circulation models are needed to account for importantprocesses known to be interrelated, such as oceandynamics, cloud feedbacks, ecological changes, andice and snow changes. The issue for policy is how tomanage risks that the scientific evidence suggests arevery large. We have no choice but to embrace thiscomplexity and corresponding uncertainty, and aim to reduce the probabilities associated with the worst risks.To deny the urgency of strong action in the face of allthe evidence is unscientific, irrational, and dangerous.It is unscientific because it dismisses sound scienceand evidence. It is irrational because such denialwould require great confidence both that the scientificfindings are wrong and the corresponding risks aresmall. Acting as if the scientific evidence were wrongwould lead us to concentrations of carbon dioxidecarrying immense risks if the science were right. Actingas if the scientific findings were right might lead us toexcessive investment in developing low-carbontechnologies and protecting forests if the findingsturned out to be wrong; but these actions arenevertheless likely to have substantial other benefits in energy security, energy efficiency, biodiversity, and so on. In order to limit the great risks from climate change,many of the policies proposed so far focus onstabilisation at 450 parts per million of carbon-dioxide-equivalent. We are likely to exceed that levelwithin the next decade but, with strong action,concentrations of greenhouse gases could peak ataround 500 parts per million and, over a long period oftime with continued strong action, return to 450 partsper million or below. The investments required toachieve this remain affordable, indeed they have verystrong returns, but the costs are rising in magnitudewith every year action is delayed. The importance of managing climate change andcorresponding issues of resource sustainability cannotbe over-emphasised. We can and must combine thesewith economic development. For billions of people,economic development is the only way out of poverty.Advances in education, health, environment andequality of opportunity - not to mention climateresilience - are often easier to realise if consumptionand income are growing. The transition to low-carbon growth, which has alreadybegun, need not materially effect growth, indeed in themedium term and long term it is the only route togrowth. By improving the efficiency with whichresources are used, a dynamic and innovativeindustrial revolution can underpin a renewed surge inproductivity. New firms and methods will drive out old,new technologies and processes will be developed.And this growth will be more energy-secure, safer,quieter, more connected, cleaner, and biologicallydiverse than what has gone before. On the other hand,GLOBAL VOICES023?

emissions reductions during the decades after 2020. Another outcome of the UN Copenhagen summit wasthe establishment of a High-Level Advisory Group onClimate Change Financing, under the co-chairmanshipof the prime ministers of Ethiopia and the UK (nowNorway). The advisory group worked on options forgenerating, by 2020, US$100 billion per year fromdeveloped to developing countries to support bothclimate adaptation and emissions reduction measures,including both public and private resources. It hasprepared clear and promising possibilities. At the same time, progress is being made on the structure of action for preserving and plantingforests, with a constructive set of meetings of theREDD+ partnership this year instigated by France andNorway with leadership now taken up by Papa NewGuinea and Japan with participation from keyrainforest nations. Corresponding mechanisms areurgently required for developing and sharingtechnology and for the objective measurement ofemissions by countries. high-carbon growth is likely to kill itself on the veryhostile environment it would create.The power of examples is crucial and it is richcountries, with their greater wealth and technologies,that should take a lead in offering them. Practicaldemonstrations of what is possible will be fundamentalto generating change. There are already a range of technologies evolving each with diminishing capital and operating costs as experience inducesinnovation and learning. These include solar cells,more efficient high-voltage DC grids (which reduce the costs of electricity transmission from widelydistributed renewable energy sources), high capacityand more efficient batteries, smarter integrated cities(which can drastically reduce energy, heating andtransport emissions), and ways to capture and storecarbon (from end-of-pipe technologies to buildingmaterials, plants and bacteria that draw carbon out ofthe atmosphere). Sustaining this technological revolution will requireclear and long-term global policy. Although the UnitedNations climate change conference in Copenhagenlast December was disappointing, it did makeimportant steps towards global agreement. TheCopenhagen Accord put forward by Brazil, China,India, South Africa, and the US has provided a basisfor discussions about co-ordinated and coherentinternational action. It has its fragilities, and theprocess of building agreement will not be easy, butfurther progress has been made through 2010. TheAccord recognises that climate policies should seek tolimit the rise in global average temperature to no morethan 2°C above preindustrial levels. Analysis at the Grantham Research Institute onClimate Change and the Environment at the LondonSchool of Economics showed that in order to have areasonable, or 50 per cent, chance of reaching the 2°Cgoal, global annual emissions of greenhouse gasesshould be reduced from about 47 billion metric tonnesof carbon-dioxide-equivalent today to about 44 billionmetric tonnes in 2020, to much less than 35 billionmetric tonnes in 2030, and to much less than 20billion metric tonnes in 2050. So far, 75 developed and developing countries,collectively responsible for more than 80 per cent ofcurrent annual global emissions of greenhouse gases,have submitted targets and intended actions that arenow listed in the appendices of the Accord. If countriesdeliver their "high intention" reductions, the planssubmitted to the Copenhagen Accord would result inglobal annual emissions of about 48 billion metrictonnes of carbon-dioxide-equivalent by 2020. Whilethis would imply that emissions would peak before2020, it would nevertheless fall short of a "climateresponsible" target of 44 billion metric tonnes. Thiscould still - at a stretch - be consistent with a 2°C goal,but would involve more rapid and costly annual024GLOBAL VOICESBelow:Dimitri Zenghelis,Senior Economic Advisor,Long Term InnovationGroup, Cisco (left) andProfessor Lord NicholasStern, London School ofEconomics (right)