When the Caribbean and Florida were hit by multiple big hurricanes last month, the question on the lips of many people was whether global warming was at fault. Climatologists had the scientifically correct answer: hard to say, probably not, but quite possibly a contributing factor. Because the environment is a complex system of system, it's very difficult to pinpoint precise cause-and-effect for specific weather or environmental effects. But that doesn't mean we can't see particular signs of change.
John Schellnhuber, research director at the Tyndall Centre for Climate Change Research in the UK, has helped to develop a list of twelve "tipping points" where small increases in average atmospheric temperature due to global warming could produce "sudden and dramatic environmental damage." The list varies from locations where changes could have significant global effects to locations where the changes would be more "canary in a coal mine" warnings. What's most troubling is the manner in which such disruptions would very often trigger positive-feedback loops -- environmental changes which would in turn serve to accelerate the effects of global warming.
Follow the link for the full list; read on for a couple of excerpts.
Occupying some 3.5m square miles of northern Africa, the Sahara desert is expected to shrink with global warming as more plentiful rain brings a flourish of vegetation to its southernmost reaches.
For those on the edge of the desert, the fertile land will undoubtedly be a boon, but the Sahara plays a broader role in the health of the planet. The dry dust that is whipped up from the desert by strong prevailing winds contains crucial nutrients that seed the Atlantic and may even help fertilise the Amazon.
As the Sahara turns from brown to green, the flux of nutrients into the ocean is expected to drop, restricting food available for plankton, the smallest of links in the marine food chain.
As the number of plankton falls, so does food for aquatic creatures further up the food chain.
That's not the only knock-on effect. Plankton lock up the greenhouse gas CO <->2 from the atmosphere, and so help counter global warming. With fewer plankton, the oceans will take less of the gas from the Earth's atmosphere.
Dust from the Sahara has other, more subtle influences. When blown out over the Atlantic, clouds of Saharan dust act to stabilise the atmosphere, suppressing the formation of hurricanes.
A greener Sahara could mean more frequent, or more severe hurricanes slamming into the Caribbean, parts of central and southern America and the south-eastern US.
Meanwhile, the now wetter Saharan regions of Sudan, Morocco and Algeria could become more prone to infestations of locusts, such as the swarms that have devastated crops in the region this year.
During March and April, the Indian subcontinent begins to heat up, reaching some of the highest surface temperatures of the year by May. The hot land produces a sharp temperature gradient between the land and sea which causes an abruptreversal of the winds from seaward to landward.
As the winds strike the Himalayas and are deflected upwards, they create a low pressure system, forcing rainclouds to release their stores of water. While the monsoon season can cause incredible flood damage, local populations are largely adapted and to some extent reliant on the weather.
If global warming has the expected effect of heating India even more, the monsoon season could become far more severe. What happens will be influenced by the level of pollution in the region. Sulphur dioxide and even dust make rain droplets smaller and so diminish overall rainfall. These substances also increase the reflectivity of clouds, which prevents the ground from heating up so much.
Both of these factors would weaken the monsoon, causing havoc for Indian agriculture, with serious consequences for food production.