Taking stock of nationally determined contributions: Continued ratcheting of ambition is critical to limit global warming to 1.5°C

As countries take stock of progress made in accomplishing their climate goals ahead of COP28 this year, it is increasingly apparent that countries must ratchet ambition in policy areas such as non-CO2 gases and carbon dioxide removal, while halting deforestation to lead the globe on a path consistent with the goals of the Paris Agreement.

Role of non-CO2 greenhouse gas emissions in limiting global warming

Current climate pledges are insufficient to achieve the aspirational goal of limiting global warming to 1.5°C. Here we discuss the critical role that non-CO2 greenhouse gas emissions might play in global climate change stabilization, and challenges and opportunities to pivot research and policy focus towards accelerated reductions of non-CO2 gases.

Ratcheting of climate pledges needed to limit peak global warming

The new and updated emission reduction pledges submitted by countries ahead of COP26 represent a meaningful strengthening of global ambition compared to the 2015 Paris pledges1,2. Yet, limiting global warming below 1.5°C this century will require countries to ratchet ambition for 2030 and beyond2-6. We explore a suite of emissions pathways in which countries ratchet and achieve ambition through a combination of increasing near-term ambition through 2030, accelerating post-2030 decarbonization, and advancing the dates for national net-zero pledges. We show that ratcheting near-term ambition through 2030 will be crucial to limiting peak temperature changes. Delaying ratcheting ambition to beyond 2030 could still deliver end-of-century temperature change of less than 1.5°C, but that would result in higher temperature overshoot over many decades with the potential for adverse consequences. Ratcheting near-term ambition would also deliver benefits from enhanced non-CO2 mitigation and facilitate faster transitions to net-zero emissions systems in major economies.

The Energy System Transformation Needed to Achieve the U.S. Long-Term Strategy

The authors designed and executed the integrated assessment modeling for the United States Long-Term Strategy. They bring diverse expertise to the modeling and analysis of United States decarbonization. Russell Horowitz, Matthew Binsted, and Haewon McJeon are scientists at the Joint Global Change Research Institute, a partnership between Pacific Northwest National Laboratory and the University of Maryland. Allen Fawcett, James McFarland, and Morgan Browning are economists at the Environmental Protection Agency's Climate Economics Branch. Claire Henly is White House Fellow at the Office of the U.S. Special Presidential Envoy for Climate. Nathan Hultman is the Director of the Center for Global Sustainability at the University of Maryland.

Heterogeneous changes in electricity consumption patterns of residential distributed solar consumers due to battery storage adoption

This study provides an empirical assessment of how adopting battery storage units can change the electricity consumption patterns of PV consumers using individual-consumer-level hourly smart meter data in Arizona, United States. We find that on average after adding batteries, PV consumers use more solar electricity to power their houses and send less solar electricity back to the grid. In addition, adding battery storage reduces electricity needed from the grid during system peak hours, helping utilities better flatten the load curves. Most importantly, we find a large degree of heterogeneity in the changes in electricity consumption patterns due to adopting battery storage that are not consistent with engineering or economic principles such as those not maximizing consumers’ economic benefits. Such heterogeneous changes imply that utilities and policymakers need to further study the underlying behavioral reasons in order to maximize the social benefits of battery storage and PV co-adoption.

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Adding battery storage changes solar consumers’ electricity consumption patterns

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Adding battery increases self-consumption of solar electricity

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Battery reduces electricity needed from the grid during system peak hours

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We find a large degree of heterogeneity in the changes in consumption patterns

Can updated climate pledges limit warming well below 2°C?

[Figure: see text].

Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer

We investigated key factors controlling mass and energy exchange by a young (6-year-old) ponderosa pine (Pinus ponderosa Laws.) plantation on the west side of the Sierra Nevada Mountains and an old-growth ponderosa pine forest (mix of 45- and 250-year-old trees) on the east side of the Cascade Mountains, from June through September 1997. At both sites, we operated eddy covariance systems above the canopy to measure net ecosystem exchange of carbon dioxide and water vapor, and made concurrent meteorological and ecophysiological measurements. Our objective was to understand and compare the controls on ecosystem processes in these two forests. Precipitation is much higher in the young plantation than in the old-growth forest (1660 versus 550 mm year-1), although both forests experienced decreasing soil water availability and increasing vapor pressure deficits (D) as the summer of 1997 progressed. As a result, drought stress increased at both sites during this period, and changes in D strongly influenced ecosystem conductance and net carbon uptake. Ecosystem conductance for a given D was higher in the young pine plantation than in the old-growth forest, but decreased dramatically following several days of high D in late summer, possibly because of xylem cavitation. Net CO2 exchange generally decreased with conductance at both sites, although values were roughly twice as high at the young site. Simulations with the 3-PG model, which included the effect of tree age on fluxes, suggest that, during the fall through spring period, milder temperatures and ample water availability at the young site provide better conditions for photosynthesis than at the old pine site. Thus, over the long-term, the young site can carry more leaf area, and the climatic conditions between fall and spring offset the more severe limitations imposed by summer drought.