Climate change and health - The threat

Human-driven climate change poses a great threat, unprecedented in type and scale, to well-being, health and perhaps even to human survival, according to academics in Canberra who contributed to the health chapter of the Impacts report of the Intergovernmental Panel on Climate Change, or IPCC.

The international body for assessing the science related to climate change released a contribution to its Fifth Assessment Report, Climate Change 2014: Impacts, adaptation and vulnerability in Yokohama last Monday.

Writing in The Conversation, Emeritus Professor Anthony McMichael of the Australian National University and professors Colin Butler and Helen Louise Berry of the University of Canberra say the consequences of human-driven global climate change as this century progresses will be wide-ranging - from declines in regional food yields, freshwater shortages and damage to settlements from extreme weather events to the loss of habitable, especially coastal, land.

The list goes on: changes in infectious disease patterns and the mental health consequences of trauma, loss, displacement and resource conflict. The human health chapter in the second volume of the IPCC's report concludes that the scientific evidence of many current and future risks to health has strengthened in recent years.

Exacerbating pre-existing health problems

During at least the next few decades, the chapter states, "climate change will mainly affect human health, disease and death by exacerbating pre-existing health problems.

"The largest impacts will occur in poorer and vulnerable populations and communities where climate-sensitive illnesses such as under-nutrition and diarrhoeal disease are already high - thus widening further the world's health disparities."

The three says that currently, the worldwide burden of ill health clearly attributable to climate change is relatively small compared with other major blights on health such as from poverty, poor sanitation and exposure to tobacco.

But rising temperatures and changing rainfall patterns have increased heat-related illnesses and deaths, altered the distribution of some water-borne infectious diseases and the insect transmitters of some diseases such as malaria, and have reduced food yields in some already food-insecure populations.

Less certainly, extreme weather events, influenced in part by climate change, are likely to have contributed to the recent rise in global food prices.

They note that the chapter on health discusses three impact categories in particular: under-nutrition and impaired child development due to reduced food yields; injuries, hospitalisations and deaths due to intense heat waves, fires and other weather disasters; and shifts in the seasonal duration and spatial range of infectious diseases.

Looking ahead to 2100, for which some modelled scenarios now project an average global warming of 4 degrees Celsius, the report foresees that in such conditions people will not be able to cope, let alone work productively, in the hottest parts of the year.

"And that's assuming social and economic institutions and processes are still intact. Some regions may become uninhabitable. Impacts on mental health could be similarly extreme, further limiting our collective capacity to cope, recover and adapt."

Harm will greatly outweigh benefits

While acknowledging that the effect of climate change on health will vary around the globe, the academics say the health chapter concludes from the evidence that harmful impacts will greatly outweigh any benefits.

These will also undermine hard-won gains achieved through social development programmes, impeding progress in the world's poorest countries.

"The chapter offers some cheer in stressing that the near-term and relatively localised health 'co-benefits' from reducing greenhouse emissions could be very large. Reducing emissions of methane and black carbon, for example, may avoid more than two million deaths per year," they say.

"In economic terms, the IPCC chapter judges that the health co-benefits from reducing emissions would be extremely cost-beneficial. They would, for example, be 1,000 times greater than the economic co-benefits to agricultural yields from reduced exposures to short-lived, crop-damaging, airborne climate pollutants.

"Overall, the up-front costs of reducing emissions could be substantially offset by early and extremely large health and other benefits."

In their own conclusion, the three say that none of this matters if human well-being, health and survival mean little: "In that case we can emit all we like, then suffer, dwindle or even die out as a species and leave this planet to recover and thrive without us. One way or another we will then emit less.

"We have a closing window of time in which to do something about global climate change."