Lochluichart wind farm - Climate Change


	Climate change

	Greenhouse gases and their sources \| How much polution can we allow
	The science of climate change
	The 1990s may have been the warmest decade on record, but how do we know that it is a consequence of man-made climate change?
	The trouble is the weather is always changing. And even climate (average weather) has cycles. Some cycles last little more than a year, like El Nino, a worldwide influence caused by the change in Pacific Ocean currents. Some last hundreds, or even thousands of years, before the cycle repeats itself.
	Ice ages, which happen roughly every 100,000 years, are a well-known cycle. Another is not due for a while yet. Most of the Northern Hemisphere enjoyed a warm spell from the 12th to 14th centuries when much of Greenland was really green.
	There then followed a "little ice age", during which the Thames regularly froze over and Londoners held ice fairs. That lasted until the early 19th century. Part of the warming seen since is certainly a recovery from that period.
	But the United Nation's scientific advisers on the Intergovernmental Panel on Climate Change (IPCC) have concluded that "the rate and duration of warming in the 20th century cannot simply be considered a recovery."
	Evidence of past temperatures gathered from analysing the thickness of tree rings, air bubbles trapped in ice cores and the chemistry of ocean sediments all suggest that the world has not been this warm since 1000 AD and probably long before. The IPCC believes that something quite unusual is going on that cannot be explained by any known natural forces.
	One possible natural cause might be sunspots—the visible evidence of increased amounts of radiation leaving the sun. Long-term cycles in solar activity are probably a cause of the warming in the Middle Ages and the cooling of the little ice age. And, more recently, sunspot activity quite closely followed global temperature changes from around 1850 to the 1970s.
	But, since then, the two curves have diverged. Solar cycles should have made the world cooler in the past 20 years; in fact, the world has become dramatically warmer. Available evidence points ever more surely to the increased greenhouse effect caused by human pollution.

	The greenhouse effect
	Human activity alters local climate in a number of ways. We produce smoke that creates smog and we churn up dust that shades us from the sun. We chop down the rainforests that recycle rainfall and make areas downwind drier.
	But the number one impact of human activity on climate is to increase the "greenhouse effect". It threatens to be global, long lasting and hard to reverse. The gases that contribute to the effect are being emitted from our power stations and vehicle exhaust pipes, our farms and our forests and they can stick around in the air for decades, even centuries.
	Some of these greenhouse gases are naturally present in the air. They help keep the planet warm. It works like this. As the sun's radiation hits the Earth's surface, some of it is reflected right back into space, but much of it is absorbed by the land and oceans as infrared radiation—or heat. Some of the heat escapes into space, but a lot is trapped by greenhouse gases close to the Earth’s surface, causing the atmosphere to heat up.
	The three most significant greenhouse gases are water vapour, carbon dioxide and methane. Without them we would freeze. But the more concentrated they are, the more we heat up the planet.
	Pumping greenhouse gases into the atmosphere is like putting an extra blanket over the Earth. We are starting to warm up. And there are other changes. Higher temperatures increase evaporation from the oceans and increase the atmosphere’s capacity to hold water. So, the air is getting wetter in many areas. And a hotter atmosphere is more energetic, so that it is able to generate stronger storms and other extreme weather events.