Updated 9/21/17: minor cleanup
Global Warming is All Man’s Fault for burning hydrocarbons to Produce Energy
This is a fundamental tenet of the Green Party Line. The basic idea is that Man has been accelerating the introduction of CO2 into the atmosphere since the start of the Industrial Revolution. Man now contributes more than the deficit of the natural carbon Cycle, so all global warming is Man’s fault.
That is, of course, possible. Chaos theory tells us that little pushes here and there can have stupendous effects in large systems, and the atmosphere can be viewed as a chaotic system. The problem with buying the Green view is that there is no conclusive proof that it is true. For example, plant respiration (the metabolic combustion of cells that produces both CO2 and H2O) contributes many times Man’s contribution of CO2. How do we know that some evolutionary change has not occurred on a large scale (e.g., grasses worldwide) that changes plant respiration? Man is certainly tinkering actively with grain crops. Maybe there is a side effect that is causing them to produce more CO2 during respiration, so they are the real problem. The point here is that nobody, including the Greens, knows because we only started measuring the Carbon Cycle a few decades ago (and we still don’t measure it very well, as I will show in a later post).
On the other hand, we have the entire geologic record that says that there is nothing special about this particular interglacial hiatus. It is behaving exactly like every one preceding it when Man had no matches. So, why is Man suddenly the prime mover in the current interglacial hiatus? The geologic record also says that even if the Ice Age is over, global warming is only bringing the Earth back up to the normal levels that have prevailed between Ice Ages for the past 500m years. So what is the problem? Maybe the Greens should be thanking Man for getting us out of the Quarternary Ice Age.
By the way, in case you are wondering if the current climate were a harbinger of the end of the current Ice Age, rather than just another interglacial hiatus, that is highly unlikely. The current Ice Age started 2.6m years ago when the Isthmus of Panama closed, greatly changing oceanic currents. Until plate tectonics moves the Americas further from Europe and Africa so that the Gulf Stream has a longer reach to warm when crossing the equator, growing in power, it is very likely the current Ice Age will continue for the foreseeable future (though the hiatuses may become more frequent).
However, the most serious flaw in this Green position is a major assumption that they make: all the other sources of CO2 in the atmosphere remain constant. That is just plain wrong, as I demonstrated in my post on geologic history. However, in this context I will just make one point. Man probably is largely responsible for the global warming of the past two centuries, but it has little to do with burning hydrocarbons. Man’s population has grown 7-fold in the past two centuries. It takes a lot of food to feed that many people, and that has serious consequences for plant and animal respiration.
Currently the largest single source of methane — which is 72 times more effective as a greenhouse gas than CO2 — is domestic cattle. The increase in domestic cattle alone could probably account for global warming in the past two centuries. Animal respiration also changes substantially as well when continents move towards the poles, as I discussed in my post on fundamental mechanisms.
In addition, different plants have different levels of metabolism. Generally speaking, trees have lower metabolisms than grasses and shrubs. More importantly, agricultural plants tend to have very high metabolisms because we breed them for rapid growth. In the past two centuries, Man has converted forests to agriculture at a prodigious rate. That increases plant metabolism’s contribution to atmospheric CO2 content — very probably far in excess of all of Man’s contribution from burning hydrocarbons.
The bottom line: Man very likely is responsible for recent global warming, but it is because he has tinkered with flora and fauna rather than burning hydrocarbons for energy. So if the Greens want to focus on Man’s role in global warming, they need to focus on overpopulation rather than burning hydrocarbons.