Seven Theories of Climate Change
The Science and Public Policy Institute (SPPI) has posted an excellent essay [here] entitled Seven Theories of Climate Change written by Joseph Bast of The Heartland Institute [here].
In Seven Theories of Climate Change [pdf here] Joseph Bast reports on AGW and six other theories regarding climate change that are not caused by human beings. Those are:
1. Anthropogenic Global Warming
2. Bio-thermostat
3. Cloud Formation and Albedo
4. Human Forcings Besides Greenhouse Gases
5. Ocean Currents
6. Planetary Motion
7. Solar Variability
Bast states in his introduction:
The theory of climate change that most people are familiar with is commonly called anthropogenic (man-made) global warming, or AGW for short. That theory holds that man-made greenhouse gases, primarily carbon dioxide (CO2), are the predominant cause of the global warming that occurred during the past 50 years.
In the past few years, confidence in the AGW theory has declined dramatically. New research points to natural causes of the modern warming, and stabilizing (by some measures, falling) global temperatures have called attention to long-recognized shortcomings of the AGW theory. Tens of thousands of scientists have signed petitions expressing their dissent from the so-called “consensus” in favor of AGW. Opinion polls show a majority of the public in the U.S. and in other countries no longer believes human activity is causing global warming. Evidence of the decline of the AGW theory is presented in the postscript to this booklet.
The demise of the AGW theory makes this a good time to look at other theories of climate change put forward by prominent scientists but overlooked in the rush to judgment. This booklet identifies seven theories – AGW plus six others that do not claim man-made CO2 is a major cause of climate change. Each theory is plausible and sheds light on some aspects of climate change that were hidden or obscured by too great a focus on the AGW theory.
In some respects these theories are not mutually exclusive: solar variability could be the sustaining force behind what I have called the “cloud formation and albedo” and “ocean currents” theories as well as being its own theory, though the mechanisms in each case differ slightly. …
The six theories of climate change that do not involve man-made greenhouse gas emissions are incompatible, though, with the AGW theory. If evidence exists that negative feedbacks offset whatever warming is caused by man-made greenhouse gases, then the warming during the past 50 years could not be due to the burning of fossil fuels. Similarly, if solar variability explains most or all of the variation in temperatures in prehistoric as well as modern times, then there is no room for speculation about a large role for man-made CO2. …
The object of this essay is not to say which of these seven theories is right or “best,” but only to present them to the reader in a format that allows reflection and balanced consideration. Such dispassionate interest in the subject has been lacking in recent years, and the scientific debate has suffered for it.
If I had to pick a favorite, it would be a combination of Numbers 3 and 6, Cloud Formation/Albedo and Planetary Motion. Science is not a popularity contest, but we can make judgments based on the available evidence.
The evidence suggests that CO2 is not a primary forcing factor of global temperatures. Over the last 15 years global temperatures have declined while atmospheric CO2 concentrations have risen.
CO2 concentration (ppmv) vs. air temperature anomaly (deg C) 1995-2010. From the Powerpoint presentation accompanying Soon,Willie and David R. Legates. 2010. Avoiding Carbon Myopia: Three Considerations for Policy Makers Concerning Manmade Carbon Dioxide. Ecology Law Currents, Vol. 37:1.
There is no correlation between CO2 and temperature change, and thus there cannot be causation. On a longer time scale some correlation has been detected, but changes in CO2 seem to lag temperature changes by as much as 800 years. That which happens later cannot cause that which happens prior.
Evidence on a long time scale shows a regular pattern of 90,000-year-long glaciations interspersed with 10,000-year-long interglacials. The regularity of that pattern (cycle) and its coincidence with eccentricities in the Earth’s orbit strongly suggest that global temperatures are linked with planetary motion.
Milankovitch Cycles and global temperature over the last million years. From the Wikipedia by Global Warming Art.
The Pleistocene has been all about ice, with temporary interruptions by interglacials at the height of Milankovitch insolation peaks. But the increase in insolation (solar radiation striking the Earth) is not, by itself, sufficient to melt all that ice.
The Ice Ages (Pleistocene) are typified by continental ice sheets that have a positive albedo feedback. The whiteness and reflectivity of ice perpetuates more ice. The 90,000-year-long glaciations exhibit generally declining temperature trends throughout. The coldest point of the Wisconsin Glaciation was the Older Dryas stadial of 15,000 years ago — at the very end of that glacial period.
There has to be some other factor which overrides the positive feedback of icy albedo. I suspect that factor is soot, either from volcanoes, comets, or smoke — combined with insolation peaks. It could also be that cloud albedo is sufficient to induce and to counter glaciations, and that cloud cover change is somehow driven by insolation change. That is, continental ice albedo is not as significant as cloud albedo over the oceans (which constitute 5/6ths of the Earth’s surface), and cloud cover over the oceans is tied to Milankovitch cycles.
If humanity has affected climate change at all, it has been through anthropogenic smoke (and charred earth), not CO2 and not methane, and only during the current interglacial, the Holocene. That’s my theory, anyway. It’s all about albedo and orbital perturbations, not GHG’s.
But that’s just my pet theory. Bast presents the outlines of seven theories proposed by actual climatologists, theories which can be combined in numerous ways.
The take home point is that AGW is just one theory, and not a very good one at that. Too many anomalies are unexplained by the AGW theory. It is time to study and test some of the other theories. The science is not over and done with; it’s just beginning.
