Trending Trends Continued: An Alternative View

No matter how much and how well we explain the methods for calculating the length of The Pause, Global Warming Enthusiasts will accuse us of cherry picking the start date.

In this post I will replicate the IPCC’s predicted estimates for temperatures, and show alternative scenarios with a range of trends to the end of 2035, through using an alternative  view which will be sure to please our friends on the other side of the fence- but will demonstrate the limited extent of the joy they should feel at the expected demise of The Pause. As well,  I will also demonstrate what temperatures will need to do before we skeptics can claim victory (our opponents will never admit defeat- that would be heresy).

In these figures I plot running trends of 12 month means of Temperatures of the Lower Troposphere (TLT) anomalies from UAH (Version 6 Beta 5), but starting from the beginning of the record (12 month means from November 1979).  Running trends will be used in this post to demonstrate the effects of changing data values over time.

Fig. 1: Running trends for global TLT to the present

Fig. 2: Running trends for global TLT to the present, closer view.

Note to GWEs: there is no cherry picking: the start is from the start of the record. Each new month’s data point will either increase or decrease the long term trend, but with decreasing effect as the record grows in length. Peaks correspond to warming events, troughs to cooling events. Note also that the recent long term trend is near the lowest it has been since 1998. With the expected increase in temperatures following the El Nino, I anticipate the long term trend to the end of 2016 will be about +1.2C per 100 years.

What of the future? Now according to the IPCC Assessment Report 5, warming for the next 20 years is locked in, no matter what emissions scenario.

“The global mean surface temperature change for the period 2016–2035 relative to 1986–2005 is similar for the four RCPs and will likely be in the range 0.3°C to 0.7°C (medium confidence). This assumes that there will be no major volcanic eruptions or changes in some natural sources (e.g., CH4 and N2O), or unexpected changes in total solar irradiance.”

( https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf p8)

If I am still around in 2035, this prediction will not be a huge priority for me. However, to illustrate various possibilities, I shall calculate possible TLTs for the next 20 years. (Yes, I know the IPCC is talking about surface temperatures. However if tropospheric temperature change doesn’t reflect surface temperature change for another 20 years there are going to be some serious arguments in climate science circles!)

First, let’s replicate the IPCC predictions for 2016-2035- and in so doing, show The Pause in all its glory. The next figures plot running 12 month mean Temperatures of the Lower Troposphere (TLT) anomalies in degrees Celsius versus global atmospheric carbon dioxide concentration in parts per million (ppm), data from NOAA.  The global record commences in 1980.

Fig. 3: Running trend of Degrees C per 100 ppm CO2

Note again the peaks and troughs, and that the current trend is the lowest it has been since 1996.  The long term trend to December 2015 is +0.65C/ 100 ppm CO2. This is confirmed in the following plot:

Fig. 4: TLT anomalies vs CO2

Now let’s break the record in two: the first half of the CO2 rise and the second half.

Fig. 5:  TLT vs CO2: 1st 30.32ppm

Fig. 6:  TLT vs CO2: last 30.32ppm

There you have The Pause: entirely un-cherry picked, as we are using exactly equal portions of the record: the first and last 30.32 ppm of the CO2 growth from 1980 to 2015.

The next graphs plot CO2 increase over time, from 2001 to 2015.

Fig. 7: CO2 growth (12 month running mean)

Using this trend equation it is possible to estimate CO2 for the next 20 years, and from that, using (A) the trend of the first half of TLT vs CO2, i.e. rapid warming; (B) that of the whole 1980-2015 period, i.e. continuing the present long term trend; and (C) that of the second half of the CO2 growth, i.e. The Pause, calculate three theoretical estimates for the TLT in the best way- from observations. Here are series A and B.

Fig. 8:  Theoretical trends calculated from observations

Note that series A approximately tracks the observed TLTs until about 2002, when the disparity begins. This shows clearly why The Pause is so inconvenient, and why so much effort has been made to eradicate it.

Amazingly, the 2016-35 high mean of 0.7 above 1986-2005, and the low mean of +0.3, as predicted by the IPCC, have been replicated almost exactly by series A and B. (The UAH 1986-2005 mean is +0.02C).  It appears that the temperature trend for the rapidly warming phase up to 2001 exactly matches the trend needed to create the upper limit of their prediction for 2016-35, and the trend overall to 2015 is very close to that of the lower limit. The IPCC is banking on the warming trend from now to 2035 being at least as much as the 1980-2015 trend, and as much as that of the rapid warming to about 2001. Any continuation of a slowdown makes that much harder.

Obviously these series are imaginary, showing the theoretical TLT calculated from CO2 concentration, and without any of the bumps and dips caused by natural variation- volcanoes, ENSO events, and the like. However, they can be used to simulate what temperatures might do over the next 20 years.

I illustrate this with these scenarios, and a fourth, below.

Scenario A allows the 2016-2035 mean to be 0.7C above the 1986-2005 mean and necessitates temperatures sharply rising then continuing at the rate of the higher of the theoretical series (A). Scenario B very slightly exceeds the lower IPCC expectation of +0.3C, and represents a continuation of the current trend. Scenario C is calculated by multiplying expected CO2 concentration by the TLT per CO2 trend for the second half of CO2 growth, indexed to the 1996-2015 mean. As expected it is virtually flat with the 2016-35 mean at +0.14C. This represents an extension of The Pause by another 20 years. Scenario D shows a sharp drop to a 20 year plateau (shown as flat as we have no idea how temperatures may fluctuate) at -0.11C, the lowest 12 month mean of the last 20 years, and about the same average as the 1980-95 period. I have smoothed the beginning months of all four scenarios.

I repeat- these scenarios are entirely imaginary and represent approximate calculated values IF TLT responds to CO2 concentration as it has to now, and nothing else.

Fig. 9: Four scenarios to 2035

I have marked in the trend line for UAH to now.  Scenario A shows what would happen if The Pause came to an abrupt end, with temperatures rising to a record high for 2016, and then keeping on rising at the theoretical rate as if The Pause had never happened. I’m sure there are some Global Warming Enthusiasts who expect temperatures will do just that.

But the IPCC has an out clause- Scenario B. If the current long term trend continues, TLTs will reach IPCC expectations. Which is why GWEs are desperate for The Pause to end and warming to resume at (at least) the slow if not steady +1.1 to 1.2C per 100 years. If it doesn’t they’re in trouble.

Temperatures will need to trend below this to falsify the predictions- and not even as much as Scenario C, which represents an extension of The Pause. Scenario D represents a significant decrease.

The next plot compares the trends under these four scenarios.

Fig. 10: Trends in degrees Celsius per 100 years to 2035 under four TLT scenarios.

Ignore the artificial shape of the curves. At December 2035 the trend for each scenario will be about:
Scenario A: 2.1C/ 100 years
Scenario B: 1.2C
Scenario C: 0.6C
Scenario D: 0.0C

The IPCC expects trends to be between those of Scenarios A and B. A small step up (to a new 20 year mean of say +0.25C) and a new pause- which is entirely possible- would probably still be claimed to be “the hottest decade ever” and “consistent with global warming projections”. We need to emphasise that a pause doesn’t have to be completely flat. A 30 year period with a trend of +0.3C per 100 years should be enough to bring the global warming models into question. However, there will need to be a significant drop in temperatures, or a much longer plateau, for us to claim victory. A 57 year pause would be most embarrassing- but then they would probably blame it on volcanoes!

Finally, even if this El Nino is followed by a strong La Nina, as suggested by NOAA,  it is unlikely The Pause will return until the beginning of 2018, perhaps a little earlier. However, that is not important. The important thing is what happens next. Watch the next two or three ENSO cycles- especially the La Nina dips.

Global Warming Enthusiasts are desperate for rapid warming to resume at least as much as Scenario B. The long term trend must rise above the current rate if they are to feel vindicated. But then, who knows what the actual temperatures will do.

Time will tell.

Tags: climate, global warming, Pause, UAH