Disease and the climate crisis
Physicist Shaun Hendy worked on New Zealand’s Covid-19 response, providing models of disease spread. In this extract from Living with the Climate Crisis: Voices from Aotearoa, Hendy writes about applying mathematical models to both Covid and the climate c
Last February, as the Australian bushfires raged, I travelled to a trans-Tasman mathematics conference. The scientific communities in Australia and New Zealand are very close. Australia has long poached New Zealand’s top talent and, in return, Australia’s better-funded, better-equipped scientists share their networks with us.
The particular conference that I go to focuses on applying mathematics to practical problems. It attracts a mix of mathematicians, statisticians, and a few physicsoriented folk like me. It is typically hosted outside the main centres, usually in Australia, although it comes to New Zealand every five years or so.
The first I attended, more than 20 years ago, was held at a golf club in Mollymook, a sleepy seaside town three hours from Sydney.
In January 2020, fleeing holidaymakers would shelter there as the worst fires in Australia’s history took the neighbouring towns.
In 2007, the conference was held at the Victorian-era Carrington Hotel in the Blue Mountains. Sydney scientist Matthew England gave the most memorable talk that year, describing the mathematics behind climate science to a large audience squeezed into the ballroom.
He finished his talk by applying a mathematical model to the future of Australia’s climate. Eastern Australia was drying out, he said, because rising temperatures were pushing the big storm systems that cross the Indian Ocean away from Australia.
The continent is used to drought, but his work showed how the rain that eventually broke those droughts was going to come to its aid less often. Thirteen years later, in January 2020, I sent a message to England to let him know that at least one person had listened to him, even if his government had not.
From similar work, we know that some parts of the motu will dry here in New Zealand too, while other regions will get wetter.
In 2019, it was Nelson’s turn to host our maths conference. A workshop on the last day had to be curtailed as the largest bushfire since 1955 swept across the nearby Pigeon Valley. I left the smokeshrouded Tasman Bay on a bus, along with a dozen or so evacuees from Wakefield.
I could have jumped on a plane, but I had just taken a year off flying because of my concerns about climate change. Every time I flew in and out of Australia for my conference, I was responsible for putting about half a tonne of carbon dioxide into the air.
Ten years after seeing England’s talk, I decided to take some responsibility for this myself, spending 2018 on the ground. I travelled around New Zealand by bus, train and electric vehicle, documenting my year using a #NoFly hashtag on Twitter. I didn’t go overseas at all, and missed the maths conference on the Gold Coast that February.
But by the end of the year I had cut the emissions for which I would otherwise have been responsible by about 95 per cent.
Yet the planes still flew. The carbon dioxide levels continued to rise. Australia continued to dry. Individual decisions like mine can’t change this, not in the models, not in the real world.
By 2020 I was back to flying again, although I had pledged to reduce my emissions by putting to use what I had learned in 2018. When an invitation came through to speak in Wa¯ naka about my #NoFly year that coming April, I booked the train and ferry to get me through to Christchurch, and an electric vehicle to take me up into the Southern Alps. But this was a #NoFly trip I was not going to make.
In early March, after watching the news from China and then from Italy, I built my first mathematical model of how Covid-19 might spread in New Zealand. It told me something very important about the future. It told me that the next few years were going to be unlike anything we’d ever seen.
Instead of heading to Wa¯ naka, I took a very different journey. After building that first model, I got in touch with two other mathematicians, Mike Plank and Alex James from the University of Canterbury. We had worked together recently on Mycoplasma bovis, the disease in cattle that the Ministry for Primary Industries had set out to eliminate in 2018.
The three of us could see the challenge facing the country: a new disease with potentially serious health consequences, spreading through a population that had little or no immunity. Over the next month, we were joined by another dozen or so of our colleagues as we raced to build mathematical models to help the government snuff out New Zealand’s first Covid-19 outbreak.
Everyone’s lives changed that March. Our team had a very privileged view of the outbreak, both through our science and through the close relationship we developed with the government officials making decisions.
It was a new disease, but the data coming out of other countries helped us build a useful model of its spread. One of our biggest challenges was capturing how individuals would behave in response to both the threat from the virus and the restrictions the government had put in place to curb the spread.
There was good evidence from Wuhan in China, where the disease was first seen, that the Chinese government’s lockdown had been very effective in halting the outbreak. Would New Zealanders be prepared to confine themselves to their homes for a month to avoid spreading disease?
With cellphone footage of police drones patrolling empty Wuhan streets coming out of China, we had to wonder whether New Zealanders would tolerate these same restrictions. In the end Kiwis did, without the need for drones.
New Zealanders listened to their government, trusted what it was saying, and acted accordingly. We all watched as the number of new cases peaked in early April and then began to fall. In fact, case numbers fell in New Zealand just as quickly as they had in Wuhan.
Sometime in early May, the last active Sars-CoV2 virus failed to find a new host before it was finally clobbered by its host’s immune system. Covid-19 had been eliminated, and life in New Zealand went back to something like normal.
There was doubt at times. There were comparisons with Australia, which appeared to be eliminating the virus with fewer restrictions on its economy. But in July, Australia’s response unravelled when returning travellers in quarantine passed the virus on to hotel workers in Melbourne.
This sparked a second wave that soon spiralled out of control with the half-measures Victoria had in place.
As I write in August, the city of Melbourne is three weeks into what will be a lengthy lockdown. At the same time, Auckland is also facing a second outbreak, origin unknown, although most likely it slipped into the city in much the same way as it did in Melbourne.
New Zealanders chose to eliminate the virus in April. We should not forget that we trusted each other enough to act to preserve the lives of others, because we will have to do it again.
We all use models of one sort or another to help navigate the world. They may be mental models that are entangled with our lived experience, or they could be mathematical models that attempt to abstract these experiences into a tidy set of assumptions.
Yet our understanding of events, our expectations and actions, are all shaped by the scope and fidelity of these models. Whether they describe Covid-19 or how you think your friends might react to a dinner invitation next week, models also contain assumptions about ourselves, others, and the choices we have. They both constrain and shape our future.
It is clear that many of our longstanding models of the world are now obsolete. The rapid development and widespread deployment of a vaccine may allow us to emerge into a world that resembles the one that we remember, but even then we will find that the problems we faced in January 2020 will just have become more challenging.
As I write, California is again dealing with widespread wildfires spurred on by climate change. It is doing so without much of its reserve firefighting force – which relies on prisoners – because its jails have been emptied by Covid-19.
The virus attacks our society just as effectively as it does our lungs. Populist governments in the United States and the United Kingdom that have spent the last few years throwing experts under the bus found that they were being told what they wanted to hear, not what they needed to hear.
Disinformation and conspiracy theories filled in the blanks, proving to be just as contagious as the disease. Rather than uniting the global community in common cause,
Covid-19 has torn it apart, showing itself to be as adept at exploiting prejudice and distrust as Donald Trump is.
It is difficult to imagine a world right now that can come together to act on climate change. This brings me to the last and arguably most important type of model.
When Greta Thunberg pledged not to fly, it wasn’t because she thought her actions alone would halt the rise of carbon dioxide in the atmosphere. As with my decision, the plane that Thunberg chose not to board still took to the sky.
But individual actions can start to make a difference if others decide to follow your lead, and Thunberg’s example has inspired millions of young people around the world to demand change. Thunberg has realised her power as a role model.
This lesson for New Zealand is clear. Even though our own greenhouse gas emissions are an insignificant fraction of the global output, as a role model for other countries we do have the power to make change.
Talking to my Australian counterparts on Zoom in late April, I learned how important it had been to them that New Zealand had aimed for elimination of Covid-19.
Much as Australia’s government has dithered on climate change and in its response to last summer’s bushfire crisis, it initially proved a reluctant manager of the Covid-19 crisis. Without New Zealand’s example, my colleagues told me, Australia’s federal government would not have been jolted into action.
As we look towards a post-Covid19 future, there is every chance that we will emerge in better shape than many countries. We will also be armed with the knowledge that we can choose a better path if we trust each other.
After all, if not us, then who?