A changing climate is bad news for a continent that doesn’t like change

time-tested haunts when they want to get a feel for how Europe is faring. The bourses of Milan or Paris provide a barometer of investor sentiment. Counting container ships coming into Rotterdam and Marseille gives a clue as to the haleness of trade. Frankfurt, where the European Central Bank sets interest rates, is worth a (brief) visit. Number-crunchers also drop into finance ministries in Athens or Dublin, where national budgets are crafted—and Brussels, where Eurocrats opine on them, before bond vigilantes in the City of London issue their own verdict. A detour via the Champs-Élysées in Paris or the Gran Vía in Madrid to see if shoppers are splurging completes the road trip. To that list add Kaub in western Germany. In medieval times the town on the bank of the Rhine began making money from charging barges navigating between the Netherlands and Switzerland. Now a gauge there provides a benchmark for water depth all along the 1,200km-long river. Repeated heatwaves and months of lacklustre rain and snowfall have pushed the measured depth at Kaub down to around 50cm. That is barely a shin’s-worth and just a quarter the usual reading at this time of year. Economists have joined meteorologists in keeping a close eye. Already ships carrying everything from car parts to chemicals up and down Europe’s main industrial valley are having to travel with half loads or less to avoid scraping their hulls on the riverbed. A further decline in water levels—which is all but inevitable as the year progresses—would make the river unnavigable. A lesser snarl a few years back caused German growth to dip noticeably until it was resolved.