JP

Global climate-change trends detected in indicators of ocean ecology

Abstract: Strong natural variability has been thought to mask possible climate-change-driven trends in phytoplankton populations from Earth-observing satellites. More than 30 years of continuous data were thought to be needed to detect a trend driven by climate change.

Here we show that climate-change trends emerge more rapidly in ocean colour (remote-sensing reflectance, R) because R is multivariate and some wavebands have low interannual variability. We analyse a 20-year R time series from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite, and find significant trends in R for 56% of the global surface ocean, mainly equatorward of 40°.

The climate-change signal in R emerges after 20 years in similar regions covering a similar fraction of the ocean in a state-of-the-art ecosystem model, which suggests that our observed trends indicate shifts in ocean colour—and, by extension, in surface-ocean ecosystems—that are driven by climate change. On the whole, low-latitude oceans have become greener in the past 20 years.

Editor's Summary: An analysis of satellite data from July 2002–June 2022 shows that ocean colour, or remote-sensing reflectance, changed significantly during this period, and that this trend is likely to be driven by climate change.

An investigation into the effects of border carbon adjustments on the Canadian economy

Abstract: This paper examines how border carbon adjustments (BCAs) may address the unintended consequences of uncoordinated global climate action, focusing on the economic implications for Canada. We investigate these implications under different BCA design features and by considering a coalition of countries and regions that adopt BCAs. We find that BCAs, in the form of import tariffs, reduce Canada’s carbon leakage to the rest of the world and improve its domestic and foreign competitiveness when Canada is part of a coalition of countries and regions that implement BCAs that includes the United States. We show that these results may change if Canada imposes BCAs on a different set of sectors than the rest of the coalition or includes export rebates and free emissions allowances to firms. When the United States is not part of the coalition, we show that Canada’s carbon leakage increases, domestic competitiveness dampens, and foreign competitiveness improves. Compared with a case where no countries have BCAs, welfare improves in Canada if revenues from BCAs, in the form of import tariffs, are transferred to households. This finding holds regardless of the United States’ participation in the coalition.

This report is also available at the Bank of Canada website.

Natural Climate Solutions must embrace multiple perspectives to ensure synergy with sustainable development

Abstract: To limit global warming to well below 2°C, immediate emissions reductions must be coupled with active removal of greenhouse gases from the atmosphere. ‘Natural Climate Solutions’ (NCS) achieve atmospheric CO2 reduction through the conservation, restoration or altered management of natural ecosystems with enormous potential to deliver ‘win-win-win’ outcomes for climate, nature and society. Yet the supply of high-quality NCS projects does not meet market demand, and projects already underway often fail to deliver their promised benefits, due to a complex set of interacting ecological, social and financial constraints. How can these cross-sectoral challenges be surmounted?

Here we draw from expert elicitation surveys and workshops with professionals across the ecological, sociological and economic sciences, evaluating differing perspectives on NCS, and suggesting how these might be integrated to address urgent environmental challenges. We demonstrate that funders’ perceptions of operational, political and regulatory risk strongly shape the kinds of NCS projects that are implemented, and the locations where they occur. Because of this, greenhouse gas removal through NCS may fall far short of technical potential. Moreover, socioecological co-benefits of NCS are unlikely to be realized unless the local communities engaged with these projects are granted ownership over implementation and outcomes.

Exploring the Role of Hydrogen in Decarbonizing Heavy Industry

Abstract: Hydrogen is increasingly being seized upon as a widespread decarbonization solution. There are a number of potential applications for hydrogen and investments are being funneled into demonstration projects. In this thesis work I explore the economic competitiveness of hydrogen in two heavy industry applications; steelmaking and high temperature heating. These processes rely on fossil fuels for multiple attributes and there is not another low carbon alternative fuel that has all of these characteristics. I find that in all regions, low carbon hydrogen production costs are currently more expensive than fossil fuels. High temperature heating with hydrogen increases the cost of clinker by 58-225%, and raw glass by 16-73%. Applications of hydrogen in steelmaking increase steel costs by 24-90%. Cost ranges represent the different costs when using Blue or Green H2. As a competing low carbon steel production pathway, I also assessed steelmaking with CCS which increased steelmaking costs by (∼14%). Using the MIT Economic Projection and Policy Analysis (EPPA) model, I examined the deployment of H2 based steelmaking and steelmaking with CCS under a deep decarbonization policy scenario. Results show that at current costs deployment is limited prior to 2050. However, if costs are reduced then these technologies can deploy rapidly (achieving up to 100% of the share of global steel production by 2050). Adoption of decarbonization technologies is regionally specific and there can be regional advantages to deploying certain production pathways.

Designing climate policy mixes: Analytical and energy system modeling approaches

Highlights

  • The efficiency benefit of carbon pricing exhibits diminishing marginal returns.

  • Modest carbon pricing delivers relatively large efficiency improvements.

  • Partial reliance on clean energy standards entails a relatively small efficiency loss.

  • Policy mixes combining standards and pricing can be near-cost-optimal.

  • Policy mixes allow policy makers to leverage the distinct advantages of each policy.

 

Abstract

A matter of debate in climate policy is whether lawmakers should rely on carbon pricing or regulations, such as low-carbon standards, to reach emission reduction goals. Past research showed that pricing is more cost-effective. However, previous work studied the two policies when implemented separately, in effect comparing two policy extremes. In contrast, we explore the full spectrum of climate policy mixes that include both types of policies but vary in how much they rely on each. We do this both analytically by extending previous theory and numerically with two energy system models.

In line with past work, increasing reliance on pricing increases the cost-effectiveness of the policy mix. However, we show that this benefit exhibits diminishing marginal returns. Thus the gain in cost-effectiveness from complementing stringent standards with modest pricing is relatively large. Our results show that relying on pricing for 20% of emission reductions (and on a standard for 80%) reduces costs by 32%–57% compared to a standard-only approach. Importantly, trading off more of the standard for pricing delivers smaller and smaller gains in cost-effectiveness. For example, a policy mix that relies on each policy for 50% of emission reductions decreases costs by 60%–81%, which is already 71%–88% as cost-effective as the theoretically most cost-effective pricing-only policy.

Thermal Responses in Global Marine Planktonic Food Webs Are Mediated by Temperature Effects on Metabolism

Abstract

Rising ocean temperatures affect marine microbial ecosystems directly, since metabolic rates (e.g., photosynthesis, respiration) are temperature-dependent, but temperature also has indirect effects mediated through changes to the physical environment. Empirical observations of the long-term trends in biomass and productivity measure the integrated response of these two kinds of effects, making the independent components difficult to disentangle. We used a combination of modeling approaches to isolate the direct effects of rising temperatures on microbial metabolism and explored the consequences for food web dynamics and global biogeochemistry. We evaluated the effects of temperature sensitivity in two cases: first, assuming that all metabolic processes have the same temperature sensitivity, or, alternatively, that heterotrophic processes have higher temperature sensitivity than autotrophic processes. Microbial ecosystems at higher temperatures are characterized by increased productivity but decreased biomass stocks as a result of transient, high export events that reduce nutrient availability in the surface ocean. Trophic dynamics also mediate community structure shifts resulting in increased heterotroph to autotroph ratios at higher temperatures. These ecosystem thermal responses are magnified when the temperature sensitivity of heterotrophs is higher than that of autotrophs. These results provide important context for understanding the combined food web response to direct and indirect temperature effects and inform the construction and interpretation of Earth systems models used in climate projections.

Key Points

  • Warming results in increased productivity, but decreased biomass, in marine microbial food webs due to the thermal dependence of metabolism

  • Higher temperatures disproportionately favor higher trophic levels, increasing the ratio of heterotrophs to autotrophs

  • Thermal responses are amplified if heterotrophic and autotrophic processes have different temperature sensitivity coefficients

Plain Language Summary

Warming oceans cause a myriad of changes to marine ecosystems, including both biological changes to the organisms themselves and physical changes to the environment. Here, we use mathematical models to isolate the effects of warming that arise directly from temperature's effect on metabolic rates, and the resulting changes to marine food webs and the global carbon cycle. We focus on how different metabolic rates (e.g., photosynthesis, grazing) may have different temperature sensitivities and the consequences of those differences on the overall thermal sensitivity of marine ecosystems. We found that marine food webs had higher productivity, but less overall biomass, when temperatures increase. These effects were amplified when grazing had greater temperature sensitivity than photosynthesis. Increased temperature also had effects on community and food web structure. These results provide important context for the kinds of global models that are used in climate change projections.

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