Continental warming, coastal cooling and shifting rainbelts 1000 years ago
Global climate is currently undergoing major change. Experts agree that this change is driven by a combination of man-made and natural factors. However, full quantification of the anthropogenic and natural components is still a matter of debate. In order to better understand the contribution of natural climate variability and distinguish this from man-made influence, researchers worldwide have gone out to the field to study Earth’s pre-industrial climate history. Of particular interest are the past thousand years, which in Europe and North America have seen the transition from a rather warm medieval period to major cooling of the Little Ice Age, followed by the temperature rebound of the Current Warm Period which was further intensified by human greenhouse gas emissions. Our understanding of medieval climate outside this well-studied North Atlantic region is unfortunately still poor.
An international team led by geoscientist Sebastian Lüning wants to change this. Lüning is a professional resources geologist who in his sparetime works on paleoclimatological studies with the Switzerland-based Institute for Hydrography, Geoecology and Climate Sciences. Together with colleagues from Poland, Nigeria, Turkey and Germany they embarked on a journey through the scientific literature to shed light on the so-called ‘Medieval Climate Anomaly’, a period comprising of the years 1000-1200 AD. The initial focus region of their study was Africa. Lüning and his team crawled through hundreds of publications and mosaiced together a fascinating picture of African medieval climate change that tracks ancient heat waves, local cooling, drought and phases of amplified rainfall. Using modern database and visualization technology, the team managed to synthesize astonishing trends from the large amount of filtered data. Lüning explains the challenge:
Understanding natural cycles the key to model projections
Sufficient rainfall is the basic condition for high-yield agriculture and food security for the population. Until recently, however, it was not possible to reliably predict rainfall several months in advance, which repeatedly led to unexpected crop failures. For some years now, however, progress has been emerging. The literature has repeatedly reported exciting correlations between temperature and air pressure patterns on the world’s oceans with rainfall and droughts in Africa and on other continents.
A group of researchers led by Horst-Joachim Lüdecke wanted to know more and meticulously searched for patterns in the monthly rainfall data of 49 African countries for the period 1901 to 2017 using statistical methods.
“Large number of robust correlations”
The scientists compared the rainfall fluctuations with five oceanic indices of natural origin that are firmly established in science, as well as with solar activity. The evaluation revealed a large number of robust correlations across the African continent with characteristic seasonal patterns. It has been known for some time that the Atlantic Ocean influences precipitation in Morocco and the Sahel via the so-called Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO). In East Africa, influences from the Indian and Pacific Oceans have been reported so far.
Although shallow magma storage at Erta Ale volcano hints at a rift-to-ridge transition, the tectonic future of the Afar region is far from certain.
Standing next to a lava lake at the summit of a massive volcano, Christopher Moore, a Ph.D. candidate at the School of Earth and Environment at the University of Leeds in the United Kingdom, could see the red haze of lava flows a few kilometers away. This might seem like a rare sight, but at Ethiopia’s Erta Ale, it’s business as usual.
Are such behaviors the first signs of a tectonic transition? This question is part of what Moore has been studying at Erta Ale. The entire Afar region in eastern Africa finds itself in the middle of changes that could split the continent, forming a new ocean basin. The magmatism at Erta Ale might be offering signs of this switch by mimicking the characteristics of a mid-ocean ridge.
The East African Rift valley, the Red Sea, and the Gulf of Aden are clearly visible in this Landsat 8 image, taken on 8 November 2019. Credit: NASA/Erik Klemetti
However, there isn’t agreement about how close the Afar region is to this tectonic transition. The geophysical characteristics of magma storage at Erta Ale could point to the region’s conversion to an incipient oceanic spreading center, but the petrology of the erupting lava might be telling us that we aren’t there yet.
Real vegetation development in southern Africa takes a very different course than claimed by climate models
By Die kalte Sonne
(German translated by P Gosselin)
Climate models provide answers to all conceivable questions about the future. Political decision-makers are grateful for this information because they can make their plans accordingly.
But are the forecasts derived from models correct at all?
A research team led by Timm Hoffman has now compared the model projections with real vegetation development in southern Africa using historical photos. The sobering result: Nature has mostly developed quite differently than assumed by the models. In contrast to the model assumptions, no significant long-term trend in precipitation could be observed. Vegetation belts, which were supposed to shrink, ended up expanding. Confidence in the models is correspondingly low.
Political planning or even CO2 damage calculations based on the simulations are not possible. Here is the abstract of the work published in the journal Anthropocene in March 2019:
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Southern Africa vegetation expanding, images show. Source: here.
The findings highlight the extent to which humans are impacting one of the world’s major ecosystems — the Miombo woodlands, which cover 2.5 million square kilometres, across countries including Angola, Zambia, Tanzania and Mozambique.
At the same time, however, the growing number of trees in remote parts of these woodlands is helping to offset the emissions, researchers say.
The study is the first to provide an in-depth analysis of areas gaining carbon while also losing it through degradation — a process where some, but not all, trees are removed, usually as a result of logging and fire.
A small asteroid hit Earth on Saturday, June 2nd, exploding in the atmosphere over Botswana before it could reach the ground. The Catalina Sky Survey in Arizona had discovered the space rock only hours earlier as it hurtled toward our planet from inside the orbit of the Moon. Sensors used to monitor rogue nuclear explosions detected the asteroid and estimated its yield near ~500 tons of TNT.
by P. Homewood, April 1, 2018 in NotaLotofPeopleKnowThat
Lake Chad – a source of water to millions of people in West Africa – has shrunk by nine-tenths due to climate change, population growth and irrigation. But can a scheme dating back to the 1980s save it?
“It’s a ridiculous plan and it will never happen.” That’s the reaction many people have to the idea of trying to fill up Lake Chad and restore it to its former ocean-like glory by diverting water from the Congo river system 2,400km (1,500 miles) away.
In Africa, food abundance may be driving violent conflict rather than food scarcity, according to a new study. The study refutes the notion that climate change will increase the frequency of civil war in Africa as a result of food scarcity triggered by rising temperatures and drought.
When the seabed loses its stability and starts to move, it often happens in much larger dimensions than landslides ashore — and at slopes with very low gradients. At the same time, discplacement of large amounts of sediment under water scan cause devastating tsunamis. However, why and when submarine landslides develop is hardly understood. Marine scientists have now published possible causes based on observations on submarine landslides off the coast of northwest Africa.
Stratospheric aerosols from large tropical explosive volcanic eruptions backscatter shortwave radiation and reduce the global mean surface temperature. Observations suggest that they also favour an El Niño within 2 years following the eruption. Modelling studies have, however, so far reached no consensus on either the sign or physical mechanism of El Niño response to volcanism
La géologie, une science plus que passionnante … et diverse
