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Abstract. The rapid rise of global temperature that began about 1975 continues at a mean rate of about 0.18 °C/decade, with the current annual temperature exceeding +1.25 °C relative to 1880–1920. Global temperature has just reached a level similar to the mean level in the prior interglacial (Eemian) period, when sea level was several meters higher than today, and, if it long remains at this level, slow amplifying feedbacks will lead to greater climate change and consequences. The growth rate of climate forcing due to human-caused greenhouse gases (GHGs) increased over 20 % in the past decade mainly due to resurging growth of atmospheric CH4, thus making it increasingly difficult to achieve targets such as limiting global warming to 1.5 °C or reducing atmospheric CO2 below 350 ppm. Such targets now require "negative emissions", i.e., extraction of CO2 from the atmosphere. If rapid phasedown of fossil fuel emissions begins soon, most of the necessary CO2 extraction can take place via improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content. In this case, the magnitude and duration of global temperature excursion above the natural range of the current interglacial (Holocene) could be limited and irreversible climate impacts could be minimized. In contrast, continued high fossil fuel emissions by the current generation would place a burden on young people to undertake massive technological CO2 extraction, if they are to limit climate change. Proposed methods of extraction such as bioenergy with carbon capture and storage (BECCS) or air capture of CO2 imply minimal estimated costs of 104–570 trillion dollars this century, with large risks and uncertain feasibility. Continued high fossil fuel emissions unarguably sentences young people to either a massive, possibly implausible cleanup or growing deleterious climate impacts or both, scenarios that should provide both incentive and obligation for governments to alter energy policies ...

Abstract. The rapid rise of global temperature that began about 1975 continues at a mean rate of about 0.18 °C/decade, with the current annual temperature exceeding +1.25 °C relative to 1880–1920. Global temperature has just reached a level similar to the mean level in the prior interglacial (Eemian) period, when sea level was several meters higher than today, and, if it long remains at this level, slow amplifying feedbacks will lead to greater climate change and consequences. The growth rate of climate forcing due to human-caused greenhouse gases (GHGs) increased over 20 % in the past decade mainly due to resurging growth of atmospheric CH4, thus making it increasingly difficult to achieve targets such as limiting global warming to 1.5 °C or reducing atmospheric CO2 below 350 ppm. Such targets now require "negative emissions", i.e., extraction of CO2 from the atmosphere. If rapid phasedown of fossil fuel emissions begins soon, most of the necessary CO2 extraction can take place via improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content. In this case, the magnitude and duration of global temperature excursion above the natural range of the current interglacial (Holocene) could be limited and irreversible climate impacts could be minimized. In contrast, continued high fossil fuel emissions by the current generation would place a burden on young people to undertake massive technological CO2 extraction, if they are to limit climate change. Proposed methods of extraction such as bioenergy with carbon capture and storage (BECCS) or air capture of CO2 imply minimal estimated costs of 104–570 trillion dollars this century, with large risks and uncertain feasibility. Continued high fossil fuel emissions unarguably sentences young people to either a massive, possibly implausible cleanup or growing deleterious climate impacts or both, scenarios that should provide both incentive and obligation for governments to alter energy policies without further delay.

The real-time monitoring of reductions of economic activity by containment measures and its effect on the transmission of the coronavirus (COVID-19) is a critical unanswered question. We inferred 5,642 weekly activity anomalies from the meteorology-adjusted differences in spaceborne tropospheric NO(2) column concentrations after the 2020 COVID-19 outbreak relative to the baseline from 2016 to 2019. Two satellite observations reveal reincreasing economic activity associated with lifting control measures that comes together with accelerating COVID-19 cases before the winter of 2020/2021. Application of the near-real-time satellite NO(2) observations produces a much better prediction of the deceleration of COVID-19 cases than applying the Oxford Government Response Tracker, the Public Health and Social Measures, or human mobility data as alternative predictors. A convergent cross-mapping suggests that economic activity reduction inferred from NO(2) is a driver of case deceleration in most of the territories. This effect, however, is not linear, while further activity reductions were associated with weaker deceleration. Over the winter of 2020/2021, nearly 1 million daily COVID-19 cases could have been avoided by optimizing the timing and strength of activity reduction relative to a scenario based on the real distribution. Our study shows how satellite observations can provide surrogate data for activity reduction during the COVID-19 pandemic and monitor the effectiveness of containment to the pandemic before vaccines become widely available.