Coronavirus Exacerbated Global Warming in February 2020
Originally written on March 16th, 2020
You might be surprised to learn that, yes, Coronavirus has exacerbated global warming/climate change this past February. Before you jump to the conclusion that I’m off my rocker, allow me to explain.
It’s true that global fossil fuel use decreased this past February (particularly in China), and you might think this is good news for climate change. But emissions reduction doesn’t actually reduce the cumulative warming effect of greenhouse gases, it just means we have slowed how quickly we’re emitting CO2. What matters for the warming effect of CO2 is how much is in the atmosphere at any given time, which is a function of how much fossil fuels we’ve burned. Right now, CO2 ppm is at about 414 parts per million.
If the rate of CO2 emissions is decreasing, how could it be that Coronavirus has exacerbated global warming this past February? The answer is that CO2 is not the only particle that can modulate global temperatures. It’s beyond established science (and basic physics and chemistry) that CO2 traps infrared radiation from the Earth and re-emits it back to the surface (as do other greenhouse gases like methane and water vapor). However, before ultraviolet radiation from the sun ever makes it to the Earth to be absorbed and re-emitted as infrared radiation that greenhouse gases can trap and re-emit, it has to pass through the atmosphere and can be reflected back into outer space by clouds, ice sheets, or salt flats. All of these have high albedo or reflectivity. Forests and water technically reflect some sunlight as well, but they are much darker and reflect a smaller percentage of incoming radiation per area.
The way COVID-19 has impacted climate change is by reducing the concentrations of aerosols in the atmosphere. Aerosols are small particles that are emitted when we burn fossil fuels , that reflect sunlight back into outer space. Unlike CO2, much of which stays in the atmosphere for hundreds to thousands of years, aerosols only stay in the atmosphere for about 4 weeks. Because we typically burn as much or a little more fossil fuels on day N+28 relative to day N (4 weeks after any starting point), the concentrations of aerosols in the atmosphere stays relatively constant.
However, the world’s largest CO2 emitter and center of industrial production, China, quarantined large parts of the country for the end of January and most of February. While this did cause a reduction in CO2 emissions for the month, it was also a sufficient enough reduction to reduce global aerosol concentrations in the atmosphere. This meant that less sunlight got reflected away from the Earth than usual, allowing greenhouse gases to trap more heat than they usually do, which warmed the Earth more than it would have been warmed had we continued emitting aerosols at the same rate globally in January and February.
Consequently, February was one of only 3 months in history where global average temperature was higher than 1.2°C above the 1951–1980 baseline, in a history that goes all the way back to 1880. This is particularly unusual given that the solar cycle was actually at a historically weak solar minimum, and that it isn’t an El Niño year. The other 2 most anomalously hot months in world history are February and March 2016, both of which were smack in the middle of a massive El Niño event. It’s also true that, since we have continued emitting CO2 non-stop since 2016, one would expect the warming effect from CO2 to continue apace. However, one wouldn’t expect that a year without an El Niño during a solar cycle minimum would be as anomalously hot as last month, unless you factor in reduced aerosols.
At this point, you might think this is good news. If aerosols effectively cool the Earth by reflecting sunlight, then maybe burning fossil fuels isn’t so bad after all. If burning fossil fuels also releases aerosols, then perhaps the effect balances out. Unfortunately, that’s not the case. Despite having a fairly consistent atmospheric concentration of aerosols for the past 50 years, global average temperatures have continued increasing. The last 5 years are the 5 hottest years globally on record, all about 1.1°C above pre-industrial temperatures. This means that atmospheric aerosol concentrations in the atmosphere for the last 5 years were ‘masking’ the actual amount of warming we should expect for the amount of CO2 emitted by burning fossil fuels, that has accumulated to 415 parts per million from a pre-industrial high of around 280 ppm in an 800,000 year ice core record. So just how much warming is masked by aerosols? A recent paper by Samset et. al (2018) notes “Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase.” In the last 5 years wehave witnessed an average of about 1.1°C above pre-industrial temps, but aerosols have masked an additional .5C-1.1°C of warming. With China’s industrial slowdown, quarantining, and social distancing, it’s no surprise that aerosol concentrations decreased alongside industrial production and that global average temperature was so anomalous last month.
While it’s true that Coronavirus exacerbated global warming via the reduction in aerosol concentrations last month, it’s not true that aerosol reductions wouldn’t have eventually happened without coronavirus. Because the impact of CO2 accumulation is greater than that of aerosols, and because we have to stop burning fossil fuels to stop planetary warming, the aerosol masking effect was bound to come off sooner or later. February 2020 is just a glimpse of climate change to come, as the 0.5°C-1.1°C of aerosol masking fades and global average temperature warms accordingly.
But in February, it was mostly just China that was quarantined and reduced industrial production/CO2 use/aerosols emitted. China’s quarantine and industrial slowdown lasted throughout February, meaning aerosol reductions from China will be observable throughout March due to the 4-week residence time. As Coronavirus spreads around the world, more and more countries are implementing social distancing, quarantines, and other measures that will reduce the amount of fossil fuels burned, and therefore the concentrations of aerosols in the atmosphere. This means that we can reasonably expect that March, April, and whatever other months quarantines are in effect will also be some of the most anomalously hot months in history, because the ‘masking’ of aerosols will be much reduced.
The warmth in these next few months will be but a prelude to the full scale warming we’d experience if all fossil fuel use stopped and all aerosols from burning fossil fuels were removed from the atmosphere, which would likely yield an additional 0.5°C-1.1°C warming. This effectively already puts us past the 1.5C target from the Paris Climate Accord, and possibly past the 2°C target as well. That eventual amount of warming will itself be modulated by how much CO2 we emit by continuing to burn fossil fuels. This is one of the main reasons why Joe Biden’s climate plan, with targets of net-zero by 2050, but no mentions of 2030 targets despite the IPCC’s statement that fossil CO2 emissions need to fall by 50% by 2030 for a 66% chance of limiting warming to 1.5C-i.e. during the potential reign of a Joe Biden presidency-is absolute trash. This is an essential reason why a Biden presidency has disastrous implications for climate change. If we don’t make scientifically necessary reductions in CO2 emissions by 2030, we will not only lock-in 1.5–2°C warming, but put ourselves on course for 2.5°C or 3°C warming, with even more possible warming down the road, if Nations don’t live up to the pledges they made in Paris in 2015.
What are the consequences of more anomalously warm months for weather this year? One place to keep an eye on is California, which just had its driest February in recorded history. If the global average of 1.2°C holds true in California, or if California experiences more regional warming than the global average, the lack of rainfall combined with what will almost certainly be record high temperature anomalies. These anomalies could make for prime conditions for fires in summer 2020, quite possibly starting earlier and lasting longer than previous fire seasons. Last year Australia was about 1.5°C warmer than its historical average in the lead-up to their catastrophic fires that burned 20% of their forests. Similarly, Europe was 3°C above the 1981–2010 average this past Winter, demonstrating how regional warming has exceeded global averages. The only upside here is that the lack of rainfall in California in February likely reduced the amount of shrub/bush growth, which will reduce fire kindling for larger trees. This does not mean that fires can’t start though, nor that once started they won’t be dangerous. There will likely be other consequences around the world in drought-stricken regions, but definitely keep an eye on the state. Californians could find themselves stuck between social distancing protocols and wildfires that force them out of their homes.
Another consequence is that the odds that 2020 is the warmest year on record just went way up. It was already a strong possibility coming into the year, despite the solar cycle minimum and lack of El Nino, just because we have continued emitting CO2 and other greenhouse gases more or less non-stop since 2016, at about 37GtCO2/year. Now that aerosol accumulation has lowered, one could make an even stronger case that 2020 will be the hottest year on record globally (barring a large volcanic eruption of VEI 6/7 or higher; these eject sulfate aerosols into the stratosphere that cool temperatures for ~1 year or so). On account of anomalous warmth engendered by aerosol reductions, it’s possible that in future years after we’ve recovered from coronavirus, we might see fossil fuel use and their associated aerosol emissions rebound. This could lead to what looks like short-term cooling relative to 2020, after adjusting for El Nino effects. Don’t let the climate deniers, skeptics, and trolls fool you: the coming years will undoubtedly be some of the hottest on record, and climate change will still be a bigger threat than ever. The planet won’t actually be cooling, there will just be more aerosols in the atmosphere, reflecting more sunlight and masking warming from CO2 and other GHG’s. So long as we continue burning fossil fuels, global average temperature will continue it’s upward trajectory, deepening the climate crisis.
