Changing ambient UVR and future skin cancer in London, Rome and Helsinki: non-melanoma skin cancer (BCC and SCC)
It is widely accepted that ambient UVR is carcinogenic (Lucas et al 2006). This assessment will focus 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 increase and, subsequently, ambient UVR is anticipated to decrease. Hence, a decrease in non-melanoma skin cancer is expected, but other factors may play an important role as well such as the aging of the population.
Scope
Description
We explore the effects of changing exposure to ambient ultraviolet radiation (UVR) on non-melanoma skin cancer (BCC and SCC), accounting for the recovery of the ozone layer due to decreasing emission of ODS and future emissions of CH4 and N20 (IPCC 2005). We also account for future demographic change.
Scenario(s) and Type of Assessment
Type of assessment: prognostic.
UVR scenarios: IPCC (2000) SRES A2 and B1: future population & emissions/concentrations of ODS, CH4 and N2O.
SRES population scenarios were downscaled from the regional to the city-level.
| IPCC Senario | SRES-A2 | SRES-B1 |
|---|---|---|
| ODS Emission | Decreasing trend
Same B1 |
Decreasing trend
same as A2 |
| CH4 Emission | Higher Increase | Lower Increase |
| N2O Emission | Higher Increase | Lower Increase |
| Population | Higher Growth | Lower growth |
| Age Structure | Slower Aging | Higher Aging |
Geographical and temporal scope
- Study area(s): City of Helsinki, Greater London, City of Rome
- Populations: 5-year age groups up to 85+; males/females
- Timeframe: 2001, 2030, 2050
Environmental and health factors
- Source: emissions of ODS (decreasing), N2O (increasing) and CH4 (increasing) ,affecting ozone fields
- Environmental hazard: ambient UVR (erythemal dose).
- Other risk factor: age
- Health outcomes: BCC and SCC incidence/mortality (rates)
Stakeholders:
| Stakeholder | Interest | Role |
|---|---|---|
| Health authorities, policy/decision makers and health promotion agencies | Healthy population | Issue recommendations on solar exposure |
| Health care providers | Disease prevention, treatment | Treatment and advice particularly to groups at risk |
| Societies (cancer, osteoporosis, etc) | Support member interests | Issue public information |
| Advocacy groups | Protecting vulnerable groups | Reduce health impacts related to UVR. |
| Researchers | Research | Further knowledge of UVR-related health effects |
Results
Main findings
UVR exposure UVR exposures are higher (and ozone recovery slower) in SRES-B1 compared to SRES-A2. The larger increase in ozone column in SRES-A2 can probably be explained by the higher abundance of CH4in this scenario.
Health impact 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/mortality in both scenarios. As population growth is highest in SRES-A2, the total number of cases and deaths is also higher in this scenario compared to SRES-B1. For Helsinki and London, skin cancer incidence and mortality rates in the total population, however, are higher in the SRES-B1 scenario compared to the results for SRES-A2; this can be explained by the faster ageing of the population in SRES-B1.
Health impact model 2 also accounts for the future recovery of the ozone layer. The modelling shows a decrease in age-specific skin cancer incidence rates due to the recovery of the ozone layer. As expected, skin cancer incidence/mortality (rates) are lower in model 2 compared to model 1. The SRES-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 SRES-A2.
Similar conclusions for model 1 and model 2 can be drawn for the DALY calculations.
The sensitivity analyses shows that the choices regarding the PAF (BCC high estimate is 0.9; low estimate is 0.5/SCC high estimate is 0.7; low estimate is 0.5 ) had a large influence on the health outcomes as expected. Hence for policy purposes, it might be recommended to present all results using both the high and low PAF estimates. Applying age weights and discounting simultaneously to the DALY calculations decreased the number of DALY’s with more circa 50% for BCC and circa 56% for SCC. The choice regarding the imr showed a very large effect on the outcomes for SCC (almost 240% increase in DALYs compared to standard setting), but not so much for BCC (circa 12%). The sensitivity analyses also shows that the additive effect of an 1°C increase in summer temperature (Van der Leun et al 2008) in 2030 (compared to baseline) could counterbalance (results for BCC) or even outweigh (results for SCC) the effect of the decreasing UVR levels on age-specific incidence and mortality rates.
Assessment Methods
Appraisal
Implications
- Decreasing UVR levels result in lower age-specific incidence and mortality rates (model 1 versus model 2).
- For the population as a whole, this positive effect of decreasing ambient UVR is offset by increasing population size and further ageing of the population. Hence, policies to prevent or treat non-melanoma skin cancer will still be relevant in the future, despite the recovery of the ozone layer.
- Based on the sensitivity analyses for Helsinki 2030 B1 model 2, it can be concluded that the positive effect of the recovery of the ozone layer could be counterbalanced or even outweighed by the possible additive effect of 1°C increase in summer temperature between 2000 and 2030,which is not very unlikely given the IPCC climate change scenarios (the national projections for Finland by Jylhä et al. (2004) indicated a temperature rise of 1-3˚C in 2010-2039 compared to 1960-1990).
Lessons learned
- The inclusive full-chain model stimulated discussion about the risk assessment context. The exclusive framework stimulated discussion about excluded system factors.
- You often have to work with what is available. This facilitated discussion on choices/assumptions made, improving the (transparency of) the assessments. The sensitivity analyses explored the impact of varying relevant input assumptions, in order to determine how ‘sensitive’ a model is to changes in the value of the parameters of the model. Further discussion with stakeholder might add to this as well, but will be very time-consuming.
- One of the biggest challenges was the downscaling of the SRES-population scenarios from the OECD region to the city level (downscaling).
- There is no one-size fits all integrated assessment approach. General principles, methods and frameworks have to be made meaningful with the specific context of the case study. This requires: creativity, transparency, open attitude, and learning by doing.
- Our inventory of important literature, supporting materials and other useful (data) sources might be useful in future assessments.
