Scientific Assessment of Ozone Depletion: 2010

Chapter 2 Scientific Summary

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Chapter 2 Authors and Contributors

Scientific Summary Chapter 2: Stratospheric Ozone and Surface Ultraviolet Radiation

Global Ozone Observations and Interpretation

As a result of the Montreal Protocol, ozone is expected to recover from the effect of ozone-depleting substances (ODSs) as their abundances decline in the coming decades. The 2006 Assessment showed that globally averaged column ozone ceased to decline around 1996, meeting the criterion for the first stage of recovery. Ozone is expected to increase as a result of continued decrease in ODSs (second stage of recovery). This chapter discusses recent observations of ozone and ultraviolet radiation in the context of their historical records. Natural variability, observational uncertainty, and stratospheric cooling necessitate a long record in order to attribute an ozone increase to decreases in ODSs. Table S2-1 summarizes ozone changes since 1980.

The primary tools used in this Assessment for prediction of ozone are chemistry-climate models (CCMs). These CCMs are designed to represent the processes determining the amount of stratospheric ozone and its response to changes in ODSs and greenhouse gases. Eighteen CCMs have been recently evaluated using a variety of process-based comparisons to measurements. The CCMs are further evaluated here by comparison of trends calculated from measurements with trends calculated from simulations designed to reproduce ozone behavior during an observing period.

Total Column Ozone

Ozone Profiles

Table S2-1. Summary of ozone changes estimated from observations.

Column ozone12-15 km20-25 km35-45 kmComment
Data sourcesGround-based, satelliteOzonesondesOzonesondes,satellites, FTIRSatellites, Umkehrs, FTIR
Northern midlatitudes 1980-1996Declined by about 6%Declined by about 9%Declined by about 7%Declined by about 10%1992-1996 column and lower stratosphere data affected by Mt. Pinatubo
Northern midlatitudes 1996-2009Increased from the minimum values by about 2% by 1998 and remained at the same level thereafterIncreased by about 6%Increased byabout 2.5%Increased by 1 to 2%, but uncertainties are large
Southern midlatitudes 1980-1996Declined by 6%No informationDeclined by about 7%Declined by about 10%
Southern midlatitudes 1996-2009Remained at approximately the same levelNo statistically significant changesNo statistically significant changesIncreased by 1 to 3%, but uncertainties are large

Polar Ozone Observations and Interpretation

Ultraviolet Radiation

Ground-based measurements of solar ultraviolet (UV) radiation (wavelength 280-400 nanometers) remain limited both spatially and in duration. However, there have been advances both in reconstructing longer-term UV records from other types of ground-based measurements and in satellite UV retrievals. Where these UV data sets coincide, long-term changes agree, even though there may be differences in instantaneous, absolute levels of UV.