Investments aimed at improving agricultural adaptation to climate change inevitably favor some crops and regions over others. An analysis of climate risks for crops in 12 food-insecure regions was conducted to identify adaptation priorities, based on statistical crop models and climate projections for 2030 from 20 general circulation models. Results indicate South Asia and Southern Africa as two regions that, without sufficient adaptation measures, will likely suffer negative impacts on several crops that are important to large food-insecure human populations. We also find that uncertainties vary widely by crop, and therefore priorities will depend on the risk attitudes of investment institutions.

Some energy services and industrial processes-such as long-distance freight transport, air travel, highly reliable electricity, and steel and cement manufacturing-are particularly difficult to provide without adding carbon dioxide (CO) to the atmosphere. Rapidly growing demand for these services, combined with long lead times for technology development and long lifetimes of energy infrastructure, make decarbonization of these services both essential and urgent. We examine barriers and opportunities associated with these difficult-to-decarbonize services and processes, including possible technological solutions and research and development priorities. A range of existing technologies could meet future demands for these services and processes without net addition of CO to the atmosphere, but their use may depend on a combination of cost reductions via research and innovation, as well as coordinated deployment and integration of operations across currently discrete energy industries.

Evaluation and communication of the relative degree of certainty in assessment findings are key cross-cutting issues for the three Working Groups of the Intergovernmental Panel on Climate Change. A goal for the Fifth Assessment Report, which is currently under development, is the application of a common framework with associated calibrated uncertainty language that can be used to characterize findings of the assessment process. A guidance note for authors of the Fifth Assessment Report has been developed that describes this common approach and language, building upon the guidance employed in past Assessment Reports. Here, we introduce the main features of this guidance note, with a Climatic Change (2011) 108:675-691

Article 2 ͉ UNFCCC ͉ climate change impacts A rticle 2 of the United Nations Framework Convention on Climate Change (UNFCCC) commits signatory nations to stabilizing greenhouse gas concentrations in the atmosphere at a level that ''would prevent dangerous anthropogenic interference (DAI) with the climate system.'' The UNFCCC also highlights 3 broad metrics with which decision-makers are to assess the pace of progress toward this goal: allow ''ecosystems to adapt naturally to climate change,'' ensure that ''food production is not threatened,'' and enable ''economic development to proceed in a sustainable manner.'' In an effort to provide some insight into impacts that might be considered DAI, authors of the Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) identified 5 ''reasons for concern'' (RFCs) in (1). Each RFC categorizes impacts of a similar type, providing a set of metrics reflecting severity of risk. Relationships between various impacts reflected in each RFC and increases in global mean temperature (GMT) were portrayed in what has come to be called the ''burning embers diagram''; the image was also included in the Summary for Policy Makers of the contribution of Working Group II to the TAR and highlighted in the Synthesis Report.In presenting the ''embers'' in the TAR, IPCC authors did not assess whether any single RFC was more important than any other; nor, as they noted, did they conclude what level of impact or what atmospheric concentrations of greenhouse gases would constitute DAI, a value judgment that would be policyprescriptive. The ''embers'' were designed primarily to communicate the associations of impacts with increases in GMT and facilitate examination of the underlying evidence for use by decision-makers contemplating responses to these concerns.The IPCC Fourth Assessment Report (AR4) states that ''the 'reasons for concern' identified in the TAR remain a viable framework for assessing key vulnerabilities'' (2). In this article, we revise sensitivities of the RFCs to increases in GMT, based on our expert judgment about new findings in the growing literature since the publication of the TAR in 2001.* Furthermore, our judgments are supported by a more thorough understanding of the concept of vulnerability that has evolved over the past 8 years, † as well as a more careful articulation of the criteria by which any specific vulnerability can be labeled ''key,'' and thus contribute to a reason for concern (3). ‡ Section 1 defines and reviews the RFCs and ''burning embers'' figure as presented in the IPCC TAR. Section 2 presents the 1 To whom correspondence may be addressed. E-mail: jsmith@stratusconsulting.com or shs@stanford.edu. *These judgments were vetted by 3 rounds of IPCC review and were approved in the Summary for Policymakers of both the AR4 Working Group 2 and Synthesis Reports by the IPCC Plenary. † Vulnerability to climate change is the degree to which geophysical, biological and socioeconomic systems are susceptible to and unable to cope with adve...

Climate policy decisions are being made despite layers of uncertainty. Such decisions directly influence the potential for "dangerous anthropogenic interference with the climate system." We mapped a metric for this concept, based on Intergovernmental Panel on Climate Change assessment of climate impacts, onto probability distributions of future climate change produced from uncertainty in key parameters of the coupled social-natural system-climate sensitivity, climate damages, and discount rate. Analyses with a simple integrated assessment model found that, under midrange assumptions, endogenously calculated, optimal climate policy controls can reduce the probability of dangerous anthropogenic interference from approximately 45% under minimal controls to near zero.

The Reasons for Concern (RFC) framework communicates scientific understanding about risks in 1 relation to varying levels of climate change. The framework, now a cornerstone of the IPCC 2 assessments, aggregates global risks into five categories as a function of global mean temperature 3 change (GMT). We review the RFC's conceptual basis and the risk judgments made in the most recent 4 IPCC report, confirming those judgments in most cases in the light of more recent literature and 5 identifying their limitations. We point to extensions of the framework that offer complementary 6 climate change metrics to GMT and better account for possible changes in social and ecological 7 system vulnerability. Further research should systematically evaluate risks under alternative scenarios 8 of future climatic and societal conditions. 9The RFC framework was developed in the IPCC Third Assessment Report (TAR) to inform discussions 10 relevant to implementation of Article 2 of the UN Framework Convention on Climate Change (UNFCCC). 11Article 2 presents the Convention's long-term objective of avoiding "dangerous anthropogenic 12 interference with the climate system." The RFC framework and the associated "Burning Embers" 13 diagram illustrating authors' risk judgments have since been widely discussed and used to inform policy 14 decisions. For example, they informed a recent dialog between Parties to the UNFCCC and experts 1, 2 on 15 the adequacy of the long-term goal of avoiding a warming of 2°C relative to pre-industrial, contributing 16 to a strengthening of that goal in the recent Paris Agreement 3 . Elaborations of the Burning Embers have 17 been used to represent climate impacts and risks at the regional level 4 and for specific systems (e.g., 18ocean systems 5 ). 19This article reviews the conceptual basis for the RFCs (Box 1) and offers an explanation of the reasoning 20 behind associated risk judgments that is complementary to, but goes beyond, the treatment in the IPCC 21Fifth Assessment Report 6 . We focus explicitly on the evidence base for transitions from one risk level to 22 the next, incorporate post-AR5 literature in those discussions, and offer thoughts about limitations of 23 the subjective judgments behind each RFC. We also improved the synthesis of RFC-related material 24 across AR5, and in turn provide both a clearer connection to evidence from AR5 that supports the RFC 25 judgments, as well as a comparison of the RFCs to similar approaches employing metrics other than 26 GMT for characterizing risk. Perhaps most importantly, we consider improvements in the framework, 27 particularly emphasizing the dynamic nature of exposure and vulnerability, two key components of risk 28 not sufficiently covered in the current approach. 29 TEXT BOX 1: Conceptual Basis 30The Reasons for Concern (RFCs) reported in AR5 are: 31 Types of risk included in each category are discussed in the next section. The categories share an 37 emphasis on going beyond changes in biophysical systems to possible consequences for society and 38...

Average global surface-air temperature is increasing. Contention exists over relative contributions by natural and anthropogenic forcings. Ecological studies attribute plant and animal changes to observed warming. Until now, temperature-species connections have not been statistically attributed directly to anthropogenic climatic change. Using modeled climatic variables and observed species data, which are independent of thermometer records and paleoclimatic proxies, we demonstrate statistically significant ''joint attribution,'' a two-step linkage: human activities contribute significantly to temperature changes and human-changed temperatures are associated with discernible changes in plant and animal traits. Additionally, our analyses provide independent testing of grid-box-scale temperature projections from a general circulation model (HadCM3).climate change ͉ double attribution ͉ global warming ͉ plant animal impacts ͉ regional climate change T he Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) Working Group I concluded that humans are changing the climate by injecting greenhouse gases and aerosols into the atmosphere (1). One line of evidence that was examined included temperature trends produced by the HadCM3 general circulation model (GCM) in response to three different scenarios: (i) only natural climatic forcings (hereafter called NF), (ii) only greenhouse gas and aerosol forcings (anthropogenic forcings, AF), and (iii) a coupling of both natural and anthropogenic forcings (combined forcings, CF). Stott and colleagues (2) compared surface-air temperature data from all three model runs to observed global surface-air temperatures. Results for the CF yield the closest match with observed temperatures over the 20th century, AF produce a good fit, but NF results are notably less skillful. Stott (3) has extended these methods to a regional analysis that yields similar results, further confirming the importance of AF for credible simulation of historical observed temperatures.Even though paleoclimatic proxies, surface thermometers, satellites, and weather balloons are recording global warming, interpretations of these instrumental records have sometimes been contentious (4, 5). Having measures of warming that are not based on the interpretations of these data allows independent testing of different external and internal factors influencing the climate. For instance, results from biological metaanalyses, which examined numerous studies to determine the occurrence of a biotic signal consistent with climatic change, indicated that ''. . . a significant impact of recent climatic warming is discernible in the form of long-term, large-scale alterations of animal and plant populations' ' (ref. 6, p. 59). The vast majority (Ϸ80%) of species exhibiting changes are shifting in the manner expected with increasing temperature (6). What has been lacking thus far, however, is statistical evidence that attributes a significant portion of the changes seen in plants and animals (6-8) directly to ...

A critical challenge in supporting climate change adaptation is improving the linkage between climate-impacts and vulnerability research and public and private planning and management decisions. We highlight the need for bottom-up/ top-down vulnerability assessment, bringing together bottom-up knowledge of existing vulnerabilities with top-down climate-impact projections, as a transparent basis for informing decisions intended to reduce vulnerability. This approach can be used to evaluate the likelihood of crossing identified thresholds of exposure, and to evaluate alternative adaptation strategies based on their ability to reduce sensitivity to projected changes in exposure and their robustness across uncertainty in future outcomes. By identifying thresholds for which adaptive capacity is limited in particular systems, adaptation and mitigation become complements where the magnitudes of climate change at which such thresholds cluster can help to define mitigation targets.