A Red-letter day

The day I feel comfortable going out to grass ....

September 3, 2019 is a day I’ll remember. It’s the publication date in the Nature journal Scientific Reports of our paper that marks the culmination of over thirty years of UV research that started for me in Lauder, New Zealand, shortly after the discovery of the Antarctic Ozone Hole. Lauder was then still part of the DSIR. Five years later would it become part of the newly-formed Crown Research Institute, NIWA.

About 15 years ago I told my colleague there, Greg Bodeker, that I could retire happily only after we’d solved the ozone problem. This paper marks that milestone. It’s the day we can finally say that the Montreal Protocol on Protection of the Ozone Layer reached its target of protecting us from increased UV radiation due to ozone depletion.

The paper analyses long-term measurements of sunburning UV made at with the highest quality instruments available at 17 sites around the world. The network of UV instruments was designed specifically for the purpose of tracking the effects of ozone depletion, and the longest of these time series goes right back to the late 1980s.

We compare these gold-standard measurements with three other estimates of UV:

1. Calculations based on ozone measurements at the same sites

2. Calculations based on projected ozone from a “World Avoided” scenario which would have occurred if there had been no Montreal Protocol

3. Calculations based on projected ozone from a “World Expected” scenario which would occur with full compliance to the Montreal Protocol

A comparison with the first demonstrates that, for unpolluted sites, long-term changes in measured UV are consistent with those calculated from ozone. This means the UV trends before the 1990s can be inferred from ozone data, and confirm that significant increases in UV occurred in the 1980s and 1990s before the effects of the Montreal Protocol kicked in, especially at high southern latitudes.

A comparison with the second showed that trends in measured UV since the late 1990s are no longer tracking that path of destruction. Without the Montreal Protocol, it would already be 20 percent more than in the 1990s, and it would have gone to increase to three or four times as high later in the century.

A comparison with the third shows that the measured changes are entirely consistent with those expected from full compliance with the Montreal Protocol. The increase in UV in the 1990s is confirmed, with a levelling off since the late 1990s, and even a slight decrease a high southern latitudes where UV increases last century were largest.

QED. What more could I want, you may ask. I want recognition that, with concerted efforts and without the interference of self-gratifying brats like Donald Trump, we can solve these problems. We’ve done it for ozone. Let’s get on with it for Global Warming. We know how to do it. We just have to get past the vested interests that stand in the way.

Or the whole 9 yards ….

Figure. Trends in measured UVI from 1996 to the present, as a function of site latitude, compared with those calculated for clear skies from observed ozone, and as calculated by the two model runs: one for the World Avoided (without the Montreal Protocol) and one for World Expected (with the Montreal Protocol). Sites where the time series spans 20 years, or more are denoted by bold text and solid symbols. The number of years of data included in the trend analysis at each site is indicated beside the site name. If data from some seasons are missing, this number can be less than the total number of years. Error bars shown are 2-sigma uncertainties of the regression model

Go here if you want to read the whole nine yards.