Earth Systems

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.

Marine phytoplankton functional types exhibit diverse responses to thermal change

Abstract: Marine phytoplankton generate half of global primary production, making them essential to ecosystem functioning and biogeochemical cycling. Though phytoplankton are phylogenetically diverse, studies rarely designate unique thermal traits to different taxa, resulting in coarse representations of phytoplankton thermal responses.

Here we assessed phytoplankton functional responses to temperature using empirically derived thermal growth rates from four principal contributors to marine productivity: diatoms, dinoflagellates, cyanobacteria, and coccolithophores. Using modeled sea surface temperatures for 1950–1970 and 2080–2100, we explored potential alterations to each group’s growth rates and geographical distribution under a future climate change scenario.

Contrary to the commonly applied Eppley formulation, our data suggest phytoplankton functional types may be characterized by different temperature coefficients (Q10), growth maxima thermal dependencies, and thermal ranges which would drive dissimilar responses to each degree of temperature change. These differences, when applied in response to global simulations of future temperature, result in taxon-specific projections of growth and geographic distribution, with low-latitude coccolithophores facing considerable decreases and cyanobacteria substantial increases in growth rates. These results suggest that the singular effect of changing temperature may alter phytoplankton global community structure, owing to the significant variability in thermal response between phytoplankton functional types.

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