PALEOCLIMATE ISTOCKPHOTO/THINKSTOCK Options for Greenhouse-Gas Mitigation

research highlights

POLICY governance and the institutional determinants other variables — such as ocean circulation Mitigation cost estimates of adaptive capacity. and topography — play a secondary role in Nature 493, 79–83 (2013) Drought preparedness in the form of the evolution of Earth’s climate. Although the monitoring and early warning systems, impact work focuses on very long timescales it has For more than ten years, international climate assessment, and mitigation and response, implications for the present, as they report that debate has focused on how to keep global is an important part of adaptive capacity. limiting greenhouse-gas emissions to meet the warming below 2 °C. Despite many scenario While at the American Association for the 2 °C warming target might still result in over analyses, cost estimates of achieving such a Advancement of Science, Washington DC, 9 m of sea-level rise in the long-term. BW target remain a challenge, due to a number of USA, Nathan L. Engle investigated drought- poorly quantified uncertainties. preparedness measures during recent NATURAL HAZARDS Joeri Rogelj worked with colleagues at the extreme events in Arizona and Georgia. Perception to action International Institute for Applied System His empirical assessment found that Risk Anal. http://doi.org/j6x (2012) Analysis, Laxemburg, Austria, to generate the adaptive capacity is highest when drought cost distributions of limiting transient global preparedness is managed at the local temperature increase to below specific values. level, plans and monitoring are flexible, They did this by considering uncertainties in and the informational support system is geophysical, technological, social and political comprehensive. Moreover, he highlights the factors. They found political choices that importance of cross-sector collaboration, delay mitigation have the largest effect on the of considering climate change at planning cost distribution, followed by geophysical stages, and of making boundary organizations uncertainties, social factors influencing future accessible and active in water management energy demand and, lastly, technological and drought-planning efforts. MC uncertainties surrounding the availability of

PALEOCLIMATE ISTOCKPHOTO/THINKSTOCK options for greenhouse-gas mitigation. © They conclude that, as it is unlikely a global Long-term relationship agreement on climate will be reached before Proc. Natl Acad. Sci. USA http://doi.org/j65 (2012) Climate change is likely to enhance the level 2020, national and local governments need of risk posed by many natural hazards. These to scale-up voluntary actions and choose Sea-level rise is a potentially significant risks can be reduced through mitigation policies that lower growth in energy demand consequence of climate change. Accurately strategies and behaviours, provided people are well before then, to safeguard the potential predicting the magnitude of change is motivated and able to do so. There is extensive achievement of the 2 °C target. MC difficult, however, because current climate literature on natural hazard risk-perception, models are unable to resolve the dynamic which can inform thinking about adaptation ADAPTATION processes that govern ice-sheet changes. to climate change. Preparing for droughts To overcome these challenges, Gavin Foster A review by Gisela Wachinger from the Climatic Change http://doi.org/j6z (2012) and Eelco Rohling, of the National Department of Social Sciences, University of Oceanography Centre Southampton, UK, Stuttgart, Germany, and co-workers considers The intensification of extreme droughts from use reconstructions of atmospheric carbon the literature on perception of risk in relation climate change raises concerns about how dioxide concentrations and sea level over the to natural hazards. Personal experience of to respond to such events. Building adaptive last 40 million years to define the relationship a hazard and trust — or lack thereof — in capacity — the ability to prepare for stresses between the two more clearly. experts and authorities are found to have the and changes or adjust and respond to their Their work identifies a clear correlation most substantial impact on risk perception. effects — can help to reduce drought impacts, between atmospheric carbon dioxide and sea Interestingly though, high risk perception but it requires a good understanding of level over geological timescales, suggesting that does not necessarily translate into personal preparedness and risk-mitigation behaviour. ATMOSPHERIC SCIENCE Wachinger et al. provide three explanations for this disconnect: (1) individuals accept the risk, Aerosol impacts J. Atmos. Sci. http://doi.org/j63 (2013) perceiving that benefits outweigh the potential impacts; (2) responsibility for action is believed An understanding of recent variability in the Atlantic Ocean is needed to predict changes to lie elsewhere; and (3) individuals lack the in the coming years, and the associated impacts on global weather patterns. Recent work resources needed to change their situation. has indicated that atmospheric aerosols were a primary driver of multi-decadal climate Personal hazard experience and variability in the North Atlantic though the twentieth century. Evidence for this hypothesis is information from trusted experts and based on model simulations using the indirect effects of aerosols, which closely reproduced authorities certainly seem to enhance hazard observations of North Atlantic basin-averaged sea surface temperature perception. However, the factors that facilitate A study by Rong Zhang at the Geophysical Fluid Dynamics Laboratory of the National translation of risk perception into risk Ocean and Atmospheric Administration, Princeton, USA, and colleagues, challenges preparedness remain much less clear, despite this work by including additional oceanic parameters in their analysis. They show major many empirical studies into precisely this discrepancies between the recently published simulations and observations in the question. It seems that the key challenge ahead North Atlantic for upper-ocean heat content, the spatial pattern of changes in sea surface will be facilitating preparedness rather than temperature and subpolar sea surface salinity. Zhang et al. suggest that these differences just highlighting risks. AB are influenced and largely caused by aerosol effects, casting doubt on the claims that aerosol forcing is a prime driver of multi-decadal variability. BW Written by Alastair Brown, Monica Contestabile and Bronwyn Wake.

98 NATURE CLIMATE CHANGE | VOL 3 | FEBRUARY 2013 | www.nature.com/natureclimatechange