2° is too much

Left to Right: Misty sunset on the Amazonian forests. French Guiana; Sea ice beneath midnight sun ... rel=
The Amazon Rainforest, the Arctic, and the Mediterranean Sea are three regions that will be severely impacted by a temperature rise of 2°C.
© L to R: Roger LeGUEN / WWF; Kevin SCHAFER / WWF; Neoneo13 / Wikimedia Commons
Today many governments and scientists agree that the world needs to keep below an average global temperature rise of 2°C (3.4°F) above pre-industrial times (circa 1800).

This takes into account that the world has already warmed by 0.7°C since pre-industrial times. The margin for manoeuvre becomes tighter.

The 2°C threshold is based on the third assessment report of the Intergovernmental Panel on Climate Change (IPCC).   

This threshold has been accepted by many governments, including the Prime ministers and Presidents of all 25 European Union member states.

The future is in our hands like never before – if we act now we can turn the tide and avoid dangerous climate change. Join us and call for a new Global Deal on climate change at the UN climate conference at Copenhagen in December 2009.

Where do we draw the line on CO2 emissions?

The difficult question is at what level CO2 concentrations in the atmosphere will have to peak – or be stabilised – to prevent 2°C being exceeded? Current concentrations of CO2 are at over 380 ppm (parts per million).

  • If CO2 concentrations were to stay below 400ppm, staying below 2°C would be likely. However, given current energy and power infrastructures, it is very unlikely that we can keep concentrations that low.
  • A level of 550ppm is very unlikely to keep us below 2°C and could even mean overshooting 4°C.
  • At 475ppm the prospect of staying below 2°C is still rather slim. If 475ppm was the peak and a rapid decrease followed, by the year 2100, we have at least options to stabilise at a temperature 2°C higher than pre-industrial times.
Note: These measurements include the effect of other greenhouse gases by attributing global warming values equivalent to CO2; greenhouse gas warming capacities are expressed in CO2 equivalents.

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Source: Meinshausen, M, What does a 2°C target mean for greenhouse gas concentrations? In ‘Avoiding Dangerous Climate Change’, 2006, Cambridge University Press
	© Malte Meinshausen
The World needs to keep below an average global temperature rise of 2°C in order to prevent the worst impacts of global warming.
© Malte Meinshausen


A 2°C rise would lead to a minimum 3.2°C temperature increase in the Arctic, and possibly twice that. The major reason for this is the melting of the polar ice. Previously white ice reflected much of the sunlight back into space, but it is now replaced by dark water which absorbs much more heat. In consequence, even with a 2°C temperature rise the Arctic will be unrecognizable, with summers featuring no or almost no ice. Traditional lifestyles are likely to become very hard to maintain. Species like the polar bear and migrating birds will find their habitats deteriorating or even destroyed.


Annual rainfall could decrease by 20% over the southern Mediterranean and summer rains could decrease by 30% in the northern Mediterranean alone. There will be increased problems with water supply for agriculture and people especially in North Africa, Spain, France and Italy. More heatwaves will mean a serious increase in forest fires, with some occurring all year round in parts of the Mediterranean. These heatwaves could also discourage summer tourism.

Eastern Canada

Important tree species in Ontario – black spruce and sugar maple, the national symbol of Canada – will be forced northwards and it is unclear whether they will be able to adapt. Timber will have to come from younger, smaller trees. A 2°C rise will also impact on Canadian fisheries and could firmly shut the door on the already endangered Atlantic salmon. The small but voracious Asian shore crab is one example of an invading species from the south which will put increased pressure on native shellfish and crab, and the fisheries that rely on them.

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