Global warming and climate change are usually thought to mean that world sea levels will rise, perhaps disastrously. But according to US government boffins, in recent times (2010 and 2011, to be precise) phenomena driven by human carbon emissions have actually caused world sea levels to fall.The seas have, of course, been rising steadily as the climate has changed for thousands of years, ever since the end of the last ice age. During the 20th century, according to estimates mostly from erratic tide gauges, sea levels rose by around 1.7mm a year. Since the early 1990s, satellites have also been...