The gulf between climate science and climate policy seems to have grown in the run-up to Copenhagen. Scientists are clear: man-made emissions of greenhouse gases are already changing the climate and these changes will gather pace this century and into the next. Even if emissions stopped now, the climate would keep changing, increasing the risks of severe damage to people and ecosystems.
Major uncertainties exist about the scale of these risks because we lack a complete understanding of climate systems, and climate change can trigger further change through feedback effects.
But humanity is not stabilising, let alone reducing, emissions. It is increasing them, greatly raising the risks.
These scientific basics were captured in the UN’s Framework Convention on Climate Change (UNFCCC), negotiated in 1992 and signed by 192 nations. It notes human activities have increased atmospheric greenhouse gases substantially (see pp 10-11), that this enhances the natural greenhouse effect, and global warming will result. Yet alongside rising emissions, the 16 full years since 1992 have seen 13 of the world’s hottest in a record stretching back 159 years, averaging 0.9°C above pre-industrial temperatures.
The scientists on the UN Intergovernmental Panel on Climate Change (IPCC) have said there is a more than 90% chance this warming is due to human activity. The panel, set up in 1988, produced its fourth set of reports in 2007: three painstakingly negotiated reviews with hundreds of authors covering the science of climate change, mitigation options plus impacts and adaptation.
December’s negotiations in Copenhagen are intended to take the world a big step closer to the UNFCCC’s central objective: stabilising greenhouse gas concentrations at a level that avoids “dangerous anthropogenic interference” with the climate system.
The IPCC scientists have not defined ‘dangerous’, preferring to paint a picture of the impacts of different levels of climate change.
Scientists advise, ministers and government leaders decide. Many policymakers are pinning their hopes of safety on limiting global warming to 2°C above pre-industrial temperatures, or 1.1°C above recent years’. Adherents include the EU, the G8 group of developed nations and the Major Economies Forum, which also includes key developing nations such as India, China and Brazil.
The EU and G8 hope to meet the 2°C limit by securing a 50% cut in global emissions by 2050. This seems the maximum that is politically possible. Even so, the major developing nations have not yet agreed to this 50% cut, fearing it implies too big an emissions-reducing effort on their part (ENDS Report 414, p 52).
So does less than 2°C avoid danger? No climate scientist will say as much, and plenty say it does not (ENDS Report 407, p 63).
With emissions rising 3% per year this century (until a downward blip caused by the recession) and tracking the topmost trajectory conjectured by the IPCC, many early effects of climate change are also exceeding expectations. The more rapid fall in Arctic sea-ice extent and accelerated melting of ice sheets in Greenland and Antarctica are notable examples.
Back in 2001, the IPCC’s third assessment report categorised risk across five types of climate impact according to temperature. It found 2°C avoided serious risks in all categories.
But a group of IPCC authors using more recent research found a 2°C limit was no longer enough to avoid serious risks to many fragile ecosystems, or to avoid a large rise in the risks of extreme weather events such as droughts, floods and heatwaves.
At 2°C warming, changing rainfall patterns will put billions at extra risk of water shortages and millions at risk from coastal flooding. For 2-3°C there would be widespread coral mortality, while up to a third of plant and animal species would face extinction.
Any warming will, in any case, be felt unevenly because oceans warm less than land. Some regions, such as the Arctic, will warm far more than a global average rise of 2°C would seem to suggest.
And even if an average 2°C rise was accepted as a safe limit, much uncertainty remains about the level and speed of emissions reductions required to prevent it being exceeded.
Issues include how sensitive the climate system is to changes in greenhouse gas levels, how quickly heat is transferred by ocean surfaces mixing with colder deeper waters and the extent to which oceans, plants and soils compensate by absorbing extra CO2.
The next IPCC report in 2014 will address these issues and uncertainty in sea-level rise, the impact of clouds and aerosols, and climate predictions covering smaller areas and shorter periods.
For now, the chances of a 50% cut in emissions by 2050 actually preventing a 2°C rise depend on which climate modellers you consult. Their probability estimates range from 80% down to 40%.
The UK Committee on Climate Change found that even if emissions peaked in 2016 then fell 4% a year thereafter (a 50% cut on 1990 levels by 2050) there would be a 56% chance of breaching 2°C.
Unless emissions peak within a decade, followed by rapid reductions that continue well beyond 2050, the 2°C limit will be breached with far bigger risks and much greater damage in store.
Humans are capable of holding conflicting views in their head at the same time and finding ways of coping. Psychologists have a name for this. The world’s leaders mostly declare that climate change is a critical issue but find it hard to agree on emissions cuts that are probably insufficient to prevent dangerous climate change. It is a case of cognitive dissonance on a planetary scale.