There’s a lot of talk these days about global temperature, in news reports, policy discussions, and casual conversation. The global temperature under discussion is surface air temperature (SAT). It’s not the depths of the ocean — even though that’s really a better measure of global warming, we don’t live in the depths of the ocean. It’s not the temperature in the upper atmosphere, we don’t live in the upper atmosphere. It’s the temperature at Earth’s surface. That is, after all, where we live.
But climate deniers don’t like that, because surface air temperature has risen so dramatically these last few years. Someone proclaims “The last five years have been the hottest on record!” and the deniers want to deny it, but they can’t use actual data for SAT because the data support the statement. But there’s a sneaky way for them to try: look for some data set — ANY data set — which you can claim represents “global temperature” but contradicts the “last five years” claim. If instead of claiming it’s global temperature, you simply say nothing at all about it so readers assume so, even better. If that data set happens to be crap — best yet!
There are lots of data sets for actual SAT: the best-known are from NASA, from NOAA (National Oceanic and Atmospheric Administration), from HadCRU (the Hadley Centre/Climate Research Unit in the U.K.), Cowtan & Way (researchers from the Univ. of York in the U.K.), and the Berkeley Earth Surface Temperature project (an independent effort from researchers in the USA). Here’s the data from NASA — yearly average surface temperature for the whole planet (which is, after all, the topic):
I’ve put red circles around the five hottest years. It turns out, they’re 2015 through 2019, i.e. the last five years. Although the year 2019 isn’t over yet I’ve plotted the year-to-date average; those who know the data well know that we’ve seen enough of it already to figure out that it’s going to end up in the top five. If I left out 2019 altogether, then the top five would be 2014 through 2018, again, the last five years.
What about data from NOAA, or HadCRU, or Cowtan & Way, or Berkeley Earth?
Golly! They ALL say that the last five years are the hottest on record!
Global temperature shows a distinct trend, but it also shows plenty of fluctuations. Lots of things cause fluctuations — things like massive volcanic eruptions (which tend to cool off the planet — temporarily) and el Niño, the warm phase of the El Niño Southern Oscillation (ENSO), (which tends to warm up the planet — temporarily). But they don’t cause trend. The trend these days is from man-made climate change (i.e., global warming).
Climate deniers love the fluctuations because they make it harder to see the trend. The data set which shows the least level of fluctuation is: total heat content in the depths of the oceans. But, humans don’t live there so it hasn’t gotten a lot of attention. What does it say? This (ocean heat content to a depth of 2000 meters, the latest, and in my opinion best, estimate from the Institute for Applied Physics IAP):
The trend is quite clear! That’s because the fluctuations are much smaller (relatively speaking) than they are in surface temperature. Trend and fluctuation go together in real data, but the fluctuations don’t tell us about climate change; they’re there even when climate doesn’t change!
Fluctuations make it harder to see and to measure the trend. That’s why climate deniers love ’em — they don’t want you to know what the trend is because that does tell us about climate change. They don’t even want to know themselves; if they faced the truth, they’d either have to abandon their attempts to sabotage the rest of us by preventing us from actually doing anything about it, or admit to themselves that they are inherently evil.
Instead, they look for a data set that has the largest level of fluctuation, in order to fool themselves and especially to fool you. There’s a natural choice: temperature in the atmosphere. Not at the surface (where we live), mind you, but in thick layers of the atmosphere above Earth’s surface. The favorite choice for many climate deniers is TLT, temperature in the lower troposphere, the lowest level of the atmosphere where most of our weather happens. Lower-troposphere temperature (TLT) shows much more fluctuation than surface air temperature (SAT), mainly because it responds much more strongly to fluctuation factors like volcanic eruptions and el Niño, a fact clearly demonstrated in the peer-reviewed literature (see, for instantce, Foster & Rahmstorf 2011).
The two best-known data sets for TLT are from RSS (Remote Sensing Systems) and UAH (University of Alabama at Huntsville). They’re based on satellite measurements of microwave emissions from the bulk of the atmosphere. Climate deniers like to imply that it’s as simple as sticking a thermometer in your ear like a doctor might — but that’s a lie. It’s extraordinarily complicated, which is why there are multiple data reductions (RSS and UAH are but two), and those have been revised over the years as we’ve learned how to do it better.
They don’t start until 1979 because the satellites providing the raw data weren’t there until 1979. Here’s what they show:
The UAH data are warming more slowly than RSS data. That’s because the UAH data are crap. When we compare them to other data sets, especially from balloons which radio their data to us after release to rise through the air, the UAH data are the outlier, the lone data set showing less warming than the others (see this and this) . That’s because the scientists who created it are two climate deniers: Roy Spencer and John Christy.
Either way, they don’t show the last five years as hottest on record. That’s because the fluctuations are so much larger than they are in surface temperature or ocean heat content. You can probably see the large peak in 1998, showing how strongly that year’s el Niño affected TLT. It also affected SAT, but not by nearly as much — the biggest fluctuations are in TLT. Biggest fluctuations == least precise trend == climate denier favorite. Also, crap data == trend too low == climate denier favorite.
Case in point: David Middleton at the WUWT blog. He objects to statements by Steven Novella, so he attempts to contradict them. The first? You guessed it! Novella says “2014-2019 have been the hottest five years on record.”
Novella’s claim is mistaken because 2014-2019 is actually six years, not five. But it’s an honest mistake, and it’s not a misleading claim because whether you include the 2019 year-to-date value or not, the last five years were indeed the hottest on record.
David Middleton attempts to mock this by showing this graph:
It’s not global temperature (at least, not where we live!). It’s lower-troposphere temperature (TLT) from UAH. What a surprise! Not.
David Middleton doesn’t discuss this. Heaven forbid you know what you’re really looking at.
This blog is made possible by readers like you; join others by donating at My Wee Dragon.