Kate Mackenzie Deaths from climate change: how a frightening number is calculated

Climate change is responsible for 300,000 deaths this year, and will be responsible for 500,000 by the year 2030, according to the Global Humanitarian Forum, led by Kofi Annan. And it gets worse. The study estimates:

…that climate change seriously affects 325 million people every year, a number that will more than double in 20 years to 10 percent of the world’s population (now about 6.7 billion).

Economic losses due to global warming amount to over $125 billion annually — more than the flow of aid from rich to poor nations — and are expected to rise to $340 billion each year by 2030, according to the report.

After those rather unpleasant figures sink in, the first question you might have (if you’re like me, anyway) is: how did they get those numbers?

The study is not online just yet (apparently it will be later today). But it has 9 pages on its methodology, and we’ve picked out some of the noteworthy aspects below.

Disasters: First (and probably most difficult): working out which weather events are caused by climate change. The report essentially compares two types of disaster, windstorms and floods, to the incidence of earthquakes, which they say are clearly not affected by climate change. (Interestingly, earthquakes rose about 52 per cent between 1980 and 2005; it’s not clear why.)

The study’s approach is based on an analysis of loss-generating events in the publication Journal of Flood Risk, which states that: ‘Assuming the socio-economic driving factors behind loss-generating events to be the same for all causes, the difference is likely to be due to climate change’.

Then, how to tally up natural disasters themselves. The study used frequency (as opposed to say, adding up  the severity) of events, because frequency shows a strong correlation with climate change and the data is reliable. The number of incidents is provided by reinsurer, Munich Re.

Time frame: The study looked at the period 1980 to 2005 – again, because there is good data and “it is the period in which it is assumed that climate change has started to have an impact”. The IPCC believes there is a high likelihood that climate change began to take effect around 1990, and while some other studies show different points between 1960 and 1990, the GHF says a few years’ difference does not affect the outcome greatly.

Using this calculation, the report’s authors estimate that 40 per cent of weather related disasters in 2010 and 50 per cent in 2030 will be caused by climate change. They say this report is similar to several studies including one by Peter Bains of Melbourne University, which came up with a figure of 37 per cent.

Gradual environmental changes: Calculating the number of deaths from natural disasters themselves is reasonably straightforward. But the report also looks at deaths and those seriously affected from more gradual environmental problems. To do this, it uses estimates from the World Health Organization on climate change variations and health outcomes. Then:

These climate-health relationships are extrapolated and linked to climate change projections and compared to a 1961 – 1990 baseline, as the climate are [sic] assumed to be more significant after this period. This, in turn, allows for estimation of the likely future health consequences of gradual environmental degradation due to climate change.

The key indicators were malnutrition, diarrhoea and malaria. The ‘risk factor’ column, in the middle of the table below, is the percentage of deaths that the GHF estimates are attributable to climate change:

Economics: The study also has some shocking numbers on the economic cost of climate change – much of which will fall on the poorer countries. For this, it used the PAGE2002 model, introduced in 2006, which incorporates IPCC concerns about climate change to find a cost of the mean marginal impact of a tonne of CO2 as US$19 per tonne of carbon.

Related story:

Global warming causing 300,000 deaths a year (Guardian)