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What will a four-degree climate rise mean for world health?

Public health experts have warned for more than two decades that climate change will harm human health. Initially their attention focused on “primary” health effects (e.g heat waves, bush fires and flooding…

It’s time to begin preparing for the “tertiary effects”. AAP

Public health experts have warned for more than two decades that climate change will harm human health.

Initially their attention focused on “primary” health effects (e.g heat waves, bush fires and flooding) and “secondary” effects (e.g disease transmission) of climate change.

It seemed plausible that the future would see more severe heat waves and storms, bringing not only discomfort but also dehydration and death from heat stress. Injuries from floods and other natural disasters were also forecast to increase.

Today, some twenty years later, these primary and secondary health impacts of climate change are very much a reality.

And if temperatures rise more than 2 degrees Celsius, we are likely to see more serious “tertiary” effects, such as worsening global food shortages.

Early concerns

From the late 1980s, a few researchers warned that warmer temperatures and altered rainfall patterns would change the distribution of disease-transmitting insects (“vectors”), such as mosquitoes and ticks.

In the late 1990s, when there was still substantial scientific debate about the reality of climate change, scientists searched for evidence of malaria occurring at higher altitudes, particularly in East Africa, where large populations, including those in cities such as Nairobi and Harare, were (and still are) largely free of this disease.

This quest was partly motivated by a wish to convince sceptical health professionals that alterations in atmospheric chemistry would have real world effects.

It was thought that increased malaria might be a sensitive signal to show not only that climate change was real but that it had demonstrable health effects.

There was also concern that the effect of climate change – heat waves, altered rainfall and substantial sea level rise – might reduce agricultural productivity and restrict access to food.

Growing evidence

Early in the 2000s, parts of Europe experienced a severe heatwave, with lethal consequences for as many as 70,000 people, especially elderly people living in Paris, a city with little physical or social preparedness for heatwaves.

Several more severe heatwaves followed until 2010, including in India, Russia and here in Australia.

In fact, in the Victorian heatwave of 2009, the physical health of more people may have been harmed by heat than by fire, though the fires wrought immense emotional and psychological costs on its survivors.

As the decade passed, the incidence of freakish weather seemed to increase around the world.

Recently, high quality evidence has been published showing that downpours are intensifying, with flow-on effects not only for flash-flooding but for infrastructure and food security. The calamitous Pakistani flood in 2010 may be a portent of the future.

Droughts can also affect health, and there are projections and some evidence that the rate and severity of droughts is changing.

Overseas, there is still debate about malaria, but strong evidence suggests Lyme disease, a tick-borne illness, is spreading north into Canada. This supports the general principle that climate change can indeed influence the spread of infectious diseases.

Australia is relatively free of severe vector-borne diseases, though Murray Valley encephalitis, Ross River fever and dengue fever are exceptions; the distribution of these may well change with warming and rainfall change.

Looming disasters

Unfortunately, the “tertiary” health consequences of severe climate change are an elephant in the room.

These tertiary effects extend beyond localised crop failure to much more serious consequences: those flowing from impaired global food security. We are at the early stages of severe climate change and there is increasing evidence that, without significant intervention, this will accelerate.

For example, food prices reached a record high worldwide in December, 2010. They remain very high. Though rising oil prices are a factor, climate change may be even more important.

Last month, flooding in the Mississippi harmed the US corn crop, and coming into summer there are severe droughts in Europe and parts of China. Grain prices are likely to remain high all this year – and beyond.

If we could limit average temperature-rise to two degrees, then the worst of the tertiary consequences might be avoidable, or at least manageable – especially as this would mean slowing the rate of environmental change, which would create more opportunity for preparation and adaptation.

But there is growing consensus that a four-degree world (i.e. a climate four degrees hotter than at present) will now be our fate.

In this world, the sea level will rise at faster rates, driving millions of people from their low-lying homes to refugee camps in the hills. Food security will decline even more.

The combination of forced migration and hunger could provoke martial conflict and further impede the course of development.

Until recently, few public health experts have warned of these tertiary effects. Perhaps it seemed premature, or perhaps such warnings were self-censored for fear of inducing pessimism and paralysis.

But the alert observer has a duty to shout “fire” on seeing smoke in a theatre. A four-degree world will likely prove catastrophic for our health. We must avoid it at all costs.

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  1. James Szabadics


    The real issue is population because despite our warming world extreme weather events show no trends. There is no trend to more frequent or more powerful extreme weather events over time if you look at the data. There is better global communication and more accessibility to news so we all hear about it when an event happens. Floods and droughts happen cyclically in various regions, this isnt new and is a regional phenomenon.

    Take a look at global rainfall timeseries here:

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  2. Byron Smith
    Byron Smith is a Friend of The Conversation.

    PhD candidate in Christian Ethics at University of Edinburgh

    Thanks for this piece on a very important topic. It would be very helpful to have had more links to the growing number of specific studies that attempt to project the likely effects of a four degrees rise, not least for food security. I agree with Prof Butler that this is the real elephant in the room, since it has the capacity to reach geopolitical tipping points at a rate even faster than our climate is changing. What kind of tipping points? Well, numerous commentators have called food price spikes (partially the result of various extreme weather events around the world) the spark that triggered the recent and ongoing events of the Arab spring. Climate change is a risk multiplier, making many of our other systemic and apparently intractable problems worse.

  3. Colin Butler

    Professor at University of Canberra


    Thanks. As you'll appreciate word limits and the number of links are very restricted for this kind of medium. I think the number of studies that try to project a 4 degree world is limited, especially conceptually, as you quickly run into all kinds of taboos. In March 2012 I attended a meeting run by the UK govt. on resource scarcity and security and a speaker there described Bangladesh as the biggest human cage in the world - as you may know, there is a fence around most of its border with…

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    1. Byron Smith
      Byron Smith is a Friend of The Conversation.

      PhD candidate in Christian Ethics at University of Edinburgh

      In reply to Colin Butler

      Thanks for sharing your experience in this area. How can we make realistic policy decisions when the implications of our present trajectory are so horrendous as to require self-censorship by the relevant researchers?

    2. Colin David Butler


      In reply to Byron Smith


      Alas, self-censorship is a necessary art to succeed in science, at least in my painfully gained experience.For example, if you very carefully read our chapter in the Millennium Ecosystem Assessment conceptual framework (Butler C.D., Chambers R., Chopra K., Dasgupta P., Duraiappah A., Kumar P., McMichael A.J. and Niu W-Y. (2003): Ecosystems and human well-being. In: Ecosystems and Human Well-being, (Editor: Millennium Ecosystem Assessment); Island Press, Washington DC) you will find a critique…

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    3. Byron Smith
      Byron Smith is a Friend of The Conversation.

      PhD candidate in Christian Ethics at University of Edinburgh

      In reply to Colin David Butler

      Yes, I'm somewhat familiar with the kinds of discourse conventions to which you refer and the ways in which they represent (and police) the limits of what is thinkable. Transgressing what is thinkable leads into nonsense, madness or profundity. This is the job of poets, philosophers and prophets - and it comes with serious risks to one's credibility. Whether contemporary risk-averse academics can belong to one of these groups remains an open question.

  4. Colin Butler

    Professor at University of Canberra


    I agree that population is very important and under-recognised, though for me, as someone who likes to think systemically, there is no single cause or main issue. Indeed, my first ever full article in the scientific literature was called "Overpopulation, overconsumption and economcis" (Lancet, 1994) - and I think each of those three key words is very important, but other aspects come to mind, eg "values", "hubris" and the fact that we are an animal species, not truly "sapiens", not yet, anyway.

    I have a piece in press in the Conversation on this topic ("human carrying capacity"). Hope you get to read it, and also some of the other 20-30 articles I have written on this topic.