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Wildfires are becoming more frequent due to the global climate change. Large amounts of greenhouse gases emitted by wildfires can lead to increases in extreme climate events. Accurately estimating the greenhouse gas carbon dioxide (CO2) emissions from wildfires is important for mitigation of climate change. In this paper, we develop a novel method to estimate wildfire CO2 emissions from the relationship between local CO2 emissions and XCO2 anomalies. Our method uses the WRF-Chem assimilation system from OCO-2 XCO2 retrievals which coupled with Data Assimilation Research Testbed (DART). To validate our results, we conducted three experiments evaluating the wildfire CO2 emissions over the conterminous United States. The four-month average wildfire emissions from July to October in 2015∼2018 were estimated at 4.408 Tg C, 1.784 Tg C, 1.514 Tg C and 2.873 Tg C, respectively. Compared to the average of established inventories CT2019B, FINNv1.5 and GFASv1.2 fire emissions, our estimates fall within one standard deviation, except for 2017 due to lacking of OCO-2 XCO2 retrievals. These results suggest that the regional carbon assimilation system, such as WRF-Chem/DART, using OCO-2 XCO2 retrievals has a great potential for accurately tracking regional wildfire emissions. [ABSTRACT FROM AUTHOR]

In the United States, state governments have been the locus of action for addressing climate change. However, the lack of a holistic measure of state climate policy has prevented a comprehensive assessment of state policies' effectiveness. Here, we assemble information from 25 individual policies to develop an aggregate index of state climate policies from 2000-2020. The climate policy index highlights variation between states which is difficult to assess in single policy studies. Next, we examine the environmental and economic consequences of state climate policy. A standard-deviation increase in climate policy is associated with a 5% reduction in per-capita electricity-sector CO2 emissions and a 2% reduction in economy-wide CO2 emissions per capita. We do not find evidence that more stringent climate policy harms states' economies. Our results make clear the benefits of state climate policy, while showing that current state efforts are unlikelyto meet the US goal under the Paris Climate Accord. In the US, states vary in their efforts to address climate change. Stronger state climate policies reduce CO2 emissions without harming the economy, but these reductions are unlikely to meet the goals in the Paris Climate Accord. [ABSTRACT FROM AUTHOR]

This study contributed to the environmental research by analyzing the nexus between innovation in climate change mitigation technologies and carbon dioxide emissions in the United States, with the gross domestic product per capita, international collaboration in green technology development, renewable energy consumption, the labor force, and trade openness as control variables from 1990Q1 to 2018Q4. First, the results suggested that renewable energy consumption, innovation in climate change mitigation technologies, and international collaboration in green technology development are significant mitigating and determining factors for carbon dioxide emissions. Second, the findings also indicated that trade openness and gross domestic product per capita were positively associated with carbon dioxide emissions. Third, the Granger causality test results validated the presence of a bidirectional nexus between innovation in climate change mitigation technologies and carbon dioxide emissions, renewable energy consumption and carbon dioxide emissions, and international collaboration in green technology development and carbon dioxide emissions. Fourth, the results validated a one-way causality between gross domestic product per capita and carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

• Pursuing a zero-carbon US electricity system would incur additional cost. • The use of non-renewable low-carbon resources reduces the additional cost. • Negative emission technologies show economic advantage to mitigate the last few percent CO 2 from the US electricity system. Decarbonizing the electricity system to zero-carbon emission is crucial for climate change mitigation. Previous studies have shown that such a transition in the United States (U.S.) may lead to higher system cost compared to a business-as-usual case, but it is not well-known how the cost of electricity generation varies at sub-regional level under the transition, and studies have rarely evaluated the trade-off between the cost and avoided climate damages, as well as the potential roles of negative emission technologies (NETs) in the electricity decarbonization. Here, we present a regionally resolved national model to quantify the cost of decarbonizing the U.S. electricity system under a set of possible scenarios. The results show that, compared to the reference scenario without a decarbonization policy, reaching zero CO 2 emission by 2050 would incur, depending on the scenarios, 335–494 billion USD additional cost to the U.S. electric power sector during 2020–2050. The regional costs of electricity generation ranges from 2.4 to 4.7 cent/kWh, largely due to the generation profiles and renewable resources availability of those regions. The additional costs can be translated to an average CO 2 abatement cost of 29–59 USD/metric ton CO 2 (with 2%–7% discount rates), which are comparable to the social cost of carbon in the literature at around 4% discount rate. The results also show that the cost of mitigating the last few percent CO 2 emission from the U.S. electricity system may exceed the costs of NETs, indicating an opportunity for NETs to contribute to electricity decarbonization. [ABSTRACT FROM AUTHOR]