Climate change
Still unpredictable
Global warming is making the weather capricious. ZDF meteorologist Dr Katja Horneffer explains the effects this has on our lives.
Dr Katja Horneffer
Graduate meteorologist and presenter in the ZDF weather team
The last five years have been the five hottest years ever to be recorded worldwide! Though the World Meteorological Organization will present its 2019 numbers not before spring 2020, it will most likely turn out in this order (starting with the hottest): 2016, 2019, 2015, 2017, 2018.
Global warming is making the weather increasingly unpredictable. The warmer our atmosphere is, the more water it can absorb. The more moisture the air contains, the more energy it has. This stirs up and fuels storms: storms that turn into hurricanes. Erratic weather conditions are occurring with great frequency. Rainstorms are often severe. In autumn 2019, an unusually large number of extremely fierce storms hit the Mediterranean region. A lot of snow fell very early on the south side of the Alps. Is this still normal?
Weather patterns out of step
It is unusual to say the least. The extremes are caused by weather patterns that did not occur with this frequency 70 years ago. Driving this phenomenon are the strong air currents, known as jet streams, that circle the globe and sometimes very significantly depart from their usual course, thereby causing large-scale weather patterns lasting several weeks. Too much of the same thing is fatal when it comes to the weather. Prolonged dry spells, resulting in drought, adversely affect agriculture, harvests and the water supply and increase the risk of forest and bush fires. Heavy rains, on the other hand, lead to flooding and mudslides. Massive quantities of new snow can trigger avalanches – as in the Alps in autumn 2019. Increasingly frequent severe weather events with violent hailstorms and powerful storms endanger harvests, but also glass facades and solar installations.
The fact that the jet stream over the temperate latitudes of the northern hemisphere is increasingly forming very large arcs is probably due to the warming of the Arctic. The result, to put it bluntly, is that the “guard rails” that normally force the jet stream into a certain corridor are lost. The repercussions in the northern hemisphere are multifaceted: they range from droughts in Central Europe to storms over the Mediterranean Sea and extremely wintry and snowy episodes in North America.
Climate trends are discernible
In addition to these long-lasting, large-scale weather patterns, however, many regional climate trends are already discernible. Summers in Germany will be drier as was the case in 2018. Heat records will continue to be broken, as at the end of July 2019, when we barely kept up with the stations where the 41 or 42 degree mark was hit.
Winters in Germany will become wetter and generally milder as a result of climate change. And as the snowfall line gets higher, winter sports in the low mountain ranges will become increasingly rare. Anyone looking for snow will have to go higher and higher. The growing period will be longer. It will start earlier and earlier. As in 2017, this can have devastating consequences if a record-high March is followed by frost in April, which makes viticulture and agriculture very challenging.
Despite these trends, a definite forecast for the next winter or summer is still impossible: the atmosphere does not show its hand so readily; and it is not possible to fully understand and model all processes in the atmosphere or in the ocean. Our forecasting models remain fragmented, in part because all human interventions would have to be taken into account.
Green roofs in large cities, for example, are making sealed surfaces accessible to the natural water cycle again. The roofs absorb the sunlight that light-coloured concrete would have reflected back. The huge fires in the Amazon, in Australia and North America, the drainage of wetlands and the construction of dams all have an influence on the Earth's energy budget, i.e. on what is reflected back into space from the earth after the sun has given it to us free of charge.
Last minute offers versus early bird discount
However, the increasingly stationary weather patterns have one advantage: if we meteorologists once again diagnose an “omega weather pattern” (i.e. when the jet stream forms large arcs), then the weather forecast for the next 8 to 14 days, which is nowadays already quite reliable anyway, is especially reliable – and plans can be made – albeit somewhat last minute.
Long-term planners won't get the information they need by looking at the weather map, but from the climate table. People who enjoy active holidays have no problem with a bit of rain in the mountains now and again. Anyone who can't stand the heat had better head to northern Europe. Mountainous islands have the advantage that the surrounding waters keep daily temperature ranges moderate, and they may have a windward and a leeward side. If rain clouds approach from the west, it may be warm and sunny on the east side, in the lee of the mountains, while the rain clouds in the west can rain down on the windward side of the mountains.
But many Germans prefer to spend their holidays at home anyway. Germany ranks first among travel destinations, and this is to be welcomed from an environmental point of view: anyone who doesn't want their own behaviour to accelerate climate change has climate-friendly alternatives when it comes to travel. Why not start from home by bike? Or go hiking in the nearby mountains? Anyone who travels by train is spared the hassle of traffic jams, the search for a parking space and usually ends up right in the centre of big cities. And holidaymakers seeking the tranquillity of nature in winter or who want to hike or snowshoe through winter landscapes experience adventures denied those on holiday in destinations where “everyone” goes.
No matter how you spend your free time: the weather brings a multitude of different stimuli that challenge our body and, in most cases, benefit our health! Take advantage of it! Today if possible – right outside your door!
Last updated and published on KfW Stories: Thursday, 12 December 2019.
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