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Extreme heat stress during the crop reproductive period can be critical for crop productivity. Projected changes in the frequency and severity of extreme climatic events are expected to negatively impact crop yields and global food production. This study applies the global crop model PEGASUS to quantify, for the first time at the global scale, impacts of extreme heat stress on maize, spring wheat and soybean yields resulting from 72 climate change scenarios for the 21st century. Our results project maize to face progressively worse impacts under a range of RCPs but spring wheat and soybean to improve globally through to the 2080s due to CO 2 fertilization effects, even though parts of the tropic and sub-tropic regions could face substantial yield declines. We find extreme heat stress at anthesis (HSA) by the 2080s (relative to the 1980s) under RCP 8.5, taking into account CO 2 fertilization effects, could double global losses of maize yield ( Y = −12.8 ± 6.7% versus −7.0 ± 5.3% without HSA), reduce projected gains in spring wheat yield by half ( Y = 34.3 ± 13.5% versus 72.0 ± 10.9% without HSA) and in soybean yield by a quarter ( Y = 15.3 ± 26.5% versus 20.4 ± 22.1% without HSA). The range reflects uncertainty due to differences between climate model scenarios; soybean exhibits both positive and negative impacts, maize is generally negative and spring wheat generally positive. Furthermore, when assuming CO 2 fertilization effects to be negligible, we observe drastic climate mitigation policy as in RCP 2.6 could avoid more than 80% of the global average yield losses otherwise expected by the 2080s under RCP 8.5. We show large disparities in climate impacts across regions and find extreme heat stress adversely affects major producing regions and lower income countries.

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The 'nexus' between water, energy and food (WEF) has gained increasing attention globally in research, business and policy spheres. We review the premise of recent initiatives framed around the nexus, examine the challenge of achieving the type of disciplinary boundary crossing promoted by the nexus agenda and consider how to operationalise what has to date been a largely paper exercise. The WEF nexus has been promoted through international meetings and calls for new research agendas. It is clear from the literature that many aims of nexus approaches pre-date the recent nexus agenda; these have encountered significant barriers to progress, including challenges to cross-disciplinary collaboration, complexity, political economy (often perceived to be under-represented in nexus research) and incompatibility of current institutional structures. Indeed, the ambitious aims of the nexus-the desire to capture multiple interdependencies across three major sectors, across disciplines and across scales-could become its downfall. However, greater recognition of interdependencies across state and non-state actors, more sophisticated modelling systems to assess and quantify WEF linkages and the sheer scale of WEF resource use globally, could create enough momentum to overcome historical barriers and establish nexus approaches as part of a wider repertoire of responses to global environmental change.

Journal article;CRP5; ISI; Southern Africa‘s hydro-economy and water security (SAHEWS)EPTD; DSGDPRCGIAR Research Program on Water, Land and Ecosystems (WLE

The Paris Agreement long-term global temperature goal refers to two global warming levels: well below 2 C and 1.5 C above preindustrial. Regional climate signals at specific global warming levels, and especially the differences between 1.5 C and 2 C, are not well constrained, however. In particular, methodological challenges related to the assessment of such differences have received limited attention. This article reviews alternative approaches for identifying regional climate signals associated with global temperature limits, and evaluates the extent to which they constitute a sound basis for impacts analysis. Four methods are outlined, including comparing data from different greenhouse gas scenarios, sub-selecting climate models based on global temperature response, pattern scaling, and extracting anomalies at the time of each global temperature increment. These methods have rarely been applied to compare 2 C with 1.5 C, but some demonstrate potential avenues for useful research. Nevertheless, there are methodological challenges associated with the use of existing climate model experiments, which are generally designed to model responses to different levels of greenhouse gas forcing, rather than to model climate responses to a specific level of forcing that targets a given level of global temperature change. Novel approaches may be required to address policy questions, in particular: to differentiate between half degree warming increments while accounting for different sources of uncertainty; to examine mechanisms of regional climate change including the potential for nonlinear responses; and to explore the relevance of time-lagged processes in the climate system and declining emissions, and the resulting sensitivity to alternative mitigation pathways.

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