This is Chapter 5 of the Arctic Climate Impact Assessment
Lead Authors: Betsy Weatherhead, Aapo Tanskanen, Amy Stevermer; Contributing Authors: Signe Bech Andersen, Antti Arola, John Austin, Germar Bernhard, Howard Browman,Vitali Fioletov,Volker Grewe, Jay Herman, Weine Josefsson, Arve Kylling, Esko Kyrö, Anders Lindfors, Drew Shindell, Petteri Taalas, David Tarasick; Consulting Authors: Valery Dorokhov, Bjorn Johnsen, Jussi Kaurola, Rigel Kivi, Nikolay Krotkov, Kaisa Lakkala, Jacqueline Lenoble, David Sliney
Depletion of stratospheric ozone over the Arctic can reduce normally high winter and spring ozone levels and allow more ultraviolet (UV) radiation to reach the surface of the earth. Arctic ozone levels exhibit high natural seasonal and interannual variability, driven primarily by atmospheric dynamics that govern the largescale meridional transport of ozone from the tropics to high latitudes. The spatial distribution of total column ozone over the Arctic is less symmetric around the pole than is the case for ozone over the Antarctic. The large natural variability in arctic ozone complicates the interpretation of past changes and the projection of future ozone levels. Observations have shown substantial late winter and early spring reductions in arctic total column ozone over the last two decades.
These reductions have been directly linked to chemical reactions occurring at low temperatures in the presence of anthropogenic chlorine and bromine compounds. Between 1979 and 2000, the trend in mean annual total column ozone over the Arctic was about -3% per decade (7% accumulated loss), while the trend in mean spring total column ozone was about -5% per decade (11% accumulated loss). Arctic ozone depletion is also strongly affected by stratospheric temperatures and polar stratospheric cloud formation.
Climate change leading to lower temperatures in the stratosphere is likely to increase the frequency and severity of ozone-depletion episodes.
Ozone levels directly influence the amount of UV radiation reaching the surface of the earth. Surface UV radiation levels are also strongly affected by clouds, aerosols, altitude, solar zenith angle, and surface albedo. These different factors contribute to high variability in UV radiation levels and make it difficult to identify changes that result from ozone depletion. Because of the low solar elevation in the Arctic, the region is subject to an increased proportion of diffuse UV radiation, from scattering in the atmosphere as well as from reflectance off snow and ice. Reflectance off snow can increase the biologically effective irradiance by more than 50%. Changes in global climate are likely to result in changes in arctic snow cover and sea ice. Snow and ice cover strongly attenuate UV radiation, protecting organisms underneath. A reduction in snow and ice cover on the surface of rivers, lakes, or oceans is likely to increase the exposure of many organisms to damaging UV radiation. Loss of snow or ice cover earlier in the spring, when UV radiation is very likely to be at increased levels, would be stressful for both aquatic and terrestrial life.
Ground-based measurements of UV radiation levels are conducted in all arctic countries. However, the current monitoring network does not provide sufficient coverage over vast regions. Available individual measurements suggest localized increases in UV radiation levels reaching the surface, but the measurement time series are not yet long enough to allow trends to be detected.
Reconstructed time series of surface UV radiation levels based on total column ozone, sunshine duration, and cloud cover suggest distinct increases, but reconstruction methods are less certain than direct measurements because they involve assumptions about the spectral characteristics of cloud and aerosol attenuation and surface reflectivity. The increases in UV radiation levels occur primarily in the spring, when ozone depletion reaches a maximum, and can result in spring UV radiation levels that are higher than those measured during the summer.
Atmospheric sampling indicates that the Montreal Protocol and its amendments have already resulted in a leveling off of some atmospheric halogen concentrations. However, climate change and other factors are likely to complicate the recovery of the ozone layer.
Changes in both the overall meteorology of the region and in atmospheric composition may delay or accelerate the recovery of the arctic ozone layer. Ozone levels are projected to remain depleted for several decades and thus surface UV radiation levels in the Arctic are likely to remain elevated in the coming years. The elevated levels are likely to be most pronounced in the spring, when ecosystems are most sensitive to harmful UV radiation. Exposure to UV radiation has been linked to skin cancers, corneal damage, cataracts, immune suppression, and aging of the skin in humans, and can also have deleterious effects on ecosystems and on materials.
Chapter 5: Ozone and Ultraviolet Radiation
5.2. Factors affecting arctic ozone variability
5.3. Long-term change and variability in ozone levels
5.4. Factors affecting surface ultraviolet radiation levels in the Arctic
5.5. Long-term change and variability in surface UV irradiance
5.6. Future changes in ozone
5.7. Future changes in ultraviolet radiation
5.8. Ozone and Ultraviolet Radiation in the Arctic: Gaps in knowledge, future research, and observational needs