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he world has an important opportunity inCancún, Mexico, to make progresstowards a global agreement on effectivelytackling climate change. But beforeconstructive negotiations can take place, carefullyassessed policy options must be put forward to promotethe key elements of any agreement. This requires understanding the magnitude of the risksfrom climate change; the economic, technological andbehavioural options for transitioning to low-carbongrowth, and how the different nations of the worldmight collaborate to achieve a fair and efficientoutcome. In the absence of such basic preparations,negotiation by international bureaucrats on issues that require complex, technical understanding and the evaluation of uncertain policies, risk beingunproductive, misguided, and chaotic. But if properfoundations are laid, then countries can go forwardwith confidence that a credible and constructiveresponse to the joint challenges of securing growth,reducing poverty and managing climate change can be found. The risks from unmanaged climate change areimmense. It was in 1824 when Joseph Fourierobserved that the surface of the earth was muchwarmer than it would be without its atmosphere. About150 years ago, John Tyndall showed that the presenceof gases such as carbon dioxide were responsible forcreating the greenhouse effect - the trapping of solarenergy as heat by the atmosphere. Since then, thescience has become ever more clear and nature isconforming to theory more closely than anyone couldhave expected.On the basis of the scientific evidence outlined by theIntergovernmental Panel on Climate Change, if we donot take action and carry on with something like"business as usual," we may reach greenhouse gas(GHG) concentrations by the end of the century thatwould imply perhaps a 50 per cent chance of a rise inglobal temperature of 5°C or more above its level in thenineteenth century by early next century. Such a globaltemperature has not been seen for more than 30million years (humans, as homosapiens, have beenaround for only around 200,000 years). The physicaland human geography of the planet would be radicallyredrawn over what, in terms of geological time-scales,is a mere blink of an eye. Because different parts of the world will warm atdifferent rates, pressure patterns will change andseasonal air currents will shift. This will cause changesin levels and the distribution of water: storms, floods,droughts, river flows and rises in sea level. In otherwords, changes in the fundamental historicaldeterminants of how and where we live our lives. As aconsequence, regions previously inundated with rainsmay turn to desert and vice versa. In addition, theclimate will no longer be cold enough to keep the ice sheets on Greenland and Antarctica stable,threatening sizable increases in the global sea level. All this could mean the movement of hundreds ofmillions or billions of people, a scale that historysuggests would likely involve extended, severe, andglobal conflicts. Yet accurately projecting the precise impact ofgreenhouse-gas emissions is far from straightforward.There is uncertainty about future emissions, about the possible magnitude of absorption of greenhousegases by the land, forests, and oceans, about themagnitude of warming from changes in greenhousegas levels, and about the effects on local climatesaround the world. Complex multidimensional general-Right: The risks fromunmanaged climatechange are immenseFOSTERING A NEW ERA OFLOW-CARBON PROGRESSAND PROSPERITY022GLOBAL VOICESTPROFESSOR LORD NICHOLAS STERN, LONDON SCHOOL OF ECONOMICS (LSE)DIMITRI ZENGHELIS, SENIOR ECONOMIC ADVISOR, LONG TERM INNOVATION GROUP, CISCO

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?