Skip to content

Another Attempt To Find The Tropical Hotspot!

September 13, 2015

By Paul Homewood  


In his latest rant against deniers, David Holub  referred to an article in the Guardian which was, even by their standards, particularly misleading. 




Written by the notoriously unreliable John Abraham, it says:


A very important study was just published in the Journal of Climate a few days ago. This paper, in my mind, makes a major step toward reconciling differences in satellite temperature records of the mid-troposphere region. As before, it is found that the scientists (and politicians) who have cast doubt on global warming in the past are shown to be outliers because of bias in their results.

It is known that there is a problem because there are multiple groups that create satellite temperature records. For instance, NOAA, Remote Sensing Systems (RSS), and the University of Alabama Huntsville (UAH). The problem is, their results don’t agree with each other. In particular, the UAH team, led by Dr. John Christy and Dr. Roy Spencer (who have discounted the importance and occurrence of climate change for years) present results that differ quite a bit from the others. In fact, in the current paper, it is stated that “Despite using the same basic radiometer measurements, tropical TMT trend differences between these groups differ by a factor of three.”

An important aspect to this issue is that for many reasons, it is expected that the tropospheric temperatures in the tropics will warm more than surface temperatures. This is called “tropospheric amplification.” According to two satellite groups, there is in fact such amplification. According to the UAH team, there is no amplification. The presence or absence of amplification is often used by some skeptics to discount the importance of global warming.

Why are there differences? Well that’s part of what this paper tries to answer.

Each of the teams try to deal with and correct for various satellite errors. For instance, sometimes the diurnal cycle effect is removed using temperatures from climate models. The RSS and NOAA teams “apply a drift correction based on the diurnal cycle from a GCM (global climate model) whereas UAH produces a microwave sounding unit mid-tropospheric temperature diurnal correction based on temperature comparisons between three co-orbiting satellites … UAH does not yet correct the diurnal drift for satellites carrying Advanced Microwave Sounding Units because they attempt to use these satellites during periods when the diurnal drift is small.”

The present paper presents a calibration scheme that allowed them to obtain a diurnal correction from the satellite measurements themselves, in particular, by solving for a common diurnal cycle correction using temperatures from all available satellites.

As the authors state in the paper, their new results agree with the two groups that show more warming. They disagree with UAH. As the authors state,

In general, our trends corrected with a GCM and trends corrected with our observationally derived diurnal cycle correction are similar to trends from NOAA and RSS … the UAH ocean trend is notably lower than trends from the other datasets.

They also discovered that the results from RSS, NOAA, and the new study all show tropical amplification and are in agreement with the expected amplification from climate models. They state, “There is no significant discrepancy between observations and models for lapse rate change between the surface and the full troposphere.”



The first thing to highlight is that the paper is talking about mid tropospheric temperatures, rather than the lower tropospheric ones which we continually compare to surface temperatures. The latter go up to around 2km in the atmosphere.

The headline, deliberately in my view, does not make this clear. As we know, many people don’t get far beyond the headline, and certainly won’t know the significance between the two layers. As a result, they will have taken home the message that satellite temperatures cannot be relied on, and that the surface data must therefore be right.

The article then compounds this by talking about “the UAH team, led by Dr. John Christy and Dr. Roy Spencer (who have discounted the importance and occurrence of climate change for years)”, leaving the impression that UAH are some sort of outlier.

As we know, of course, UAH and RSS data for the lower troposphere, TLT, follow each other very closely since 1979, and both have been rapidly diverging from the surface data in recent years.


The actual topic of the article is the tropospheric hotspot, which climate models say should exist. As Marcel Crok explains:

Based on theoretical considerations and simulations with General Circulation Models (GCMs), it is expected that any warming at the surface will be amplified in the upper troposphere. The reason for this is quite simple.

More warming at the surface means more evaporation and more convection. Higher in the troposphere the (extra) water vapour condenses and heat is released. Calculations with GCMs show that the lower troposphere warms about 1.2 times faster than the surface. For the tropics, where most of the moist is, the amplification is larger, about 1.4.

This change in thermal structure of the troposphere is known as the lapse rate feedback. It is a negative feedback, i.e. attenuating the surface temperature response due to whatever cause, since the additional condensation heat in the upper air results in more radiative heat loss.


Measurements from both satellites and radiosondes have repeatedly shown that the hotspot does not exist.





This has of course been a huge embarrassment for both the models and their supporters, and naturally the topic is a hot one, which has been well covered elsewhere. Earlier this year, UNSW researchers claimed that the hotspot did exist after all, but only after retrospectively “adjusting” radiosonde data!

This paper by Bo-Chedley talks in the Abstract of using a homogenized TMT dataset. Alarm bells should start ringing when we hear that term.


However, it is worth taking a look at the RSS graphs themselves, which show things are not quite as the Guardian boldly claims:

First, the graphs for the Tropics, lower and mid troposphere.





We can see that:

1) The TLT trend is higher than the TMT, opposite to what the models would predict.

2) Both show a flatlining since 1998.

3) Both also show little change between 1979 and 1997, followed by a step change brought about by the El Nino of 1998.


Recall that for the tropics, where most of the moist is, the amplification should be about 1.4 times the warming at the surface. Also remember that GISS surface data has been diverging from the RSS TLT data at a rapid rate of knots since 1998. Therefore it is apparent that the RSS data does not support the theory that Tropical mid-tropospheric temperatures are rising faster than the surface ones, (or at least not as reported by GISS!).






For reference, the UAH TMT trend for the Tropics since 1979 is 0.06C per decade, just slightly below RSS.


GISS surface trend for the Tropics is much higher at 1.07C per decade.

  1. Joe Public permalink
    September 13, 2015 4:49 pm

    “An important aspect to this issue is that for many reasons, it is expected that the tropospheric temperatures in the tropics will warm more than surface temperatures.”

    Perhaps it is simply that the expectation is wrong?

  2. AndyG55 permalink
    September 13, 2015 8:21 pm

    Apart from the 1998 – 2001 El Nino, which added about 0.26ºC,

    …. there has been no warming in the LT in the whole satellite record. None at all !

  3. September 13, 2015 9:35 pm

    Reblogged this on CraigM350.

  4. September 13, 2015 9:55 pm

    It took the events of September 11, 2001, Climategate emails in late November 2009, and six years of official excuses for fraudulent science to open my eyes to this unwelcome empirical reality:'S_SCIENCE

  5. September 13, 2015 10:55 pm

    Thanks, Paul. Very good work.
    I hope that soon WFT will have UAH Version 6 LT temperatures available.

  6. Alan permalink
    September 14, 2015 9:20 am

    I see Harrabin and the Met Office are at it again…

    Typically one sided article.

  7. Tim Hammond permalink
    September 14, 2015 9:31 am

    So we change real, actual data with “adjustments” from models, and that makes the real, actual data more accurate.

    And we have to do that, because the real, actual data doesn’t agree with our other real, actual data that we have already adjusted.

    Are these people serious?

  8. TOnyM permalink
    September 16, 2015 2:18 am

    The missing hot spot is at the bottom of the Pacific Ocean with the rest of the missing heat from the surface.

  9. JustAnotherPerson permalink
    September 17, 2015 1:28 am

    I have no idea what The Guardian is talking about. As you can see here, ( there is hardly this “lowballing” they speak of; rather, it seems that UAH and RSS agree with each other quite well for the mid-troposphere tropics. Actually, if you look at the end of the graph, UAH has a higher anomaly than RSS does. The fact that this is considered journalism (they even link to SkS, see here: is surprising, to say the absolute least. Then if you look at RSS’s lower troposphere tropics data ( compared to HadCRUt4’s surface tropics data ( we get a trend of 0.101 K per decade for RSS and a trend of 0.127163 C per decade for HadCRUt4 ( (Forgive me, but I am fairly sure that K and C in this case are interchangeable, and I ask you to correct me if I am mistaken.) Either way, the trend for HadCRUt4 surface trend is higher than the one for RSS, which is the exact opposite of what this article claims and what was predicted by the climate models.

    This is slightly off topic, but another thing I found interesting is that (again, contrary to what the models predict, since most warming was supposed to be at the poles) there was actually cooling at the South Pole in the lower troposphere since satellite temperatures began. (

  10. January 24, 2016 11:07 am

    ” The fact that this is considered journalism (they even link to SkS, see here: is surprising, to say the absolute least. ”

    That’s because The Guardian is a comic and SkS is run by a bunch of comedians, who can’t believe their luck how the gullible are impressed by quotes plucked from sciency sounding sources.

Comments are closed.

%d bloggers like this: