Climate change and human health in search of magic numbers…

1. Climate change and human health in search of magic numbers… NCAR Summer colloquium 28 July 2004 R Sari Kovats Centre on Global Change and Health Dept of Public Health and Policy London School of Hygiene and Tropical Medicine

2. STRATOSPHERIC OZONE DEPLETION • Global problem • Health and environmental impacts • Skin cancer • Cataracts • Information from epidemiological • studies

3. 2050 2100 Time 2020s 2050s 2080s Modelling impacts of climate change Greenhouse gas emissions scenarios Defined by IPCC Global climate scenarios: Generates series of maps of predicted future distribution of climate variables 30 year averages Impact models Estimates of populations at risk or attributable burden of disease 2020s 2050s 2080s

4. Deaths, 2000 World Africa

5. Estimated death and DALYs attributable to climate change. Selected conditions in developing countries Floods Malaria Diarrhoea Malnutrition 120 100 80 60 40 20 0 0 2 4 6 8 10 Deaths (thousands) DALYs (millions) 2000 2020

6. Health-impact models • Process-based/Biological models • Malaria/vectorial capacity [MIASMA] • Heat budget models • Empirical statistical • Temp-mortality (Kalkstein, Moser, etc.) • Temp –Diarrhoeal disease • Rainfall -flood-death • Temp/rainfall- Dengue, Malaria [spatial correlations]

7. Survival probability Incubation period Biting frequency 1 0.35 50 0.3 0.8 40 0.25 0.6 30 0.2 (per day) (days) (per day) 0.15 0.4 20 0.1 0.2 10 0.05 0 0 0 15 20 25 30 35 40 10 15 20 25 30 35 40 10 15 20 25 30 35 40 Temp (°C) Temp (°C) Temp (°C) TRANSMISSION POTENTIAL 1 Martens et al. 1999, van Lieshout et al. 2004 0.8 0.6 0.4 0.2 0 14 17 20 23 26 29 32 35 38 41 Temperature (°C)

8. Can global models reveal regional vulnerability? • Increase: East Africa, central Asia, Russian Federation • Decrease: central America, Amazon [within current vector limits] A1 A2 B1 B2

9. Mid-range scenario (SRES B2 greenhouse gas emission scenario, best guess climate sensitivity) Present Present 2050 2050 2100 2100 High-range scenario (SRES A2 greenhouse gas emission scenario, high climate sensitivity) Potential distribution of Aedes aegypti in the North Island based on 10°C midwinter isotherm limit for a mid- and high-range climate change scenario. Source: Hotspots dengue fever risk model developed by the International Global Change Institute, University of Waikato, with the assistance of funding from the Health Research Council

10. Empirical-stats models • EXTRAPOLATION • Can you extrapolate the exposure-response relationship beyond the bounds of the observed temperature range? • VARIATION • Can you extrapolate the exposure-response relationship derived from a different population. • ADAPTATION • Responses to climate change - acclimatization • MODIFICATION • What is likely?– • changes to exposure response relationship

11. Predicted distribution of the malaria vector (mosquito Anopheles atroparvus) in present day Europe, and in the 2080s with SRES A2 climate scenario. [Kuhn, LSHTM, 2002] Current climate 2080s

12. Temperature-salmonellosis [fully adjusted models] England & Wales Switzerland Netherlands Scotland

13. Netherlands: time series 250 200 150 100 50 0 Total weekly cases 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

14. Climate change and air pollution, UK Health Assessment 2002

15. Outcomes... • Shift in “climate envelope” • Additional population at risk • Definitions of risk • Relative risk • Absolute risk • additional/excess cases/deaths • Disability-adjusted life-year [DALY] • COSTS

16. Simplified causal web linking exposures and outcomesWHO model

17. Attributable fractions vs attributable deaths/cases • Population change • Growth • Ageing • Countries have national projections • Which baseline disease incidence used to estimate attributable cases. • Current or future?

18. Scenarios • Climate • Averages, extremes • Population • Population growth ✔✔ • Population ageing ✔ • Urbanisation, coastal migration • “socio-economic”

19. Non climate scenarios • Vector presence/abundance • Baseline disease prevalence • Cardiovascular disease • HIV/AIDS • Millennium Development Goals • Population • Income/GDP per capita/PPP per capita • Technology • Malaria vaccine • Qualitative “Knowledge is King, Big is Beautiful”

20. Relevance of attributable vs avoidable burden • Avoidable burden more policy-relevant • Why calculate attributable burden?

21. WHO Definitions… • A health impact assessment is a combination of procedures or methods by which a proposed policy, programme or project may be judged as to the effects it may have on the health of a population. • The basic principles underlying such an assessment are democracy, equity, sustainable development and evidence-based advice.

22. Uncertainty • Climate scenario • >1 climate model • >4 emissions scenarios • Regional model • Downscaling • Exposure response relationship • Key uncertainties/assumptions in the models • Confidence intervals • Monte Carlo simulation/Bayes

23. Qualitative High Established but incomplete Well-established Level of agreement, consensus Speculative Competing explanations Low High Amount of evidence Low

24. three research tasks Empirical studies [epidemiology] learn ?analogues mechanisms detection attribution predictive modelling 2004 2010 2080 Past [climate/weather-health relationships] Present [highland malaria] Future [map malaria]