B y the time the World Health Organization declared COVID-19 (scientifically referred to as the severe acute respiratory syndrome-coronavirus 2 or SARS-CoV-2) a pandemic on 11 March 2020, the virus had already spread from China to other Asian countries, Europe and the United States. As of 5 July 2020, cases have been identified in 188 countries or regions 1. This has led to unprecedented enforced and voluntary restrictions on travel and work. This in turn has led to reductions of both GHG emissions and air pollutants 2-4. Analysis of mobility data from Google 5 and Apple 6 shows that mobility declined by 10% or more during April 2020 in all but one of the 125 nations tracked. Mobility declined by 80% in five or more nations (Supplementary Fig. 1). Associated declines in air pollution have been observed from satellite data and from local ground-based observations 7,8. The large pollution declines are expected to be temporary as pollution levels are already returning to near-normal in parts of Asia 9,10. Here we build an estimate of emission changes in GHGs and air pollution due to the COVID-19 global restrictions during the period February-June 2020 and project these into the future. These emission changes are then used to make a prediction of the resultant global temperature response. We examine the temperature response of a direct recovery to pre-COVID-19 national policies and emission levels, and also explore responses where the economic recovery to COVID-19 is driven by either a green stimulus package or an increase in fossil fuel use. Emission trends Bottom-up emission-trend analyses have traditionally relied on laborious collection of various energy-industry-related indicators and statistics from multiple sources 11. The unprecedented recent access to global mobility data from Google and Apple gives a unique opportunity to compare trends across many countries with a consistent approach. We use these data to develop a new method of emission-trend analysis. The advantage over previous approaches is the possibility of near-real-time analysis, national granularity and a systematic consistent approach across nations and over time. The disadvantages are the loss of a direct connection between energy and emissions and the need to make assumptions about these relationships. There are also disadvantages over the short time history of the mobility data and opacity from the data providers around their detailed methodologies and uncertainties. Here we make a simple set of assumptions to deduce estimates of emissions change from the mobility data and test the estimates extensively against the approach of Le Quéré et al. 3. Google and Apple mobility changes and the Le Quéré et al. 3 data all indicate that >50% of the world's population reduced travel by >50% during April 2020 (Fig. 1a). Google mobility trends indicate that >80% of the population in the 114 countries in the dataset (4 billion people) reduced their travel by >50%. Google mobility data and emission reduction estimates based on confinement level analysis in L...

Research reported during the past decade has shown that global warming is roughly proportional to the total amount of carbon dioxide released into the atmosphere. This makes it possible to estimate the remaining carbon budget: the total amount of anthropogenic carbon dioxide that can still be emitted into the atmosphere while holding the global average temperature increase to the limit set by the Paris Agreement. However, a wide range of estimates for the remaining carbon budget has been reported, reducing the effectiveness of the remaining carbon budget as a means of setting emission reduction targets that are consistent with the Paris Agreement. Here we present a framework that enables us to track estimates of the remaining carbon budget and to understand how these estimates can improve over time as scientific knowledge advances. We propose that application of this framework may help to reconcile differences between estimates of the remaining carbon budget and may provide a basis for reducing uncertainty in the range of future estimates.

U‐Pb dating of calcite is an emerging but rapidly growing field of application in geochronology with great potential to inform problems in landscape, basin, and mountain belt evolution, through age determination of diagenetic cements, vein mineralization, and geological formations difficult to date otherwise. In this brief, we present isotope dilution U‐Pb isotope measurements on a sample of calcite (WC‐1) that has been and will continue to be used as a reference material for in situ U‐Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) dating, and which is suitable to be distributed to the geochronological community. We present in situ measurements using LA‐ICP‐MS to demonstrate the suitability of WC‐1 for use as a U‐Pb dating reference material, in spite of it not being isotopically homogeneous. The WC‐1 calcite sample is 254.4 ± 6.4 Ma old and comprised 85–98% radiogenic lead. It presents a suitable reference material that can facilitate dating of calcite ranging in age from Precambrian to late Neogene age.

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