Changing ambient UVR and future future skin cancer

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The text on this page is taken from an equivalent page of the IEHIAS-project.

This case study was carried out as part (work package 3.7) of the EU-funded INTARESE project, which contributed to the development of this Toolbox.

The assessment set out to assess climate-related health impacts due to exposure to ultraviolet radiation (UVR) and ambient heat. The attached document reports on the UVR assessment.

It is widely accepted that ambient UVR is carcinogenic (Lucas et al 2006). This assessment focuses on the impact on non-melanoma skin cancer: basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

The international mechanism for protecting the ozone layer is the “Montreal Protocol on Substances That Deplete the Ozone Layer” that came into force in 1989 and its subsequent amendments (UNEP 2006). The production of the most harmful ozone depleting substances (ODS) are now phased out worldwide. The atmospheric concentrations of these gases is anticipated to decline over the next decades (IPCC 2005). As a result stratospheric ozone is expected to decrease ambient UVR. Hence, a decrease in non-melanoma skin cancer is expected, but other factors may play an important role as well such as the ageing of the population.

The UVR assessment estimates the impact of different UVR exposures (scenarios) based on status of the ozone layer (depletion and recovery). We focus on UVR-attributable incidence (rates), Mortality (rates and disease burden (in Disability Adjusted Life Years -DALYs) for malignant melanoma skin cancer (CMM), basal cell cancer (BCC) and squamous cell cancer (SCC). Three cities were selected as case studies as they covered different climates and latitudes within Europe: Helsinki, London, and Rome.

An important aspect of the case study is that future health impacts are assessed. We estimated future impacts for heat and UV for two time periods: years 2030 and 2050. Due to the uncertainties about the future, both in terms of exposures and other health determinants, a scenario-based approach was used. Specifically, we used the SRES emissions scenarios developed by the IPCC that quantify the emissions and concentrations of greenhouse gases and ozone depleting substances over the coming century, and their key drivers. For our assessment we selected the SRES B1 and A2 scenarios. Population scenarios were downscaled from the OECD-region to the city level.

The status of the ozone layer (and therefore ground level UV) is influenced by emissions of ozone depleting substances (regulated by the Montreal Protocol) and emissions of methane (CH4) and nitrous oxide (N2O). Current and future ambient UVR exposures were calculated by applying ozone fields from the Oslo Chemical Transport Model. UVR exposures are higher (and ozone recovery slower) in the B1 scenario compared to A2.

The health impact calculations were performed for 5-year age groups and for males and females separately. Changes in ambient UV (annual erythemal dose) were combined with dose-response functions derived from scientific literature. Mortality rates were estimated using incidence-mortality ratios. The results were combined with the population estimates in order to calculate skin cancer incidence (rates) and mortality (rates). These were translated into DALYs using disease models derived from existing literature (WHO and Australian burden of disease studies) and WHO standard life tables. Attributable incidence, mortality and disease burdens were calculated using the upper and lower estimates of population attributable fractions as estimated by the WHO.

Model 1 only accounts for future change in population size and structure, without accounting for future changes in incidence and mortality rates. The growing and ageing population results in a future increase in skin cancer incidence and mortality in both scenarios. As population growth is highest in A2, the total number of cases and deaths is also higher in this scenario compared to B1. For Helsinki and London, skin cancer incidence and mortality rates in the total population, however, are higher in the B1 scenario compared to the results for A2; this can be explained by the faster ageing of the population in B1.

Besides incorporating the future changes in population size and structure, model 2 also accounts for the future recovery of the ozone layer. The modelling predicts a decline in UVR levels throughout the upcoming decades and thus a decrease in age-specific skin cancer incidence rates. The main reason for this result is the recovery of the ozone layer from successful reduction of ozone depleting substances. As expected from the decreasing ambient UVR levels, skin cancer incidence (rates) and mortality (rates) are lower in model 2 compared to model 1. The B1 scenario (i.e. the alternative with the lower recovery of the ozone layer) has somewhat higher UVR levels and, consequently, higher age-specific incidence rates than A2.

Similar conclusions for model 1 and model 2 can be drawn for the DALY calculations. DALYs are highest for the more lethal melanoma compared to BCC and SCC.

The sensitivity analyses (applied to model 2 for Helsinki, SRES B1-2030) explores standard model setting versus alternative model setting for e.g. ambient UVR, cloud cover, PAF, incidence: mortality ratios, additive effect of increasing summer temperature, and DALY calculations (age weights, discounting; adjustment for co-morbidity). The results show that the choices regarding the PAF (high estimate versus low estimate) has a large influence on the outcomes. Hence for policy purposes, it might be recommended to present all results using both the high and low PAF estimates. The choice regarding the incidence:mortality ratios showed a very large effect on the outcomes for SCC and a relative large effect on the outcomes for CMM, but not so much for BCC. Finally, the sensitivity analyses shows that the additive effect of an 1°C increase in summer temperature in 2030 (compared to baseline) could counterbalance (results for BCC) or even outweigh (results for SCC and CMM) the effect of the decreasing UVR levels on age-specific incidence and mortality rates.

See also

Integrated Environmental Health Impact Assessment System
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