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Panelists shared their expertise on the science, technology and policy of decarbonization in presentations and in conversation with invited sponsor representatives and other energy industry stakeholders. Discussions underscored the potential of unique Joint Program assessment strategies and tools to quantify the economic and environmental impacts of large-scale decarbonization and support investment and policy decisions in this space.

Abstract: Distributional impacts of environmental policies have become an increasingly important consideration in policymaking, but current studies have focused on just a few countries individually. To evaluate the country-specific impacts of carbon pricing with different revenue recycling schemes, we integrate national economic models for the USA and Spain with household microdata that provides consumption patterns and other socio-economic characteristics for thousands of households in each country. Using these combined models, we explore the applicability of results from one country to other countries by focusing on different revenue recycling schemes.

We find that, with some exceptions, the USA and Spain overall show similar patterns of distributional impacts for the two revenue recycling schemes, despite their differences in size, existing tax structure, energy sources and prices, level of income inequality, consumption patterns, etc. We find that in both countries an equal household rebate has progressive welfare impacts that are positive for the majority of income ventiles while the payroll tax reduction tends to be proportional or slightly regressive. We also explore welfare impacts for different household classifications, the impact of the policy design on overall inequality, and the role of inequality aversion on the social welfare implications of the policy design.

MIT oceanographers have an explanation for the Arctic’s puzzling ocean turbulence

The increasing atmospheric burden of the greenhouse gas sulfur hexafluoride (SF6)

Abstract: We report a 40-year history of SF₆ atmospheric mole fractions measured at the Advanced Global Atmospheric Gases Experiment (AGAGE) monitoring sites, combined with archived air samples, to determine emission estimates from 1978 to 2018. Previously we reported a global emission rate of 7.3±0.6 Gg yr⁻¹ in 2008 and over the past decade emissions have continued to increase by about 24 % to 9.04±0.35 Gg yr⁻¹ in 2018. We show that changing patterns in SF₆ consumption from developed (Kyoto Protocol Annex-1) to developing countries (non-Annex-1) and the rapid global expansion of the electric power industry, mainly in Asia, have increased the demand for SF₆-insulated switchgear, circuit breakers, and transformers. The large bank of SF₆ sequestered in this electrical equipment provides a substantial source of emissions from maintenance, replacement, and continuous leakage. Other emissive sources of SF₆ occur from the magnesium, aluminium, and electronics industries as well as more minor industrial applications. More recently, reported emissions, including those from electrical equipment and metal industries, primarily in the Annex-1 countries, have declined steadily through substitution of alternative blanketing gases and technological improvements in less emissive equipment and more efficient industrial practices. Nevertheless, there are still demands for SF₆ in Annex-1 countries due to economic growth, as well as continuing emissions from older equipment and additional emissions from newly installed SF₆-insulated electrical equipment, although at low emission rates. In addition, in the non-Annex-1 countries, SF₆ emissions have increased due to an expansion in the growth of the electrical power, metal, and electronics industries to support their continuing development.

There is an annual difference of 2.5–5 Gg yr⁻¹ (1990–2018) between our modelled top-down emissions and the UNFCCC-reported bottom-up emissions (United Nations Framework Convention on Climate Change), which we attempt to reconcile through analysis of the potential contribution of emissions from the various industrial applications which use SF₆. We also investigate regional emissions in East Asia (China, S. Korea) and western Europe and their respective contributions to the global atmospheric SF₆ inventory. On an average annual basis, our estimated emissions from the whole of China are approximately 10 times greater than emissions from western Europe. In 2018, our modelled Chinese and western European emissions accounted for ∼36 % and 3.1 %, respectively, of our global SF₆ emissions estimate.

The global methane budget 2000–2017

Abstract: Understanding and quantifying the global methane (CH₄) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH₄ continue to increase, making CH₄ the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO₂). The relative importance of CH₄ compared to CO₂ depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH₄ sources and from the destruction of CH₄ by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations).

For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH₄ yr⁻¹ (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH₄ yr⁻¹ or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH₄ yr⁻¹ or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is 29 Tg CH₄ yr⁻¹ larger than our estimate for the previous decade (2000–2009), and 24 Tg CH₄ yr⁻¹ larger than the one reported in the previous budget for 2003–2012 (Saunois et al., 2016). Since 2012, global CH₄ emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH₄ yr⁻¹, range 594–881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (∼ 65 % of the global budget, < 30^∘ N) compared to mid-latitudes (∼ 30 %, 30–60^∘ N) and high northern latitudes (∼ 4 %, 60–90^∘ N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters.

Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH₄ yr⁻¹ lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH₄ yr⁻¹ by 8 Tg CH₄ yr⁻¹, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH₄ measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning.

The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

A comprehensive quantification of global nitrous oxide sources and sinks

Abstract: Nitrous oxide (N₂O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N₂O concentrations have contributed to stratospheric ozone depletion¹ and climate change², with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N₂O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. Here we present a global N₂O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N₂O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N₂O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N₂O emissions were 17.0 (minimum–maximum estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7) teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N₂O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N₂O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N₂O emissions exceeds some of the highest projected emission scenarios^3,4, underscoring the urgency to mitigate N₂O emissions.

Exploring biogeochemical and ecological redundancy in phytoplankton communities in the global ocean

Abstract: Climate change induced alterations of oceanic conditions will lead to the ecological niches of some marine phytoplankton species disappearing, at least regionally. How will such losses affect the ecosystem and the coupled biogeochemical cycles?

Here, we couch this question in terms of ecological redundancy (will other species be able to fill the ecological roles of the extinct species) and biogeochemical redundancy (can other species replace their biogeochemical roles). Prior laboratory and field studies point to a spectrum in the degree of redundancy. We use a global three-dimensional computer model with diverse planktonic communities to explore these questions further. The model includes 35 phytoplankton types that differ in size, biogeochemical function and trophic strategy. We run two series of experiments in which single phytoplankton types are either partially or fully eliminated.

The niches of the targeted types were not completely reoccupied, often with a reduction in the transfer of matter from autotrophs to heterotrophs. Primary production was often decreased, but sometimes increased due to reduction in grazing pressure. Complex trophic interactions (such as a decrease in the stocks of a predator’s grazer) led to unexpected reshuffling of the community structure. Alterations in resource utilization may cause impacts beyond the regions where the type went extinct.

Our results suggest a lack of redundancy, especially in the ‘knock on’ effects on higher trophic levels. Redundancy appeared lowest for types on the edges of trait space (e.g. smallest) or with unique competitive strategies. Though highly idealized, our modelling findings suggest that the results from laboratory or field studies often do not adequately capture the ramifications of functional redundancy. The modelled, often counterintuitive, responses - via complex foodweb interactions and bottom-up versus top-down controls - indicate that changes in planktonic community will be key determinants of future ocean global change ecology and biogeochemistry.

The Covid-19 effect on the Paris Agreement

Abstract: The pandemic and efforts to control it are causing sharp reductions in global economic activity and associated fossil energy use, with unknown influence on longer-term efforts to limit greenhouse gas emissions under the Paris Climate Agreement. To explore this effect, estimates of economic recession and recovery in near-term months are extended to cover a return to full employment in future years, to be compared with an estimate of growth had COVID-19 not occurred.

On the assumption that the Paris emissions pledges for 2020 will be met in any case, projection of global emissions with and without the pandemic show that, through its growth impact alone, it will yield only a small effect on emissions in 2030 and beyond. Other COVID legacies may include residual influences in patterns of consumption and travel, and the direction of recovery funds to low carbon investments.

Most important, however, will be the effect of the economic shocks on the willingness of nations to meet (or augment) their existing Paris emissions pledges. The main effect of the pandemic on the threat of climate change, therefore, will be not its growth impact but its influence on national commitments to action.

Improving Evaluation of Energy Policies with Multiple Goals: Comparing Ex Ante and Ex Post Approaches

Abstract: Sustainability policies are often motivated by the potential to achieve multiple goals, such as simultaneously mitigating the climate change and air quality impacts of energy use. Ex ante analysis is used prospectively to inform policy decisions by estimating a policy’s impact on multiple objectives. In contrast, ex post analysis of impacts that may have multiple causes can retrospectively evaluate the effectiveness of policies. Ex ante analyses are rarely compared with ex post evaluations of the same policy. These comparisons can assess the realism of assumptions in ex ante methods and reveal opportunities for improving prospective analyses.

We illustrate the benefits of such a comparison by examining a case of two energy policies in China. Using ex post analysis, we estimate the impacts of two policies, one that targets energy intensity and another that imposes quantitative targets on SO₂ emissions, on energy use and pollution outcomes in two major energy-intensive industrial sectors (cement, iron and steel) in China.

We find that the ex post effects of the energy intensity policy on both energy and pollution outcomes are very limited on average, while the effects of the SO₂ emissions policy are large. Compared with ex ante analysis, ex post estimates of benefits of the energy intensity policy are on average smaller, and differ by location in both sign and magnitude. Accounting for firm-level heterogeneity in production processes and policy responses, as well as the use of empirically grounded counterfactual baselines, can improve the realism of ex ante analysis and thus provide a more reliable basis for policy design.

MIT Global Change

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