Earth’s average global surface temperature is increasing. It has risen about 1ºF in the last century, and is expected to go up another 3 -11ºF in the next 100 years. This climate change has been dubbed “Global Warming”. Although the magnitude of warming may seem insignificant, many natural processes have been profoundly affected. For example, a number of changes in the water cycle have been documented, and many more are under investigation. Global warming intensifies the movement of water through the cycle, because many of the processes involved are temperature-dependent.
Individual storms, heat waves, or other weather phenomena can’t be blamed on global warming – hurricanes, droughts, blizzards, and the like have been occurring for millennia. However, the increasing temperature has been accompanied by an increase in extreme weather events. Floods and droughts at the end of the 20th century were significantly more widespread, severe, and frequent than they were in the early 1900s. Global warming may be making severe weather more common.
Floods often occur when rain falls or snow melts faster or in greater amounts than the ground can absorb water or rivers can carry it away, or when storm winds push seawater onshore.
In a special issue of OCEANOGRAPHY (Vol. 21, No. 1, 2008) devoted to ocean salinity, Arnold Gordon and Claudia Giulivi of Columbia’s Lamont-Doherty Earth Observatory (LDEO) compared historical trends in surface salinity of the subtropical North Atlantic and North Pacific Oceans. They found that there were significant departures from the long-term trends on time scales of a decade or so; even more interestingly, the two oceans varied in the opposite direction. An important lesson from these studies is that the global intensification of the water cycle will be modified by a patchwork of regional fluctuations, and perhaps even extreme regional fluctuations. Higher surface ocean temperatures will lead to greater year-to-year variability in the water cycle for much of the world because ocean temperates affect the atmospheric circulation patterns that carry moisture. Although circulation is often driven by known forcing, such as ENSO, future rainfall distributions will be difficult to anticipate. (Climate Matters)