What would the world look like after 4°C of global warming?

The global delay in reducing emissions is taking us on a pathway towards 4°C of warming that we may find difficult to avoid, say scientists.
Just a few months ago, the UN’s chief climate negotiator was telling chinadialogue that it was still possible to avoid 2C (degrees Celsius) of warming, avoiding what scientists call "dangerous climate change". 
While the latest UN climate summit reaffirmed the plan to to adopt a legal agreement to cut emissions "as soon as posisble and no later than 2015", it may not be enough to prevent a much higher 4C of warming. 
As researchers at Manchester University have pointed out recently, to limit emissions to around 2 to 2.4C, countries would actually have to start reducing them by 2015 – very different from simply "agreeing" to cut them. At present, they explain, current global greenhouse gas emissions are taking us on a pathway towards 4C of warming.
For many countries that kind of warming is a drastic prospect.

The Doha outcome puts the world on track for three, four or even five degrees of warming, Mónica López Baltodano, of Centro Humboldt Nicaragua, an environmental NGO, has said. She attended Doha as a delegate from the South Pacific island nation of Nauru and represents the Alliance of Small Island States – the ones most likely to be wiped out first by rising sea levels.

"We’re not talking about how comfortable your people (in developed world) may live but whether our people live. The lives of our people are on the line here," said Baltodano.

It is not just low-lying island states that will be effected either. As the World Bank reported recently, a 4C world would be one of unprecented heat waves, severe drought and major floods in many regions.

The UK meteorological office produced a illustrative map a few years ago, detailing what a 4C world would look like. You can see the 4C map in full on their website. Although the average temperature rise over the globe is 4C (7 Farenheit) the rise will not be spread uniformly across the globe. The land will heat up more quickly than the sea, and high latitudes, particularly the Arctic, will have larger temperature increases. The average land temperature will actually be 5.5C above pre-industrial levels.

The impacts of the temperature rise will include a decline in major cereal crop yields, water availability issues in western China, where much of the river flow comes from glacial melt water and risks of flooding and storms to low-lying coastal regions (see chinadialogue article on flooding risk in Shanghai).