Carbon reduction

Carbon levels
The main greenhouse gas (which cause global warming by trapping heat from the sun) is carbon dioxide (CO2). CO2 is collecting in the atmosphere at an alarming rate, far more rapidly than anticipated.

The level of carbon dioxide in the atmosphere is measured in parts per million (ppm) in a volume of air; before the industrial revolution, the figure was about 280ppm; the latest reading, however, was 387ppm, and the figure is rising.

The average growth rate for 2007 was 2.14ppm - the fourth year in the last six with an increase of more than two ppm. From 1970 to 2000, the concentration rose by about 1.5ppm each year, but since 2000 the annual rise has jumped to an average 2.1ppm.
 
Reduction goals
In 1996, the European Union called for the world to take action to limit the global temperature rise to two centigrade above pre-industrial levels.  Jim Hansen, NASA's top climate scientist, who delivered the first warning of climate change to the United States Congress in 1988, believes,  however, that even a two centigrade  rise may not prevent dangerous large-scale impacts such as melting of ice sheets and drought. He argues that world CO2 should not be allowed to remain higher than 350ppm. This is significantly below its current level, and will require CO2 to be removed from the atmosphere and buried.  What is certain is that carbon emissions need to be curbed.
 
Targets and timetables
The UK Met Office recently warned that global greenhouse gas emissions would have to start falling by three per cent each year from 2010 to avoid a global temperature rise of more than two centigrade . Global emissions are, however, currently rising.
 
Scientists have warned that a two centigrade rise will put at least twenty per cent of species at risk of extinction and one to two billion people could suffer increasingly difficult access to water; above two centigrade, plants and soil will absorb substantially reduced amounts of carbon; and above four centigrade  experts warn there is a danger of passing a 'tipping point' at which methane release from permafrost and the collapse of big ice sheets will accelerate the problems.
 
Responsibility for significant reductions in emissions, in the early years at least, would have to be taken by developed countries.
 
Several countries have pledged to cut their emissions. The British government recently pledged to cut the UK's greenhouse gas emissions by 80 per cent by 2050. 
 
To achieve these reductions, substantial changes will need to be made, including a rapid increase in the use of renewable energy, improvements in public transport, increased cycling and walking, and changes in diet. There will also be much pressure for the UK to end plans for a third runway at Heathrow and the building of new coal-fired power stations.

What might happen by 2050?

The Hadley Centre considered three possible scenarios regarding the cutting of global emissions, ranging from 'early and rapid' to 'late and slow' cuts, and compared them with what would happen if no action were taken. It believes that if cuts begin in 2010 and quickly reach three per cent a year, then the temperature increase is likely to be two centigrade  above pre-industrial levels by 2100.
 
By comparison, an 'early but slow' decline, of oneper cent from 2010, would lead to predicted temperature rises of 2.9 centigrade by the end of the century; a 'late and slow' decline, beginning in 2030, would generate likely temperature increases of four centigrade by 2100.
 
Likely effects of varying rates of emission reduction:

Source: Met Office