C. Gradual environmental degradation due to climate changeBasic reasoning
Gradual environmental degradation due to climate change has a range of human impacts, including water stress, food insecurity, poverty and displacement. Several of these are linked to measurable health outcomes. Some of these have been linked to the effects of climate change, particularly malnutrition, diarrhoea and malaria. It is these health outcomes that are used as the basis for estimating the human impact of climate change in terms of seriously affected and deaths. These are certainly not the only human impacts of gradual environmental degradation due to climate change but they represent a reliable starting point for estimation.
Poor health outcomes frequently have a dynamic effect by exacerbating other areas of human development, including poverty and security. These effects are difficult to measure and current scientific research does not do this in detail and reliably enough to apply in global estimates. It is evident that populations that are vulnerable to the human impact of climate change often live in regions that are already affected by general development challenges and often also complex emergencies.
Model and approach applied
The estimates used in the Human Impact Report of the health outcomes that can be attributed to gradual environmental degradation due to climate change are based on the Global Burden of Disease Study by the World Health Organization. The study uses existing models that describe observed relationships between climate variations, either over short time periods or between locations, and a series of health outcomes. These climate–health relationships are extrapolated and linked to climate change projections and compared to a 1961–1990 baseline, as the climate are 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 results of the study are presented in terms of climate change risk factors per region – i.e. the factor by which climate change is increasing the underlying disease burden. A risk factor of 4 percent means that 4 percent of the overall disease burden (total number of cases) can be attributed to climate change. The WHO model is widely regarded to be the only model that provides a global estimate of the impact of the health consequences of climate change. It is a widely acknowledged model, and during the course of consultations, a majority of experts have indicated this as the most reliable study.
Key indicators
• Climate change risk factor for malnutrition - i.e. the percentage by which climate change increases the risk of malnutrition
• Climate change risk factor for diarrhoea- i.e. the percentage by which climate change increases the risk of diarrhoea
• Climate change risk factor for malaria- i.e. the percentage by which climate change increases the risk of malaria
Assumptions and calculations
• The risk factors, which are computed for lives lost, are also applied for the number of people affected. The original study describes climate change induced disease burden in terms of number of lives lost and disability adjusted life years, (DALYs – a time-based measure combining years of life lost due to premature death and disability, see further details in Glossary). To estimate the number of people affected, this report applies the same risk factors to the number of people seriously affected by disease, such as people who contract malaria, people suffering from malnutrition, and the number of diarrhoea
incidences.
• The number of cases approximately equals the total number affected: (1) Malnourishment cases over one year equal about the total number of people affected by malnutrition, (2) recorded malaria cases approximately equal the total number affected by malaria each year (and assumes some potential underreporting of cases due to data availability challenges), and (3) diarrhoea incidences approximately equals the number of people affected by diarrhoea. Results are based on best estimates available currently.
• Any overlaps, whereby the same individual suffers from malnutrition and also diarrhoea or malaria could lead to some overestimation. This is likely offset by potential underreporting of overall disease levels, possible underestimation of climate change risk factors and having the health impacts account for all impacts of gradual environmental degradation.
• All health consequences measured refer to the gradual impact of climate change and no major additional gradual onset impacts are left out.
• The global disease burden is kept constant as it is assumed that future population growth will counteract intervention gains.
• The climate change scenario used is the mid range of the HadCM2 global climate model (i.e. one of several alternative global climate models) used previously by the IPCC.
Human Impact Report, page 88
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