speeds up the breaking up and melting of the ice. Hansen also found that other greenhouse gases – and soot particles – are speeding up melting in the Arctic. This is because the dark flecks absorb more heat. As a result, he warned, an average temperature rise of just 1°C could lead to a sea level rise of between 2 and 6 metres. If Greenland’s ice sheets melt quickly this will change the temperature in the Atlantic ocean, with dramatic effects on the world’s weather systems.
If a small amount of human-induced global warming triggers massive natural warming, the result is likely to be climate change that happens over decades rather than centuries.
The great ocean conveyor belt Ocean currents redistribute heat around the planet, (below), for example bringing warm water from the tropics to the UK via the Gulf Stream, and cold water to Newfoundland, with striking effects on both countries’ climates. Source: IPCC.
uncertainty and the sceptics
The complexity of the Earth’s climate means that there has been some scientific uncertainty about global warming. Although the theory of the greenhouse effect was first put forward more than 100 years ago, clear evidence that it was happening was not readily available until the 1970s.
Today there is little room for doubt that climate change is happening and that it is caused by human activity. The IPCC – a naturally cautious body – stated in 2007, ‘Most of the observed increase in global average temperatures since the mid-20th century is very likely (>90 per cent) due to the observed increase in anthropogenic greenhouse gas concentrations.’
But earlier scientific uncertainty has proved a fruitful area for media debate, amplifying the doubts of people who have questioned climate change. Some have exploited scientific doubt to spread complacency and confusion because they have seen addressing climate change as a threat to their interests. Certain companies, for example, have tried to divert attention from the environmental impact of fossil fuels.
“Some will always make a case for doubt in an issue such as this, partly because its implications are so frightening. But what is not in doubt is that the scientific evidence of global warming caused by greenhouse gas emissions is now overwhelming.
Tony Blair, UK Prime Minister (1997-2007)
Scientists have explored alternative theories on the rising temperatures – for example, that they are down to variation in the sun’s cycles. But this does not explain the fit between rising levels of greenhouse gases and rising temperatures. In fact, computer models looking at the effect of the sun’s output on our current climate show that if natural variations were the cause, the Earth should now be cooling, not getting hotter.
The sun’s activity has in fact been decreasing since 1985. Natural phenomena simply do not explain why temperatures have risen in the past 30 years.
An assessment of more than 900 scientific studies on climate change, published over a ten-year period, found that none of the research disputed the consensus view that human activity is responsible for global warming.
fuelling the scepticism
While some scientists have pursued legitimate lines of enquiry over the science of climate change, others have deliberately exploited doubts for commercial and political gain. In the United States PR strategists advised the oil industry on how to set up groups to stir up doubts over the science and influence public opinion – in much the same way as the tobacco industry had earlier tried to persuade the public that smoking did not damage their health.
Oil has been key to the global economy for a century, and action to tackle emissions from fossil fuels has been seen to threaten the industry. So it is perhaps not surprising that politicians and many others were at first persuaded not to take global warming seriously.
the scientific consensus
The Intergovernmental Panel on Climate Change (IPCC) is an international body set up by the United Nations and the World Meteorological Organisation (WMO) to assess scientific information on climate change. It brings together climate scientists and government experts to consider research from around the world. In 2007 it shared the Nobel Peace Prize with Al Gore, the maker of An Inconvenient Truth.
four climate hotspots
Scientists have identified a number of hotspots around the world that could trigger fundamental changes in the global climate, including:
Amazon rainforest: Changes in the Sahara could reduce the fertility of the Amazon region, speeding up destruction of the rainforest.
North Atlantic ocean current: Melt-water from Arctic ice sheets could slow the North Atlantic ocean current, leading to cooling in northern Europe.
Asian monsoon: Changes to weather systems in the Atlantic could have a serious effect on the reliability of Asia’s annual rainfall.
Sahara desert: Dust from the Sahara fertilises the Amazon, but if the region gets wetter, there will be less soil erosion and more chance of plants returning to the Sahara.
Scientists are working to understand how such hotspots could affect the climate – and what impact climate change will have on the hotspots themselves.
The IPCC’s fourth report, issued in 2007, highlighted the growing evidence of observed climate change from around the world and looked at future predictions.
Its evidence is based on a consensus among the scientists involved. It is mainstream thinking – endorsed by international governments – and as such it can err on the side of caution. Some have suggested that the IPCC is in fact presenting a ‘bestcase scenario’, underplaying the evidence for more violent climate change. One author based at the Met Office Hadley Centre Richard Betts says that means that the result is ‘bullet proof’ in terms of the certainty of the science it contains. ‘When I read this [the IPCC report] for the first time I did feel fear – I had worked on it for three years and I knew it was right,’ he says.
what will the world be like with a changed climate?
Scientists can predict with increasing accuracy how the climate will respond to rising levels of pollution in the atmosphere. In 2007 the IPCC highlighted the scientific predictions about the impacts of climate change over the next 50 to 100 years, revealing a world in which billions of people will be at risk. Sub-Saharan Africa, large river delta areas in parts of Asia, small island states and the Arctic regions are likely to be particularly vulnerable.
“ It’s the poorest of the poor in the world, and this includes poor people even in prosperous societies, who are going to be the worst hit and who are the most vulnerable as far as the impacts of climate change are concerned.
Rajendra Pachauri, Chair of the IPCC
the Hadley Centre’s global climate models
The UK’s Met Office Hadley Centre is spearheading international research. Early climate models were simplistic replicas of
