Are we in for warmer, wetter and wilder weather?
European researchers studying the effects of changes in atmospheric greenhouse gases on North-Atlantic climate models think we could well be in for warmer, wetter and wilder weather. But the Norwegian, German and Russian scientists behind the study say there could be a silver lining, at least, in Northern Europe – bigger fish catches, longer growing seasons and potential savings in energy costs. On the wild side, we could expect coastal storms and increased avalanche risk.
The NAO has been around for several thousand years, say experts (at least as long as the Norwegian Sea has been ice-free). Strong low-pressure systems south of Iceland give a positive NAO-index reading, leading to strong south-westerly winds, high temperatures and precipitation over northern Europe, while southern Europe and the Mediterranean has fine weather and little precipitation under these conditions. Weaker low-pressure activity south of Iceland (giving a negative NAO-index) leads to strong winds and heavy precipitation in the south and cold northerlies, together with dry weather, in the north.
One of the fundamental questions climate researchers are now asking is how do increasing man-made greenhouse gases affect natural weather systems – in Europe's case, the North Atlantic Oscillation?
An EU-backed research group – made up of the Nansen Centres in St Petersburg (RU) and Bergen (NO), the Geophysical Institute and the Bjerknes Centre at the University of Bergen, and the Max-Planck Institute of Meteorology, Hamburg (DE) – published findings to answer this question. Their paper, entitled The North-Atlantic Oscillation and greenhouse-gas forcing, appeared recently in the scientific journal Geophysical Research Letters, published by the American Geophysical Union.
The group then carried out two simulations of what the climate might be like decades from now. The first simulation used constant (present-day) levels of CO2 in the atmosphere and the second showed atmospheric CO2 levels increasing by 1% each year – roughly to levels that we might expect at the end of this century.
“The first simulation gives us the natural variation of the NAO-system, while the second gives us the natural variation and the effect of increasing greenhouse gas [emissions],” explains Johannessen. By comparing the two simulations and calculating the difference (trend), the team set out to measure what – if any – impact greenhouse gases have on the NAO weather system.
The resulting NAO trend shows a marked increase in greenhouse gases in the atmosphere over recent decades, clearly higher than the simulations using constant CO2. So this means the NAO-index is already indicating weather changes due to increasing greenhouse emissions. Future simulations point to the same conclusion: eight of the 12 models show a considerable increase (30-40%) in the NAO-index with climbing emission rates.
For the weather, the higher NAO-index means increased low-pressure activity which, in turn, leads to warmer weather, more precipitation and more storms, the researchers warn. “It should be mentioned that this result is based on simulations 80 years [from now], but since we analysed 12 climate models from the best climate research institutes worldwide, the results still give a good indication of what will happen with the low-pressure activity (the NAO-weather system) in this century,” says Johannessen.
If the team's prediction rings true, it will have major – positive and negative – consequences, such as more rain in northern Europe which could improve hydro-based electricity options, warmer climate leading to longer growth seasons for crops and lower heating costs, expanded fishing areas during winter and better conditions for oil- and gas-exploration. But the downside could be more storms along the coast affecting sea transport, fisheries and coastal populations, while warmer weather and more precipitation could increase the risk of avalanches and flooding.
“It is, therefore, important to focus our research on how greenhouse gas release[s] into the atmosphere will influence the natural climate variations, and to increase our understanding in order to predict this better in the future,” the researchers say in a statement.NERSC
Read the findings (on NERSC, [166 Kb])