Earth Systems

Attribution of space-time variability in global-ocean dissolved organic carbon

Plain Language Summary: The ocean has absorbed roughly 40% of fossil fuel carbon dioxide (CO2) emissions since the beginning of the industrial era. This so-called “ocean carbon sink,” which primarily sequesters emissions in the form of dissolved inorganic carbon (DIC), plays a key role in regulating climate and mitigating global warming. However, we still lack a mechanistic understanding of how physical, chemical, and biological processes impact the ocean DIC reservoir in both space and time, and hence how the storage rates of emissions may change in the future.

Here we use a global-ocean biogeochemistry model Estimating the Circulation and Climate of the Ocean-Darwin, which ingests both physical and biogeochemical observations to improve its accuracy, to map how ocean circulation, air-sea CO2 exchange, and marine ecosystems have modulated the combined natural and anthropogenic ocean DIC budget for 1995–2018. We find that in the upper ocean, circulation provides the largest supply of DIC while biological processes drive the largest loss. Year-to-year changes in the ocean carbon sink are dominated by El Niño-Southern Oscillation events in the equatorial Pacific Ocean, which then affect DIC globally.

In summary, our data-constrained, global-ocean DIC budget constitutes a significant step forward toward understanding climate-related changes to the ocean DIC reservoir.

Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

Abstract: The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past two decades, primarily as a result of the phaseout of ozone depleting substances under the Montreal Protocol and the use of HFCs as their replacements. Projections from 2015 showed large increases in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 °C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries.

Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2-eq inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2-eq yr−1) but are about 20 % lower than previously projected for 2017–2019, mainly because of lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and lower reported consumption of HFC-143a in China. Because this time-period preceded the beginning of the Kigali controls, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications, in anticipation of national or global mandates.

A new HFC scenario is developed based on current trends in HFC use and current policies in several countries. These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2-eq yr−1 to 1.9–3.6 GtCO2-eq yr−1. The provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2-eq yr−1 in 2050. Without current policies, HFCs would be projected to contribute 0.28–0.44 °C to the global surface warming in 2100, compared to 0.14–0.31 °C with current policies, but without the Kigali Amendment. In contrast, the Kigali Amendment controls are expected to limit surface warming from HFCs to about 0.04 °C in 2100.

The case for real-time, high-frequency measurement networks is very strong, and AGAGE observations and their interpretation are recognized widely for their importance to ozone depletion and climate change studies—and to verification issues arising from the Montreal Protocol (ozone) and Paris Agreement (climate) Protocols. AGAGE is distinguished by its capability to measure globally, at high frequency, all the important species in the Montreal Protocol and non-CO2 gases in the Paris Agreement.

Advanced Global Atmospheric Gases Experiment (AGAGE) collaborative project: MIT component

First held in 1970, Earth Day is an annual observance on April 22 that promotes the need for environmental protection. Earth Day now comprises multiple events around the world under the coordination of EarthDay.org. The official theme for this year's Earth Day is Invest In Our Planet, To that end, the Earth Day 2022 website states:

Four new videos highlight the impact of the MIT Joint Program on the Science and Policy of Global Change

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