“ Global warming is a natural phenomenon – look at the ice ages. Where is the evidence that human impact plays a part?
” Global temperatures have varied in step with carbon concentrations in the atmosphere, and these concentrations have suddenly shot up way above anything experienced over the past half million years. Human activity is the only explanation for this sudden surge.
Climate scientists talk about temperature, greenhouse gas concentrations and emissions. To understand what they are saying you must be prepared to study figures, think bout probability and allow for scientific complexity being reduced to media simplicities.
First: temperature. There is broad consensus that global temperatures should not be allowed to rise more than 2 C above pre-industrial levels, although Professor Rajendra Pauchauri, head of the International Panel on Climate Change (IPCC) with its 2500 climate scientists, now says that 1.5 C would be more appropriate. Land-based temperatures have already risen 0.8 C, and current levels of emissions in the atmosphere commit us to a rise of 1.3 C due to the time lag between cause and effect. The biggest danger is runaway global warming. For example, if the area of arctic ice reduces there is more dark water to absorb heat from the Sun. This, in turn, causes more ice to melt – exposing more dark water – causing more melt – more dark water – more melt. This is a chain reaction that could cause temperature to rise without any further help from us.
Second: greenhouse gas concentrations. The Stern Review (2006) stated that greenhouse gas concentrations at the time it was written were at 430ppm CO2e (parts per million of carbon dioxide equivalent). A figure of 382ppm is sometimes mentioned but this does not include methane (CH4) and nitrous oxide (N2O). Before the industrial revolution the figure was 280ppm. According to the Stern Review, “stabilisation at 450ppmCO2e is almost out of reach, given that we are likely to reach this level in ten years”. It therefore set a target for stabilising at 550ppmCO2e.
Third: Emissions. Despite the Kyoto Protocol (adopted in 1997), emissions have been rising at an ever-increasing rate. In 2006 James Hansen, who heads the US NASA Goddard Institute for Space Studies, said: “A global tipping point will be reached in ten years if levels of greenhouse gases are not reduced. Global warming at this point becomes unstoppable.” The prestigious Tyndall Centre for Climate Change, in a 2006 report ‘Living Within a Carbon budget’, said that a 90 percent cut in UK greenhouse gas emissions, including those from shipping and airlines, is needed by 2050, adding that emissions must reduce by “an unprecedented nine per cent a year from 2010 for up to 20 years”. With this sort of reduction oil refineries would no longer be viable, so we would be moving to a carbon-free economy.
What about sea levels? Greenland is the size of France and Spain combined and mostly covered with ice two kilometres (km) deep. Melt-water is dropping down crevasses and lubricating the base so that glaciers are sliding into the sea faster than anticipated. It was predicted that Greenland would lose 80km3 of ice in 2006. NASA’s Grace satellite showed that it actually oat 287km3 that year.If greenhouse gas emissions are not stabilised within a decade, sea levels could rise several metres before the end of this century.”
Alastair Sawday (2008: 11-12) What About China?