Wow, it was unusually cold last week. In a small fraction of the globe. For a couple of days. And what does that cold snap, that big wiggle in the Polar Vortex that carries high-atmospheric winds around the North Pole, imply about “climate change”, also known as “global warming”, also known as “global weirding”?
The answer is very simple. Nothing.
If you heard anyone suggest otherwise — whether they said that the extreme cold implies that there is no global warming going on, or they said that the extreme cold implies that global warming is happening — you should seriously question anything that person says when it comes to climate change. Because that person does not respect (or perhaps even understand) the difference between anecdote and evidence; between weather and climate; between a large fluctuation and a small but long-term trend. Or between media hoopla and science.
In the interest of an imperfect analogy: Let me ask you this. Are you generally happier, or less happy, than you were five years ago? Answer this as best you can.
Now let me ask you another question. Did you, within the last month, have a really, really bad day, or a really, really good one?
Does the answer to the second question have much to do with the answer to the first one?
Barring an exceptional recent disaster in your personal or professional life, the fact that, say, last Thursday your car broke down, you locked yourself out of your house, your dog vomited on the carpet and you got caught in the rain without your umbrella does not have anything to do with whether you are a happier person than you were five years ago. Being a happier person has more to do with whether you have a better job, a happier family, a better sense of self-esteem, and things like that. And even if you love your job, you know there are going to be really bad days in the office sometimes. That’s just the way it goes. We all know that.
It’s the same with daily and monthly and yearly fluctuations in the stock market compared to the slow but fairly steady century-long growth of the U.S. economy (both curves corrected for inflation.)
So why, when there’s a big fluctuation in the daily, monthly or even seasonal weather, do people jump up and down about what the implications are for the long-term trends in climate?
Any one fluctuation, whether hot or cold, dry or wet, windy or calm, is by itself irrelevant. Weather fluctuates; that’s just how it is. It’s by no means unusual, now or in the distant past, for temperatures in the central United States to swing by 50ºF (28ºC) in just a few hours. Here’s a fun story by the Weather Channel listing a few extreme temperature swings, all of which were more dramatic than the recent cold spell. Weather in the U.S. has seen extremes since before Europeans arrived here and started recording their experiences, and it will continue to do so whether global warming persists or not.
Moreover, the recent cold wasn’t as exceptional as portrayed in the press, or as it seemed to people under the age of 40. One of the reasons that so many records were set this past week was that January 7th, over the past century, hasn’t previously seen an exceptionally cold day in the southeast. Specifically, let’s look at Greensboro, North Carolina, which was described in the press as follows:
- “Greensboro, N.C., also witnessed a major drop in its record low temperature, going from a previous record of 14 degrees to 5 degrees. “
Well, what were (before this year) the record temps in that town during the first 10 days of January? (see http://www.erh.noaa.gov/rah/climate/data/gso.daily.records.temp.precip.html)
Jan 1: 8
Jan 2: 5
Jan 3: 7
Jan 4: 3
Jan 5: 3
Jan 6: 5
Jan 7: 14 ==> 5 in 2014
Jan 8: 6
Jan 9: 2
Jan 10: 1
Jan 11: -5
In other words, the previous century or so of January 7ths were unusual — every other day in early January had already seen a very cold day! All this recent cold snap did was bring it into line with other cold early January days! A similar story held true in Atlanta. In short, despite the “record cold” media hype, quite a few of the new “records” weren’t especially exceptional for January… they were “normal” records, not worthy of the amazement expressed by reporters and citizens alike.
The issue this highlights is that if you want to tell whether the climate is getting warmer, the record high and low temperatures on a given day aren’t going to tell you much! The record temperatures fluctuate and are subject to random, extraordinary events. We don’t know how rare those exceptional events are, and the more wild and spectacular they are, the less we know about them. If something happens once every one, three or ten centuries, but we only have one century of records, we’ve only seen it happen once or perhaps twice, if ever. So when it happens, we can’t say “aha, that’s something that would not have happened if it weren’t for climate change”. We can’t draw such a conclusion, anymore than we can conclude that your stunningly bad day at work last week implies that your job, in the grand scheme of things, isn’t going to be as fulfilling in future as it used to be.
Take a look at this plot, from the website Weather Underground, which tells us something about the weather and climate in San Antonio, Texas.
It shows, for each day of the year, over many years, the average high and average low temperatures in blue, and the record daily highs and lows in red. [Unfortunately I do not know exactly how many years are included in this data; I would estimate 60 years, but Weather Underground does not provide this important information --- and they should.] Of course the average and record highs and lows all trend higher in the summer and lower in the winter, as expected. But notice:
- the average highs and lows are smooth curves
- the record highs and lows are jagged curves
Why is that?
Because for each day, every year contributes to the average. Year-to-year fluctuations for each day get smoothed out, as do day-to-day fluctuations in each year. So the curve showing the average is smooth as you move from one day to the next.
By contrast, only special, unique, remarkable, extraordinary days contribute to the record high and record low on a particular day. These are subject to large day-to-day fluctuations, because something extraordinary may have happened on January 9th of some 20th century year, but not on January 10th or 8th.
So a specific event with record heat or record cold isn’t useful for telling us about climate change. Though impressive, it just represents the vagaries of life that get in the way of us understanding the real long-term trend, just as a truly bad day can make someone forget, for a short while anyway, that his or her life is going pretty well on the whole.
It’s the same with extreme hurricanes and tornadoes, droughts and floods. These are too rare, and require too many elements to come together in a unique mix, for us to easily conclude anything about them. Hurricanes Irene and Sandy were a big deal in and around New York City; but are they signs of global warming?! What about the devastating 1938 hurricane that hit eastern New England? What about the two strong hurricanes that struck New England, a month apart, in 1869? It’s impossible to conclude that Irene and Sandy are related to global warming/weirding. Only if you see something steady over decades — the average storm becoming stronger, or the average number of storms rising — or a dramatic trend — Irene and Sandy-like storms ceasing to be rare and becoming once-every-other-year events over decades — will you be able to draw any conclusions from hurricanes that the climate has really changed.
No… if you want to determine whether global warming is occurring, you must set aside the record high or low temperatures, the extreme storms, the exceptional events… the ones that the media reports, and the ones that you yourself easily remember. Instead, you need to look at the averages — which is where the data is sufficient, and sufficiently stable, for some conclusion that the Earth has slightly warmed (by just 1 – 2 ºF = 0.5 – 1.1ºC –which is still enough to melt a lot of glaciers) to be drawn. And even our current 100 years of data from around the globe is just barely enough to make that possible. I’ll cover that issue another time.
So let’s not waste our time fishing for red herrings. Yes, it is possible that an overall small increase in the temperature of the globe will make wild weather more common. But it will be decades before we have enough data to tell whether, in fact, the rare events of which we have so few examples really are more or less common than they used to be. And no one event, in isolation, should ever be mentioned in the same sentence as “climate change”.