Earlier this year, I was on the faculty of a summer school at the University of Heidelberg. My daily walk to the campus took me across a footbridge over the Neckar. By British standards the Neckar, like most rivers that have chunks of a continent to drain, rather than just slices of an island, is impressively large. It is also impressively constrained. For most of its span, the footbridge passed over a system of weirs and gates which, when open, let the river tumble a few metres with a pleasing power into a downstream bed laced with gravel banks and willow trees. At the north end a drop-free navigable channel allowed barge traffic to remain above the fray as it moved to and from a set of locks downstream. The weir gates opened and closed according to a logic I could not fathom; the barges passed through according to the rhythms of trade.
In his excellent book “The Conquest of Nature”, David Blackbourn tells the story of how the Germans came to control their often unruly rivers. The star of the show is the upper Rhine, into which the Neckar flows at Mannheim, about 20 kilometres downstream. In its southern part the upper Rhine was, in the 18th century, a broad, braided maze of lagoons and backwaters; in the north, a higgledypig of meanders. In both parts it was capricious, changing its mind regularly about which way to flow, flooding towns and villages regularly and, sometimes, permanently.
In the 19th century it was brought to heel, in large part by Johann Gottfried Tulla and those who carried on his vision after his death. “No river…needs more than one bed,” Tulla declared, and he set about putting the upper Rhine into what he decided was its place. Its course was shortened, its flow quickened, its lines straightened. The process Tulla set in train continued through the 19th century to the 20th, constraining Germany’s rivers more and more.
Learning all this added to my appreciation of the subject that had brought me to Heidelberg in the first place. The summer school was being held for the benefit of young researchers from all sorts of disciplines who had an interest in climate geoengineering—the deliberate use of technology to counteract, in whole or in part, the anthropogenic warming of the planet. Such efforts could well be seen as Tulla’s sort of thing: one of the justifications he gave for his great labours in “On the Rectification of the Rhine” was that “the climate along the Rhine will become more pleasant”. To his Enlightenment mind, improving on nature through grand engineering schemes seemed, well, second nature—a second nature, superior to the first, that it was human nature to create.
The subordinate Neckar of today might reinforce Tulla’s feelings that human control over nature was possible and justified. But looking a little further shows some of the drawbacks. Tulla was motivated mostly by a desire to do away with floods—but to a large extent he merely moved them downstream, as critics warned would be the case. The rectification of the upper Rhine let floodwaters from the Alps and the Black Forest get to the lower Rhine quicker, to the soggy detriment of Koblenz, Bonn and Cologne; the flood defences they then put in place led to the floods moving yet farther north as water from the heart of the continent found itself reaching the end of the Rhine twice as fast as in years gone by.
There were other drawbacks. The new belief that people could safely farm right up to the banks of the Rhine meant that its beautiful riverbank forests of oak, elm, alder and willow were cut down, its otters driven out. And though navigability had never been part of Tulla’s agenda, his better-controlled river encouraged larger barges, which in turn encouraged straightening and deepening well beyond that needed for flood control. It was, indeed, for navigation, not flood control, that they chained the Neckar in the early 20th century. The swifter rivers, stripped of sandbanks and still waters, lost their salmon and sturgeon, gaining eels, carp and perch instead. No one appears to know why there is a fish-ladder on the weir at Heidelberg; no fish seem to use it.
All of which holds lessons for would-be geoengineers. The first: there will be unintended (if not unforeseen) consequences. Tulla was not planning to flood Koblenz. The second: those consequences may be as likely to lead to calls for further engineering as to calls for stopping what has been started. Anyone who thinks that they can start re-engineering the planet just a bit and that no one will take the ideas further needs to know that history is against them. This is all the more so because once you engineer for one purpose, other applications have a way of following on. If Tulla had no thought for the navigation that now dominates the Neckar, he certainly didn’t care about the modest amount of hydropower generation that now takes place at its weirs.
The flow of history is less easily channelled than that of rivers, and anyone who thinks otherwise has no business trying to change it. Climate geoengineering would be a radical step with unforeseeable consequences. It is surely not to be undertaken rashly, for the sake of a few, or as a seemingly simple way out of the world’s problems. At the same time, it is worth remembering that even great change comes to be accepted, even quotidian. The smooth-flowing Neckar above the weir is grand, its park-like verges happy playgrounds; the messy bit below the weir is charming too. The great barges carry people’s livelihood. And on a stone pier above it all perches a heron, hopeful and beautiful.