Almost all of us live on land, not the ocean. And, most of us live in the northern hemisphere, not the southern. For the benefit of most of us, let’s take a closer look at how temperature has changed, in the northern hemisphere, on land.
There are several data sets to choose from. I’ll focus on two of them, from NASA and NOAA. It’s bound to arouse the ire of the usual deniers; whenever data show that global warming might be a serious problem, their main tactic is to slander both the data and the scientists who release it.
Some of you might even remember some years back when the Berkeley Earth Surface Temperature project was organized by Berkeley physicist Richard Muller because he suspected that something might be fishy with global temperature data sets; the climate scientists might be just plain mistaken through lack of competence, or might even be “fudging” the data to make global warming look serious. He was determined to create a new, comprehensive but uncompromised, global temperature estimate. The denier community was thrilled; they eagerly awaited confirmation from a skeptic that all those other guys tracking global temperature had got it wrong. Anthony Watts, one of the most adamant data assassins, said that he would accept the results no matter what they were.
Unfortunately for them, not only did the Berkeley Earth data show that the other guys got it right, Richard Muller turned out to be a genuine skeptic rather than denier. When he saw the results with his own eyes, he believed what he saw. All the deniers who had so adored and embraced Muller, and swore to believe what was discovered, turned on him like a pack of wolves.
But the Berkeley Earth temperature data isn’t kept constantly up-to-date like that from NASA and NOAA. It will, however, be useful to display what I was able to get of it for northern hemisphere land in order to show how my two choices, NASA and NOAA, compare to the Berkeley data — the one the deniers said they’d love until they found out what it shows.
First let’s compare Berkeley data to NASA in those months for which both report results, with Berkeley data in blue and NASA data in red:
The match is excellent, the main difference being that the Berkeley data, the one the deniers said would settle the issue once and for all, actually show a wee bit more warming than the NASA data. Here’s a comparison of Berkeley and NOAA data, with Berkeley again in blue and NOAA in red:
The match is, quite simply put, remarkable enough to remark on. The main difference, if you study the differences closely, is that again the Berkeley data show a wee bit more warming that NOAA data.
We want to know what has happened up to the present, which for monthly averages means through June of this year. To make things easier to see I’ll compute yearly averages, and even though 2015 is only half complete I’ll include this year’s year-so-far average so we can see how 2015 is shaping up by comparison. Let’s start with NASA:
Several things are worth noticing. One is that since about 1970 temperature has risen steadily and consistently. It certainly shows a lot of fluctuations, jiggling and wiggling up and down in addition to its steady long-term rise, but the trend is consistent. It has consistently gotten warmer for over 40 years now, it hasn’t stopped, it hasn’t even slowed down.
The same is true of global (not just northern hemisphere) temperature combining land and ocean (not just land), but that hasn’t stopped deniers from clinging to the idea that earth’s temperature has stopped rising (they call it a “pause,” I call them “pausemaniacs”) or at least slowed down (they call it a “hiatus”). Their chosen “pause time” (which I call “denial time”) varies, but it usually starts in 1998 and ends with 2013 or 2014:
To get an idea of the trend, apart from those up-and-down fluctuations, we can apply a bit of mathematics. One good way to identify real trend changes, not just wiggling around that might look like a trend change, is to apply the technique called change-point analysis. It identifies several times in the past when we can have some confidence that the actual trend, the rate of global warming, changed. There isn’t any change point in at least 40 years, temperature really has kept going up and not slowed down. The estimated trend it gives is the type of mathematical function which is referred to as piece-wise linear.
Another useful analysis is to smooth the data, i.e. find a smooth curve that approximates the trend not the fluctuations. For these data the two methods give very similar results (piecewise linear in blue, smooth in red):
Another noteworthy sign is that this year, so far, is on track to beat the pants off any previous year for hottest on record.
That’s what the NASA data say, what about NOAA? It shows much the same story, but estimates that this year isn’t just on track to beat the pants off the hottest on record. It is, so far, (to use the vernacular) “wicked hot”:
We can apply the same mathematical techniques to NOAA data, which again finds no change point (no trend change) for over 40 years, and again the two trend estimates are quite similar:
Kinda puts “denial time” in the trash bin.
Finally, let’s zoom in on more recent times, since 1970. Here’s the NASA data:
The red line is a fit to the data by least-squares regression. This makes abundantly clear that in addition to its rising trend, temperature shows constant fluctuations up and down. It also shows how silly it is to claim that temperature has “paused” — only those who aren’t willing or able to face the truth believe that those fluctuations somehow make a genuine change in trend.
NOAA data show the same thing, as well as just how hot this year-so-far is:
Analysis of the NASA data suggest that the land area of the northern hemisphere is warming at a whopping 2.87 deg.C/century. On a scale more familiar to most Americans, that’s 5.2 degrees Fahrenheit per century. Imagine, if you will, the entire northern hemisphere land area getting over 5 degrees Fahrenheit hotter. That’s what NASA data put the present trend at. And that’s just the present trend; we expect within a decade or two that warming will get even faster.
NOAA data, however, put the trend at 3.12 deg.C/century, which for most Americans translates to 5.6 degrees Fahrenheit per century. Now, imagine the whole northern hemisphere land area getting even hotter than the NASA trend suggests.
Then imagine the warming rate getting even faster. Suddenly the phrase “wicked hot” seems like a frighteningly apt description.