Earth Systems

Two veteran environmental economists at MIT, John Reilly (left) and Henry "Jake" Jacoby, briefly outline a couple of the most important, and least appreciated, facts about human-driven climate change. One is that the system has enormous inertia, preventing any quick fix. Another is that deep uncertainty surrounds the most consequential aspects of what's to come (pace and extent of warming, sea-level rise, for instance).

This project aims to understand pathways in which ocean ecosystems are subject to change and to quantify states of ecological vulnerability. The researchers propose to use existing satellite measurements, particularly ocean color, in situ datasets, along with numerical model output and theory, to address spatial, temporal and depth-dependent changes to marine ecosystems with a focus on how best to detect these changes and characterize vulnerability using satellite measurements.

This project seeks to advance our understanding of the climate impacts of ship emissions and to better assist relevant policymaking aimed at mitigating such emissions. It is apparent that exclusion of detailed dynamical aerosol-climate interactions in the coupled ocean-atmosphere system in previous studies has been a major bottleneck in revealing the full spectrum of climate impacts associated with pollutants emitted by international shipping.

Recent studies have suggested that the combined effect on climate of increases in the concentrations of several trace gases (principally CH4 and N2O) could rival or even exceed that of the increasing concentration of carbon dioxide (CO2), due to their much stronger abilities in absorbing infrared radiation. Despite their high potential for climate feedback, the specific sources, magnitudes and changes of these trace-gas emissions are still not well understood.

Mercury (Hg) contamination is an issue of a growing environmental and public health concern. Atmospheric chemistry transport models for Hg are a critical tool for understanding the sources, processes, and fate of Hg. Uncertainties in multiple aspects of atmospheric Hg models, however, limit their application for policy evaluation and for monitoring global trends in atmospheric Hg concentrations. This review aims to identify uncertainties in atmospheric Hg modeling that are relevant in the context of policy and for informing decision-making. We focus on specific requirements of the Minamata Convention on Mercury, a global treaty signed in 2013 to protect human health and the environment from Hg, to demonstrate how existing uncertainties in atmospheric Hg modeling can influence our ability to evaluate source-receptor relationships. Modeling studies of source attribution suggest that major uncertainties in atmospheric Hg modeling arise from anthropogenic emissions, biogeochemical cycling, and atmospheric chemistry. Uncertainties in these aspects of modeling are expected to increase under the Convention, with regulation of anthropogenic emissions, changes in atmospheric conditions, and legacy and natural Hg source contribution to the global biogeochemical cycle. These uncertainties can interact with one another and with the current Hg species measurement capability and pose challenges to effectively monitoring trends in atmospheric Hg. Developing additional means to attribute simulated atmospheric Hg trends and improve source-receptor relationships in atmospheric Hg models would improve our ability to evaluate the Convention’s effectiveness.

© Springer International Publishing AG 2016

New objectively balanced observation-based reconstructions of global and continental energy budgets and their seasonal variability are presented that span the golden decade of Earth-observing satellites at the start of the twenty-first century. In the absence of balance constraints, various combinations of modern flux datasets reveal that current estimates of net radiation into Earth’s surface exceed corresponding turbulent heat fluxes by 13–24 W m−2. The largest imbalances occur over oceanic regions where the component algorithms operate independent of closure constraints. Recent uncertainty assessments suggest that these imbalances fall within anticipated error bounds for each dataset, but the systematic nature of required adjustments across different regions confirm the existence of biases in the component fluxes. To reintroduce energy and water cycle closure information lost in the development of independent flux datasets, a variational method is introduced that explicitly accounts for the relative accuracies in all component fluxes. Applying the technique to a 10-yr record of satellite observations yields new energy budget estimates that simultaneously satisfy all energy and water cycle balance constraints. Globally, 180 W m−2 of atmospheric longwave cooling is balanced by 74 W m−2 of shortwave absorption and 106 W m−2 of latent and sensible heat release. At the surface, 106 W m−2 of downwelling radiation is balanced by turbulent heat transfer to within a residual heat flux into the oceans of 0.45 W m−2, consistent with recent observations of changes in ocean heat content. Annual mean energy budgets and their seasonal cycles for each of seven continents and nine ocean basins are also presented.

© 2015 the authors

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