Climate change policy: IPCC consensus is not enough.

Intergovernmental Panel on Climate Change (IPCC) consensual scientific knowledge on climate change and its effects is to some extent the known truth, but not necessarily the entire truth. Consensual scientific knowledge is only a minimum common denominator for thousands of scientists of different disciplines and thousands of studies that, due to their multiplicity, heterogeneity, and complexity, may sometimes mismatch. If we, scientists and science managers just prosecute credibility and consensus, we may end up misguiding society. For the sake of humanity, we must also take into account the possibility of events and scenarios that have not yet gained consensus. It is, of course, impossible to adapt to the worst possibilities in any aspect of the global change. However, society must keep an eye on nonlineal, steep, catastrophic possibilities and should prudently create a reaction system that would mobilize people and resources to face unexpected, rapid, and severe events. We call here for the implementation of such reaction policy by the United Nations (UN). The IPCC has accomplished an incredible task in assembling scientific evidences that a climate change is occurring as a consequence of CO2 emissions and landuse changes, and showing that present trends can produce catastrophic effects if they continue in a near future. The IPCC AR4 SYR Summary for Policymakers (1) states that ‘‘confidence has increased that a 1.5–2.58C increase in global mean temperature above pre-industrial levels poses significant risks to many unique and threatened systems including many biodiversity hotspots’’ and that ‘‘key vulnerabilities may be associated with many climate sensitive systems, including food supply, infrastructure, health, water resources, coastal systems, ecosystems, global biogeochemical cycles, ice sheets, and modes of oceanic and atmospheric circulation.’’ This is quite clear. However, the IPCC documents are far from clear for the reference values that could serve to guide mitigation and adaptation strategies that human society should implement in order to avoid negative impacts. From the IPCC statements, policymakers could deduce that we might try to limit warming to 28C above present average temperature by stabilizing the atmospheric CO2-equivalent around 550 ppm. This way, we could avoid excessively negative impacts on Earth systems. IPCC models suggest that a rise of global carbon prices could serve to stabilize greenhouse gases at around 550 ppm CO2-eq by 2100. This seems overly optimistic because we already have 450 ppm CO2-eq right now, with higher rates of increase each year. Recent data (2) indicate that the 28C and 550 ppm CO2-eq thresholds could be exceeded much before the end of the century. The consensus may be also too optimistic regarding impacts. Let us focus, for example, on one of the effects of the climate change considered to be most likely, sea-level rise. It seems that in this consensual scenario, the sea-level rise might be kept lower than 50 cm at the end of the century. The IPCC AR4 SYR Summary for Policymakers indicates that its moderate model predictions ‘‘exclude future rapid dynamical changes in ice flow.’’ It recognizes that there are ‘‘ice dynamical processes seen in recent observations but not fully included in the assessed ice sheet models,’’ and that ‘‘the risk of additional contributions to sea level rise from both the Greenland and possibly Antarctic ice sheets may be larger than projected by ice sheet models and could occur on century time scales.’’ This does not seem very worrying. However, scientific assessments that have not yet found scientific consensus indicate that i) glaciers can run faster than expected (3), ii) when ice shelves split from the continent, glaciers in that continent find no obstacle, and there is an increase in the rate of ice discharge into the sea, and iii) under the Antarctic ice, there is a system of liquidwater lakes, more or less interlinked, and there is a risk that a part of that water would also flow to the sea, if obstacles are removed. These phenomena could produce much steeper rises of sea level than those predicted by IPCC. They are less probable, but they can occur. Furthermore, in the other pole, the decrease of ice surface in the Arctic Ocean is proceeding at an unpredicted rate because positive feedbacks are at work (4). In addition, of course, there are many other examples of positive feedbacks that can act in other Earth system processes. For instance, even with a mere 28C increase and a decrease in rainfall, fire and droughts can become the driving factors in desertification of the Mediterranean and other semiarid regions. Meanwhile, although some companies and some nations are implementing programs driving to a more sustainable model, most activities around the world continue to be run ‘‘business as usual,’’ ignoring even the consensual IPCC assessments. A minimum of caution calls for human society to consider also scenarios resulting from scientific knowledge but that have not gained consensus. It is impossible to adapt to any one of the worst possibilities or even to many of them, but we must strongly recommend that, apart from using consensual scientific knowledge for most initiatives, we take into account nonlineal, steep, catastrophic possibilities, and, while doing that, we develop a reaction system to face unexpected, fast changes, mobilizing people and resources to fight these kind of events. The United Nations has already created the Hyogo Framework, a plan of action to advise policymakers of the different countries on reducing our collective vulnerability to natural hazards, and the Global Platform for Disaster Risk Reduction, in order to increase the commitment of nations by advising them on ways to strengthen public infrastructures, coastal facilities, and homes to withstand more extreme weather, flooding, and rising waters, and to develop better drought management, better early warning systems and evacuation plans, stronger building codes, improved land and water management policies, expanded disaster education programs for local communities, etc. All of this should be backed by stronger institutions and proper funding, even from the economic point of view. A recent expert study in the United States shows that one dollar invested today in disaster risk reduction saves four dollars in the future cost of relief and rehabilitation—a bargain by any standard (J. Holmes, 2007, First Session of the Global Platform for Disaster Risk Reduction). However, national commitments will be slow, and many countries do not have the means to follow these recommendations. Meanwhile, we need a UN environmental emergency force, including resources (people, equipment, money) for medical assistance and for fighting fire, floods, severe droughts, and other hazards. A continuous multiscale, multifactorial monitoring of the Earth system is vital to keep an eye on these not-yet-consensual possible environmental changes, and a renovated United Nations economic and political effort is necessary to develop such a reaction system. These are two important challenges for science and society in this emerging twenty-first century. We call here for their consideration. After all, this is what is done in many other smaller-scale