Superstorm Sandy. A March heat wave. The warmest year in the United States since 1895 (the first year with a climatological data base of sufficient quality to be included in the so-called modern record).
Obama's Inaugural pledge to do something about climate change (maybe a pledge to stop tilting at windmills while tilting toward subsidies for large scale wind farms).
Predictably, these and other recent climatic anomalies have triggered a renewed interest in global warming (aka climate change). Thus, a new round of exchanges between the so-called climate change deniers and the anti-climate change deniers. Thus, conspiratorial accusations: special pleading, charges of cooking the books, whether by the fossil fuel industry or the environmental ("Green") lobby. Thus, Al Gore style rhetoric about rapid and dangerous climatic change with an attendant threat of more superstorms, droughts, floods, famines and who knows what else.
All of which has caught my attention, mostly because climatology is one of the very few things that I can legitimately claim to know something about. So, for what it's worth, here are some of my thoughts on the subject. First, it is foolish to deny that the planet as a whole is going through a warming period. And it is foolish to categorically deny that human activity, burning of fossil fuels especially, has not contributed to the observed and well documented warming trend.
But it is equally foolish, I think, to contend that global temperatures are rising so rapidly as to pose a clear and immediate threat to human civilization and/or to the earth's ecological systems. So far as I know, the record, at best, shows only modest warming since the warm El Nino year of 1998. More significantly, however, any recent temperature increases have been significantly lower than the increases predicted by various climatological models.
But a word of caution. We should not become complacent: climate changes do sometime happen suddenly and dramatically. We could perhaps reach a "tipping" point which would trigger a sudden, major shift in the world's climate. The Little Ice Age of the 14th century, for example, did hit Europe quite hard, quite suddenly and certainly unexpectedly.
Moreover, the recent climatic record is something of a mixed bag. Several recent Russian and Alaskan winters, for example, have been unusually snowy and cold. On the other hand, we have recently experienced a number of unusually warm episodes such as the March heat wave of last year.
This suggests, among other things, that one should not use individual "freak" climatic occurrences as indicators of or predictors of long-term climatic shifts. Many such events have happened in the past, perhaps with greater frequency or intensity than any recent occurrences (e.g. the heat and drought of the 1930s).
Yet again a word of caution: if certain abnormal events were to occur repeatedly over a sustained period of time (two decades perhaps), one could then reasonably conclude that something climatically significant was taking place. (An excellent example of which is provided by the persistent warmth that has characterized Upper Midwest winters since the 1980's).
But the bottom line. What can we say with reasonable certainty regarding the CAUSE of the global warming of the past three or four decades? As the man once said, the answer to this question is beyond my pay grade. Thus, I can only repeat what others have said, taking it for granted that their various hypotheses are plausible (i.e. leaving aside the conspiratorial palaver about the fossil fuel folks and/or the leftist elitists).
There is, of course, the so-called greenhouse gas hypothesis, a hypothesis that is quite consistent with observed temperature patterns in the Upper Midwest if not in the Northern Hemisphere generally). Always remember, however, that greenhouse gasses include water vapor, methane, etc., not CO2 alone. And be intellectually honest enough to admit that the earth's climatic system is exceedingly complex: that there are factors that we understand only in part and/or factors that we may understand not at all (and that -- much to our surprise and perhaps with a jolt to our now accepted understanding of the climate system-- may someday come to our attention. In this regard, never forget Karl Popper's falsification principle).
In closing, I would also note that global warming could result in part from the recent lack of climate changing volcanic activity, cleaner air (the cooling that took place in the U.S. in the 1960s and 1970s was attributed by some to atmospheric pollution and the ensuing warming to the cleaner air of recent years, China and India excepted). There is also the much debated issue of solar influences, a factor that even the International Panel on Climate Change (IPCC) admits could account for at least some of our recent warming.
And, at least for now, I rest my case.