Local researchers explore weather’s role in COVID-19 spread

Maggie Sugg and Jennifer Runkle
CHECKING THE WEATHER: Maggie Sugg, left, and Jennifer Runkle are co-lead authors of the new study, which finds that humidity is significantly related to COVID-19 transmission. Photos courtesy of Runkle

It’s not the heat — it’s the humidity.

Thanks to a recently released study from a team of Western North Carolina scientists, the old chestnut about miserable summer weather may get a new interpretation for the COVID-19 era. The research, published in the journal Science of The Total Environment, suggests that humidity plays a greater role than does the temperature in the spread of the novel coronavirus.

Lead author Jennifer Runkle, an environmental epidemiologist with the Asheville-based North Carolina Institute for Climate Studies at N.C. State University, emphasizes that the results are preliminary due to the limited available data for a disease with no recorded U.S. cases until January. But she says the findings could nonetheless help inform health officials about what to expect from COVID-19 and manage the ongoing pandemic.

“There are so many factors at play: testing capacity, human behavior like handwashing, even access to care,” Runkle explains. “Weather is just another factor that we need to be incorporating in our infectious disease modeling. That’s what our pitch is to the scientific community.”

Coast to coast

The study analyzes weather conditions and coronavirus transmission in eight U.S. cities where viral spread was apparent early in the pandemic, such as Seattle and New York City. By comparing temperature, absolute humidity and sunlight for each city on a given day with the number of cases later reported, the researchers were able to find associations between the weather and COVID-19.

In three of the study cities — Chicago, New Orleans and Albany, Ga. — a day of low humidity was a significant predictor of new COVID-19 cases for the following two weeks. The risk of viral transmission was up to twice as high as normal in those cities when humidity fell within a specific low range. In contrast, neither temperature nor sunlight were strongly associated with coronavirus spread.

Study co-lead author Maggie Sugg, an assistant professor of medical geography at Appalachian State University in Boone, says that the humidity finding is consistent with patterns observed for other viral diseases such as the flu, which generally spreads most during dry winter conditions. “This is because the virus itself lives longer in low-humidity environments, and people’s respiratory systems are also more vulnerable to disease,” Sugg explains.

Runkle notes that the results also match up with early findings from China, where the coronavirus that causes COVID-19 (SARS-CoV-2) originated. She says her team’s work is among the first research to examine the ties between weather and COVID-19 transmission in the U.S., an important piece of the global puzzle for a disease that hasn’t been seen before.

While infection rates of coronaviruses and other respiratory viruses generally vary by season, Runkle says, that pattern won’t necessarily be the case for SARS-CoV-2, which is spreading into a world with no existing immunity. “What makes it complicated when looking at COVID-19 is that it’s a novel coronavirus,” she says. “These viruses typically don’t behave like their normal selves until they become established in the population, so scientists around the country and globe have been tackling different aspects of it.”

Storm a-brewin’

Sugg says the team plans to follow up on the research later in the year, when they will be able to draw on more months of data and better adjust their mathematical models for the effects of different social distancing measures on case counts. “Typically when we do these types of studies, we work with several years of data,” she points out. “We’re working with not even a full season.”

One important question to be resolved is whether higher humidity in the coming months will hinder COVID-19 transmission. The study’s authors say it’s too soon to draw that conclusion from the data, and they emphasize that limiting social interactions and promoting good public health practices like mask wearing will go much further toward slowing the spread of the virus than will changes in humidity.

But as North Carolina moves into the summer and fall, notes Sugg, a different aspect of the weather could become considerably more important than humidity. Hurricane season, which runs from June through November, could drive mass evacuations from the coast, bringing people from different parts of the state into closer contact. “Any time you have greater mobility, you’re going to have a greater introduction of a new disease,” she says.

Climate change, Sugg adds, is making extreme weather events such as hurricanes more dangerous, especially for the state’s residents of color and those living in poverty. According to the N.C. Climate Risk Assessment and Resilience Plan published in June by the state Department of Environmental Quality, “vulnerable communities will be most at risk of flooding occurrences due to hurricanes; with hurricanes happening in short succession, vulnerable communities will struggle to recover between hurricanes.”

“These are just compounding risks for populations that are already really vulnerable,” Sugg says. “COVID and climate change working together are going to amplify climate vulnerability for populations that are already struggling.”


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About Daniel Walton
Daniel Walton is the former news editor of Mountain Xpress. His work has also appeared in Sierra, The Guardian, and Civil Eats, among other national and regional publications. Follow me @DanielWWalton

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2 thoughts on “Local researchers explore weather’s role in COVID-19 spread

  1. C-Law

    Their research is a step in the right direction, minus the global warming hysteria. But at least they’re trying to use science…

    Let’s look at physics and mathematics folks.

    We’ll start with a single cough or sneeze.

    Everyone “knows” that if you cover a cough or sneeze, and you should do it into your sleeve instead of your hand, this will reduce the risk of someone else getting a virus you may have, right?


    It doesn’t. So says the science! This is a myth, just like it is a myth that you can wear a mask and reduce transmission.

    Wait — you say! YUCK; that’s obvious that it helps.

    Well, no.

    Here’s why.

    You sneeze and a huge loogie comes out your nose. Yuck! Nasty! Mucus, full of germs.

    It goes, if uncovered…… downward, on the floor.

    And harms nobody.

    It’s disgusting, but that’s it. You should still do it anyway because it’s disgusting not to, but you won’t stop a virus by doing so.

    What? If I stop the loogie then how come that doesn’t do anything?

    Because in addition to the loogie out come a bunch of large drops, each also laden with virus. Maybe a few hundred drops. Yuck! Thus covering or physically blocking those will reduce transmission to other people, right?

    Wrong again, statistically speaking.


    Because in that same forceful exhale are an enormous number of sub-micron water droplets that are formed as the saturated vapor in your lungs (100% RH in expired air) cools slightly as it travels up from the lungs to the trachea and out the mouth or nose and comes into contact with the ambient air (well, unless it’s over 98.6F in the air where you are anyway!)

    Remember your basic physics: As any saturated vapor cools it condenses. Any saturated vapor that cools by even a tiny amount will condense — that is, coalesce the individual vapor molecules into larger aggregates.

    Ordinary “tidal volume” (that is, the amount of air you move in a resting condition with each inhalation) is about 500ml. For a cough or sneeze it is much larger; the maximum volume of air that can be inspired in adult human lungs typically is in the range of 4-6L, or eight to 12 times the “at rest” breathing amount.

    When we breathe normally we produce very few or no large droplets. When we sing, play a wind instrument, yell, scream, cough or sneeze we produce a fairly large number of them.

    But none of this matters at all, statistically, because with each breath we produce millions of small condensate drops, and all of them which do not aggregate beyond the pore size of the medium in a mask will go right through said mask in either direction, most of those condensed molecules are produced between the lungs and either before or just after exit from the body due to condensation of the 100% RH water vapor and each of them, if you are infected with a virus, carries enough virons to infect another person.

    We’ve all “seen our breath” outside when it’s cold.

    That’s aggregation and condensation to a great enough degree that the aggregates are visible; there are thousands to millions more said aggregates that are too small to see and when it’s not cold outside none of them aggregate and condense sufficiently to be visible but they are all still there.

    This is why physics says that masks don’t work against viruses and exactly zero RCTs show that they do.

    ——Xiao, J., Shiu, E., Gao, H., Wong, J. Y., Fong, M. W., Ryu, S….Cowling, B. J. (2020). Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures. Emerging Infectious Diseases, 26(5), 967-975. https://dx.doi.org/10.3201/eid2605.190994.

    Never mind the repeated attempts to do so including in 1918, which did nothing to prevent the spread.

    Every single person that has ever “seen their breath” in the winter months knows, if they think about it for 30 seconds, why masks can’t work and don’t.

    They can’t work because blocking 1,000 pretty-large droplets sounds like it’s great except hundreds of thousands or even millions of condensed water vapor molecule clusters were also expelled, they have enough virons on them to infect another person and very nearly zero of those are caught by the mask in either direction. Worse, every one of those, unless condensed out or breathed in by someone else can remain in the air for hours since they are small enough to remain within the purview of brownian motion of air molecules; that is, they “float” so to speak because the energy of said molecular vibration and ordinary air currents, even indoors, is large compared to the pull of gravity toward the ground and thus they remain suspended in the air.

    The reason we have a flu season, as I’ve noted, is that the higher the absolute humidity, which tracks with temperature, the greater the odds that further agglomeration of these clusters of molecules will occur and once they get large enough gravity takes over as they are too heavy and they fall to the ground harmlessly.

    So your mask stopped the nasty-looking and smelling loogie which can infect exactly one person, unless you wipe it around on people, and 1,000 of the 5,000 modest-size droplets you expelled. This is why the mask gets nasty all over the inside (which, by the way, if left on for any length of time or reused will breed bacteria on the inside surface which you can inhale, and it will be very bad for you if you do so.)

    But it’s worthless in terms of protecting anyone else because at the same time you expelled the 5,001 droplets and stopped 1,001, which sounds like a decent hazard reduction, you also expelled hundreds of thousands or even several million micrometer-size drops, an effective none of which were stopped, all of which are infectious, and thus you actually caught materially less than 1% of the potential infections that can screw someone else!

    1% is not statistically significant. Filtering out 0.1-1% of the infectious events out at the source DOES NOTHING.

    The reason workers in a virus lab wear moon suits, go through triple sets of sealed doors with decontamination procedures before that suit is removed and breathe pressurized outside air while inside the lab is that these are facts and said virus — any virus — will go right through any “mask.”

    Oh, and don’t run any bull**** about “oh it’s only so-called droplets”; nonsense. There’s zero scientific evidence for that. I’m not the only one who’s noticed this — there’s a group of 239 scientists who signed a letter to the WHO.


    Not that they should have needed to; unless you’re a mouth-breathing idiot the early outbreak in an apartment building at Wuhan where there were no plumbing traps and thus gas (aerosol) from people’s scat was getting into other people’s apartments and the outbreak occurred across floors units where the individuals had no reasonable possibility of personal or droplet contact along with the choir group that took all manner of reasonable precaution yet got infected anyway all make clear that in fact the so-called “large drop only” theory is nonsense. It not only has no basis given the spread we have observed it has no basis in physics either.

    Further, as I’ve repeatedly noted, that Covid-19 isn’t following the laws of physics on the agglomeration that occurs with absolute humidity is very strong evidence (but not proof), again on the science, that it is not predominantly being transmitted through the air but rather by contact with contaminated surfaces and since we know intact virus is found in feces fecal contamination is very likely involved (exactly as it is with polio, which also didn’t follow the laws of physics on aerosol transmission because it wasn’t, in the main, transmitted that way.)

    We have known all of this since February, as I have documented.

    Physics is not a list of suggestions folks.

    It is a list of natural laws that nobody can violate.

    Masks are worthless when it comes to viral transmission and in addition they are obviously also worthless against transmission that occurs due to contact with contaminated surfaces or objects. That’s the physics of it and nobody has ever demonstrated an ability to modify the laws of physics.

    Grow up, deal with the fact that masks are worthless, learn to live with the fact that this virus will not be responsive to voodoo or magical incantations by governors, mayors or anyone else. Manual removal of potential contamination from your hands by washing with soap and water will help, but there is no guarantee because as we know this virus can spread through multiple vectors. The sooner those who are not significantly harmed by this virus get it and thus inhibit transmission the sooner it will be equivalent in its impact to seasonal flu or less.

    There is no other reality folks, and for reasons I’ve explained before a vaccine is unlikely to work either. Don’t get your hopes up for that as you are very likely to be disappointed.

    If this nation cannot face the realities of physics then we are back to the persecution of Galileo and the burning of “witches” at Salem. There is utterly no point in my, or any other thinking person’s continued engagement on any matter of economics, politics, public health or other policy if that is to be the regression of intelligence and logic among the people of this nation as what was America is doomed to collapse back into the Dark Ages.

  2. Science has also firmly established the fact of human-driven global climate change. See https://www.ipcc.ch/sr15/, Chapter 1, executive summary. “Human-induced warming reached approximately 1°C (likely between 0.8°C and 1.2°C) above pre-industrial levels in 2017, increasing at 0.2°C (likely between 0.1°C and 0.3°C) per decade (high confidence).”

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