Climate crisis: recent European droughts 'worst in 2,000 years'
The series of severe droughts and heatwaves in Europe since 2014 is the most extreme for more than 2,000 years, research suggests.
The study analysed tree rings dating as far back as the Roman empire to create the longest such record to date. The scientists said global heating was the most probable cause of the recent rise in extreme heat.
The heatwaves have had devastating consequences, the researchers said, causing thousands ofearly deaths, destroying crops and igniting forest fires. Low river levels halted some shipping traffic and affected the cooling of nuclear power stations. Climate scientists predict more extreme and more frequent heatwaves and droughts in future.
The study also found a gradual drying of the summer climate in central Europe over the last two millennia, before the recent surge. The scientists ruled out volcanic activity and solar cycles as causes of this long-term trend and think subtle changes in Earth’s orbit are the cause.
“We’re all aware of the cluster of exceptionally hot and dry summers we’ve had over the past few years,” said Prof Ulf Büntgen, of Cambridge University, who led the study. “Our results show what we have experienced is extraordinary. The series is unprecedented for the last 2,000 years.” The available data ends in 2018, but 2019 and 2020 also had very hot European summers.
The scientists said changes in the position of the jet stream and the circulation of air over the continent caused the droughts, and that climate change was probably the underlying driver. “Climate change [means] extreme conditions will become more frequent, which could be devastating for agriculture, ecosystems and societies as a whole,” said Büntgen.
Prof Mrislav Trnka, of the CzechGlobe research centre in Brno, who was part of the study team, said the sharp increase in droughts was particularly alarming for agriculture and forestry. “Unprecedented forest dieback across much of central Europe corroborates our results,” he said.
Dr Friederike Otto, of Oxford University, said a lack of historic data often hindered the clear identification of the drivers of observed events, making the new work important and useful. “It corroborates from a longterm perspective that the huge increase in heat extremes observed over Europe in the summer, which has clearly been attributed to human-induced climate change, does indeed change the nature of summer in Europe,” she said.
The study, which was published in the journal Nature Geoscience, analysed 27,000 growth rings from 147 oak trees. Living oaks were used for the last century, then timber from old buildings such as churches. For the middle ages, the researchers used oak that had been preserved in river deposits or gravel beds, and for the Roman period they used remains such as wood used to construct wells.
Previous climate reconstructions from tree rings used width and wood density to determine temperature. The Büntgen-led study used measurements of carbon and oxygen isotopes to show how much water was available to the trees, giving a record of droughts. This showed that the high frequency of recent European droughts was unprecedented, even compared with severe historical droughts such as the Renaissance drought in the early 16th century.
The wood samples come from the Czech Republic and Bavaria in Germany, and represent climate conditions across central Europe. High temperatures were the main cause of recent droughts, and these have been seen across Europe.
The climate crisis is also linked to extreme wet weather in winter. The rainfall in the UK on 3 October 2020 was the highest in records dating back to 1891, and a study published last Wednesday said this had been made three times more likely by global heating. The research by the UK Met Office also found that such downpours will be 10 times more likely by 2100 without major cuts to carbon emissions.
My friend and colleague Don Mason, who has died aged 86, will be remembered for his discoveries about cells of the body’s immune system, notably the regulation of lymphocytes, and how fast and with what specificity their receptors recognise parts of foreign molecules.
He began this work in 1973, joining the Medical Research Council’s cellular immunology unit in the Dunn School of Pathology, Oxford University. He stayed for 26 years until his retirement in 1999, by which time he was its director.
Precision separation of cell populations in fluid suspension became possible in the mid-1970s, with Don driving the early adoption in Oxford of fluorescence-activated cell sorting. Combined with the then new monoclonal antibodies against the cell surface, developed by the unit’s second director, Alan Williams, cellular immunology was transformed. With their coworkers, they showed that one of the first monoclonals could turn off CD4 T cells, implying the value of such antibodies for treating disease. Such immunotherapy is now an established drug treatment for many diseases, including cancer.
Don and his colleagues found that CD4 cells comprise two sub-populations, one an initiator and the other a controller of immune responses. This work on regulatory T cells has contributed to a much better understanding of diabetes, and of gut and nervous system autoimmunity.
Don was born in Rochester, Kent, to
William, a foreman at the Short Brothers aircraft factory, and his wife, Doris (nee Tew). He attended the Sir Joseph Williamson Mathematical school, then studied physics at University College London. He worked for 10 years on the plasma physics of controlled thermonuclear fusion at Harwell and Culham.
The death of his firstborn son, Donny, of childhood leukaemia pivoted Don’s life towards medicine, which he studied at Oxford (1968-73) before embarking on his immunology research. Strong and principled concern about societal issues permeated his life. Turning vegan in 1977, he discovered the Quakers through CND activism in the 80s while protesting against cruise missiles and the presence of F1-11 nuclear bombers at USAF Upper Heyford, in Oxfordshire.
A week spent in prison for civil disobedience gave him insights that were useful in his later activities as a prison visitor, and for his campaigning on the Campsfield House migrant detention centre near Oxford. In retirement he published Science, Mystical Experience and Religious Belief (2006), topics of enduring interest to him.
He is survived by his wife, Mahalla (nee Thomson), whom he married in 1961, their four children, Jack, Ruth, Jo and Jonathan, and three grandchildren, Amy, Bethany and Milosh.