shifting" of the climatologicalmean storm tracks emerge as the leading sectoral patterns of variability. Based on the analysis presented, storm-track variability on the spatial scale of the two Northern Hemisphere sectors appears to be largely, but perhaps not completely, independent. Pulsing and latitudinally shifting storm tracks are accompanied by zonal wind anomalies consistent with eddy-forced accelerations and geopotential height anomalies that project strongly on the dominant patterns of geopotential height variability. The North Atlantic Oscillation (NAO)-Northern Hemisphere annular mode (NAM) is associated with a pulsing of the Atlantic storm track and a meridional displacement of the upper-tropospheric jet exit region, whereas the eastern Atlantic (EA) pattern is associated with a latitudinally shifting storm track and an extension or retraction of the upper-tropospheric jet. Analogous patterns of stormtrack and upper-tropospheric jet variability are associated with the western Pacific (WP) and Pacific-North America (PNA) patterns. Wave-mean flow relationships shown here are more clearly defined than in previous studies and are shown to extend through the depth of the troposphere. The Southern Hemisphere annular mode (SAM) is associated with a latitudinally shifting storm track over the South Atlantic and Indian Oceans and a pulsing South Pacific storm track. The patterns of storm-track variability are shown to be related to simple distortions of the climatological-mean upper-tropospheric jet. © 2010 American Meteorological Society. Source

Kolstad E.W.,Bjerknes Center for Climate Research
Quarterly Journal of the Royal Meteorological Society | Year: 2011

Polar lows (PLs) are small-scale and intense low-pressure systems that form at high latitudes in both hemispheres. Due to their limited spatial scale and brief lifetimes, weather and climate models are often unable to resolve these systems. One way to overcome this problem is to define a suitable proxy for PLs, with which the likelihood of PL formation can be assessed even in coarse-resolution datasets. This study draws on previous studies and an empirical database of 63 PLs to quantify the respective influences of low-level static stability and upper-level forcing on PL formation, as both of these factors are known to favour PL development. Little redundancy between the two parameters is found. After defining threshold values for the two parameters, climatological properties of favourable conditions for PLs are computed for the North Atlantic, the North-West Pacific and the Southern Hemisphere. The low-level static stability, which is strongly modified during marine cold-air outbreaks, puts important constraints on where PLs can form, while the upper-level forcing determines whether or not they will form. As a result of the climatologically lower tropopause in the Labrador Sea region, favourable conditions for PLs occur more often there than in the Nordic Seas, which has long been believed to be the main PL region in the Northern Hemisphere (NH). In the Southern Hemisphere, favourable conditions for PLs occur substantially less often than in the NH. The PL index defined here is suitable for other climatological studies and PL forecasting. © 2011 Royal Meteorological Society. Source

Kolstad E.W.,Bjerknes Center for Climate Research | Kolstad E.W.,University of Bergen | Charlton-Perez A.J.,University of Reading
Climate Dynamics | Year: 2011

The Northern Hemisphere stratospheric polar vortex is linked to surface weather. After Stratospheric Sudden Warmings in winter, the tropospheric circulation is often nudged towards the negative phase of the Northern Annular Mode (NAM) and the North Atlantic Oscillation (NAO). A strong stratospheric vortex is often associated with subsequent positive NAM/NAO conditions. For stratosphere-troposphere associations to be useful for forecasting purposes it is crucial that changes to the stratospheric vortex can be understood and predicted. Recent studies have proposed that there exist tropospheric precursors to anomalous vortex events in the stratosphere and that these precursors may be understood by considering the relationship between stationary wave patterns and regional variability. Another important factor is the extent to which the inherent variability of the stratosphere in an atmospheric model influences its ability to simulate stratosphere-troposphere links. Here we examine the lower stratosphere variability in 300-year pre-industrial control integrations from 13 coupled climate models. We show that robust precursors to stratospheric polar vortex anomalies are evident across the multi-model ensemble. The most significant tropospheric component of these precursors consists of a height anomaly dipole across northern Eurasia and large anomalies in upward stationary wave fluxes in the lower stratosphere over the continent. The strength of the stratospheric variability in the models was found to depend on the variability of the upward stationary wave fluxes and the amplitude of the stationary waves. © 2010 The Author(s). Source

Paasche O.,Bjerknes Center for Climate Research | Lovlie R.,University of Bergen
Geology | Year: 2011

The primary succession history of magnetotactic bacteria (MTB) is reconstructed in postglacial lake sediments using a rock magnetic approach that discriminates biologically produced magnetite from nonorganic magnetic carriers. MTB are among the oldest prokaryotes found in the fossil record, but little is known about how they have colonized and recolonized habitats around the world. Here we observe how MTB synchronously colonized 4 freshwater lakes 9760 ± 160 yr ago. The lakes are more than 1400 km apart, representing both coastal and inland regions, and have altitudinal differences of almost 800 m. The synchronous colonization of Norway (and possibly Sweden) suggests that the pathways were extremely efficient, and that the sources must have been wide ranging. We propose that birds could have carried and spread the bacteria as northward migration routes were reestablished following the onset of the current interglacial. This unique data set underscores the tenacity of MTB as evolutionary survivors, and also demonstrates their response to large-scale environmental changes in ways not previously anticipated. © 2011 Geological Society of America. Source

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