Limited impact of COVID-19 recovery packages on near-term CO2 emissions pathways

Part of the economic recovery plans implemented by governments following COVID-19 is directed towards the energy transition. To understand the potential effects of these post-COVID green recovery packages on reductions of global greenhouse gas emissions until 2030, we investigated three different approaches. First, we analyzed simulation results of Integrated Assessment Models (IAMs) to infer the change in CO2 intensity of GDP that could result from post-COVID low-carbon investment plans. Second, we investigated the scenarios the International Energy Agency (IEA) provided based on a bottom-up energy system model. Combining the two approaches, we found that green recovery packages implemented and planned globally can lead to an emissions reduction of merely 1%-6% from the 2030 baseline levels at most. Third, we looked into the results of the Adaptative Regional Input-Output model, which simulates the dynamic effects of economic crisis and fiscal stimuli through supply chains following labor shortage. The third approach shows that the increase of activity driven by fiscal stimuli leads to a rebound of CO2 emissions even if they do not target carbon-intensive sectors. We conclude that green recovery packages targeting low-carbon technologies have a limited impact on near-term CO2 emissions and that demand-side incentives, as well as other policy efforts to disincentivize the use of fossil fuels, are also crucial for scaling up climate mitigation.

Global patterns of daily CO2 emissions reductions in the first year of COVID-19

Observed daily changes in CO2 emissions from across the globe reveal the sectors and countries where pandemic-related emissions declines were most pronounced in 2020. Day-to-day changes in CO2 emissions from human activities, in particular fossil-fuel combustion and cement production, reflect a complex balance of influences from seasonality, working days, weather and, most recently, the COVID-19 pandemic. Here, we provide a daily CO2 emissions dataset for the whole year of 2020, calculated from inventory and near-real-time activity data. We find a global reduction of 6.3% (2,232 MtCO(2)) in CO2 emissions compared with 2019. The drop in daily emissions during the first part of the year resulted from reduced global economic activity due to the pandemic lockdowns, including a large decrease in emissions from the transportation sector. However, daily CO2 emissions gradually recovered towards 2019 levels from late April with the partial reopening of economic activity. Subsequent waves of lockdowns in late 2020 continued to cause smaller CO2 reductions, primarily in western countries. The extraordinary fall in emissions during 2020 is similar in magnitude to the sustained annual emissions reductions necessary to limit global warming at 1.5 degrees C. This underscores the magnitude and speed at which the energy transition needs to advance.

Decreased Aviation Leads to Increased Ice Crystal Number and a Positive Radiative Effect in Cirrus Clouds

Travel restrictions in the wake of the COVID-19 pandemic resulted in an unprecedented decrease of 73% in global flight mileage in April-May 2020 compared to 2019. Here we examine the CALIPSO satellite observations and find a significant increase in ice crystal number concentrations (Ni) in cirrus clouds in the mid-latitudes of the Northern Hemisphere, which we attribute to an increase in homogeneous freezing when soot from aircraft emissions is reduced. A relatively small positive global average radiative effect of 21 mW m(-2) is estimated if a decrease in aircraft traffic continues, with an average of up to 64 mW m(-2) over the area where aviation is most active. We infer from this analysis that the worldwide adoption of biofuel blending in aircraft fuels that lead to smaller soot emissions could lead to a significant change in the microphysical properties of cirrus clouds but a rather small positive radiative effect.

Climate impact of aircraft-induced cirrus assessed from satellite observations before and during COVID-19

Aircraft produce condensation trails, which are thought to increase high-level cloudiness under certain conditions. However the magnitude of such an effect and whether this contributes substantially to the radiative forcing due to the aviation sector remain uncertain. The very substantial, near-global reduction in air traffic in response to the COVID-19 outbreak offers an unprecedented opportunity to identify the anthropogenic contribution to the observed cirrus coverage and thickness. Here we show, using an analysis of satellite observations for the period March-May 2020, that in the 20% of the Northern Hemisphere mid-latitudes with the largest air traffic reduction, cirrus fraction was reduced by similar to 9 +/- 1.5% on average, and cirrus emissivity was reduced by similar to 2 +/- 5% relative to what they should have been with normal air traffic. The changes are corroborated by a consistent estimate based on linear trends over the period 2011-2019. The change in cirrus translates to a global radiative forcing of 61 +/- 39 mW m(-2). This estimate is somewhat smaller than previous assessments.