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global warming
Warming trends: Nonlinear climate change
Most studies assume that temperature trends are linear. Now, a study from the University of Hamburg demonstrates that warming trends are nonlinear, that warming accelerated over most of the twentieth century and is much stronger since 1980 than calculated by linear methods.
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arctic
Arctic influence on subseasonal midlatitude prediction
Researchers at the Alfred Wegener Institute (AWI) explore the influence of improved Arctic forecasts during wintertime on the performance of Northern Hemisphere midlatitude prediction. They find that the largest midlatitude improvements are over eastern Europe, northern Asia and North America, and that the strength of the linkage between the Arctic and the midlatitudes is flow dependent.
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Future increases in Arctic precipitation linked to local evaporation and sea-ice retreat
Precipitation changes projected for the end of the 21st century show an increase of more than 50 per cent in the Arctic regions. This increase, among the highest globally, is largely attributed to enhanced poleward moisture transport from lower latitudes. However, this study from the Royal Netherlands Meteorological Institute (KNMI) shows that the projected increase in Arctic precipitation instead is mainly due to strongly intensified local surface evaporation, which is mostly a result of retreating winter sea ice.
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high impact events
Heavier summer downpours with climate change revealed by weather forecast resolution model
Projecting changes in precipitation extremes on sub-daily timescales is a highly uncertain issue. Researchers at the Met Office Hadley Centre perform the first climate change experiments with a very high resolution (1.5 km grid spacing) model for a region of the UK. The model shows future increases in hourly rainfall intensities in winter; however, it also shows an intensification of short-duration rain in summer, with significantly more events exceeding the high thresholds indicative of serious flash flooding.
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Arctic amplification decreases temperature variance in northern mid- to high-latitudes
Shifts in both the mean climate and in variability have caused certain extreme weather events to increase in frequency and/or severity. This study shows, however, that subseasonal cold-season temperature variability has significantly decreased over the mid- to high-latitude Northern Hemisphere in recent decades. This is partly because northerly winds and associated cold days are warming more rapidly than southerly winds and warm days, and so Arctic amplification acts to reduce subseasonal temperature variance.
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sea level
Projecting twenty-first century regional sea-level changes
This study presents regional sea-level projections and associated uncertainty estimates for the end of the 21st century, resulting from changing ocean circulation, increased heat uptake and atmospheric pressure in CMIP5 climate models. These are combined with model- and observation-based regional contributions of land ice, groundwater depletion and glacial isostatic adjustment, including gravitational effects due to mass redistribution. Regional differences are found to be significant.
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hydrological cycles
A precipitation shift from snow towards rain leads to a decrease in streamflow
In a warming climate, precipitation is less likely to occur as snowfall. A shift from a snow- towards a rain-dominated regime is currently assumed not to influence the mean streamflow significantly. However, researchers at the Delft University of Technology argue that mean streamflow is likely to reduce for catchments that experience significant reductions in the fraction of precipitation falling as snow, which can have substantial socio-economic consequences.
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