The result of putting more carbon into the atmosphere than can be taken out of it is a warmer climate, a melting Arctic, higher sea levels, improvements in the photosynthetic efficiency of many plants, an intensification of the hydrologic cycle of evaporation and precipitation, and new ocean chemistry.All of these have knock-on effects both on people and on the processes of the planet.
There is growing evidence that global warming is speeding up the hydrologic cycle that is, the rate at which water evaporates and falls again as rain or snow.
The global average withdrawal of fresh water was 9% of the amount that flowed through the world's hydrologic cycle.
The only water truly lost in a hydrologic system is through evapotranspiration, since no one can make further use of it once it is in the atmosphere.
In particular, the different effects on the surface and the atmosphere mean that the hydrologic cycle would be changed.
Its hydrologic and environmental consequences could be enormously harmful.The project links China's two great rivers through three new channels.
It also helps that Curtis Foltz, GPA's boss, has green inclinations of his own, having electrified the port's cranes and refrigerated-tanker racks and reduced diesel consumption by 2.1m gallons a year.Yet green promises and hydrologic engineering models only tell what might happen, not what will.
Sound barriers, pesticides, fishing, pheromones, barriers of bubbles and complete hydrologic separation of the Mississippi and Great Lakes watersheds are all being considered.
It encourages the reader to think of the practicalities of what goes where, and why, of what should drain (city streets, through porous surfaces into the ground beneath) and what should soak (seaside levels, released from the hydrologic corsets of Victorian planners), of what should be wild and what be tamed.Mr Kohn's book is a richer, harder and more rewarding read than Mr Kahn's.
Other things being equal, the models also agree that geoengineering tends to suppress the hydrologic cycle, with less evaporation and less rainfall.Some researchers, however, want to go beyond modelling.
