On the surface, global warming may seem like a pretty simple process. Excess "greenhouse" gases trap heat in the atmosphere, making the world warmer. But that's not all that happens. Our climate is actually very complex and intimately connected to life on Earth. Seemingly minor changes can have profound repercussions.

Consider ocean currents. Remember that big blockbuster movie a few years ago based on the theory of rapid climate change? Well, it wasn't exactly rocket science, but it was based on a kernel of truth. In the movie, global warming triggers a collapse of the "thermohaline circulation," a system of currents including the Gulf Stream that circulate water in the Atlantic. Eastern North America and Western Europe depend on this circulation to bring warmer water up from the tropics and help moderate their climates. According to the Hollywood version, a collapse of the thermohaline circulation would thrust New York and London into an instant ice age. Reality is less dramatic, of course, but recent evidence has found that this massive system can indeed be disrupted and it has happened fairly recently. A study by NASA's Goddard Institute for Space Studies looked at the last event, which is thought to have occurred 8,200 years ago when an ice dam in Canada burst, sending a massive flood of freshwater into the Arctic Ocean. This reduced the Arctic's salinity and slowed the thermohaline current, dropping temperatures in Greenland by up to seven degrees Celsius for three centuries.

Results of another study, published this fall in Nature, show that the thermohaline current may again be weakening, this time as a result of melting snow and glaciers due to climate change. Last year, a team of scientists from the U.K.'s National Oceanography Centre sampled water temperature and salinity every 50 kilometres in the Atlantic between the Bahamas and the Canary Islands. They compared data from these samples to data from water collected on four other trips dating back as far as 1957 and concluded that today's current seems to be 30 per cent weaker than it was 50 years ago. So far, air temperatures in Western Europe do not appear to have been affected by the change.

In the tropics, however, small changes in air temperature attributed to global warming are believed to be responsible for the widespread extinction of amphibians. According to a recent paper published in Nature, climate change is altering cloud cover in the mountains of Central and South America, leading to cooler days and warmer nights. This change creates ideal living conditions for a pathogenic fungus, which attaches itself to amphibians, such as frogs, causing dehydration and eventually death.

The fungus has taken a real toll in the tropical Americas, where 67 per cent of 110 species of harlequin frog in the region have died out in just 20 years. Hardest hit have been those species living at mid-elevations, where researchers surmise conditions are optimal for growth of the fungus. They conclude that, "climate-driven epidemics are an immediate threat to biodiversity."

Indeed, a changing climate has also been implicated in the increase of nematode parasites in musk oxen and the continuing destruction of pine forests by the mountain pine beetle. The relationship between an increase in pathogens and a changing climate is also cause for concern in regards to human health. A warmer world may be a sicker one for humans as well.

Climate change is not a simple process. Our atmosphere, our oceans, and all life on the planet are interconnected. Seemingly small alterations in one area can reverberate through the entire system, affecting the health of a tremendous variety of species - including us.

Take the Nature Challenge and learn more at www.davidsuzuki.org.



Source: David Suzuki Foundation

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