Improving satellite-based estimations of UV index and dose and first assessment of UV in a world-avoided

The UV index (UVI) and dose (UVD) are quantities of UV irradiance weighted for its
effect on organisms. Both quantities are widely used as informative tools or as proxies
for UV irradiance, commonly used in e.g. skin cancer research. The UVI and UVD can
be measured using groundbased spectrometers, or modelled using satellite observations
of ozone. The Royal Netherlands Meteorological Institute has developed a UV model
with a unique spatial and temporal coverage. This study describes the update of this
model. Updates include changing the computation and data sets used, regarding: ground
elevation, surface albedo, cloud cover and error estimation. The updated model is used
to compute UVI and UVD from the long-term Multi-Sensor Reanalysis of ozone, and
compared with ozone fields that would have been present if the 1987 Montreal Protocol
had not been adopted. We find that the northern hemisphere ozone depletion event of
2011, which is greatly exaggerated in absence of the Montreal Protocol, has only little
effect on UV irradiance. Comparing scenarios with and without Montreal Protocol, we
find that by the year 2012 the implementation of the Montreal Protocol has prevented UV
levels from shifting nearly 10 degrees poleward in summer, an increased global sunburn
rate by 9.9%, while also preventing a 14.5% increase in (sun related) vitamin D production.
For UVD thresholds relevant for vitamin D sufficiency, we found an order of magnitude
estimation of the effect of the Montreal Protocol: Removing part of the ozone layer, which
the Montreal Protocol prevented, has a similar effect on surface UV irradiance as removing
all cloud cover throughout the year.