Causes & Effects


The big cause of climate change has been creeping up on the planet since the start of the Industrial Revolution, around 1750.

As manufacturing and transport used more and more fossil fuels – first coal, then oil and gas - millions of tonnes of their carbon content were released into the atmosphere as a gas, carbon dioxide (CO2). This gas was naturally there already - indeed, its presence has helped all life on Earth. It lets sunlight through to hit the surface of the planet and particles in the air, creating the warmth that life needs. CO2 also stops most of the warmth escaping into space again, which makes it (like some other vapours, such as methane and nitrous oxide) a ’greenhouse’ gas.

Earth has known dramatic swings of climate, some triggered at long intervals by variation in the planet’s orbit round the sun. The hillside above me is strewn with rocks scattered in the passage of glaciers. But even in the 10,000 years since the last ice age, there have been periods of marked natural warming and cooling. Right now we are in an ‘interglacial’ – a mild period between ice ages. But in the last few centuries, the artificially-boosted ‘greenhouse’ has been trapping more and more heat, as carbon dioxide in the amosphere rose from 280 parts per million (ppm) before about 1750 to more than 400 ppm today.


The evidence for global warming has been gathered from many fields of science by the Intergovernmental Panel on Climate Change (IPCC). It has listed signs of warming to be found in natural systems all round the world.

There are more and more lakes, and bigger ones, where glaciers have melted. Mountainsides thunder with avalanches of rocks, released by thawing ice. Along with the earlier dates in spring – of bud-burst, bird migration, first flowerings and so on – come changes in the range of plants and animals - they move northward, or up to higher, cooler land. In the ocean, there are shifts of plankton and fish, not always in ways that match predators to prey.

The IPCC has made predictions of how warming might develop in this century. If CO2 emissions continue to rise unchecked, their level could double by the end of the century, producing a global average warming of 3C to 4C. That could have cataclysmic impacts on many human societies and natural ecosystems. Even in Ireland, the projection is for more than 2C. in the next 40 years; perhaps 3C by the century’s end. On any one day, an extra 2C of warmth might seem little enough, but with averages come extremes. In the intricate machinery of climate, of living ecosystems and sea level, the demands on nature’s adaptation will often be hard to meet.

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