Agricultural production is sensitive to weather and thus directly affected by climate change. Plausible estimates of these climate change impacts require combined use of climate, crop, and economic models. Results from previous studies vary substantially due to differences in models, scenarios, and data. This paper is part of a collective effort to systematically integrate these three types of models. We focus on the economic component of the assessment, investigating how nine global economic models of agriculture represent endogenous responses to seven standardized climate change scenarios produced by two climate and five crop models. These responses include adjustments in yields, area, consumption, and international trade. We apply biophysical shocks derived from the Intergovernmental Panel on Climate Change's representative concentration pathway with end-of-century radiative forcing of 8.5 W/m 2 . The mean biophysical yield effect with no incremental CO 2 fertilization is a 17% reduction globally by 2050 relative to a scenario with unchanging climate. Endogenous economic responses reduce yield loss to 11%, increase area of major crops by 11%, and reduce consumption by 3%. Agricultural production, cropland area, trade, and prices show the greatest degree of variability in response to climate change, and consumption the lowest. The sources of these differences include model structure and specification; in particular, model assumptions about ease of land use conversion, intensification, and trade. This study identifies where models disagree on the relative responses to climate shocks and highlights research activities needed to improve the representation of agricultural adaptation responses to climate change.climate change adaptation | model intercomparison | integrated assessment | agricultural productivity C limate change alters weather conditions and thus has direct, biophysical effects on agricultural production. Assessing the ultimate consequences of these effects after producers and consumers respond requires detailed assessments at every step in the impact chain from climate through to crop and economic modeling.Comparisons of results from global studies that have attempted such model integration in the past show substantial differences in effects on key economic variables. Studies in the early 1990s found that climate change would have limited agricultural impacts globally, but with varying effects across regions (1-3). Adaptation and carbon dioxide (CO 2 ) fertilization effects were the two largest sources of variation in the results. New simulation approaches emerged in the mid-2000s, with gridded representation of yield impacts and more comprehensive coverage of variability in climate model projections (4, 5). However, these studies still relied on a single crop model and a single economic model. The number of economic models used for these types of analysis has remained relatively limited, and there has been no attempt to compare their behavior systematically. The Fourth Assessment Report of the Inte...

Summary By 2050, the global demand for land and water for agricultural use is projected to increase. Climate change is likely to affect agricultural production through increased temperatures as well as through altered precipitation patterns, which are likely to increase water deficiency in many regions. Measures seeking to increase water efficiency and resilience of the agricultural sector to climate change will therefore be critical. The benefits of more efficient irrigation systems are especially apparent in regions already suffering from water shortages, such as the Mediterranean Basin, or those that are likely to suffer in the future, such as the Southern Cone of South America. However, unless incentives for saving water are in place, farmers may decide to expand their area of irrigated land, or to switch to water‐intensive, higher‐value commodities. Extending irrigation generally constitutes mixed blessings. In regions experiencing water deficits, extending irrigation may lead to greater water stress on irrigated agriculture. Meanwhile, when applied globally and governed carefully, efficient irrigation techniques and extending irrigation can yield overall increases in agricultural production that can reduce agricultural commodity prices. Stimulating water‐efficient irrigation systems may thus prove crucial in improving farmers' resilience over time, though such measures should be supported by other economic instruments such as water pricing or water trading, where necessary.

Transforming the global food system is necessary to avoid exceeding planetary boundaries. A robust evidence base is crucial to assess the scale and combination of interventions required for a sustainable transformation. We developed a risk assessment framework, underpinned by a meta-regression of 60 global food system modeling studies, to quantify the potential of individual and combined interventions to mitigate the risk of exceeding the boundaries for land-system change, freshwater use, climate change, and biogeochemical flows by 2050. Limiting the risk of exceedance across four key planetary boundaries requires a high but plausible level of ambition in all demand-side (diet, population, waste) and most supply-side interventions. Attaining the required level of ambition for all interventions relies on embracing synergistic actions across the food system.

<p>Diversity and diversification in agricultural systems are often presented in the literature as having multiple benefits such as enhancing resilience, increasing food production and decreasing risks in production systems and is often postulated to benefit food and nutrition security in low- and middle-income countries. Our study aims to provide an overview of the potential for agricultural diversification to improve food security status as reported in recently published research articles analysing the diversity-food security relationship. We consider results for different scales, from individual to global and for different food security dimensions: availability, access, stability and utilisation.</p><p>We carried out a literature review that includes exhaustive, comprehensive searching. We search for peer-reviewed publications in the Web of Science core collection (v.5.32) written in English, between 2010 and February 2020 on the association between diversity in agricultural systems and at least one dimension or measure of food security. From the original list of articles we exclude all publications that (1) focus on a study area outside a low- to middle income country; (2) do not include at least one metric of farm-, regional-, or global-level diversity as specified with the search terms; (3) do not explicitly measure at least one food security dimension, or (4) were exclusively focussed on describing drivers and trends in diversity or food security.</p><p>We find that a total number of 87 research articles assessed a total of 328 diversity-food security relationships using one or more statistical modelling approach. About half of them are positive (54%) and mostly refer to the diversity-food access relationship on the individual, household and farm scale as this was the food security dimension and spatial scale most analysed. Of all results for food access 60% were positive relationships and only 4% were negative relationships with the remainder having no or ambiguous relationships. Twenty-nine studies used household dietary diversity as a measure of food access and 10 studies used at least one food access indicator that is a validated proxy for nutrient adequacy. Positive relationships were more often reported for food availability (65%) than for food utilisation (33%) also because for food utilisation there are a lot of mixed findings for different measures of anthropometric and nutritional status. The most common spatial scale assessed was the household and farm scale (58%).</p><p>There is no food security dimension that primarily has a negative relationship with agricultural diversity but there is a considerable number of relationships that are found to be neutral or ambiguous. Diversity can be an important driver of food security, but the magnitude of the contribution depends on the  socio-economic and biophysical characteristics of the local farming system. We conclude that farmers mostly see diversification as a potential strategy to improve livelihoods, agricultural production and/or food and nutrition security where other strategies are more expensive but not as a desirable characteristic of the agricultural systems at all costs especially in the presence of other strategies that can achieve the same outcome.</p>

No abstract