Tag Archives: Global Warming Basics

Trend and Fluctuation (One More Time)

A recent comment says:

The Gistemp temperature anomaly for June 2015 was 0.79 degrees Celsius.
The Gistemp temperature anomaly for February 2016 was 1.32 degrees Celsius.
In 8 months the temperature anomaly increased by 0.53 degrees Celsius.

The question is, how much of the 0.53 degrees Celsius increase was caused by man-made global warming?

Let me propose an analogous question:

The temperature on March 1st reached 2°C. The temperature on March 2nd reached 18°C. In 1 day the temperature increased by 16°C. How much of the 16°C increase was due to the progress of the seasons from winter toward spring and on to summer?

Maybe it’s obvious, even to the author of the aforementioned comment. But just in case, the answer is: the day-to-day fluctuation in temperature swamps the amount of trend change in a single day.

Only a fool would claim that most, or even a sizeable fraction of, the 16°C rise from one day to the next was due to the passing of the seasons. Only a bigger fool would ask the question with a straight face. Only the biggest fool would attempt to use the day-to-day fluctuations in temperature as evidence that there’s no seasonal trend and no reliable evidence that summer will be hotter than winter.

Global average temperature data from NASA GISS looks like this:


The black line follows the monthly average temperature anomaly. The thicker red line shows the trend estimated by linear regression. The blue circles mark the values in June 2015 and February 2016.

Fluctuations come and go, but over the long haul they average out to nothing. Trends persist, so over the long haul they can accumulate to large changes in spite of the fact that in the short term they amount to very little. That’s why, just since 1970, the net trend change in the NASA GISS data is 0.84°C, considerably bigger than the short-term change from June 2015 to February 2016 which is due to fluctuation.

Global warming is about the trend, not about the fluctuations. The progress of the seasons is about the trend, not the fluctuations.

If the trend continues at the present rate, then by January 2100 the net warming due to trend will be 2.34°C above the 1970 value. And of course, it’s possible the average rate over the remainder of this century will be higher than it has been recently, especially if warming triggers feedback in the carbon cycle (releasing natural stores of CO2 or CH4).

Let’s avoid that.

Let’s also stop treating claims or questions which conflate trend and fluctuation in the most ludicrous way, as being serious claims or questions, let alone worthy of “debate.”

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State of the Climate: Earth’s Temperature

“Everybody complains about the weather, but nobody does anything about it.”

That now-famous saying is often attributed to Mark Twain, but in reality he only popularized it when, in a public lecture, he quoted its originator: his friend and sometime co-author Charles Dudley Warner.

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Global Warning

A story in the Washington Post highlights the fact that scientists have been warning us about man-made climate change for a long time.

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Global Warming Basics: Trend Games

Climate is the rules of the game;
weather is the roll of the dice.

One of the things I emphasize most often and most strongly is that, while global temperature is forever fluctuating, it’s also showing a trend.

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Global Warming Basics: Loaded Dice

I read Shakespeare and the Bible, and I can shoot dice. That’s what I call a liberal education.
— Tallulah Bankhead

People have been playing with dice for at least 5,000 years. They come in all shapes and sizes, but have a common purpose: to generate randomness. When dice are rolled (or “thrown” or “cast” or “tossed” or “shot,” depending on your verb of choice) many results are possible, but what actually happens isn’t known until it happens. Dice (or one die, to use the singular) are the world’s original random-number generator. We may not know what they’ll give but at least we can figure out what to expect.

If they’re fair, that is.

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Global Warming Basics: What Has Changed?

I started the “Global Warming Basics” posts specifically to help people who are interested in what’s going on, wondering whether we should do something about it and what, but want to keep things simple. My purpose isn’t to turn you into a scientist — it’s just to give you enough information to make sense out of what you hear about the subject. Alas, that can be all too difficult, because so many people, and politicians, are willing to distort the truth.

Perhaps the most basic question for a lot of people is “What has changed?” Has climate changed already? In what way? What have we seen in the last few decades that concerns us? What did we see last year? Last month? What’s been going on, really?

Let’s take a look.

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Global Warming Basics: Greenhouse Gas

Heat is a form of energy, but it’s certainly not the only one; there are so many I won’t bother you with a list. In any complex system — an automobile engine, the human body, planet Earth — energy is constantly changing from one form into another, so if some object has energy (and it always does), sooner or later that energy will distribute itself among the various available forms. Since one of those is heat, in general terms when you gain energy you’ll end up with more heat, when you lose energy, there’s less of it to go around and that means less can be heat.

Another important form of energy is electromagnetic waves. It’s a fancy science term but in at least one form it’s something we’re all familiar with: light. More generically we can call it radiation.

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Global Warming Basics: Signal and Noise — and Trend

Even when climate is constant, unchanging, the weather is not.

Temperature is one aspect of weather (and therefore of climate), so it’s in constant flux, whether we’re looking at a single location or an average over the whole globe. The changes we observe, whether of ever-changing temperature or any other weather variable, can be divided into two broad categories: signal and noise.

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