Discussions on carbon footprints and how to reduce emissions intensify with each new report. Statistics, targets and goals abound. David Adam explains how such climate goals are set, and why they may not be enough
David Adam
guardian.co.uk,
Tuesday October 07 2008 10:11 BST
From supermarkets and oil companies to individuals, nations and continents, people are talking about reducing their carbon footprints. Statistics, targets and goals abound. But what do the aims such as the 80% cut by 2050 suggested in Britain's climate watchdog? How does your country's pledge measure up? And just how many parts per million carbon dioxide are too many?
Here, we explain how such climate goals are set, and why they may not be enough.Carbon levels
The level of heat-trapping carbon dioxide in the atmosphere is measured in parts per million (ppm) in a given volume of air. The figure was about 280ppm before the industrial revolution and has been creeping up since. The latest reading was 387ppm, and the figure is rising at about 2ppm each year as emissions continue unabated.
But carbon dioxide is not the only greenhouse gas: methane, nitrous oxide and numerous others also trap heat as they accumulate in the atmosphere, and must be included in calculations. To do this, scientists group them together, work out how much heat they trap, and calculate the amount of carbon dioxide that would be needed to cause a similar effect. The two figures are then added together, and called carbon dioxide equivalent - CO2[e].
The extra load from the other greenhouse gases bumps up the pure carbon dioxide concentration by up to a fifth. So, roughly, 400ppm CO2 = 450ppm CO2[e] and 550ppm CO2 = 650ppm CO2[e].
In predicting the likely temperature rise under a given emissions scenario, the all-inclusive CO2[e] figure is the important one, though this is not always made clear.Stabilisation goals
In 1996, the European Union said the world should limit the global temperature rise to 2C above preindustrial levels, and that this meant limiting carbon dioxide in the atmosphere to 550ppm CO2[e]. In reality, the relationship between carbon dioxide levels and eventual temperature rise is less precise. Scientists now talk only about likely ranges. The 2006 Stern Review said that 550ppm CO2[e] would drive temperatures up by between 1.5 and 4.5C, with a median rise of 3C. It said the world should aim for a stabilisation goal of between 450 and 550ppm CO2[e].
The lower end of that range (450ppm CO2[e]) is now commonly associated with a 2C rise, and the upper end (550ppm CO2[e]) with a 3C rise. In fact, scientists say that at 450ppm CO2[e] there is still a 50% chance that the 2C target will be exceeded.
Jim Hansen, Nasa's top climate scientist, says that even a 2C rise may not avoid dangerous large scale impacts such as melting of ice sheets, and says world CO2 should not be allowed to remain above 350ppm CO2, significantly below its current level – that means removing CO2 from the atmosphere and burying it.Targets and timetables
The world has not yet set a global goal to limit carbon dioxide in the atmosphere, but 450ppm CO2[e] is often used as an example. In 2007, the G8 group of nations converted this target to a 50% cut in world emissions by 2050. As any new climate deal is likely to permit developing countries to continue increasing their emissions for the foreseeable future, the bulk of this burden will fall on rich countries such as the US and Britain. Britain's share of the load could be as much as a 95% cut of national emissions by 2050.
In anticipation of such a demand on them, several countries including Britain have unilaterally pledged to cut their emissions. Several have also set interim targets, such as the EU's pledge to reduce emissions 20% by 2020, rising to 30% if enough countries follow its lead. Cities, companies and states have also set targets. Here is a selection:
Moving the goalposts?
Some scientists have criticised climate targets as based on "anecdotal rather than systematic" information. Others point out that they can fail to include all sources of emissions. Britain's original climate change bill, for example, failed to include pollution from aviation and shipping, though its climate watchdog now recommends they are included.
David King, former chief scientific adviser to the government, has said it is critical that official targets are "seen to be achievable". This has led to a stand-off between both campaigners and scientists who complain that domestic targets are not ambitious enough, and politicians who fear setting unrealistic goals. Some scientists are even saying that the G8's global goal of 50% reductions by 2050 - already very difficult to achieve - is not enough.
In May, experts from the Intergovernmental Panel on Climate Change said the G8 goal "will not avoid global impacts". They said the target should be tightened to a 80% cut in world emissions by 2050.
Many observers believe radical political leadership is essential if such severe cuts are to be achieved, with the summit taking place in Copenhagen in December 2009 seen as a pivotal moment. The scale of the task was highlighted this month by the UK Met Office, which warned that global greenhouse gas emissions would have to start falling by 3% from 2010 to stand a chance of limiting warming to 2C. Global emissions are currently rising.
David Adam
guardian.co.uk,
Tuesday October 07 2008 10:11 BST
From supermarkets and oil companies to individuals, nations and continents, people are talking about reducing their carbon footprints. Statistics, targets and goals abound. But what do the aims such as the 80% cut by 2050 suggested in Britain's climate watchdog? How does your country's pledge measure up? And just how many parts per million carbon dioxide are too many?
Here, we explain how such climate goals are set, and why they may not be enough.Carbon levels
The level of heat-trapping carbon dioxide in the atmosphere is measured in parts per million (ppm) in a given volume of air. The figure was about 280ppm before the industrial revolution and has been creeping up since. The latest reading was 387ppm, and the figure is rising at about 2ppm each year as emissions continue unabated.
But carbon dioxide is not the only greenhouse gas: methane, nitrous oxide and numerous others also trap heat as they accumulate in the atmosphere, and must be included in calculations. To do this, scientists group them together, work out how much heat they trap, and calculate the amount of carbon dioxide that would be needed to cause a similar effect. The two figures are then added together, and called carbon dioxide equivalent - CO2[e].
The extra load from the other greenhouse gases bumps up the pure carbon dioxide concentration by up to a fifth. So, roughly, 400ppm CO2 = 450ppm CO2[e] and 550ppm CO2 = 650ppm CO2[e].
In predicting the likely temperature rise under a given emissions scenario, the all-inclusive CO2[e] figure is the important one, though this is not always made clear.Stabilisation goals
In 1996, the European Union said the world should limit the global temperature rise to 2C above preindustrial levels, and that this meant limiting carbon dioxide in the atmosphere to 550ppm CO2[e]. In reality, the relationship between carbon dioxide levels and eventual temperature rise is less precise. Scientists now talk only about likely ranges. The 2006 Stern Review said that 550ppm CO2[e] would drive temperatures up by between 1.5 and 4.5C, with a median rise of 3C. It said the world should aim for a stabilisation goal of between 450 and 550ppm CO2[e].
The lower end of that range (450ppm CO2[e]) is now commonly associated with a 2C rise, and the upper end (550ppm CO2[e]) with a 3C rise. In fact, scientists say that at 450ppm CO2[e] there is still a 50% chance that the 2C target will be exceeded.
Jim Hansen, Nasa's top climate scientist, says that even a 2C rise may not avoid dangerous large scale impacts such as melting of ice sheets, and says world CO2 should not be allowed to remain above 350ppm CO2, significantly below its current level – that means removing CO2 from the atmosphere and burying it.Targets and timetables
The world has not yet set a global goal to limit carbon dioxide in the atmosphere, but 450ppm CO2[e] is often used as an example. In 2007, the G8 group of nations converted this target to a 50% cut in world emissions by 2050. As any new climate deal is likely to permit developing countries to continue increasing their emissions for the foreseeable future, the bulk of this burden will fall on rich countries such as the US and Britain. Britain's share of the load could be as much as a 95% cut of national emissions by 2050.
In anticipation of such a demand on them, several countries including Britain have unilaterally pledged to cut their emissions. Several have also set interim targets, such as the EU's pledge to reduce emissions 20% by 2020, rising to 30% if enough countries follow its lead. Cities, companies and states have also set targets. Here is a selection:
Moving the goalposts?
Some scientists have criticised climate targets as based on "anecdotal rather than systematic" information. Others point out that they can fail to include all sources of emissions. Britain's original climate change bill, for example, failed to include pollution from aviation and shipping, though its climate watchdog now recommends they are included.
David King, former chief scientific adviser to the government, has said it is critical that official targets are "seen to be achievable". This has led to a stand-off between both campaigners and scientists who complain that domestic targets are not ambitious enough, and politicians who fear setting unrealistic goals. Some scientists are even saying that the G8's global goal of 50% reductions by 2050 - already very difficult to achieve - is not enough.
In May, experts from the Intergovernmental Panel on Climate Change said the G8 goal "will not avoid global impacts". They said the target should be tightened to a 80% cut in world emissions by 2050.
Many observers believe radical political leadership is essential if such severe cuts are to be achieved, with the summit taking place in Copenhagen in December 2009 seen as a pivotal moment. The scale of the task was highlighted this month by the UK Met Office, which warned that global greenhouse gas emissions would have to start falling by 3% from 2010 to stand a chance of limiting warming to 2C. Global emissions are currently rising.
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