How Much is too Much?

One of the most important questions for scientists and policy makers is: what is dangerous climate change?

Of course, this will depend on where you live. For example, low-lying islands are far more susceptible to sea-level rise than large land masses. In 2005, Britain was hosting the G8 summit in Gleneagles, Scotland. The meeting came up with a ‘magic number’ of 2  above pre-industrial average temperature; below this threshold, there would be both winers and losers due to regional climate change, but above this figure everyone is likely to lose. This is backed up by the IPCC, an independent scientific body of thousands of scientists worldwide.

Thus 2 seems to be the point at where numbers increase radically, i.e. a climate threshold/tipping point. For this reason 2 degrees Celsius has become a powerful symbol of the challenge facing human society. The major problem is that we are unlikely to be able to keep mean global temperature below the magic 2 degrees Celsius as nation states haven’t been proactive enough in their carbon reduction proposals and execution of them.

Today's global surface temperature increase since pre-industrial times is 0.8° C (NASA GISS 2013). Even if we were to keep atmospheric carbon dioxide levels at the 2,000 levels this would still another 0.6 degrees Celsius at least (Maslin, 2008), so without doing anything we are at 1.4 degrees Celsius. Not to mention the fact that in 2013 atmospheric carbon dioxide passed a new high of 400ppm! Thus surpassing the critical 2 degrees Celsius is a likely, if not inevitable event in our lifetime.

Below is a list, taken from Maslin (2008), of likely impacts of increasing global average temperature.

·      1-2 degrees Celsius  above pre-industrial  

• Major impacts on ecosystems and species
• Increases of heat waves, droughts, floods and spread of infectious disease.

·      2-3 degrees Celsius above pre-industrial

.
•     Major loss of coral reef system and other species.
•         Large impacts on agriculture, water resources and health.
•     Significant increases in droughts and extreme rainfalls.
•      Up to 74cm sea level rise in next100 years.
•      Terrestrial carbon sink becomes a source, accelerating global warming.

·      1-3 degrees Celsius bove pre-industrial? 

• Greenland ice-cap starts to melt (7m).

·      1-4 degrees Celsius above pre-industrial?

• North Atlantic circulation collapse

·      3-4 degrees Celsius above pre-industrial  

• Major species extinction.

·      2- 4.5 degrees Celsius above pre-industrial?

•     1-3 billion people suffer from water scarcity
•     Food yields fall everywhere, global production plummets.
•     Fifth of world population effected by flooding.
•      Significant increase in human deaths due to malnutrition, disease, heat wave, flood and drought.

·      5-6 degrees Celsius or higher above pre-industrial 

•      Don’t go there…..

Reference


Maslin, M. (2008) Golbal Warming. A Very Short Introduction. Oxford University Press, Oxford.