Earth Systems

Future energy: In search of a scenario reflecting current and future pressures and trends

Abstract: Growing societal pressures, technological trends and government and industry actions are moving the world toward decarbonization and away from “business-as-usual.” As such, the concept of a single/obvious “business as usual” or “reference” scenario is no longer relevant. Instead, there are multiple plausible futures that should be explored. We contribute one such scenario that carefully considers emissions-reduction trends and actions that are likely in the future, absent a globally coordinated mitigation effort. We explore the long-term implications for energy, emissions and temperature outcomes if the world continues to address climate change in the way it has so far—through piecemeal actions and growing social and technological pressures.

This Growing Pressures scenario results in a central scenario outcome of about 3°C of surface temperature warming, which is higher than the “well below 2°C” level aspired to by the Paris Agreement, but lower than many widely used “no-policy” scenarios. Ongoing and growing pressures of change, the roots of which are clearly visible today, could deliver a plausible energy transition scenario to near-zero emissions that plays out over the coming century.

While a more aggressive transition is clearly required, this finding highlights the need to bring actions forward in time to achieve an improved outcome making use of clearly identifiable policies and technologies.

Coastal Integrated HydroTerrestrial Modeling: A multi-agency invited workshop

From the Executive Summary: This report describes the results of the November 2020 Coastal Integrated Hydro-Terrestrial Modeling (C-IHTM) workshop series. Organized around five sessions held over five days, the workshop series focused on the challenges of modeling and evaluating coastal landscapes of co-evolving human and natural systems subject to influences and stressors, including extreme weather events, sea level rise, natural and anthropogenic disturbances, and other impacts from climate change. The effort was jointly planned and undertaken by the federal interagency C-IHTM Coordinating Group within the U.S. Global Change Research Program (USGCRP) and the MultiSector Dynamics (MSD) research community. The five-day virtual workshop included robust participation from a wide range of science and engineering research communities.

Climate change and the green transition in South Africa

Abstract: Climate change is one of the most complex challenges facing South Africa as the country designs plans and policies for future economic growth and development. Higher temperatures and more variable rainfall are already affecting the economy and are expected to continue for decades. The degree to which climate change affects different regions in South Africa is likely to vary significantly, characterized by wide ranges in the direction and magnitude of change in key climate variables, especially precipitation. These uncertainties interact with South Africa’s growth and development challenges and complicate planning and policy formation in support national development objectives.

This chapter presents key research on changes in climate experienced in South Africa in recent years, along with projected changes in years to come. It illustrates the uncertainties related to climate change and the key channels through which climate change affects the economy. The economic and developmental impacts of such changes are presented along with the lessons for adaptation policy. As energy will be a key focus area for mitigation efforts in the country, this chapter also outlines the implications of such a transition and the factors that need to be accounted for in limiting the impacts on vulnerable populations.

Bottom-heavy trophic pyramids impair methylmercury biomagnification in the marine plankton ecosystems

Abstract: Methylmercury (CH3Hg+, MMHg) in the phytoplankton and zooplankton, which form the bottom of marine food webs, is a good predictor of MMHg in top predators, including humans. Therefore, evaluating the potential exposure of MMHg to higher trophic levels (TLs) requires a better understanding of relationships between MMHg biomagnification and plankton dynamics.

In this study, a coupled ecological/physical model with 366 plankton types of different sizes, biogeochemical functions, and temperature tolerance is used to simulate the relationships between MMHg biomagnification and the ecosystem structure. The study shows that the MMHg biomagnification becomes more significant with increasing TLs. Trophic magnification factors (TMFs) in the lowest two TLs show the opposite spatial pattern to TMFs in higher TLs. The low TMFs are usually associated with a short food-chain length. The less bottom-heavy trophic pyramids in the oligotrophic oceans enhance the MMHg trophic transfer. The global average TMF is increased from 2.3 to 2.8 in the warmer future with a medium climate sensitivity of 2.5 °C.

Our study suggests that if there are no mitigation measures for Hg emission, MMHg in the high-trophic-level plankton is increased more dramatically in the warming future, indicating greater MMHg exposure for top predators such as humans.

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