Temperature goals heat China climate talksUnited Kingdom
Nicola Ranger and Alex Bowen
The government must use the UN climate change talks in China this week to set a realistic limit on global temperature rise
The Conservative party conference in Birmingham may be the focus of UK politics this week, but government representatives will be taking part in crucial discussions in China that could have profound implications for every country.
Like other negotiating teams at the United Nations climate change talks in Tianjin, they will be trying to answer a fundamental question during their last scheduled gathering before a crucial summit in Cancun, Mexico, at the end of the year.
That question is: how high should global temperature be allowed to rise?
The Copenhagen accord, which was put forward by Brazil, China, India, South Africa and the United States at the end of last December's UN conference, recognised "the scientific view that the increase in global temperature should be below 2C".
However, it also noted that the accord should be assessed in 2015, including "consideration of strengthening the long-term goal referencing various matters presented by the science, including in relation to temperature rises of 1.5C ".
Although 139 of the 194 parties to the United Nations Framework Convention on Climate Change have now agreed to the accord, there is still disagreement about the ultimate temperature goal.
The latest version of the negotiating text for the talks in Tianjin offers warming of 1, 1.5 or 2C above pre-industrial temperatures all as possible goals.
Yet the global average temperature has already increased by 0.8C since the end of the 19th century and it would be almost certainly impossible to prevent a further rise of at least 0.2C.
More importantly, the scientific and economic analysis we have carried out with colleagues at the Met Office indicates that even if global annual emissions of greenhouse gases were reduced from the present level of about 47bn tonnes to 44bn tonnes in 2020 and then cut to zero every year afterwards, there would still be a greater than 50% chance of the temperature reaching more than 1.5C above its pre-industrial level.
Current "high-ambition" pledges by countries, if delivered, would only reduce annual emissions to about 49bn tonnes in 2020. So a warming of more than 1.5C is now very likely, if not quite certain.
Therefore, countries should now be focusing on how global emissions should be reduced to offer a reasonable chance of avoiding warming of more than 2C. Our analysis suggests that this would require annual emissions to be below 49bn tonnes in 2020, much less than 35bn tonnes in 2030 and well under 20bn tonnes in 2050.
We are likely to exceed a warming of 2C unless annual emissions peak within the next 10 years and then decline rapidly afterwards to less than half their current level by the middle of this century.
We know that the impacts of a rise of 2C would be significantly greater than the effects of climate change we have experienced so far. But there is little evidence that exceeding a rise of 2C would be like falling off a cliff and that the world would suddenly be engulfed by catastrophe.
A warming of 2C could cause localised devastation in some parts of the world. Some low-lying coastal areas and islands would be lost forever to a small but significant rise in sea level, unless they are saved by the costly construction of many thousands of miles of new defences, and most of the world's coral reefs would also die because of higher sea temperatures.
This is why some vulnerable small island states, such as Tuvalu, have not signed up to the 2C goal in the Copenhagen Accord - it seems like a death warrant for their nations.
But it should be recognised that we cannot be certain how exactly the global temperature will react to future changes in greenhouse gas concentrations. An emissions path that offers a 50-50 chance of avoiding an increase of more than 2C will also create a 50% chance of greater warming, including a 5% chance of exceeding a rise of more than 3C.
A warming of more than 3C would not only have impacts that are more damaging and widespread but would also increase the possibility of crossing potential "tipping points", such as irreversible large-scale melting of the land-based ice sheets in Greenland and West Antarctica, leading to even further warming.
If the negotiations over a temperature goal drag on beyond Cancun in December, not only will a 1.5C target continue to be virtually impossible, but the 2C target might also cease to be possible and a warming of more than 3C would become increasingly likely.
That is why countries need to reach agreement as soon as possible on a temperature goal and to begin to reduce greenhouse gas emissions accordingly. Only then will we be able to limit the real and serious risks that we face due to climate change.
El contenido de las noticias que se presentan en esta sección es responsabilidad directa de las agencias emisoras de noticias y no necesariamente reflejan la posición del Gobierno de México en este u otros temas relacionados.
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