"A new study suggests that the ban on ozone depleting chemicals may have also impacted the rise in global temperatures. CFC gases were responsible for a massive hole in the ozone layer but they also had a powerful greenhouse effect.
The authors link a ban on their use to a "pause" or slowdown in temperature increases since the mid 1990s. The research is published in the journal Nature Geoscience.
The subject of a hiatus or standstill in global temperatures rises since 1998 has been the subject of intense debate among scientists, and it has been used as a key argument by some to show that the impacts of global warming have been exaggerated.
There have been a number of theories as to why the rise in emissions from CO2 and other gases has not been mirrored in temperatures since the late 1990s.
These include increases in China's use of coal, changes in solar output, and the impact of the El Nino weather cycle.
One report earlier this year suggested that it was caused by long-term changes in the warming of waters in the eastern Pacific.
Now this latest piece of research says that it has been caused by attempts to protect the ozone layer. A team of researchers carried out a statistical analysis on the connection between rising temperatures and rates of increase in concentrations of greenhouse gases in the atmosphere between 1880 and 2010.
They concluded that changes in the warming rate can be attributed to specific human actions that affected greenhouse gas concentrations.
The onset of the current pause coincides with a spike in upper ocean heat uptake around 2002 (lower graph).
- It may have begun when energy trapped by greenhouse gases was buried below the surface of the ocean
- However, the continuation of the pause in global surface warming beyond 2004 coincides with a decline in upper ocean heat uptake
- Understanding the cause of this decline in upper ocean heat content is crucial for explaining the continuation of the pause in surface warming
They were able to show that when emissions were reduced during both world wars and the Great Depression, temperature rises also stalled.
The treaty phased out the use of chlorofluorocarbons (CFCs). These chemicals, used as spray can propellants and in refrigeration, had helped thin the ozone layer over Antarctica.
But CFCs were not just damaging the ozone layer, they were also having a warming impact, as they are 10,000 times more powerful than carbon dioxide and can last up to 100 years in the atmosphere. Their removal, say the authors, was a critical factor in the slowdown.
"Our analysis suggests that the reduction in the emissions of ozone-depleting substances under the Montreal Protocol, as well as a reduction in methane emissions, contributed to the lower rate of warming since the 1990s," the authors write.
In a commentary on the research, Felix Pretis and Prof Myles Allen from Oxford University suggest that the CFC ban is "unlikely to be the whole story", but they acknowledge it did make a difference.
"The impact of this change is small but not negligible: without the reduction in CFC emissions, temperatures today could have been almost 0.1C warmer than they actually are."" charts from UK Met Office
11/10/13, "Ozone-hole treaty slowed global warming," Nature.com, Hannah Hoag, "Montreal Protocol helped to curb climate change and so did world wars and the Great Depression."
8/8/12, "Profits on Carbon Credits Drive Output of a Harmful Gas," NY Times, Rosenthal, Lehren
"Carbon trading has become so essential to companies like Gujarat Fluorochemicals Limited, which owns a coolant plant in this remote corner of Gujarat State in northwest India, that carbon credits are listed as a business on the company Web site. Each plant has probably earned, on average, $20 million to $40 million a year from simply destroying waste gas, says David Hanrahan, the technical director of IDEAcarbon, a leading carbon market consulting firm. He says the income is “largely pure profit.”
And each plant expects to be paid. Some Chinese producers have said that if the payments were to end, they would vent gas skyward. Such releases are illegal in most developed countries, but still permissible in China and India.
As the United Nations became involved in efforts to curb climate change in the last 20 years, it relied on a scientific formula: Carbon dioxide, the most prevalent warming gas, released by smokestacks and vehicles, is given a value of 1. Other industrial gases are assigned values relative to that, based on their warming effect and how long they linger. Methane is valued at 21, nitrous oxide at 310. HFC-23, the waste gas produced making the world’s most common coolant — which is known as HCFC-22 — is near the top of the list, at 11,700....
Since the United Nations program began, 46 percent of all credits have been awarded to the 19 coolant factories, in Argentina, China, India, Mexico and South Korea. Two Russian plants receive carbon credits for destroying HFC-23 under a related United Nations program.
“I was a climate negotiator, and no one had this in mind,” said David Doniger of the Natural Resources Defense Council. “It turns out you get nearly 100 times more from credits than it costs to do it. It turned the economics of the business on its head.”"...
Gas dispersals illegal in developed countries are still legal in China and India:
June 8, 2013, "U.S., China agree to reduce use of hydrofluorocarbons," Reuters
"HFCs are used in refrigerators and air conditioners. They came into wide commercial use to replace ozone-depleting chemicals that are being phased out under the 1987 Montreal Protocol, but they are a big source of greenhouse gases that contribute to climate change."...