10:30 AM | *Weather and its potential impact on the coronavirus*

The worldwide distribution of coronavirus cases with the equator shown (white line). Map courtesy Johns Hopkins CSSE, ESRI, FAO, NOAA.

Overview

In the ocean of bad news and pessimism that we have hearing in recent days regarding the coronavirus perhaps there is a small island of hope and optimism, and, believe it or not, it is related to the weather.  The weather has an important impact on all kinds of things ranging from, for example, the price of coffee to the sweetness of your wine to the distance that a baseball can travel on a summer night.  The weather also has an impact on the spreadability and survivability of respiratory viruses including influenza which tends to thrive as weather conditions become colder.  While there is much unknown about this particular new strain of coronavirus, there is hope that its impact will diminish as temperatures, humidity and hours of sunlight climb as the northern hemisphere transitions from late winter-to-spring-to-summer. 

Discussion

The latest map of the worldwide distribution of coronavirus cases shows a noticeable difference between the northern and southern hemispheres with many more cases north of the equator. While this could simply be related to the fact that nearly 90 percent of the human population lives in the northern hemisphere, it could also be a consequence of the difference in the weather as the southern hemisphere is in the latter stages of its summer season with generally higher temperatures and humidity levels when compared to the northern hemisphere. 

The number of confirmed coronavirus cases on a country-by-country basis (map courtesy CDC, NY Times).

In recent communications as reported by AccuWeather, Inc., Hong Kong University pathology professor John Nicholls supported the notion that the “environment is a crucial factor” when it comes to viruses.  While referencing the SARS outbreak from 2002 to 2003, Nicholls said he thinks similar weather factors may also shut down the spread of this new strain of the coronavirus. Specifically, Nicholls said that there are three things the virus does not like: 1) sunlight, 2) temperature and 3) humidity.  In terms of sunlight Nicholls said, "Sunlight will cut the virus' ability to grow in half so the half-life will be 2.5 minutes and in the dark it's about 13 to 20 [minutes]…Sunlight is really good at killing viruses."  In addition, he said that "The virus can remain intact at 4°C (39°F) or 10°C (50°F) ... but at 30°C (86°F) then you get inactivation." As far as humidity is concerned, Nicholls added this comment: “high humidity—the virus doesn’t like it either”. “I think it will burn itself out in about six months.” (Credit AccuWeather, Inc at accuweather.com)

In terms of humidity and the flu virus which is, of course, much more well known than COVID-19, the Centers for Disease Control and Prevention (CDC) did a study years ago and found that at humidity levels of 23 percent, 70 to 77 percent of the flu virus particles were still able to cause an infection an hour after the coughing simulation. But when humidity levels were raised to 43 percent, just 14 percent of the virus particles had the ability to infect. Most of the flu particles became inactive 15 minutes after they were released into the humid air. High humidity was just as detrimental to small flu particles as large ones. That's important because small flu particles tend to hang in the air for a longer time, while large particles fall to the ground. Researchers already knew that humidity levels affect flu transmission. One reason flu transmission is thought to be lower during the summer months is because of the high humidity. 

Summary

As the seasons change in coming months, the weather and climate will very likely be crucial in the ability of the coronavirus to spread and survive. There is some optimism that the role of weather will be a positive one with respect to the impact of the coronavirus across the northern hemisphere in coming months as temperatures, humidity, and hours of sunlight climb.  However, a word of caution is certainly in order here given the very limited experience that we have with this particular strain of coronavirus.  Furthermore, in the short-term, the rise of coronavirus cases may actually spike dramatically in the US as testing becomes much more prevalent.  Perhaps by later April or May we will have a better sense as to whether the change of season will indeed be a beneficial one with respect to the overall impact of the coronavirus. 

Final Comments

As far as the price of coffee is concerned, it is largely a response to the worldwide supply in a given year and that is largely a result of local weather conditions in such places as Brazil – the top producing country in the world.  The optimal temperature range of the coffee Arabica tree is 64-70°F, which is most consistently found in higher elevations of tropical countries such as in Brazil.

As far as wine is concerned, local weather and climate is crucial in its overall production process and ultimately, in its taste, with sunlight, temperatures and rainfall all being important parameters.  In general, grapevines tend to thrive best in climates with rainy winters and long warm summers which enables the grapevine to flower, fruit set and ripen.  However, wine is actually grown in a quite a wide range of climates. For this reason, wine regions are grouped in two major climate types: warm climate versus cool climate.  In the warm climate regions such as California, Argentina and southern Italy, grapes ripen more easily, leading to lower acidity, darker color, and higher sugar levels (i.e., sweetness).

Finally, the distance a baseball will travel on a summer night (or fall, spring nights as well) largely depends on the weather. A baseball will travel farthest in air that is the least dense which happens to be in hot and humid conditions.  Warm air is less dense than cold air and – perhaps contrary to what one might think - humid air is less dense than dry air.  As a result, the least dense air mass would be one that is hot and humid and it certainly helps a baseball travel farther if the wind is blowing out.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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