During the twentieth century, the earth’s surface warmed by about 0.74° C, according to the Intergovernmental Panel on Climate Change (IPCC). Science has made great strides in determining the potential causes for that change. The IPCC’s Fourth Assessment Reports in 2007 stated that warming of the climate system is “unequivocal” and that most of the observed increase in global average temperatures since the mid-twentieth century is “very likely” due to the rise in greenhouse gases generated by human activity.

The IPCC’s Fourth Assessment Report observed that between 1970 and 2004, greenhouse gas emissions increased by 70 per cent, and carbon dioxide (CO2) – by far the largest source with 77 per cent of total emissions – grew by about 80 per cent. Atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N20), the IPCC found, had risen markedly since 1750 due to human activity, and today, far exceed pre-industrial values.

Projections indicate that if emissions are allowed to rise at their current pace and double from pre-industrial levels, the world would likely face a 2° - 4.5° C temperature rise by 2100, with a 3°C increase most likely.

There is near universal acceptance that complete avoidance of climate change is now impossible and that adaptive capacity needs to be improved everywhere, including in high-income countries. Disruption in the climate system is manifesting itself around the world through more frequent floods, droughts and heat waves whose severity will only increase. A wide range of adaptation options is available, including disaster risk reduction efforts, insurance and other risk transfer mechanisms. Their widespread use is needed to reduce the vulnerability of high-risk communities to inevitable climate impacts.

Under the IPCC’s most stringent emissions reduction scenario, the world has a 50 per cent chance of limiting further temperature increases to 2° C. Achieving that would require a comprehensive global mitigation effort, including a further tightening of existing climate policies in developed countries and concurrent emissions reductions in developing nations. In other words, the world would need to see an emissions peak before 2020 and a 50 per cent reduction below 1990 levels by 2050. For industrialized nations, that translates to a 25-40 per cent emissions reduction below 1990 levels by 2020.

The impacts associated with such a scenario are serious but widely regarded as more manageable if a risk reduction approach is fully embraced. However, without action, there is overwhelming scientific evidence that climate change will threaten economic growth and survival of the world’s most vulnerable populations:

Examples of climate change impacts

• By 2020, some 75 to 250 million people in Africa will face increased water shortages. Yields from rain-fed agriculture (dominant method) could fall by up to 50 per cent in some African countries.
• About 20-30 per cent of plant and animal species will likely face increased risk of extinction if global average temperature increases exceed 1.5°-2.5° C.
• Widespread melting of glaciers and snow cover will create risk of flash floods and, over time, reduce annual melt water from major mountain ranges (i.e.: Hindu-Kush, Himalaya, Andes), where more than one billion people live.
• Seven of ten disasters are now climate-related.
• More than 20 million people were displaced by sudden climate-related disasters in 2008 alone. An estimated 200 million could be displaced as a result of climate impacts by 2050.

Sources: IPCC, UN, Stern Review 2006