With the onset of winter's cold each year we can look forward to the reliable appearance of Skepticana deniacus, an increasingly popular bird of prey that feeds on ignorance and fear. With the regularity of a finely tuned pendulum, as soon as the temperature hits freezing this annoying species of fowl cries out with indignation that global warming must be a farce. After all, how could the world be warming if snow is falling outside?
Likewise, every winter we see newspaper editors across the country trot out the old and tired cartoon of the global warming group meeting canceled due to snow and ice. Give me a minute here -- I'm doubled over in pain from the laughter.
Whew. Now that we've recovered from that laugh riot, we can be sobered by the reality that newspaper editors and much of the general public all suffer from the common misunderstanding that weather and climate are equivalent. They are not.
Climate describes atmospheric behavior averaged over long time periods of decades and centuries across large geographic areas. Weather describes actual local atmospheric conditions over short periods of time, from hours to days. Weather is all about the actual state of the atmosphere with respect to wind, temperature, moisture, pressure, cloud cover and other instantaneous measurements. Climate is a composite of weather conditions averaged over many years. Think of weather as a single datum point and climate as a large collection of those data.
Better yet, think of weather as a one-night stand. Then climate would be raising the kid resulting from that night for the next two decades. One immediately leads to the other, but the two are completely different phenomenon. And that is why we have two distinct fields of study: meteorology and climatology.
The distinction between weather and climate becomes critical in understanding global warming. Let's look at what is happening right now. A persistent high pressure over the Arctic is acting like a big boulder in a fast moving river, causing the jet stream to flow south deep into the United States. With that big dip in the jet stream comes cold Arctic air. So we are all freezing our fannies off this week. But that has absolutely nothing to do with global warming. We can see catastrophic effects of climate change with an increase in average global temperature of just 2 to 3 degrees. If the arctic air warmed from -70 to -67 degrees, you would still freeze your buttocks off when that air blew south, but the impact on the global climate would nevertheless be profound over time. Weather is right now, the need to put on a thick winter coat to stop that cold arctic air from nipping off a limb from frost bite. Climate is the fact that the arctic air is warmer than expected, even if still cold enough to kill. Arctic air will always be brutally cold even in the most extreme cases of global warming. Snow and ice will always be a winter reality. So stop already with the embarrassing nonsense that climate change can't be real because it is cold outside. Nobody ever said climate change meant the end of winter. Grow up.
Another favorite foul fowl from deniers is the old canard that global warming is nothing but a sign of natural variation in climate. That claim is fascinating on two levels. First, the idea implies that scientists themselves never thought of the idea that the earth's climate varied over the past 4 billion years. Hmmm. If they had only known this one misunderstanding would have been cleared up! Second, the deniers only know of such natural variation from the field of climatology and from climatologists! So deniers believe climatologists when they say there has been natural variation, while suggesting that those scientists actually never thought of such variation! One of the oddest twists of logic I've ever encountered.
But I believe the real confusion between weather and climate derives from the fact that most of us have difficulties with the concepts of averages and trends. These are seemingly simple and self-evident ideas, but that simplicity is deceptive. How many of us remember from school the difference between average, mean and median? How many of us remember how to do a polynomial regression to uncover a trend? Averages and trends are not so simple after all -- but are critical if we are ever going to move beyond the silly idea that a cold winter means climate change is not real.
But forget the math; let's take a hypothetical example instead. Let's say for the sake of discussion that in Austin, Texas, in 1990 the average winter low was 40 degrees and the average winter high was 60 degrees. Then in 1991 the averages were 40.1 degrees and 60.1 degrees, respectively. Would you feel any difference? Of course not! In fact, even if the average temperature was .1 degrees higher, you could still have record lows that year if you had a greater number of days above average. But sure enough as soon as that record low was recorded a denier would be on TV claiming global warming a hoax. Local record low temperatures are a weather phenomenon, not a climate issue. But in 10 years if that trend continued the new averages would be 41 and 61 degrees. In another 10 years the numbers would be 42 and 62. In just 30 years the average temperatures would have risen 3 degrees, an increase that climatologists agree would have catastrophic impacts. The weather would not be changing noticeably even as the trend was rising dangerously. So of course we will experience cold winters, with deep freezes, snow and ice and maybe even record lows. That weather has absolutely nothing to do with the reality of global warming.
Now let us all go out and do some polynomial regressions. And please spare us the pain of another bad cartoon with global warming scientists huddled outside a room boarded up with a sign that says "Closed due to snow and ice." A 5-year old might find that funny the first time, but this is too serious for juvenile humor to guide our policy decisions. Skepticana deniacus needs to go the way of the dodo bird so we can get on with the business of planning for the future.