In light of the highly anticipated Summit on Climate Change, and a (seemingly trivial) scrap recently over emails suggesting pro-climate change data had been manipulated, it’s a good opportunity to put in plain language the science behind global warming.
In the last 100 years, the earth’s average temperature has increased by 0.74 degrees celsius. Sea levels have risen about 15-20cm. Glaciers across the world have retreated dramatically (meaning that more ice is melting than is being replaced).
Most importantly, temperatures and sea levels are rising much more quickly now than they have over the past 100 years and glaciers are melting at faster rates.
In 2007, the UN’s International Panel on Climate Change (IPCC) released its fourth report on climate change. Some of its key findings included:
• The amounts of methane and carbon dioxide in the atmosphere in 2005 far exceeded the average levels for the last 650,000 years
• Of the 12 hottest years recorded since 1860, eleven had occurred between 1995 and 2006
• Since the 1970s, there had been an increase in hurricane intensity in the North Atlantic, correlating with an increase in sea surface temperatures
• Sea levels rose by about 1.8 mm a year during the last half of the 20th century. In the decade from 1993 to 2003, sea levels had risen by an average of 3.1 mm a year
Earth is blanketed by a layer of gases that allow sunlight to penetrate, but stop warmth from escaping. These gases, fittingly called greenhouse gases, keep the world warm enough to support its population and ecosystems.
As more greenhouse gases are emitted, more heat is trapped, and the Earth’s temperature rises. Water expands as it gets warmer, and so the Earth’s sea levels rise. Melting glaciers and loss of ice mass from Greenland and Antarctica contribute to this further.
To some extent, carbon dioxide is absorbed by forests and oceans (called ‘carbon sinks’). But emission levels have become too high for those carbon sinks to soak up – currently removing only around 20-25% of carbon dioxide from the atmosphere.
Changes in climate can be caused by natural factors like changes in the Earth’s orbit.
However, the term ‘climate change’ refers to anthropogenic, (meaning human) influence on the Earth’s climate, caused mainly by emissions of greenhouse gases such as methane, nitrous oxide and carbon dioxide.
The IPCC’s report concluded that the increase in the Earth’s temperature since the mid-20th century was “very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”
Greenhouse gases are emitted by fuel and energy use such as heating, transport and industry. Gases are also emitted by agriculture – livestock emit methane, and chemical fertilisers emit nitrous oxide.
In 2008, 31.5 billion tonnes of carbon dioxide were emitted, mostly through burning coal, oil and gas for energy. In 1970, that figure was 16 billion.
And as the Earth’s population grows, so too does our demand for energy – human-made carbon emissions grew four times faster in the years 2000 to 2008 than in the 1990s.
The IPCC projects that as the Earth’s climate changes, so too will the type, intensity, and frequency of weather patterns, bringing more frequent floods, fires, storms, droughts, heat waves and hurricanes.
Such extreme weather is projected to cause crucial food and water shortages, as well as mass migration (as people flee from famine and conflict).
Climate change also puts pressure on ecosystems, damaging rainforests and varying season lengths; impacting, for example, feeding and migratory patterns for birds.
Increases in sea surface temperatures cause coastal erosion, bleach coral beyond repair, and affect polar and cold sea communities.
Increases in air temperatures make it easier for diseases such as malaria and dengue fever to spread to more people and new areas, with the IPCC predicting that malaria will affect 290 million extra people by 2080.
Climate change also means increased costs for taxpayers, insurers and governments as countries deal with the after effects of extreme weather. The Stern Report (on the economics of climate change) estimated the cost of not taking action to be between five and twenty percent of global GDP (output) every year.
Climate change sceptics (or ‘deniers’) mostly accept that the world might be getting warmer, but maintain that any warming or cooling is caused by the earth’s natural cycles – not us.
They say that climate science is unreliable, and that climate scientists cherry-pick their findings to back up claims of global warming.
But a much greater number of scientists agree that a huge reduction in emissions is essential.
So in the face of such overwhelming evidence, the 98 world leaders attending the Copenhagen conference this week are now trying to back up this science with action to improve the lives of Earth’s future inhabitants.
By Natalya King