The Course of Reason

CFCs responsible for global warming? Not likely

June 7, 2013

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A University of Waterloo study is claiming that CFCs, not carbon dioxide, are causing global warming. In a press release put out by the University, Qing-Bin Lu, a professor of physics and astronomy, biology and chemistry at Waterloo states:

“Most conventional theories expect that global temperatures will continue to increase as CO2 levels continue to rise, as they have done since 1850. What’s striking is that since 2002, global temperatures have actually declined – matching a decline in CFCs in the atmosphere,” Professor Lu said. “My calculations of CFC greenhouse effect show that there was global warming by about 0.6 °C from 1950 to 2002, but the earth has actually cooled  since 2002. The cooling trend is set to continue for the next 50-70 years as the amount of CFCs in the atmosphere continues to decline.”

Unsurprisingly, this study has raised a collective, “What?” from climate change scientists as the study and Lu’s statements go against conventional and well-accepted ideas about the relationship between carbon dioxide and global temperatures.

For starters, global temperatures haven’t declined. This is a bit of a myth that is perpetuated by climate change “skeptics”. It is possible to back the claim with data, but it’s heavily dependent on the data set being used along with using short time periods to talk about a long-term issue. Andrew Glikson writes:

Warming and “heat accumulation” is measured through various different climate indicators. One of the most cited is global-mean surface temperature. The last decade has shown continued warming in global mean surface temperature, not cooling. The warming has occurred at a slower rate in the past decade compared to the 1990s, but it has still warmed. The years 2006 and 2010 were the warmest peaks since 1998.

However, this is balanced by the fact that ocean heat content (a measure of heat accumulated in the ocean depths) has dramatically increased over the same period at 0 to 700 meter depth. That draw-down of heat into the oceans has resulted in slower warming in the atmospheric temperature at the surface of the oceans, which transfers to slower warming in the global mean surface temperature.

Lu seems to be ignoring the absorption of heat by the oceans and is cherry-picking data to suit his needs.

Skeptical Science puts it bluntly: “there are numerous fundamental flaws in the paper.”   

Lu’s hypothesis can be disproven very simply.  He argues that the radiative forcing (global energy imbalance) from CFCs matches global surface temperatures better than that from CO2 over the past decade. This is because as a result of the Montreal Protocol, CFC emissions (and emissions of hydrofluorocarbons, which replaced CFCs) have been flat over the past decade, and global surface air temperatures have also been essentially flat during that short timeframe, while CO2 emissions have continued to rise.

However, a global energy imbalance doesn’t just impact surface temperatures. In fact, only about 2% of global warming is used in heating the atmosphere, while about 90% heats the oceans. Over the past decade, ocean and overall global heating have continued to rise rapidly, accumulating the equivalent of about 4 Hiroshima atomic bomb detonations per second

So while CFCs might match surface temperature changes better than CO2 emissions over the past decade, CO2 emissions better match the relevant metric – overall global heat accumulation. Since a global energy imbalance influences global heat content and not just surface temperatures, this by itself is sufficient to falsify Lu’s hypothesis.

Lu appears to have looked at the relation between CFCs and surface temperatures while ignoring the ocean temperatures. Doing so creates a correlation between CFCs and global warming. However, it conveniently ignores a major component of the planet’s temperature: the oceans. I recommend reading the Skeptical Science article in full for a complete overview of the problems found in the study.

This is an example of how not to do science: Picking and choosing your data, and ignoring important aspects that may contradict your proposed idea. 


 

 

About the Author: Chris Burke

Chris Burke's photo
Chris Burke holds a Bachelors in Environmental Studies: Honours Environment and Business from the University of Waterloo. Next he will be working towards a Masters of Environmental Studies in Sustainability Management. He's an active member of the Atheists, Agnostics, and Freethinkers of Waterloo student group. In his spare time he enjoys reading and playing music.

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