IN 1979 the then US president, Jimmy Carter, commissioned a report on the enhanced greenhouse effect and its implications for energy policy.
The report concluded that humanity "is setting in motion a series of events that seem certain to cause a significant warming of world climates over the next decades unless mitigating steps are taken immediately''.
But there was good news, although it came with a warning: "Enlightened policies in the management of fossil fuels and forests can delay or avoid these changes but the time for implementing the policies is fast passing."
Thirty years on and we have not achieved much in terms of reductions in emissions; in fact we have rapidly increased them: today global emissions are more than 60 per cent higher than in 1979. The predicted warming has come to fruition as well: global average air temperatures have risen almost 0.6 of a degree since 1979. This is a big acceleration in warming on the multi-decade time scales that concern us most: the preceding 70 years had just 0.2 of a degree warming.
Today satellite and ice measurements show Greenland and Antarctic ice sheets are losing mass at an accelerating rate. Melting of mountain glaciers and ice caps has also sped up over the past 20 years. Summer Arctic sea ice is melting and thinning well beyond the expectations of climate models of only a few years ago. Global average sea level rise is also occurring well above projections, consistent with a doubling in contribution from the melting of glaciers, ice caps and ice sheets.
To make matters worse, natural carbon buffers appear to be weakening. The oceans and land surface have combined to absorb more than half our post-industrial emissions, yet the ability of these stores to absorb and retain carbon is changing. Fifty years ago natural carbon sinks removed about 600 kilograms of every tonne emitted. Today, only about 550 kilograms are removed.
Scientists often talk about trying to stabilise net greenhouse gases at or below the equivalent of 450 parts per million carbon dioxide. Yet 450 parts per million comes with a 50-50 chance of exceeding 2-degrees warming; a level of warming that would reduce food productivity over key parts of Australia and increase the severity of bushfire seasons and heat waves. Many understandably argue that 350 would be a safer goal. The problem is that we have already exceeded 450 in terms of total greenhouse gases and there's no known way to extract these gases from the atmosphere in large quantities.
If warming stabilises at 3 degrees then the changes become more extreme and the possibility emerges that the West Antarctic and Greenland ice sheets are set on course to gradually disintegrate over the coming centuries, raising sea level by about 10 metres and displacing hundreds of millions of people.
The science is clear that to avoid warming of more than 2 degrees, emissions need to peak within the next 10 years and then fall rapidly. This is becoming increasingly unlikely with every year of delayed action.
Matthew England is professor of ocean physics at the University of NSW.