Nothing fundamental is changing in the Alps for the time being: in the north, spring flowers are waving in the foehn, in the south it is raining or snowing heavily. This week, we look beyond the Alps and take a look at tropical oceans and fire-breathing mountains in Indonesia.
Last week, a volcano called Kelud erupted in Indonesia. The column of ash in the air reached a height of 13 to 20 kilometers, at a distance of 7 kilometers a layer of ash of 20 cm covers the ground, at 150 kilometers it is still one centimeter. People died because the roofs of their houses collapsed under the weight of the ash. Air traffic is severely disrupted. Over 5,000 people died in an eruption of Kelud in 1919, and 30 people died in another eruption in 1990. The volcanic explosivity index (VEI) of the most recent eruption is estimated at 4. The 8-level, logarithmic VEI scale defines the "explosiveness" of volcanic eruptions based on the volume of ash produced and the height of the eruption column, among other things. At level 4, the Kelud eruption would be comparable to that of Eyjafjallajökull in 2010.
Volcanic eruptions of this magnitude usually have no discernible impact on the global climate, but can have regional effects under certain circumstances. Eruptions with a VEI of 6 or more are certainly reflected in the global temperature. For example, the eruption of Krakatoa in 1883 was followed by a global cooling of 0.5-0.8° C. Similar effects were caused by the Santa Maria volcano (1920) and most recently Pinatubo (1991):
The last eruption with a VEI of 7 was the eruption of the Indonesian volcano Tambora in 1815. This was followed by the infamous "Year Without a Summer" in 1816, also known as the "Eighteen Hundred and Frozen". In Central Europe and the American Northeast in particular, cold weather and severe storms led to failed harvests, and the following years were characterized by famine and mass emigration in the affected areas.
A new study by scientists at the University of Bern shows that severe volcanic eruptions in the tropics not only affect global temperatures, but can also have an impact on precipitation in southern and central Europe. A weakening of the African and Asian summer monsoon can also weaken the Hadley circulation, which in turn changes the circulation in Europe and causes more precipitation. Scientists believe they have thus found an explanation for the particularly wet "year without a summer".
Such phenomena are known as meteorological "teleconnections": When X happens on one side of the Earth, it results in Y on the other side. Typical teleconnections are, for example, the ENSO phenomena La Niña and El Niño, or the North Atlantic or Arctic Oscillation (NAO and AO). In an analysis of the unusually intense series of storms that have recently hit the British coast, the British Weather Service has identified another teleconnection that could be partly responsible for the unusual weather this winter. They suspect that the Pacific jet stream has been knocked off its usual path by unusually heavy rainfall in Indonesia and the western Pacific tropics, with the precipitation linked to unusually high sea temperatures in the same area. Combined with the vagaries of the polar vortex driving the Atlantic jet, this then makes for all sorts of exciting weather.
The dramatic impact of global climatic changes on human civilizations is impressively shown in the following graphic, which the WeatherBlog found by chance during the research for today's topic and would like to present here:
