The second section of the Copenhagen synthesis report, Social and Environmental Disruption, discusses the dangers ofÂ climate change relating to society and the environment, noting that scientific research provides a wealth of relevant information which is not receiving the attention one might expect.Â Â Â
Considerable support has developed for containing the rise in global temperature to a maximum of 2 degrees centigradeÂ above pre-industrial levels, often referred to as the 2 degreesÂ guardrail. The report however indicates that even at temperature rises less than 2 degrees impacts can be significant, though some societies could cope through pro-active adaptation strategies.Â Beyond 2 degrees the possibilities for adaptation of societies and ecosystems rapidly decline, with an increasing risk of social disruption through health impacts, water shortages and food insecurity.
The observed temperature rise to date, about 0.7 degrees, is already affecting health in many societies; the increasing number of extreme weather events, such as heat waves, floods, and storms, is leading to a growing toll of deaths and injuries from climate-related natural disasters. Beyond the direct impacts on health, climate change also affects the underlying determinants of health â€“ quantity and quality of food, water resources, and ecological control of disease vectors.
Noting the strong connection between human health and water systems the report points out the already apparent impacts on water systems and the fact that they are likely to accelerate for several decades irrespective of abatement of emissions. Droughts and drying are leading to social instability, food insecurity and long-term health problems in some regions now.Â Water resources will be severely affected in many parts of the world with only 1 to 1.5 degree rises in temperature. Lack of clean water in many of the mega-cities is a further issue of serious concern.Â
A paragraph on the destructive effects of extreme events such as cyclones and storms, likely to increase, points to the potentially severe consequences for coastal communities around the world, from small fishing villages on Pacific atolls to mega-cities on Chinese river deltas.Â Sea level rise will exacerbate this vulnerability.
Increasing ocean acidity is serious.Â The report acknowledges that the precise effects are not yet clear, but it is thought that when atmospheric CO2 reaches 450 ppm, large areas of the polar oceans will likely have become corrosive to shells of key marine calcifiers, an effect that will be strongest in the Arctic. Already, loss of shell weight in planktonic Antarctic calcifiers has been observed. The rate of change in ocean chemistry is very high, faster than previous ocean acidification-driven extinctions in Earthâ€™s history, from which it took hundreds of thousands of years for marine ecosystems to recover. Ocean acidification will continue to track future CO2 emissions to the atmosphere, so urgent and substantial emission reductions are the only way of reducing the its impact.
On biodiversity generally the report is emphatic. There is a looming biodiversity catastrophe if global mean temperature rises above the 2 degrees guardrail, ocean acidification spreads and sea-level rise accelerates. These climate-related stressors will interact with a wide range of existing stressors on biodiversity.Â The result will be the extinction of a significant fraction of biological species within the next 100 years, a substantially reduced range and higher risk of eventual extinction for other species, and the degradation of ecosystem services on which human well-being depends. Limiting temperature rise to 2 degrees or less, along with strong pro-active adaptation in conservation policy and management can limit the magnitude of the crisis but not entirely eliminate it.
Tipping elements in the Earth System are the next measure of potentially dangerous change examined by the report. These occur when a small change in an important variable such as temperature causes a rapid and unexpectedly large change in a feature of the climate, altering its condition or pattern of behaviours. Arctic summer ice and the Greenland ice sheet are two such elements, and it is possible that a rise in global temperature of 1-2 degrees would be enough to trigger them, though in the case of Greenland another study indicates 3.1 degrees would be the threshold. But although the magnitude of warming required for various tipping elements is not well known, even a small risk of triggering them should be considered as dangerous. The societal effects of such tippingÂ elements as the abrupt change of the Asian monsoon to a substantially drier state, or the eventual loss of water storage capacity in Himalayan glaciers would be profound.
In summary the report concludes that even the 2 degree guardrail commonly accepted as avoiding dangerous climate change carries significant risk of harmful effects on society and the environment.
This section of the report ought to sharpen the awareness of countries as they prepare for the UNFCCC meeting at Copenhagen. The societal effects of some of the dangers laid out would be enormous and should provide focus and add resolve to the negotiating teams and their governments.
Interestingly, this section of the report was highlighted by a post recently published on RealClimate which saw it as partly the outcome of having economists and social scientists as well as climate scientists present at the congress. And for any who wonder about the authority that can reasonably be accorded to the report this sentence from the RealClimate post may help: Â â€œThe Synthesis Report is the most important update of climate science since the 2007 IPCC report.â€