The international treaty to protect the ozone layer turns 20 this year. But is there really much reason to celebrate?

Environmentalists have made numerous apocalyptic predictions over the past several decades, virtually none of which has come to pass. Yet each time, the greens and their political allies proclaim victory, arguing that their preventive prescriptions averted disaster.

Such is the case with the 1987 Montreal Protocol On Substances That Deplete The Ozone Layer (Montreal Protocol). The lurid predictions of ozone depletion-induced skin cancer epidemics, ecosystem destruction and others haven't come true, for which Montreal Protocol proponents congratulate themselves. But in retrospect, the evidence shows that ozone depletion was an exaggerated threat in the first place. As the treaty parties return to Montreal for their 20th anniversary meeting it should be cause for reflection, not celebration, especially for those who hope to repeat this "success story" in the context of global warming.

The treaty came about over legitimate but overstated concerns that chlorofluorocarbons (CFCs, a then-widely used class of refrigerants) and other compounds were rising to the stratosphere and destroying ozone molecules. These molecules, collectively known as the ozone layer, shield the earth from excessive ultraviolet-B radiation (UVB) from the sun. The Montreal Protocol's provisions were tightened in 1990 and again in 1992, culminating with a CFC ban in most developed nations by 1996.  

So what do we know now? As far as ozone depletion is concerned, the thinning of the ozone layer that occurred throughout the 1980s apparently stopped in the early 1990s, too soon to credit the Montreal Protocol. A 1998 World Meteorological Organization (WMO) report said that, "since 1991, the linear [downward] trend observed during the 1980s has not continued, but rather total column ozone has been almost constant …" However, the same report noted that the stratospheric concentrations of the offending compounds were still increasing through 1998. This lends credence to the skeptical view, widely derided at the time of the Montreal Protocol, that natural variations better explain the fluctuations in the global ozone layer.

More importantly, the feared increase in ground level UVB radiation has also failed to materialize. Keep in mind that ozone depletion, in and of itself, doesn't really harm human health or the environment. It's the concern that an eroded ozone layer will allow more of the sun's damaging UVB rays to reach the earth that led to the Montreal Protocol. But WMO concedes that no statistically significant long-term trends have been detected, noting earlier this year that "outside the polar regions, ozone depletion has been relatively small, hence, in many places, increases in UV due to this depletion are difficult to separate from the increases caused by other factors, such as changes in cloud and aerosol." In short, the impact of ozone depletion on UVB over populated regions is so small that it's hard to detect.

Needless to say, if UVB hasn't gone up, then the fears of increased UVB-induced harm are unfounded. Indeed, the much-hyped acceleration in skin cancer rates hasn't been documented. U.S. National Cancer Institute statistics show that malignant melanoma incidence and mortality, which had been undergoing a long-term increase that predates ozone depletion, has actually been leveling off during the putative ozone crisis.

Further, no ecosystem or species was ever shown to be seriously harmed by ozone depletion. This is true even in Antarctica, where the largest seasonal ozone losses, the so-called Antarctic ozone hole, occur annually. Also forgotten is a long list of truly ridiculous claims, such as the one from Al Gore's 1992 book "Earth in the Balance"that, thanks to the Antarctic ozone hole, "hunters now report finding blind rabbits; fisherman catch blind salmon."

Overall, the Montreal Protocol isn't making these bad consequences go away -- they were never occurring in the first place.

The parallels with global warming are striking. Again we face a real but greatly overhyped environmental problem. In both cases, virtually everything the public has been told that sounds terrifying isn't true -- and what is true isn't particularly terrifying. But doomsayers such as Gore simply soldier on. His claims of blind animals from ozone depletion have been replaced by equally dubious assertions in his book "An Inconvenient Truth," including predictions of a massive sea level rise that would wipe away south Florida and other coastal areas.

Perhaps decades from now, participants in the Kyoto Protocol, the global-warming treaty modeled after the Montreal Protocol, will meet and congratulate themselves because none of their scary assertions came true. But how many resources will have been spent to save a world that never really needed saving in the first place?

Ben Lieberman is senior policy analyst in the Thomas A. Roe Institute for Economic Policy Studies at the Heritage Foundation.