Earth Systems

Chapter 38: Meeting the Goals of the Paris Agreement: Temperature Implications of the Shell Sky Scenario

Abstract: The Paris Agreement (UN, 2015) has established a global target of keeping the increase in the global average surface temperature to “well below” 2°C relative to preindustrial levels, and to pursue efforts to limit the temperature rise to 1.5°C. There are numerous scenarios for greenhouse gas (GHG) emission trajectories that are consistent with the climate stabilization at different levels. Many examples are included as part of the scenario assessment by the UN Intergovernmental Panel on Climate Change (IPCC, 2014) that summarizes the results from the scientific literature from different modeling groups. Fossil fuels are a primary source of human-induced GHG emissions and fossil fuel producers recognize the importance of energy-related emissions (Shell, 2013; BP, 2018; ExxonMobil, 2018). To provide an assessment of the temperature implications of the latest Shell scenario called “Sky” (Shell, 2018), we apply the MIT Integrated Global System Modeling (IGSM) framework (Sokolov et al., 2018) that combines a representation of a global economy and the Earth components (land, ocean, atmosphere).

Predictability of U.S. regional extreme precipitation occurrence based on large-scale meteorological patterns (LSMPs)

Abstract: In this study, we use our analogue method and Convolutional Neural Networks (CNNs) to assess the potential predictability of extreme precipitation occurrence based on Large-Scale Meteorological Patterns (LSMPs) for the winter (DJF) of Pacific Coast California (PCCA) and the summer (JJA) of Midwestern United States (MWST). We evaluate the LSMPs constructed with a large set of variables at multiple atmospheric levels and quantify the prediction skill with a variety of complementary performance measures.

Our results suggest that LSMPs provide useful predictability of extreme precipitation occurrence at a daily scale and its interannual variability over both regions. The 14-year (2006-2019) independent forecast shows Gilbert Skill Scores (GSS) in PCCA range from 0.06 to 0.32 across 24 CNN schemes and from 0.16 to 0.26 across 4 analogue schemes, in contrast to those from 0.1 to 0.24 and from 0.1 to 0.14 in MWST.

Overall, CNN is shown to be more powerful in extracting the relevant features associated with extreme precipitation from the LSMPs than the analogue method, with several single-variate CNN schemes achieving more skillful prediction than the best multi-variate analogue scheme in PCCA and more than half of CNN schemes in MWST. Nevertheless, both methods highlight that Integrated Vapor Transport (IVT, or its zonal and meridional components) enables higher prediction skill than other atmospheric variables over both regions. Warm-season extreme precipitation in MWST presents a forecast challenge with overall lower prediction skill than in PCCA, attributed to the weak synoptic-scale forcing in summer.

Challenges in simulating economic effects of climate change on global agricultural markets

Summary: Previous studies on the impacts of climate change on agriculture have the following shortcomings: a) most focus only on a few major crops (maize, wheat, rice or soybeans); b) site-level and global gridded crop models (GGCMs) provide very different impacts of climate effects on crops; c) effects of climate change on livestock are well documented, but rarely quantified; d) there are several elements, causal relations and feedbacks among biophysical, environmental and socioeconomic aspects usually not taken into account in these studies. The goal of this paper is to investigate at the global level how alternative assumptions about these four aspects may affect agricultural markets, food supply, consumer well-being and environmental metrics.

To that end, this study simulates changes in crop yield and livestock productivity in a large-scale socio-economic model of the global economy with detailed representation of the agriculture sector, the MIT EPPA-Agriculture model. The economic model considers many complex socio-economic relationships and feedbacks, such as changes in management and land-use allocation, shifts in demand for food as prices and incomes change, and changing patterns of global trade. The climate shocks considered were median agricultural productivity changes taken from several site-level crop models revised by IPPC and several GGCMs.

The researchers find global welfare impacts several times larger when climate impacts all crops and all livestock. At the regional level, food budget impacts are 10% to 25% in many developing countries, which may challenge food security. Most of the results are due to the role of land area expansion as a major source of adaptation. Climate impacts from site-level crop models revised by the IPCC generate most challenging socio-economic outcomes, while median climate impacts from GGCMs on yield were positive for major crops. However, due to the wide range of impacts from these two types of models, caution is warranted in comparing those median effects.

The study’s conclusions indicate that the agricultural research community should expand efforts to estimate climate impacts on many more crops and livestock. Also, careful comparison of the GGCMs and traditional site-level models are needed to understand their major differences and implications for agricultural systems and food markets.

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