The third section of the Copenhagen congress synthesis report considers the global targets and timetables that will be necessary to keep warming to no more than 2 degrees.Â The report acknowledges that 2 degrees introduces considerable risk to human society and natural ecosystems. However global average temperature has already risen by 0.7 degrees, and inertia in the climate system makes 1.4 degrees inevitable. So 2 degrees may be the best we can hope for.
How much do we have to reduce emissions to retain climate on the right side of what the report calls the 2 degree “guardrail”? Copenahgen is in broad agreement with the IPCC in estimating that atmospheric CO2 concentration should not exceed 400 parts per million CO2 if the global temperature rise is to be kept within 2.0 â€“ 2.4 degrees. In terms of CO2-equivalents they suggest that a concentration of 450 ppm would give a 50-50 chance of limiting the temperature rise to 2 degrees or less. (CO2-equivalents include the combined warming effects of CO2 and the non-CO2 greenhouse gases, excluding water vapour, as well as the net cooling effect of aerosols in the atmosphere.) [Gareth adds: At a very rough estimate, current aerosol cooling brings the effective forcing down to about 390 ppm. This implies that if we are too effective at cleaning up aerosol pollution, we could “unmask” a lot of warming – something of a quandary. For example. closing down coal power stations may be essential, but could lead to more warming in the short term!]
This means that weâ€™re already at levels predicted to lead to global warming of between 2.0 and 2.4 degrees. If society wants to stabilise greenhouse gas concentrations at this level, then global emissions should, theoretically, be reduced by 60-80% immediately, the actual amount being dependent upon how much will be taken up by oceans and land.Â Such drastic immediate reduction is impossible and an overshoot of the level needed to constrain global warming to 2 degrees is inevitable.Â To limit the extent of the overshoot, emissions should peak in the near future. The conclusion from both the IPCC and later analyses is simple â€“ immediate and dramatic emission reductions of all greenhouse gases are needed if the 2 degrees guardrail is to be respected.
At this point the report names short-term financial concerns, political and institutional constraints and lack of public awareness and concern as the greatest barriers to immediately initiating ambitious emission reduction. The congress included social scientists in its number and the report moves into policy areas in claiming that a critical step in curbing emissions is that businesses and consumers face an appropriate price for emitting greenhouse gases, whether that is established by cap and trade schemes or taxes or a combination of both.Â This will provide signals to investors, consumers, and innovators about the future market environment and thus encourage investments and ultimately reduce the cost of attaining a given mitigation goal. Regulations to promote energy efficiency are also critical, along with the widespread uptake of low-carbon technologies.
Without global cooperation, ambitious climate protection will be virtually impossible. To achieve mitigation goals, it is critical to move as quickly as possible to achieve widespread participation of all major countries in comprehensive mitigation action, though not so tightly connected that collapse of a single element in the system could lead to collapse of the whole.
Moving on from economic and political constraints the report points to the importance of technical bottlenecks. It briefly mentions several areas receiving attention, from carbon capture and storage to energy efficiency measures to technical innovation in renewable energy systems. It points to energy-environment-economy modelling which suggests that a low-carbon pathway is feasible at moderate cost even to a low 400 ppm CO2-equivalents target which would give us a 75% chance of staying under 2 degrees warming. It would require the full suite of technologies to be developed and employed, including large-scale biomass use and options to capture and store CO2.
The message toÂ policy makers from this section of the report is that there is no leeway for emission reduction.Â It needs to start very soon and be well established by 2020.Â A few developed countries are actually under way, though certainly not New Zealand.Â The accompanying message is that with political will we can get there.Â It is not technically impossible.Â
Itâ€™s all too easy to despair of political will, but we must keep hammering away.Â I was glad to see the synthesis report didnâ€™t bow out when it came to policy. Scientists who understand what is happening to the global climate should not restrict themselves to presenting the science. Their pressure is needed in the political world, where they bring an insistence on the urgency and feasibility of action.