Just what is global warming anyway? On this page you will find a page of definitions. This post will examine some of them. This is important because one cannot intelligently discuss global warming, or anything else, until one knows exactly what one is talking about.
Now one thing that should be obvious is that a genus cannot be defined in terms of a species thereof. And yet that is precisely what some of the definitions on the linked page do. For example,
An increase in the Earth's temperature caused by human activities, such as burning coal, oil and natural gas.
This fails as a definition of 'global warming' because it is too specific. Not all global warming is anthropogenic (man-made). And even if all global warming were anthropogenic, it is not a matter of definition that this be so. The opposite mistake is committed by the following 'definition':
Also called climate change.
This is too general. All global warming is climate change, but not all climate change is global warming. There is also global cooling. And again, even if, contrary to fact, there never has been in the history of the earth any case of global cooling, this is not a question that ought to be decided at the level of a definition. Here is another defective definition:
the theoretical increase of global temperatures caused by the greenhouse effect.
Theoretical as opposed to what? What is the difference between a theoretical increase and an increase? What does 'theoretical' add? And why is a cause specified in the definition? Suppose something other than the greenhouse effect is the cause of global warming. Would it not still be global warming? The business of a definition is to isolate the phenomenon in question, to say what it is. The question as to what causes it is logically secondary and does not belong in the definition. Here is a real winner:
Increased levels of gases such as carbon dioxide that trap heat in the earth's lower atmosphere potentially causing global warming.
Where's my logic stick? First, causes should be left out of definitions. Second, global warming can occur without the build-up of gases like carbon dioxide. Third, the weasel word 'potentially.' Fourth, the definition is circular: the definiendum occurs in the definiens. The following definition seems adequate:
Global warming is a term used to describe an increase over time of the average temperature of Earth's atmosphere and oceans.
I would delete the pleonastic 'over time.' How could there be an increase that was not 'over time'? More importantly, note the word 'average' which I think is essential to a good definition. The claim that global warming is taking place is not the claim that at every place at or near the surface of the earth the temperature is higher than it was at that place and on that date in the past. Dennis Prager, an AM talk jock whom I respect, seemed to fall into this fallacy recently. He cited a place at which there had been a record low temperature as evidence against global warming. But it is nothing of the sort. A record low at a particular place is consistent with a general warming trend.
It should be obvious that an average increase in some quantity need not be steady or ubiquitous. Suppose the average price of a house in some locality has increased over a ten year period from X to Y. This is consistent with (i) some houses losing value, and (ii) the average value being at some times during the period less than X.
The last definition strikes this layman as adequate. But it leaves wide open the question whther global warming is occurring, and if it is, how fast and from what causes. But these are empirical questions for the climatologist.