Guest essay by Steven Capozzola
Even though declining ozone cooled the stratosphere in the 20th Century, the IPCC says this cooling proves solar variability doesn’t impact surface temperatures.
The climate community has repeatedly dismissed solar variance as a key driver of rising temperatures during the 20th Century. But their reasoning may have a key flaw, with the Intergovernmental Panel on Climate Change (IPCC) unwittingly supplying the evidence.
A November 2013 statement from the World Meteorological Organization (WMO) explains the prevailing sentiment against solar variability: “…if warming had been caused by a more active sun, scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere and a warming at the surface and in the lower parts of the atmosphere.”
The observation they’re referring to is that, from roughly 1960 to 1995, stratospheric temperatures showed a net cooling. This decline occurred at the same time that surface temperatures were rising (driven, presumably, by increasing concentrations of CO2.) Thus, the absence of a parallel rise in stratospheric temperatures negates the possibility of a solar connection.
But what’s important to note is that ozone is the primary “greenhouse gas” of the stratosphere. As NASA explains it, “Ozone is both a major absorber of incoming ultraviolet in the stratosphere (leading to stratospheric heating) and a strong emitter in the thermal infrared spectrum.” Simply put, stratospheric temperatures are maintained by concentrations of ozone. If ozone levels decline, temperatures fall.
Certainly, the IPCC recognizes the connection between declining ozone and stratospheric cooling. Various reports establish this link, including a 2005 report, ‘Safeguarding the Ozone Layer and the Global Climate System,’ which notes: “Stratospheric ozone depletion has led to a cooling of the stratosphere. A significant annual-mean cooling of the lower stratosphere over the past two decades (of approximately 0.6 K per decade) has been found over the mid-latitudes of both hemispheres.”
This helps explain why, even as increased solar activity was driving a rise in surface temperatures, declining ozone was leading to a progressive cooling in the stratosphere.
The direct relationship between ozone and stratospheric temperature became apparent during the mid-Twentieth Century. Ozone suffered an existential threat as the continued release of chlorofluorocarbons (CFCs) ate away at its concentrations. Stratospheric ozone levels tumbled steadily from the late 1950s onward, creating a serious, and recognized, international problem. It wasn’t until the implementation of the Montréal Protocol in 1989 that real action to reduce CFCs took effect. Revisions to the Protocol subsequently led to a more complete ban on CFC production in 1996.
As NOAA’s Ozone Depleting Gas Index demonstrates, the Montreal Protocol has succeeded in gradually restoring ozone concentrations in the stratosphere. Specifically, CFC levels in the stratosphere continually rose until roughly 1996, the point at which the effects of the Montreal Protocol began to fully register. Starting in 1996, stratospheric CFC levels actually began to decline.
This action to restore ozone shows a remarkable correlation with recent stratospheric temperatures. Whereas cooling in the stratosphere was continually evident from 1960-1996, and tracked closely with falling ozone levels, temperatures have subsequently leveled off. Specifically, net temperatures in the stratosphere have remained essentially unchanged since the late 1990s.
Unfortunately, at the IPCC, one hand seems not to know what the other is doing. And so it’s questionable whether the IPCC has considered the ozone variable when citing stratospheric cooling as an invalidator of the solar activity thesis.
What’s rather striking, though, is that the flat-lining of stratospheric temperatures since roughly 1998 corresponds quite remarkably with the current “pause” in surface temperatures. This prompts a question: Could the stabilization of ozone levels in the stratosphere help to explain the subsequent ‘pause?’
If so, would the IPCC wish to promote this fact? Such a correlation would finally solve a vexing, recent climate mystery. But it would also establish a more concrete solar connection to temperature variability.
The evidence is compelling, and the subject deserves further scrutiny.