Over 100 people are dead and many more are reported missing after deadly floods swept large parts of western Germany this week. The shock is huge, with people losing friends, relatives, and homes. Such devastating floods have not been seen in decades. Meteorologists warn, however, that extreme weather events are likely to become much more familiar in future.
"Extreme rainfall is going to become more frequent in a warmer world," Andreas Fink from the Institute of Meteorology and Climate Research at Karlsruhe Institute of Technology told DW.
One reason for this is that global warming is causing the atmosphere to change, said Dr. Sebastian Sippel from the Institute for Atmospheric and Climate Science in Zurich told DW: "For every increase in temperature of one degree Celsius, the atmosphere can absorb about 7% more moisture. […] The additional moisture caused by global warming will lead to higher amounts of precipitation in the long term, especially when there is heavy rainfall."
Climate change is to blame
There is no doubt that human-made climate change is heating up the atmosphere. Asked about the current floods in Germany, Dr. Carl Friedrich Schleussner from the geography department of Humboldt University in Berlin said in a statement: "In 2021, it is not a question of whether climate change played a role but simply how much."
There is a consensus among scientists about thermodynamic processes, the increasingly warm atmosphere and its increased capacity for moisture. However, there is another factor that some experts believe is probably contributing to extreme weather events such as the floods in Europe this week and the recent heat wave on the west coast of the US and Canada, but this has yet to be determined conclusively.
It concerns the air currents, which ensure that high-pressure and low-pressure areas in Europe's temperate latitudes tend to move on quickly. Climate researchers such as Andreas Fink believe that the jet stream, a westerly wind that blows at a height of about nine kilometers around the North Pole, has lost momentum in recent years, causing waves in what used to be a steady air flow.
"These waves then stay in place and they can, depending on where they are, cause extreme heat waves such as those we have seen in North America, or cause floods" he said, explaining that the floods caused by the recent storm Bernd were the result of the fact that cyclones and anticyclones were not being pushed on so vigorously and meant that a storm could concentrate in one place.
Experts believe that the jet stream, which is fueled by the difference in temperature between the Arctic and the tropics, is buckling because temperatures are rising in the Arctic and as the difference becomes smaller the air flow is weaker.
Irregularity in the moon's orbit
Another concern is that tides are predicted to be higher and lower than usual in the coming decade because of an irregularity of the moon's orbit. Though this occurs every 18 years, by the 2030s sea levels might have risen to such an extent that it could be disastrous.
On its website, the National Aeronautics and Space Administration (NASA) explains: "In half of the Moon's 18.6-year cycle, Earth's regular daily tides are suppressed: High tides are lower than normal, and low tides are higher than normal. In the other half of the cycle, tides are amplified: High tides get higher, and low tides get lower. Global sea level rise pushes high tides in only one direction — higher. So half of the 18.6-year lunar cycle counteracts the effect of sea level rise on high tides, and the other half increases the effect."
Researchers predict long-lasting floods with catastrophic consequences. Combined with the growing number of other extreme weather events caused by climate change, this is particularly troubling.