Saving our Skins: Chapter 22. Going Viral
Saving our Skins: Chapter 22. Going Viral
Atmospheric Reflections from a Lauder Stargazer
The title takes new meaning. A timely digression into how Covid-19 fits into the story.
It’s April 2020 and we’re in the grips of the deadliest pandemic since the 1918 Spanish ‘flu. With the exception of the climate change crisis, the Covid-19 pandemic is arguably the biggest global crisis in my cosseted lifetime. So I can’t finish without digressing to that still-evolving story, especially since I’ve just heard that my old colleague Sir John (JTH) Houghton - a giant of atmospheric research and climate change – sadly just succumbed to the virus on April 15 at age 88. He was just one of the 778 UK victims (and 138,475 worldwide) that day, but my closest brush with it so far. And a huge loss to atmospheric research.
Although I’m very aware of his work - a well-thumbed copy of his “The Physics of Atmospheres” sits on my desk bookshelf - I didn’t know him well personally. Of course I’d met him a few times when I was at Oxford (see chapter 7) and I also hosted him at Lauder when he visited twenty years ago. In trying to remember what year that was, I came across a couple of his emails (below), which include a bit of history: like faxes, overhead transparencies, media demands on his time, and the obvious absence of mobile phones (coverage is still a bit patchy at Lauder today).
The first one’s addressed to Jim Salinger, who worked at NIWA’s Auckland office until he was sacked in 2009 for talking to the media without the permission of management. He’d had his own share of controversy before, with climate deniers trying to pick holes in his famous 7-station record (and updated 11-station record) showing temperature increases in New Zealand over the last hundred years matched predictions. He’d also worked with John on the IPCC Assessment.
Date: 1/21/2000 14:21
From: Sir John Houghton
To: Jim Salinger
cc: Richard McKenzie
Dear Jim
Thank you for your note. Re lecture, I will use overhead transparencies. I can also bring slides if they work better in the particular venue. Please let me know which are better. I do not have a complete text. But I will ask Paul van der Linden to send you an article on Global Warming and Climate Change which I have recently written which is a reasonable summary of my main points.
In Queenstown I will be staying at ….. I am willing to be contacted there by the media but please note that I leave on the Monday on a plane that flies out at 1220….. My outward travel remains the same but I’m coming via Tokyo where I am giving a lecture … I arrive in Queenstown on Thursday the 10th in the afternoon. I would be grateful for advice as to what are the things I should really do in that part of New Zealand. I would love to explore some of the mountains and go on a decent walk/climb and also see some of the spectacular scenery I expect to hire a car. I am also copying this to Richard McKenzie as I am hoping to get out to see his lab while I am there.
With best wishes, John
Sir John Houghton IPCC WGI Co-chair Hadley Centre Met Office London
This second message was shortly before his visit. He was obviously combining business with pleasure.
Message Date: 2/3/2000 18:54
From: Sir John Houghton
To: Richard McKenzie
Dear Richard
Very many thanks for your fax and the enquiries you have made for me. I am keen to do the Routeburn walk but will take your advice and book when I arrive in Queenstown after checking the weather and my state of jetlag! Your plan for a visit to Alexandra and Lauder is good -thank you. Please book me into a motel in Alexandra for the Sunday night. I will meet you at the Routeburn Office in Queenstown (where I will have left my luggage) where I will wait after returning on Sunday. On Thursday night I am staying at …… Arthurs Point. I will try and phone you that evening but I may well be in bed rather early! If I am not on the walk I will get in touch later on. I look forward to seeing you again and to seeing your lab -sorry it is such a rushed visit, but I expect to be enthused to come back sometime
Best wishes, John
Sir John Houghton IPCC WGI Co-chair Hadley Centre Met Office London.
Houghton must have decided against hiring a car, because I well remember driving him from Lauder to Dunedin’s Momona Airport via the Middlemarch route after his visit. The route was a bit longer than I’d remembered and our late departure from Lauder made for a hair-raising drive. But we made it, with minutes to spare. Of course I had to tell him as we passed the “Welcome to Dunedin” signs in the middle of nowhere that Dunedin city was one of the largest in the world in area. Though its population was only 120 thousand (about the same as Oxford), in area it surpassed London.
In New Zealand as I write this after learning of JTH’s death, we’re in our 4th week of phase 4 lockdown against infection from Covid-19. That means no contact with people outside your bubble. We’re told to stay at home. And we’re told not to engage in outdoor activities like golf. But is that the best advice?
Covid-19 is part of the story because its genetic material is subject to breakdown by UV radiation. So, just like the vitamin-D story I discussed in chapter 16, there are potential benefits from outdoor UV exposure. I wrote a post about this last week,[1] but because this isn’t in the peer-reviewed literature, I’ll discuss it in some detail here.
One thing that makes the outdoors different from indoors is its presence of UV-B radiation from the Sun. Those wavelengths aren’t transmitted indoors by glass windows.
While it’s said that Covid-19 can survive on surfaces for several days, that may not always be the case for outdoor surfaces exposed to UV-B in sunlight. Viruses contain RNA or DNA, which are susceptible to damage by UV-B radiation. If they’re anything like other micro-organisms, that sensitivity will be extremely high. In a paper I co-authored with Sasha Madronich and Lars Olof Björn, we found that the lifetime of much microbial life investigated was only a few minutes in sunlight.
Is it the same for the Covid-19 virus? To help answer the question, I started by assuming the wavelength dependence for damage by UV is similar to that for DNA, for which the wavelength dependence is rather steeper than that for skin damage (i.e., erythema).
I also assumed that the dose of UV-C (from a mercury lamp emitting mainly at 254 nm) that’s required to inactivate 90 percent of the virus population is about 20 J/m2, at the low end of the range suggested by previous workers.
Then I calculated the strength of peak UV, weighted by those two functions, for the first day of each month at Lauder. For sunburning UV there’s a huge seasonal variation, with the summer peak being ten times more than winter. The seasonal range is even larger for DNA damage, with winter values being only 5 percent of those in summer. Similar seasonal variations would be seen at unpolluted mid-latitude sites in the northern hemisphere.
From those, I calculated how long it would take to reach the target of 20 J/m2 required to inactivate 90 percent of the virus from that midday sunlight. My calculations showed that inactivation of the virus can occur in less than an hour in summer, but outside the summer period, there is little chance of inactivation (so the virus will survive without damage by UV). I assumed the UV remains constant throughout that period, whereas in the real world the UVI decreases sharply outside the noon period, so the inactivation times required will continue to increase rapidly. Therefore, at this location in Southern New Zealand, for the entire period between 1 April and 1 November there is insufficient UV throughout the entire day to inactivate 90 percent of the virus.
That’s no doubt an important factor leading to viral infections being so much more serious in winter. In northern New Zealand the winter UV is much higher than in the south, so useful inactivation can occur over a longer summer season. That’s also consistent with viral infections being worse in the south of the country (further from the equator).
Unfortunately, there are huge uncertainties in these calculated inactivation times for the virus. The sensitivity to UV damage has been reported for several viral strains and the range between them varies over a couple of orders of magnitude. Nor are we confident about the wavelength dependence of damage. Some say it will be similar to that for DNA, while others say that it’s not nearly as steep. If the latter is true, then longer UV wavelengths which are much more intense come into play, and the time to inactivate the virus would be much shorter. For example, assuming an action spectrum for RNA damage that was published in 2019, the inactivation times calculated above reduce by more than a factor of two.
Further light was shed on the issue at an infamous White House press briefing on April 23, 2020, though we weren’t so sure about it at the time. Press releases aren’t the most reliable source of scientific results, especially when people like Donald Trump are involved. The peer-reviewed literature is much more reliable and I was sceptical, especially since the same briefing achieved notoriety when Trump suggested that we could ingest bleach to protect against the ravages of Covid-19. But the result of interest to me from the briefing was a report from The Homeland Security Lab that showed much shorter inactivation times than I’d calculated. A slide from the briefing is reproduced below. Their reported half-life of just 2 minutes corresponds to a 90 percent inactivation time of about 7 minutes, less than a tenth of the time I’d calculated.
My initial scepticism turned out to be unfounded, because their results were confirmed in the peer-reviewed literature a few weeks later. Their measurement must have been potentially hazardous, as they were dealing with live population samples of the deadly virus. They had measured its survival directly, after exposure to known doses of UV from a solar simulator. I corresponded with the lead author, who mentioned that there were potential problems with the measurement. A follow-up paper by the same group seems to have put that to rest, but I’d be more confident if the experiment were repeated using real sunlight instead of the solar simulator.
If their results are correct, then either the UV-C inactivation dose for Covid-19 must be less than 1 Jm-2, (much less than for other SARS viruses), or the action spectrum for damage must be less steep than the ones I’d used (or both).
More work is needed to find why there is such a discrepancy between theory and measurement., but it appears that the virus is inactivated in sunlight much more quickly than other similar viral strains. Consequently, outdoor surfaces exposed to sunlight will have significantly less Covid-19 contamination than indoor surfaces.
Some outdoor exposure to UV in sunlight may also be useful for personal virus protection, but strict personal hygiene is probably more effective in most cases as that’s not limited to body surfaces that are exposed to sunlight. Also, even with a 90 percent inactivation time as short as 7 minutes, more than 1 percent will still survive after an exposure period long enough to cause skin damage. So any strategy to lower your personal risk of infection from the virus by exposure to sunlight would come at a cost. But, given that your vitamin D will also increase, some UV exposure for short periods when the sun’s high in the sky with its attendant risk of skin damage may be a price worth paying.
Just make sure you avoid sunburn because that’s a risk factor for skin cancer. About 500 New Zealanders will die from skin cancer this year (a few more than the number killed on our roads). At the time of writing it remains to be seen if Covid-19 is better or worse. It’s certainly worse from a time perspective: mortality from it occurs within days or weeks of infection, compared with decades after UV exposure for skin cancer. At the time of writing only 22 Covid-19 deaths have been recorded in New Zealand. That’s largely due to our effective moat and stringent lockdown rules. But those rules are increasingly being flouted.
I know I won’t be hiding from the sun anyway, at least until a vaccine for Covid-19 becomes available. As you read this at some time in the future, the immediacy of this particular threat may have already gone (I certainly hope so) but consider this a snapshot of a time of incredible self-doubt in world history. It surely won’t be the last.
And, as we lock down against the coronavirus plague it’s already apparent that, quite apart from the tragic human cost, there are potential benefits as well through improved air quality as factories close and travel is restricted. But the long-term effects there are yet to play out fully.
However that ends, the problem of climate change will inexorably continue. It’s so frustrating. While the world shovels money into the short-term gains from fixing Covid-19, we continue to sit on our hands when addressing the much more serious climate change issue that will plague our children and their children’s children. If even a fraction of the trillions of dollars spent on combating Covid-19 had been spent on transitioning us away from our dependence on fossil fuels, we’d already be well down the path to its solution.
Depressingly, the world will have similar Covid-19 fire-fighting expenses all over again when the next viral pandemic arrives.
That was a digression. It’s back to the main issues in the concluding chapter of Saving our Skins. If you want to read the whole book, please click below start at the beginning