At the crossroads of climate change and global security.

• Author: Schellnhuber, Hans Joachim
• Position: Essay

Recent extreme events witnessed around the world are drastically visible reminders of ongoing environmental perturbation's on our planet, many of which are linked to global climate change. The last decade has seen an exceptional number of extreme heatwaves with resulting severe consequences. The 2010 Russian heatwave is estimated to have cost the lives of 55,000 people and destroyed 25 per cent of the country's annual crop. In the United States, the drought in 2012 has been the most severe since the 1930s, impacting about 80 per cent of agricultural land. Hurricane Sandy was yet another stark showcase of the forces of nature and our vulnerability in the face of destabilized weather and climate patterns.

It fits this picture that 2012 has been the warmest year in the contiguous United States since record keeping began in 1880 while, globally, all 12 years to date in the twenty-first century have ranked among the 14 warmest ever recorded. Some changes in the Earth system are occurring at faster rates: the extent of the Arctic sea ice during summer plummeted to a new minimum in September 2012, almost 50 per cent below the long-standing average, whereas sea levels are rising faster than expected, fuelled in part by the accelerated melting of the Greenland ice sheet.

While natural variability plays a big role in those complex phenomena, the human influence has become a decisive driver on the planetary scale. Beyond reasonable scientific doubt, global climate change is caused by emissions of greenhouse gases from human activities, notably C[O.sub.2] from the combustion of coal, oil and gas. Despite efforts to curb emissions at the local, national and international levels, the aggregate global total reached yet another record in 2012 and keeps on increasing. In early May 2013, news went around the world that carbon dioxide levels in the atmosphere have climbed above 400ppm, a concentration probably not realized for at least 3 million years. As it stands, the world is on a course for an increase in global mean temperature of around 4[degrees]C (7.2[degrees] F) by the end of the century as compared to pre-industrial times.

The consequences would be severe, as pointed out by a recent World Bank flagship report authored by scientists of the Potsdam Institute for Climate Impact Research: sea levels will likely rise by 0.5 to 1 metre by the year 2100, with several metres of additional surge over the coming centuries, thereby putting the livelihoods of...