Northern Eurasia is made up of a complex and diverse set of physical, ecological, climatic and human systems, which provide important ecosystem services including the storage of substantial stocks of carbon in its terrestrial ecosystems. At the same time, the region has experienced dramatic climate change, natural disturbances and changes in land management practices over the past century. For these reasons, Northern Eurasia is both a critical region to understand and a complex system with substantial challenges for the modeling community. This review is designed to highlight the state of past and ongoing efforts of the research community to understand and model these environmental, socioeconomic, and climatic changes. We further aim to provide perspectives on the future direction of global change modeling to improve our understanding of the role of Northern Eurasia in the coupled human-Earth system. Modeling efforts have shown that environmental and socioeconomic changes in Northern Eurasia can have major impacts on biodiversity, ecosystems services, environmental sustainability, and the carbon cycle of the region, and beyond. These impacts have the potential to feedback onto and alter the global Earth system. We find that past and ongoing studies have largely focused on specific components of Earth system dynamics and have not systematically examined their feedbacks to the global Earth system and to society. We identify the crucial role of Earth system models in advancing our understanding of feedbacks within the region and with the global system. We further argue for the need for integrated assessment models (IAMs), a suite of models that couple human activity models to Earth system models, which are key to address many emerging issues that require a representation of the coupled human-Earth system.

Observations show that the 50-year drying trend (weakening of India summer monsoon) in north central India reversed in the past decade. The finding indicates improved water security and reduced socioeconomic impacts for the region in coming decades.

Background: The Indian summer monsoon (ISM) delivers about 80% of the Indian subcontinent’s annual precipitation and thus impacts the livelihood of more than 1/5 of the world’s population. The timing (typically June – September) and location of the ISM has far-reaching impacts—including floods and droughts—on farming and many other economic activities, and on the availability of water for people and livestock. These factors are of particular concern for north central India, which experienced a significant reduction in summer monsoon rainfall in the second half of the 20th century, resulting in degraded water security and widespread socioeconomic impacts.

Main point: Based on global climate models and multiple hypotheses, scientists expected this drying trend to continue unabated into the 21st century, but a new study in Nature Climate Change shows that the trend has reversed.

Findings: Using data obtained from ground-based and satellite measurements, researchers at the MIT Joint Program on the Science and Policy of Global Change find that since 2002, monsoon rainfall has increased in north central India at a rate of 1.34 millimeters per day per decade. They ascribe the revival of ISM precipitation to a combination of stronger warming over the Indian continent and slower rates of warming over the Indian Ocean. Today’s global climate models—and several hypotheses that have been proposed to explain the long-lasting drying trend in the second half of the 20th century—fail to capture the observed rainfall revival and corresponding trends in the underlying land-ocean temperature differences. In addition, the researchers find that this trend reversal of the Indian summer monsoon  significantly mismatches the overall behavior of Northern Hemispheric monsoonal systems, raising the question of whether conditions unique to India, such as high concentrations of anthropogenic aerosols, are causing this phenomenon.

Significance: Prediction of long-term monsoonal rainfall variations is critical to securing water supplies and planning agricultural and other economic activities in monsoonal regions. Enhanced knowledge about such variations can also help scientists to improve current Earth-system models to more accurately project future climate change.

While climate change impacts on crop yields has been extensively studied, estimating the impact of water shortages on irrigated crop yields is challenging because the water resources management system is complex. To investigate this issue, we integrate a crop yield reduction module and a water resources model into the MIT Integrated Global System Modeling (IGSM) framework, an integrated assessment model linking a global economic model to an Earth system model. We assess the effects of climate and socio-economic changes on water availability for irrigation in the US as well as subsequent impacts on crop yields by 2050, while accounting for climate change projection uncertainty. We find that climate and socio-economic changes will increase water shortages and strongly reduce irrigated yields for specific crops (i.e. cotton and forage), or in specific regions (i.e the Southwest) where irrigation is not sustainable. Crop modeling studies that do not represent changes in irrigation availability can thus be misleading. Yet, since the most water-stressed basins represent a relatively small share of US irrigated areas, the overall reduction in US crop yields is small. The response of crop yields to climate change and water stress also suggests that some level of adaptation will be feasible, like relocating croplands to regions with sustainable irrigation or switching to less irrigation intensive crops. Finally, additional simulations show that greenhouse gas (GHG) mitigation can alleviate the effect of water stress on irrigated crop yields, enough to offset the reduced CO2 fertilization effect compared to an unconstrained GHG emission scenario.