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Heatwaves, mozzies, dengue and droughts - how climate change threatens our health

The most obvious health impacts due to climate change are from extreme weather conditions. AAP

Climate change is affecting rates of illness, disease, injury and death in Australia and elsewhere, and the risk it poses will only escalate in future.

As Australians argue about carbon pricing and its impact on future electricity bills, we continue to miss the much more serious threat posed by climate change. To change the world’s climate as we are now doing is to endanger the natural environment’s life-support processes upon which our health depends.

Climate change endangers foreshores, physical infrastructure, export crop yields, the Snowy Mountains corroboree frog and Great Barrier Reef. But the risks to property, bank balance, consumer satisfaction and recreational amenity pale by comparison with risks to food yields, water supply, stability of infectious disease patterns, social stability and protection from weather disasters.

Implications of temperature increases

The most obvious health impacts due to climate change are from extreme weather events. Heatwaves, floods, bushfires and cyclones are killers – and they leave a trail of infectious disease risks, mental depression and community destruction.

As the world warms and the climate becomes more variable, periods of extreme heat will become more frequent. The annual frequency of very hot days has increased in Australia since the 1960s. The severe heatwave in south-eastern Australia in early 2009 underscored the risks to health.

Melbourne experienced three consecutive days of temperatures at or above 43 degrees Celsius in late January 2009. This caused an estimated 62% increase in the death rate - 980 deaths, versus 606 that would have been expected during that episode if usual seasonal rates had applied.

There were also increases in non-fatal heart attacks, strokes and severe heat stress. Computerised modelling by our Australian National University team of how future warming will affect death rates in Australian cities during heatwaves predicts a steady rise in risk during this century, reaching several thousand extra deaths per summer.

Climate change will also increase exposure to heat extremes in many workplaces, especially outdoors workers and those in uncooled premises. Impaired work capacity and adverse health effects, and hence reduced productivity, will result.

Heatwaves, here and elsewhere, have been becoming more severe, consistent with predictions that climate change will cause greater climatic variability. This year’s extreme floods and cyclone, in Queensland and Victoria, were probably amplified by the warmer ocean surface-water.

Meanwhile, farm yields have been declining in parts of south-east and south-west Australia as regional drying emerges. Brief extremes of climate come and go, but the anticipated longer-term drying trends pose great risks to community morale, livelihoods, mental health and nutrition, especially in lower-income families. They will also contribute to a growth in illnesses stemming from exposures to heat and dust.

Infectious diseases

Changes in temperature, rainfall and humidity will influence many of the worlds’ infectious diseases: bacterial growth, viral multiplication, and mosquito proliferation are all sensitive to climatic conditions.

Regional climate trends will also affect various infectious diseases in Australia. Our research team’s estimation of future health risks due to climate change for the national Garnaut Review (2008) forecasts increases in the geographic range of mosquito-borne dengue fever and in the rates of infectious gastroenteritis (diarrhoeal disease).

By 2050, under medium-to-high levels of global greenhouse emissions, the area of potential dengue transmission would extend southward on both east and west coasts – where large and growing populations live. Ross River virus infections, Australia’s most numerous mosquito-borne viral disease, and several other mosquito-borne viral diseases may also be affected.

Recent studies have reported increases in various infectious diseases in association with localised warming trends: malaria in eastern African highlands, water snail-borne schistosomiasis in southern China, tick-borne encephalitis in Scandinavia, among others.

The health impacts of climate change will vary in range and severity around the world. The floods in Pakistan last August displaced 18 million people and killed several thousand; whole villages were destroyed. The Brazil floods in January this year killed 600 people versus 30 in wealthier Queensland. The risks of post-disaster infectious disease epidemics and food shortages are much greater in low-income populations.

Secondary consequences

There will be many other adverse health effects of climate change, in this country and elsewhere. These include situations where population displacement - due to water shortage, crop failures, sea-level rise - causes crowding in slums and temporary settlements, amplifying risks of respiratory, gastrointestinal and other infections.

Competition for dwindling food and water resources may cause open conflict. Many governments are paying increasing, though discreet, attention to the likelihood of social and political instability due to these human impacts of climate change. The Asian Development Bank has, this year, forecast that climate change will cause substantial increases in flows of displaced people in the Asia and Pacific regions.

Climate change will affect much of the world’s food-producing capacity, mostly adversely. However, some gains will also occur, in higher-latitude regions – at least in the early stage of climate change. Food shortages endanger human nutrition, child development, and survival.

Yields have reportedly begun to decline in parts of under-fed western and southern Africa, in association with recent declines in seasonal rainfall. Reductions in regional rainfall also compromise sanitation, hygiene and drinking-water safety.

Although risks to human health are, at last, being discussed, they are still often treated as regrettable ‘collateral damage’. That misses the point. The real ‘bottom line’ risk posed by climate change is to health and survival – and hence, also, to social and geopolitical stability.

Much of the climate change debate is being conducted in local or national terms. The problem, of course, is of global scale, with a long time horizon. If climate change continues on its current course, then people from all regions of the world will face great and increasing risk to wellbeing, health and survival.

What’s more, there will be increasing tensions, perhaps conflict, if the flows of environmental refugees increase. It is crucial that we understand that the threats to human health and survival are the most serious eventual risk that we face from global climate change.

Economies can be shored up, infrastructure can be rebuilt, but to allow continuing damage to life-support systems that are difficult or impossible to restore is sheer folly.

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