Читать книгу What on Earth is Going On?: A Crash Course in Current Affairs - Arthur House - Страница 15
ОглавлениеIs it really happening?
Yes. In 2007 the Fourth Assessment Report of the IPCC (Intergovernmental Panel on Climate Change) established that global warming is a certainty and provided overwhelming evidence that man is to blame. It concluded that ‘warming of the climate system is unequivocal’ and that ‘most of the observed increase in global average temperatures since the mid-20th
century is very likely due to the observed increase in anthropogenic [man-made] greenhouse gas concentrations’. Their findings have largely silenced the minority of politicians, industrialists and lobbyists who had previously denied the reality of climate change despite the mounting evidence.
How do greenhouse gases cause climate change?
Most greenhouse gases (carbon dioxide, methane, nitrous oxide, chlorofluorocarbons (CFCs) and others) are naturally produced by the earth’s ecosystem and are essential to maintaining its temperature by absorbing and emitting radiation in the atmosphere. However, an excess of greenhouse gases leads to a phenomenon known as radiative forcing, whereby heat that would normally leave the earth becomes trapped, causing the atmosphere to warm up. By examining ice cores which contain bubbles of the earth’s atmosphere dating back thousands of years, IPCC scientists have shown that greenhouse gases have increased ‘markedly as a result of human activities since 1750 and now far exceed pre-industrial values’. CO2 levels are now the highest they have been for over 650,000 years, due to an increase of around 30% in the last 50 years, and there is over twice as much methane in the atmosphere now as there was in pre-industrial times.
Which human activities create greenhouse gases?
Burning fossil fuels and land use change are the two main causes of global increases in carbon dioxide, the principal greenhouse gas. Fossil fuels—such as coal, oil and natural gas—are hydrocarbons, and are burnt in order to generate electricity, provide heating and power transport. The most common example of land use change is the destruction of forests to make way for agriculture. Deforestation accounts for at least a fifth of daily carbon emissions, leaving CO2 in the atmosphere which would otherwise be removed by trees for use in photosynthesis. Increases in methane, the other most significant greenhouse gas, are principally due to agriculture (especially rice cultivation and flatulence in livestock), leakage during fossil fuel production and the burning of biomass (plant matter).
Positive feedbacks
As the atmosphere warms, its capacity to hold water vapour (in the form of clouds and humidity) increases; water vapour is itself a greenhouse gas, and so the warmer the atmosphere gets, the greater its potential to continue doing so. This is one of several ‘positive feedback’ processes associated with climate change. Ice and snow reflect sunlight, so in areas where they are melting, solar energy is absorbed instead by the sea or land beneath, causing the earth to heat up further. Permafrost, the deep frozen soil of the arctic and subarctic regions which locks away carbon dioxide and methane in the form of long-dead vegetation, is also melting as the earth warms, releasing more and more of the greenhouse gases into the atmosphere. Rising sea temperatures are threatening to wipe out plankton, microscopic organisms which act as a vital carbon ‘sink’ by ingesting carbon dioxide. This would leave yet more of the greenhouse gas in the atmosphere. Some scientists also fear that rising sea temperatures could cause a sudden release of methane from clathrate compounds on ocean floors. These are vast deposits of solid water crystals containing methane which, if melted, could create a runaway greenhouse effect. Such an occurrence is believed to have caused the Permian-Triassic event, or the ‘mother of all mass extinctions’, around 250 million years ago.
How does global warming cause the climate to change?
Increases in average air and ocean temperatures destabilise climate systems and create extreme and unpredictable weather. In some regions this means heavier rainfall, which causes flooding (and often more erosion and subsequent desertification), whereas other areas experience longer droughts, heat waves and forest fires. When water gets warmer, it expands, which, along with the extra meltwater from disappearing ice caps, snow and glaciers, is causing sea levels to rise at the rate of several millimetres per year. The incidence of strong hurricanes (category 4 or 5) has nearly doubled in the past thirty years. Their relationship with global warming remains uncertain, although they have been linked to increased evaporation caused by rising tropical sea temperatures.
What could be the effects of climate change for life on earth?
It is well known that climate change is endangering the polar bear, but according to the International Union for the Conservation of Nature (IUCN) there are as many as 10,000 species likely to become extinct as a result of climate change in the next 50 years alone. The bleaching of coral reefs and death of plankton caused by rising sea temperatures will seriously affect marine biodiversity and the ocean food chain (and dependent bird species). Amongst many other adverse effects on ecosystems, global warming is causing infestations of tree-killing beetles and playing havoc with the migratory habits of animals and birds.
What could be the human costs of climate change?
It depends on how much action we take to stop it. If allowed to continue unchecked, the potential costs are huge. Rising temperatures will diminish yields of staple food crops such as rice and wheat, creating more hunger and malnutrition in developing countries. Mosquitoes will inhabit more of the planet as it warms, enabling malaria to spread further. Flooding caused by heavier rainfalls or meltwater could contaminate water supplies, damage homes and spread water-borne diseases. Heat waves will continue to kill people (35,000 died in the European heat wave of 2003). The world’s freshwater supply will decrease as snow and glaciers melt. Island states such as Tuvalu and the Maldives are likely to be submerged or become uninhabitable during this century, while low-lying countries (e.g. Bangladesh, the Netherlands) and coastal cities (e.g. New York, Shanghai) could soon be threatened. Desertification is causing pasture to disappear, creating competition over land—this has already been a cause of war (see Darfur). A World Health Organisation study in 2005 established that around 150,000 people die every year from the effects of global warming, a number which could almost double by 2020. In economic terms, it will cost much less to act now to combat climate change than to pay for it later (1% of global GDP compared to 20%, according to the 2006 Stern Review into the Economics of Climate Change).
Are there any positives?
In the UK, we’re already enjoying shorter winters and warmer average temperatures as a result of climate change, and tourism and agriculture could benefit from the rising temperatures in the short term. In the Arctic, the melting ice sheet is likely to open up the Northwest Passage (between Canada and the North Pole) within a couple of decades, dramatically shortening shipping times from Asia to Europe. It is also going to enable access to the vast reserves of oil and gas believed to lie under the Arctic seabed; international squabbling over their ownership has already started, with Russia sending a mini-submarine to plant a flag on the seabed beneath the North Pole in August 2007. Whoever gets their hands on the oil and gas, it will all get burnt, warming up the atmosphere that little bit more.
