CDN Crystal Ball: Tropical Troposphere Transcript
Where exactly is “ground zero” of climate change?
Some experts say it’s the Arctic.
Although others say it’s the tropics.
Or maybe Alaska.
But possibly Chad.
Unless it’s Greenland.
Although other experts insist it’s Florida.
Except it could also be the entire landmass covering Eastern Europe, Scandinavia, the former Soviet Union and Northern China.
Anyway you get the idea. Climate scientists make enough guesses to cover the whole world, then no matter what happens or where it happens, they can point to it afterwards and say Aha! Just like we predicted. And journalists everywhere can say their own nation is hardest hit.
But the real ground zero of global warming isn’t on the ground at all. It’s up in the air, about 10 km high over the equator, in a region of the atmosphere called the Tropical Troposphere. For forty years now, climate modelers have been saying that if you want to see the earliest and clearest sign of greenhouse gas-induced warming, you should look there. So it’s what we’re about to do.
For the Climate Discussion Nexus I’m John Robson and this is a CDN Crystal Ball check on the tropical troposphere hotspot.
The lowest layer of the Earth’s atmosphere, up to about 1 kilometer, is called the boundary layer.
The next layer up is called the troposphere, and above that is the stratosphere.
The top of the troposphere is about 10 km above the polar regions, but in the tropics it rises to about 16 km. The troposphere layer is where the big air movements take place that create our weather patterns. This includes convection, wind patterns, cloud formation, storms and turbulence of all kinds. Jet aircraft aim to fly at the top of this layer where the air is more stable.
The troposphere over the tropics plays a key role in the climate system. Most of the solar energy that drives our climate enters here. And because water vapour is a powerful greenhouse gas and tropical air is so moist, there are powerful positive feedbacks here that drive global warming.
At least that’s the theory. And it’s been the theory for a long time. In this 1985 report of the US Department of Energy we get to see some of the earliest predictions by NASA climate scientist James Hansen and his colleagues. And they said, look to the tropical troposphere if you want to see the warming.
So we’re about to, just as soon as I explain about this tropical tropo-thingy terminology thats potentially confusing because of the two “tropos” words one being the “tropics”, which is the bit of the Earth between the northern and southern parts, and the second being the “troposphere”, which the bit of the atmosphere between the stuff that’s really low down and the stuff that’s way up high. So yes, there’s a non-tropical troposphere and a tropical troposphere. And we are looking at the latter.
Specifically, the chart on the left showing warming in the winter and the one on the right shows warming in the summer. We’ll focus on the one on the left for now.
The bottom, left-to-right, axis is geographic, extending from the North pole at the left to the South pole at the right. So the tropics are the band in the middle, from 20N to 20S.
Meanwhile the down to up axis is also geographic, but going from down at the Earth’s surface to way up in the sky. And it’s marked in kilometers on the left and pressure in “millibars” on the right which, which obviously vary together. And the troposphere goes from just above the surface to about 16 km up.
OK, though, where’s temperature if it’s north-to-south on the X axis and earth to sky on the Y? And here’s the clever bit. The various lines on that chart are like the “contour lines” on one of those topographical maps that you so enjoyed in high school geography. Except instead of those lines indicating height, they represent temperature change.
Of course you could do such a chart with them measuring temperature. But what interests us here is how much the atmosphere in the middle of the chart, that is, in the tropics going left to right and in the troposphere going bottom to top, how much the temperature of the atmosphere there has changed since 1979 and how much the models and the modelers thought it was going to if CO2 doubled.
So now, colouring in where the increase is greatest, that red circle on the left stands for 7 degrees C warming in the winter, and the one on the right between 6 and 7 C warming in the summer, which we’ll average to 6.5 degrees.
So that’s what the computers said 38 years ago would happen if CO2 doubled. In fact it has risen since then by over 20 percent. So we’re a fifth of the way to CO2 doubling. Which means we should have seen about a fifth of their prediction come true by now. (Or a bit more, because global warming theory says temperature responds more at lower levels of CO2 than at higher ones.)
So a fifth of 6.5 degrees is 1.3 degrees. That’s how much warming the models predicted if CO2 went up as much as it did over the last 38 years. And spread out over 3.8 decades it’s 0.34 degrees per decade. But since the models also predict a bit of a delay before the system fully responds to increased GHGs, we’re rounding it down to about 0.3 degrees per decade. That’s the rate of warming we should have seen over the past 40 years in the tropical troposphere.
If the models are roughly right.
While not all climate models predict warming that fast, they do all predict the warming will be fastest in the same part of the atmosphere, the tropical troposphere.
And models also indicated we should have seen the pattern by now. In a 2006 report from the US Climate Change Science Program they said this is the pattern we should have seen over the period from 1958 to 1999.
And in the 2007 IPCC Report the authors said this is the pattern we should have seen over the whole 20thcentury:
That 2007 report also said it’s the pattern we’ll see in the future as CO2 levels keep going up.
And we won’t have to wait long because it emerges quickly in response to greenhouse gas emissions. In Chapter 10 of the 2007 IPCC report, specifically on pages 764-65, it says:
Upper-tropospheric warming reaches a maximum in the tropics and is seen even in the early-century time period. The pattern is very similar over the three periods, consistent with the rapid adjustment of the atmosphere to the forcing. These changes are simulated with good consistency among the models.
Got the picture? And yes, graphics got better between the 1980s and the 2000s. So that big hot red boil in the middle of the diagram is ground zero, or air zero if you like, for global climate change. It, not Ottawa or Auckland, is where the effects of global warming should be most evident. And luckily, we have some actual evidence here as well as some computer models’ predictions.
Temperatures in the troposphere have been measured independently by weather satellites since 1979 and weather balloons since 1958, so there’s data we can check. Which they did in that 2006 U.S. Climate Change Science Program report. And found a problem.
Here’s the pattern as colourfully predicted by 4 different climate models:
Remember yellow, orange and red mean warming, and blue and purple mean cooling. So a hot time in the old troposphere this decade. Except here’s what the weather balloon data showed:
Not the same, is it? Instead of a lot of warming in the tropical troposphere, it’s a mix of a little warming and a little cooling. And as the report authors had to admit, it’s kind of awkward.
Narrator: A potentially serious inconsistency, however, has been identified in the tropics. Figure 4G shows that the lower troposphere warms more rapidly than the surface in almost all model simulations, while, in the majority of observed data sets, the surface has warmed more rapidly than the lower troposphere. In fact, the nature of this discrepancy is not fully captured in Fig. 4G as the models that show best agreement with the observations are those that have the lowest (and probably unrealistic) amounts of warming.
How is it that the models that best fit the actual data are said to have “probably unrealistic” amounts of warming? This is a very new kind of science.
Despite which the mismatch caught peoples’ attention. Of course it’s no big deal if some models get some detail here and there wrong. It’s not an exact science, to put it mildly. But in this case it is a big deal because the prediction that didn’t fit observed data is one all the models make. They say if you want to see the warming effect of greenhouse gases, it will be fastest and strongest in the tropical troposphere and should be very evident by now so look there.
This finding led to the great tropical troposphere controversy.
Some authors said the data are probably right but the lack of warming isn’t a big deal, it’s bound to come soon. Others said maybe the data are wrong and we’ll soon discover that the warming has been there all the time. And over the years since 2006 the tropical troposphere has warmed a little more. But still not nearly as much as predicted. Instead, over time the gap between models and observations has just kept growing.
As climate models proliferated and were refined, they all continued predicting rapid warming in the tropical troposphere, at rates ranging from 0.16 (point-one-six) to about 0.44 (point-four-four) degrees per decade. Perhaps because their creators were certain it would happen and built it in. But nature has not cooperated: weather balloons and satellites have only recorded between about 0.06 (point-zero-six) and 0.12 (point-one-two) degrees per decade.
By 2018, the gap had widened to the point that the temperature observations from the middle of the tropical hotspot had fallen below the low end of the model projections. Here’s a more familiar sort of graph, showing time on the X axis along the bottom and temperature in the middle of the predicted tropical “hotspot” going up the Y axis.
There’s been one attempt to move the goalposts by focusing away from the failure to get the warming trend right and focusing instead on what’s called the “amplification ratio”. What the modelers say here is all they can really predict is the troposphere will warm faster than the surface. If the models predict too much warming at the surface it gets amplified into way too much warming up above. If they dial down the surface warming in the models to something closer to the real world, the troposphere wouldn’t look so bad either.
OK, but it still means the models have a warming bias, it just moves it down to the surface from ten kilometers up.
And even still, the models get the amplification rate wrong. When a pair of expert statisticians looked at how to measure real world amplification ratios, they discovered most data sets report they “are less than one indicating less warming in the lower troposphere than at the surface.” – in other words the models significantly overstate the amplification rate too.
So here we are in 2021, fifteen years after the “potentially serious inconsistency” was noted in that government report. The models predict too much warming and too much amplification. Yes, there’s been some observed warming. But there’s been nothing like what was predicted. And the inconsistency isn’t going away.
On the contrary, in the latest generation of climate models it’s worse than before.
The literature drawing attention to an upward bias in climate model warming responses in the tropical troposphere extends back at least 15 years now (Karl et al., 2006). Rather than being resolved, the problem has become worse, since now every member of the CMIP6 generation of climate models exhibits an upward bias in the entire global troposphere as well as in the tropics.
So apparently the people who make the models took seriously the idea that those models that actually matched the data were unrealistic and those that did not were spot on. But as Chico Marx once said, ““Who ya gonna believe? Me or your OWN eyes?” (Yes, Chico not Groucho, in Duck Soup, admittedly while his “Chicolini” was impersonating Groucho’s Rufus T. Firefly.)
We now have multiple data sets and they all tend to say the tropical troposphere isn’t warming the way the models predicted. So could all the data be wrong? Let’s ask an expert.
John Christy is an award-winning Professor of Atmospheric Science at the University of Alabama in Huntsville. He’s spent his career developing and analysing global temperature monitoring systems. He and his colleague Roy Spencer pioneered the technique for using satellites to measure atmospheric warming, an achievement which earned them NASA's Medal for Exceptional Scientific Achievement.
Well that has been around for at least 20 years, that our models are right, it's the real world that’s wrong. And so various ways to try to explain the way the observations have occurred. But over time we’ve had more than one satellite data set independently produced, more than one balloon data set independently produced, we’ve had reanalysis where the big weather centres create these maps of temperature and so on. And they all show the same thing, that that part of the atmosphere is not warming. So with so many independent empirical pieces of evidence it's hard to make that case anymore that the observations might be wrong.
Over the last 50 years or 40 years, whatever, you would think there would be an increase in the agreement between observations and the models. And in some cases, some variables, that's true but here in this very fundamental variable, the bulk temperature of the atmosphere — and this is what greenhouse warming is, is how much extra heat is accumulating in the atmosphere — that without getting that right it indicates to you that the physics, or I should say that the model components, are straying even further from the physics and not getting closer to them.
And so we see the result which indicates to you — and this is the basic problem with models is they’re not based on fundamental physics, they’re based upon approximations of what happens in the atmosphere. And so when they tune these approximations to fit the surface records, those approximations don’t work in the upper atmosphere. Which means they’re not correct and they need to go back to the drawing board in that part.
From what we’ve found, the amount of heat that is being retained by the models is much greater than what we actually see in the real world. So this is important in the sense that it's a test metric. In other words all the models show this should be happening when you increase greenhouse gasses, when you increase that heating amount, and that's something we don't find. Which means the real atmosphere evidently has ways to expel that heat that the models don’t allow.
Turns out that the models that agree most with the actual observations — they’re still too warm but they’re closer to it — are the ones that are least sensitive to carbon dioxide. The ones that have the lowest warming rate at the surface. Scientifically it's just amazing or almost incomprehensible, because in the scientific method we make a claim and then we test that claim against independent data and if a claim fails in that test we go back to the drawing board and restate the claim, or modify or result, or just say our result is wrong. We don’t see that here. We see model after model continuing to come forward with these scary scenarios of temperature rates that are just still not happening in the real world.
Remember, what we were comparing in our papers, recent publications, is the temperature changes that should have already happened if the models are correct on carbon dioxide. So this is a real simple and direct scientific test of these claims. Remember a climate model is only a hypothesis, it's only a claim. And to show that there’s a real problem with this claim meets with some vociferous responses because there is so much built upon the notion of climate alarm or climate crisis or climate emergency that when you show up with very simple and direct evidence that these claims can be falsified, you are touching a huge well-funded organization that will not like to see that message out.
So this mismatch is a very serious problem. And in discussing it the 2006 report did look at what might be causing it.
"It may arise from errors that are common to all models, from errors in the observational data sets, or from a combination of these factors. The second explanation is favored, but the issue is still open."
“The second explanation is favoured”. Got that? Given a choice between the models and the theory being wrong, or the data being wrong, “the second explanation is favoured”. Why? Not because the evidence supports it, that's the whole problem. Just possibly because we’re determined to believe it no matter what that silly old data says.
So yes, the tropical troposphere is “ground zero” for climate change. Including the fundamental scientific, and ethical, issue of what to do when the predictions don’t fit the data.
For the Climate Discussion Nexus, I'm John Robson, and that's our "Crystal Ball" check on the tropical troposphere hotspot.