The hydrologic cycle is the process by which water evaporates from the land and the surface of oceans, lakes and rivers, is carried by the wind and then falls as rain or snow. Since the oceans cover 71% of the earth's surface, most of that evaporation and precipitation occurs over the oceans, and can be monitored via changes in surface salinity. Where evaporation is strong the remaining water will be saltier. In areas of heavy rainfall, surface water will be fresher.
Preliminary findings from ocean salinity research indicate that the global water cycle has been speeding up since the 1950s. According to the research team, salty areas have become saltier than expected, and relatively fresh areas of ocean have become even fresher. That means that both evaporation and rainfall have become more intense as a result of global warming - dry areas will get drier and wet areas will get wetter. Climate models predicted such changes long ago - thus the warnings of increased droughts and flooding as the planet warms.
What is surprising is the rate of change. The research shows the water cycle is accelerating at a rate of 8% (+/- 5%) per degree of warming, or a roughly 4% acceleration since 1950. This rate is twice what is predicted by computer models. If it continues, we might see a 20% acceleration in the hydrologic cycle by the end of the century.
The initial predictions were worrisome enough, but these forecasts, if they are borne out, would be very bad news. Remember last year's drought across the southern U.S.? Imagine droughts that are 20% more intense on average, meaning quite a few will be a lot worse. Images of the Dust Bowl spring to mind. Remember the devestating floods in northern England a few years ago? Picture downpours that dump 20% more rain on average onto swollen rivers, with more than a few storms producing even heavier rainfall.
While this research was conducted by a well-respected team of scientists and peer-reviewed before publication, it is based on older datasets going back fifty years or more. New and more comprehensive data is being gathered by a recently launched NASA satellite called Aquarius. Thus, it is possible that Durack, Wijffels and Matear have overstated the case, that the weather related impacts from climate change are not as severe as they have predicted.
I hope they are wrong, but we simply can't afford to wait. The Aquarius data won't be ready for years, and it very well may confirm these research findings. If we fail to mitigate climate change by reducing emissions, we lock ourselves and our children into even greater adaptation costs and lock in ever-greater suffering.
