Since 1988, the United Nations Intergovernmental Panel on Climate Change (IPCC) has reviewed scientific research, and provided governments with summaries and advice on climate problems. In its most recent report, the IPCC concludes that the average temperature of the earth’s surface has risen by 0.6 °C since the late 1800s. It is expected to increase by another 1.4–5.8 °C by the year 2100 – a rapid and profound change. Even if the minimum predicted increase takes place, it will be larger than any century-long trend in the last 10 000 years. The principal reason for the global increase in temperatures is a century and a half of industrialization, with the burning of ever-greater quantities of oil, gasoline, and coal; the cutting of forests; and use of certain farming methods.
Climatic changes already are estimated to cause over 150,000 deaths annually.
That estimate includes deaths as a result of extreme weather conditions, which may be occurring with increased frequency. Changes in temperature and rainfall conditions also may influence transmission patterns for many diseases, including water-related diseases, such as diarrhoea, and vector-borne infections, including malaria. Finally, climate change may affect patterns of food production, which in turn can have health impacts in terms of rates of malnutrition. There is further evidence that unmitigated greenhouse gas emissions would increase disease burdens in the coming decades. The risks are concentrated in the poorest populations, who have contributed the least to the problem of greenhouse gas emissions.
Over a decade ago, most countries joined an international treaty – the United Nations Framework Convention on Climate Change – to begin to consider what can be done to reduce global warming and to cope with whatever temperature increases are inevitable.
In 1997, the Kyoto Protocol, which has more powerful (and legally binding) measures, was developed by governments as an addition to the treaty. This protocol came into force on 16 February 2005. The Kyoto Protocol is signed by 128 nations, and commits the participating industrialized countries to cut emissions of greenhouse gases by over 5% below 1990 levels by the period 2008-2012.
In addition to addressing the root causes of climate change, it is also important to take action to adapt to a changing climate. This includes actions that immediately improve the health of the poorest communities and also to reduce their vulnerability to climate change effects in the future.
A paper in Nature Climate Change this week compares the death rates of people over the age of 65 in New England to temperature records. Although we can probably expect more extreme heat in future, and possibly (although not definitely) less extreme cold, the study suggests that milder winters wouldn’t compensate for more extreme summers. Intriguingly, the study also finds that rapidly fluctuating temperatures are dangerous all on their own.
Sharp swings leave no time to adjust
The researchers used temperature data taken from satellite surface temperature measurements, allowing them to track the temperatures of blocks as small as square kilometres throughout the region. They then compared the temperature data with all of the nearly 900,000 deaths in people over the age of 65 recorded by Medicare in New England between the years 2000 and 2008.
When the average temperature in summer went up by 1°C, the death rate rose by approximately 1 percent. If the average temperature in winter went up by the same amount, you might hope that as many lives might be saved by the lack of extreme cold, but the decrease in death rate was only 0.6 percent. The higher summer death rates were only observed when there were abnormally hot summers—people seemed to have acclimatised to the normal heat of summer.
What seemed to be especially dangerous was wide fluctuation in temperatures. When temperatures fluctuated more wildly from day to day, death rates increased. An average increase in temperatures might be a problem for future public health, the authors write, but “the excess public health risk of climate change may also stem from changes of within-season temperature variability.”
Plenty of gaps to be filled
It’s important to note that for all of these statistics, there is a range of uncertainty calculated by the researchers, and that range is quite wide. Higher death rates associated with increased temperature fluctuations fall between 0.2 percent to 5.2 percent higher than normal, while higher summer temperatures were associated with death rates between 0.6 percent and 1.5 percent higher. These wide ranges introduce a level of uncertainty into the results.
People do adapt to the climates that they live in, which is why the researchers suggest temperature fluctuations as an important potential problem: when the temperature changes rapidly from day to day, people don’t get this chance to acclimatise. Although past research has indicated that temperature variability is associated with higher death rates, it’s not clear why this is. We know from experiments that people who exercise in consistently hot conditions improve their tolerance, while those who alternate between hot and cold conditions don’t. This suggests that temperature variability affects adaptation, the authors write.
This research has quite a few limitations. For a start, it’s purely correlational, and there could be other factors that need to be taken into account in building an accurate picture of what’s going on. Strong correlational research needs a good explanation for why the factors are linked, and there isn’t yet a strong explanation for how fluctuating temperature could affect human health.
Secondly, the ranges in increased death rates calculated by the authors are large, and the population they studied is limited. The authors themselves suggest that this paper is a starting point for more research into climate and health. For instance, people in warmer climates might be adapted enough to higher temperatures that rising summer temperatures may have a smaller effect on them. The effects of higher and fluctuating temperatures are likely to be more extreme in certain climate zones and among certain groups of people, making it possible that some populations are more likely than others to be vulnerable to these effects.
Public health is a facet of climate change that’s poorly researched and poorly understood, so although this research has its limits, it’s an important jumping-off point, inviting further investigation into a vital question: will we die of heat exposure before we drown in rising tides?