thin blanket of gases around the Earth prevents some of the sun’s energy from escaping back into space.
five warming signs
Higher temperatures: Scientists have established that the global average temperature has increased by 0.76°C in the past century. Records going back over 150 years show that globally 19 of the 20 hottest years have occurred since 1980.
Melting ice: Arctic and Antarctic ice is thinning and sections of ice shelves are breaking off completely. Temperatures in the Arctic are rising twice as quickly as the global average.
Coral bleaching: Scientists have found a rise of 2°C can kill coral. Reefs are home to around a quarter of known marine species.
Rising seas: We saw an increase of 17 cm during the 20th century.
Drier: Droughts have become more intense over the past 30 years, and have lasted longer, particularly in the tropics and sub-tropics.
fossil fuels and the greenhouse effect
Plants, trees and ocean plankton containing carbon absorbed many millions of years ago fossilised underground to form oil, coal and gas. When these are burnt the carbon is released, and combines with oxygen to form carbon dioxide. The first person on record to recognise the power of fossil fuels to change the climate was Svante Arrhenius, a Swedish scientist who published his ‘greenhouse law’ in 1896. Arrhenius estimated that doubling carbon dioxide levels in the atmosphere would lead to a rise in temperature of 5 °C and thought this promised a warmer climate in colder parts of the world. His maths wasn’t far off but few people today would agree with his predictions that rising temperatures are a good thing.
greenhouse gases
The greenhouse gases include carbon dioxide, methane, nitrous oxide ozone, water vapour, sulphur hexafluoride and halocarbons. They make up quite a small proportion of our atmosphere; some have a more powerful warming effect than others.
carbon dioxide
Carbon dioxide (CO2) is naturally occurring. People and animals produce it when breathing out whereas plants absorb and metabolise it, releasing oxygen in return.
The level of carbon dioxide in the atmosphere is measured in parts per million (ppm); or simply by weight (kg, tonnes).
Scientists believe carbon dioxide levels have been much higher in the Earth’s distant past. Geological evidence suggests that in the Cretaceous period (65-144 million years ago) it was three to six times higher than today.
RING LEADERS:
Trees are in the frontline of defence against climate change – the vast sub-arctic forests of the north being among the most important. The United States, for instance, would be having an even greater impact on global warming if its forests weren’t absorbing around a tenth of its carbon dioxide emissions.
The world was also 10-15 °C warmer then and there was no ice at the Poles. For much of the time that people have been on Earth, carbon Carbon moves between dioxide levels have been stable at around 270-280 ppm. But land, sea and air. This cycle since the Industrial Revolution they have been rising quickly, was in a finely tuned reaching 380 ppm in 2005. This is largely a result of our use of natural equilibrium, but coal, oil and gas: producing, distributing and burning fossil fuels it’s being disturbed by accounts for three quarters of all the emissions of carbon humankind’s use of fossil dioxide caused by humans. The rest comes from changes in fuels, land use change and the way land is used, particularly cutting down and burning deforestation. This trees. Scientists have calculated that carbon dioxide is diagram shows where and responsible for 63 per cent of global warming. And it can stay how much carbon is stored in the atmosphere for up to 200 years. Its long lifespan means and the yearly changes in that carbon dioxide released today will still be affecting the billions of tons of carbon climate for hundreds of years. (GtC).
Carbon moves between land, sea and air. This cycle was in a finely tuned natural equilibrium, but it’s being disturbed by humankind’s use of fossil fuels, land use change and deforestation. This diagram shows where and how much carbon is stored and the yearly changes in billions of tons of carbon (GtC).
CHILDREN OF THE REVOLUTION:
With their economies run on fossil fuels, the countries of the developed world have been responsible for 77 per cent of carbon dioxide emissions since the start of the Industrial Revolution.
carbon and carbon stores
Often described as the building block of life, carbon is present in all living things. It is the fourth most common element in the universe and is found in millions of different compounds. Commonly found in mineral form as coal, it is also in oil and methane (the main constituent of natural gas). When burnt, carbon combines with oxygen to form carbon monoxide (CO) and, more often, carbon dioxide (CO2). The world’s oceans, forests and soils absorb huge quantities of carbon, in the form of carbon dioxide, from the atmosphere.
Plants take carbon dioxide out of the atmosphere through photosynthesis. When a tree is cut down and burnt, some of the stored carbon in the tree converts back into carbon dioxide and escapes into the atmosphere.
Oceans absorb around half of the carbon dioxide in the atmosphere mostly as dissolved bicarbonate. Like plants, plankton in the sea take up carbon dioxide through photosynthesis. But as oceans warm they absorb less. The increasing concentration of carbon dioxide in the atmosphere is also increasing the acidity of the oceans and damaging marine life.
Organic material in soil takes carbon dioxide out of the atmosphere. More carbon is held in the world’s soils than in the atmosphere. But the capacity of the soil is limited and over time the amount of carbon dioxide escaping into the atmosphere will increase.
methane
Methane (CH4) is a naturally occurring greenhouse gas but levels in the atmosphere have more than doubled since the pre-industrial era. Farming contributes a huge amount: one dairy cow produces an estimated 500 litres of methane daily, mainly when burping – and there are some 10 million cattle in the UK. But methane also comes from landfill sites, burning fossil fuels, wetlands and drying peat bogs (swamp gas). It has a relatively short life span, of 11-12 years. Even so, methane is a powerful greenhouse gas, absorbing 20-25 times more infrared energy than carbon dioxide, and it is responsible for 24 per cent of global warming.
AN ILL WIND:
Domestic animals produce about a quarter of the world’s methane emissions – around 100 million tonnes annually. That’s more in carbon dioxide equivalent than emissions from transportation.
nitrous oxide
Like other greenhouse gases levels of nitrous oxide (N2O) have increased as
