What Will the Weather Be After Coronavirus?

June 5, 2020

By Marco Tedesco

Our planet is a huge physics experiment. We learn how it works over time by observing what happens. Understanding the impact of the drastic measures taken to address the pandemic on global warming is as important as it is difficult, given the absolute novelty of what’s happening. The data that scientists are collecting are beginning to provide some clues to frame the first pieces of the puzzle that will help us better understand how our planet is responding to this unprecedented stimulus.

dome and city skyline at sunset

Earth Institute researchers have measured temporary reductions in air pollution over New York City. The benefits are likely to be short-lived. Photo: Ricardo Toledo-Crow

Let’s start with the air pollution. According to an analysis by colleagues from the University of York in the United Kingdom, air pollution levels decreased by more than 40 percent in several cities across the country during the blockade. Even if this is good for the population, it may not be good for the planet. Professor Francis Pope, an atmospheric science expert at the University of Birmingham, recently stated in this regard that a reduction in the level of some pollutants could lead to higher temperatures in the short term. ‘Short-lived pollutants, such as particulates, can have a ‘refreshing’ effect on our atmosphere,” said Pope. Preliminary analysis of the University of York research on the effect of the blockade on UK pollution has shown that levels of polluting nitrogen dioxide (NO2) have been significantly reduced in recent weeks. The presence of these particles in the atmosphere causes a reduction in the amount of solar radiation that can reach the surface of the planet, acting as a shield, and effectively reducing the heating due to solar energy. Air pollutants remain suspended in the air only for days or weeks and, therefore, their removal (as has happened over the past few months) can lead to localized short-term heating which, possibly, can accumulate over time.

Gavin Schmidt, director of the NASA Goddard Institute of Space Studies (GISS), which is responsible for generating estimates of global temperatures for NASA, believes that the impact of reducing aerosols will lead to an increase in temperatures, albeit modest, and that the impact of the suspension of CO2 emissions on global levels will be very small, not conducive to cooling. “I’m not sure it will be detectable on a global scale. We are working on it,” said Schmidt.

Unlike aerosols, in fact, carbon dioxide tends to reside in the atmosphere for a long time. So if it is true that reducing emissions in the past few months has favored the reduction of CO2 concentrations at a local level, we must remember that, in order for these actions to be effective, they must be sustained for long periods. Furthermore, precisely because of the long periods of residence of carbon dioxide in the atmosphere, the heating caused today is also the consequence of the cumulative effect of emissions in past decades — even if we had to turn off all the machines that emit carbon dioxide now, the planet would continue to heat up for several decades, due to CO2 residence times.

Unfortunately, the most recent data from the U.S. National Oceanic and Atmospheric Association (NOAA) show that global CO2 levels have not decreased but, on the contrary, have increased. In April of this year, the average concentration of CO2 in the atmosphere was 416.21 parts per million (ppm), the highest since measurements began in Hawaii in 1958 and, according to data obtained from ice cores, the highest in the last 800,000 years. The data confirm not only the increase but also the acceleration of CO2 levels in the atmosphere — between April 2019 and April 2020, CO2 levels increased by 2.88 ppm, compared to an average of 2.4 ppm for the period 2010 – 2019 and 0.9 ppm during the 1960s. April this year was the second warmest April on the planet since record-keeping began in 1880, only 0.07 °C below the record set in April 2016. Furthermore, the period included between January and April 2020 ranks as the second-hottest period ever recorded, after 2016, again according to the NOAA agency. The indications so far, therefore, do not indicate a reversal of the trend of global warming and CO2 concentrations linked to the shock of COVID-19.

Scientists are also scrutinizing the skies to understand how the reduction of air traffic is reducing the amount of high-altitude clouds formed by contrails of planes (those white or silky filaments that you see in the skies). These types of clouds (cirrus clouds) promote the warming of the planet because they trap more heat that escapes from the Earth’s surface than they reflect into space. NASA scientists and some European research teams hope to take advantage of the clear skies to better understand the effect of condensation trails on global warming. This is important not only because commercial aviation generates about 2 percent of global CO2 emissions but also because contrails double the effective contribution of commercial aircraft to global warming, adding to the effects of their emissions. The new research is inspired by the lessons learned after the September 11 terrorist attacks forced the grounding of flights for a few days. Then a study showed that skies without aircraft had had an impact on temperature changes in the United States, although some researchers say that the results may have been caused by natural variations.

The information we have about the impact of the suspension of activities due to COVID-19 on the climate and atmosphere of our planet suggests that, in the short term, improving the air quality in our cities could have a counterproductive effect on temperatures, favoring localized heating. The reduction in commercial flights may slow down warming, but the question is still open. The long-term benefits of freezing global warming activities are minor, with the planet not only continuing to heat up, but doing so at an ever faster pace.

Whether, in the near or distant future, we will still be able to admire this fascinating experiment that we call Earth depends on the choices we, as a society, operate day after day. Single individuals can and should do a lot, but it is up to governments and institutions to show a way for a sustainable society in which the profit is not in the short-term interest of a few but a long-term benefit for many. It is imperative to think about preserving the future while improving the present. This should be one of the basic principles of an evolved and sustainable society.

Adapted and translated from a piece originally published in La Repubblica.

Marco Tedesco is a research professor at Columbia University’s Lamont-Doherty Earth Observatory.

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