Water Cycle Changes in a Warming World: The Scientific Background

Global climate change is rapidly approaching the threshold of what is considered safe by the global climate research community. There is ample and robust evidence that extreme weather events are occurring more frequently across the globe. Also, it is now a well-established fact that the warming catalysed by the industrial revolution is caused by human emissions of greenhouse gases into the atmosphere, primarily in the form of Carbon Dioxide (CO2). While fossil fuels have allowed society to evolve into its current modern iteration, their effects may also wreak havoc on the stable climate we depend upon in the long term. In the course of the last two centuries, scientists have determined that the planet warms with every ton of CO2 emitted, and also that weather becomes increasingly extreme due to the associated changes in the global water cycle. Since the beginning of the rapid ‘modern’ global warming 40 years ago, many of the changes the scientific community predicted—underpinned by a very solid understanding of the physics of the atmosphere and the climate system—have indeed materialised. Heat extremes have become hotter, drought episodes have become longer, extreme rainfalls have become more extreme. In essence, it is very likely that the hydrological cycle during the wet season has already intensified. This review article introduces the theory behind warming-induced changes of the global water cycle and includes a discussion of the implications of this theory at global and regional levels. A few recent attribution studies demonstrate how the role of humans in altering the odds of extreme weather occurring is quantified.