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Covid-19 is a perfect example of an oft-noted environmental principal: Everything is connected. All life is related through biological evolution. The planet shapes life through geological change while life shapes the planet through biochemical processes and human technology. And for that matter, Earth intertwines profoundly with the sun and the fate of the universe.

Standing at the intersection of life and non-life, viruses are biological structures that reproduce only inside the cells of living hosts. According to the Centers for Disease Control, coronaviruses have evolutionary ancestors stemming from thousands and perhaps millions of years ago. They typically reside long-term in birds and a few mammals, including bats and pigs. As these animals diversified over eons, coronaviruses evolved with them. Bats are especially suitable "reservoir" hosts because, as the only mammal that flies, they endure severe biological stress and have thus evolved strong immune systems, allowing the virus to reside in bats without killing them.

The name "coronavirus" comes from the spiky crown-like proteins covering their surface. These spikes are long, slender, much-folded protein molecules whose structure has evolved to grab and penetrate the outer walls of animal cells. Each spike includes a hook that grips onto host cells, and a cleaver that acts like a can opener to allow the virus to crack and enter cells. Once inside, the virus co-opts the cell's DNA and forces it to produce thousands of identical copies of the virus. Being made mostly of DNA, viruses evolve quickly in response to changing circumstances, such as new hosts.

Coronaviruses comprise a broad family of flu-like organisms that came to human attention during the 2003 SARS epidemic in China and the 2012 Middle East Respiratory Syndrome (MERS) originating in Saudi Arabia. There are several other relatively harmless coronaviruses that cause about one-third of all childhood colds.

According to a study appearing in the journal Nature Medicine, the new virus probably originated in bats and was transferred either directly to humans or indirectly via an intermediate host, such as illegally trafficked mammals called pangolins. The transfer probably occurred at a meat market in Wuhan, China, and demonstrates the danger of "zoonotic diseases," transmitted from other animals to humans. According to the World Health Organization, evidence suggests camels are reservoirs for the MERS coronavirus, and bats (with civets as an intermediate host) are reservoirs for the SARS coronavirus.

We should have seen this coming. Pulitzer-prize-winning science journalist Laurie Garrett's 1994 book The Coming Plague predicted scenarios similar to covid-19, citing zoonotic precedents such as Ebola and swine flu. According to the CDC, Ebola originates in bats or non-human primates (apes or monkeys), while swine flu (which includes H1N1) originates in North American pigs. These, along with SARS in 2003 and MERS in 2012, were four wake-up calls.

Let us now, belatedly, prepare for future outbreaks. Pandemics have come and gone over many millennia, but today's overpopulated planet, megacities of 38 million and counting, pervasive air travel and human encroachment on natural habitat provide a perfect setting for novel infectious diseases.

To some extent, and in common with global warming, ozone depletion, pollution and nuclear weapons, covid-19 is a product of the improper use of modern technology. The antidote is education and heightened respect for the downsides of modern technology.

But everything is connected, and believe it or not there's a welcome connection between covid-19 and an even more serious threat, namely global warming: Covid-19 depresses the economy, which depresses economic activity, which decreases anthropogenic greenhouse gas emissions.

The Group of Twenty trading nations estimates the disease has already cost the world economy $1 trillion in production. It could easily cost $2 trillion in all, representing a 2.5 percent reduction in gross world product. Anthropogenic emissions are caused by industrialization and are roughly proportional, in any given year, to that year's GWP. So it's reasonable to expect the slowdown to reduce anthropogenic emissions by 2.5 percentage points below what emissions would have been without covid-19. 2019 emissions totaled 36.8 billion tons of carbon dioxide, an increase of 0.6 percent from 2018. If we assume that, without covid-19, another 0.6 percent increase would have occurred in 2020, then covid-19 turns that increase into a 1.9 percent reduction in emissions. Thus, this disease means we will turn a significant corner, reducing emissions by nearly 2 percent or 0.7 billion tons.

Nature is forcing us to slow down. It's a small step toward getting emissions where they need to be, namely zero, but it's refreshing.

Commentary on 03/31/2020

Print Headline: A welcome connection

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