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.
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.
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.
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.
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.