I’ve moved to WordPress. This post can now be found at RSS MSU TLT Time-Latitude Plots…
...Show Climate Responses That Cannot Be Easily Illustrated With Time-Series Graphs Alone
In this post, I’ll illustrate natural heat redistribution from the tropics to the mid-to-high latitudes of the Northern Hemisphere, using the Time-Latitude plot for Lower Troposphere Temperature (TLT) anomalies available from Remote Sensing Systems (RSS). The post provides an introduction to the Time-Latitude plot for those new to it and comparisons of Time-Latitude plots to time-series graphs. It ends with a series of illustrations intended to show the natural causes for the rises in global TLT anomaly since 1979, with an emphasis on the mid-to high latitudes of the Northern Hemisphere.
THE TIME-LATITUDE PLOT
Figure 1 shows a Remote Sensing Systems (RSS) MSU Time-Latitude plot for Lower Troposphere Temperature (TLT) anomalies. It illustrates much more information than a time-series graph, but it is rarely used to show global temperature variations over the past 30 years. Accuweather’s Brett Anderson posts it occasionally on their Global Warming blog.
If you’re not familiar with the RSS TLT Time-Latitude Plot, it’s relatively easy to read. The scale at the bottom shows the range of colors they use to indicate TLT anomalies. The x-axis is time, the same as a time-series graph. The y-axis is latitude, with the South Pole at the bottom and the North Pole at the top. The point in time that stands out in Figure 1 is the big reddish patch in the tropics around 1998. It shows the TLT response to the 1997/98 El Nino.
The graphic is available from RSS here (their Figure 8):
There is a wealth of information contained in the TLT Time-Latitude Plot, but it fails to show some subtleties. In the following, I’ve combined TLT Time-Latitude Plots and time-series graphs in many of the illustrations, using both to clarify what is being presented by the other. Figure 2 shows the Time-Latitude Plot and Time-Series graph of Global TLT anomalies from January 1979 to April 2009. Global TLT anomalies in the Time-Series graph appear to modulate above and below 0 deg C until the mid-to-late 90s, then rise in a step after the 1997/98 El Nino. In the Time-Latitude Plot, it’s easy to see that the majority of the warming after the 1997/98 El Nino took place in the mid-to-high latitudes of the Northern Hemisphere. There was also a comparatively minor warming in the tropics after the 1998/99/00 La Nina, but there was little to no warming in the extreme high latitudes of the Southern Hemisphere.
There are a few items that need to be clarified before discussing the redistribution of heat from the tropics to the mid-to-high latitudes of the Northern Hemisphere. The first are the…
TIMING OF ENSO EVENTS AND VOLCANIC ERUPTIONS
It’s well known that the explosive volcanic eruptions of El Chichon in 1982 and of Mount Pinatubo in 1991 lowered global temperatures temporarily. Figure 3 illustrates the TLT Time-Latitude Plot and a graph of Stratospheric Aerosol Optic Thickness (Sato Index) data as a proxy for volcanic influence. It clarifies the timing of the eruptions, but shows that the volcanic aerosol impact on TLT can be hard to see in the Time-Latitude Plot due to the timing of other natural climate perturbations.
And those other perturbations are El Nino and La Nina events. Refer to Figure 4. In addition to the Time-Latitude Plot, it illustrates a Time-Series graph of NINO3.4 SST anomalies. I’ve also highlighted the ENSO events with ovals in the tropics of the Time-Latitude Plot.
The significant El Nino of 1982/83, though similar in magnitude to the 1997/98 El Nino, did not have the same tropical TLT signature, because the 1982/83 El Nino was suppressed by the 1982 eruption of El Chichon. Refer to Figure 5. Likewise, the eruption of Mount Pinatubo suppressed the El Nino of 1991/92 and the El Nino conditions (not a full-fledged El Nino on the ONI scale) that occurred in 1993.
Let’s also take a look at two latitude bands before illustrating the redistribution of heat of El Nino events.
In Figure 6, I’ve enclosed the tropics (20S-20N) with a green box to isolate it for comparison with the corresponding time-series graph of the tropical TLT anomaly data. The magnitude of the 1997/98 El Nino stands out above all else.
Comparing the tropical TLT anomalies to scaled NINO3.4 SST anomalies, Figure 7, shows the correlation between the two datasets.
The two agree well after the 1997/98 El Nino. This shows how significant NINO3.4 SST anomalies (a small section of the tropical Pacific) are to TLT anomalies for the Tropics. Before the 1997/98 El Nino, there are divergences between the two datasets. The El Chichon and Mount Pinatubo eruptions, as noted earlier, are responsible for a good portion of those differences. Refer to Figure 8. I’ve added the Sato Index of Stratospheric Aerosol Optic Thickness (also scaled) to the comparative graph to illustrate the timing of the volcanic eruptions and their lingering effects.
And the last preliminary discussion is of…
THE MID-TO-HIGH LATITUDES OF THE NORTHERN HEMISPHERE
I’ve highlighted the Northern Hemisphere Mid-To-High Latitudes in Figure 9 for comparison with the time-series graph of the corresponding TLT anomaly data. Looking at the Time-Latitude Plot, the mid-to-high latitudes of the Northern Hemisphere appear to warm in the mid-1990s and remain warm through 2009. But the visual effect is misleading, because the cause of the mid-90s warming is obvious in the time-series graph. The warming in the mid-1990s is simply a rebound from the cooling effect of stratospheric aerosols emitted by Mount Pinatubo.
There is also a minor surge in TLT anomalies for the Northern mid-to-high latitudes in 1995, Figure 10, but this appears to be a response to the 1994/95 El Nino.
THE IMPACT OF THE 1997/98 EL NINO ON THE MID-AND-HIGH LATITUDES OF THE NORTHERN HEMISPHERE
So, in Figure 11, I asked a question (with an obvious answer) about the TLT anomalies of the mid-to-high latitudes of the Northern Hemisphere. If the short period of warming in the mid-90s is simply a rebound from Mount Pinatubo-induced cooling, then what could be the cause of the period of elevated TLT anomalies that began in 1998? The answer: The 1997/98 El Nino, the “Super El Nino”, the “El Nino of the Century”. Before that El Nino, the mid-to-high latitude Northern Hemisphere TLT anomalies averaged -0.03 deg C, and after it, they averaged +0.44 deg C. Nothing else happened at that time that could have caused that sudden rise. The 1997/98 El Nino produced an upward step change in TLT anomalies of the Northern mid-to-high latitudes of approximately 0.47 deg C.
The heat from the 1997/98 El Nino (Figure 12, Cell a) was redistributed poleward to mid-and-high latitudes of both hemispheres, with most migrating north. This El Nino-induced heat was not radiated completely into space over the next four years. Only a portion. The La Nina of 1998/99/00 HAY HAVE reduced the mid-and-high latitude warming, but its effect is not apparent.
Let me reinforce something. El Nino and La Nina events correlate well with TLT of the TROPICS. This indicates that El Nino AND La Nina events have similar impacts on TLT of the tropics. It appears, however, that El Nino and La Nina events do not have equal but opposite effects on mid-to-high latitudes of the Northern Hemisphere. If they had equal but opposite effects, Northern Hemisphere mid-to-high latitude TLT anomalies would have responded fully to the 1998/99/00 La Nina, but, in actuality, they responded very little to that multiyear La Nina event.
The subsequent El Nino events of 2002/03, 2004/05, and 2006/07 (Figure 12, Cell b) redistributed additional heat from the tropics to the mid-and-high latitudes, primarily to the Northern Hemisphere. This maintained the elevated TLT anomalies there. Then, as a result of the 2007/08 La Nina (Figure 12, Cell c), TLT anomalies of the Northern Hemisphere mid-to-high latitudes cooled slightly.
THE 1982/83 AND 1986/87/88 EL NINO EVENTS
Figure 13 is provided solely as a reminder: the 1982/83 El Nino was comparable in magnitude to the 1997/98 El Nino.
So the poleward heat redistribution of the 1982/83 El Nino should have been similar in scale to the 1997/98 El Nino (refer to Figure 14, Cell a), but, again, it was suppressed by the eruption of El Chichon.
In addition to the 1997/98 El Nino event, there was only one other significant El Nino event since 1979 that wasn’t impacted by a major volcanic eruption. It was the multiyear El Nino of 1986/87/88. Refer to Figure 14, Cell b. It also redistributed heat from the tropics to the mid-to-high latitudes to an extent that it’s noticeable in the TLT Time-Latitude plot, but the transport wasn’t as great as the 1997/98 El Nino.
The RSS TLT data is available here:
The ERSST.v3b data used for the NINO3.4 SST anomaly graph is from the KNMI Climate Explorer website:
I read your stuff over at wuwt but this is my first visit here. This is a brilliant analysis. My own opinion is that the only data set of value are those from the satellites. They show warming of between 1.4 and 1.7 degrees per century but, as you point out the volcanoes have had a huge effect. If they had not occurred, then what would the warming (or cooling) trend be.
Another way of looking at it is that it is absence of volcanoes that is causing the warming.
Shane, the volcanoes may have cooled in 1982 and 1991 and for the few years that followed, but it was the El Ninos of 1986/87/88 and 1997/98 that caused the upward step changes.
That's a very interesting analysis, Bob. Are you aware of any published literature on this? Or "established" climatological principles relating to it? I wonder how this can be explained in the context of the traditional three cell model of global atmospheric circulation?
I think the thing this presentation shows most dramatically is the "natural" origin of the warming of the past few years. The sudden "step" change in the northern latitudes can be seen clearly, and is not consistent with what should be a more gradual and continuous influence from AGW.
Basil: I attempted to post this comment at Climate Progress yesterday, but as usual my comment was deleted by the moderator.
Regarding the well-documented Polar Amplification, refer to RealClimate thread here:
Real Climate writes, "Whether the warming is from greenhouse gases, El Nino's, or solar forcing, trends aloft are enhanced. For instance, the GISS model equilibrium runs with 2xCO2 or a 2% increase in solar forcing both show a maximum around 20N to 20S around 300mb (10 km):”
The following are two illustrations from the RealClimate thread. The first shows the tropical enhancement and polar amplification for a doubling of CO2 and the second illustrates the same effects for a 2% increase in solar irradiance.
RealClimate continues: “The first thing to note about the two pictures is how similar they are. They both have the same enhancement in the tropics and similar amplification in the Arctic. They differ most clearly in the stratosphere (the part above 100mb) where CO2 causes cooling while solar causes warming. It's important to note however, that these are long-term equilibrium results and therefore don't tell you anything about the signal-to-noise ratio for any particular time period or with any particular forcings.
“If the pictures are very similar despite the different forcings that implies that the pattern really has nothing to do with greenhouse gas changes, but is a more fundamental response to warming (however caused). Indeed, there is a clear physical reason why this is the case - the increase in water vapour as surface air temperature rises causes a change in the moist-adiabatic lapse rate (the decrease of temperature with height) such that the surface to mid-tropospheric gradient decreases with increasing temperature (i.e. it warms faster aloft). This is something seen in many observations and over many timescales, and is not something unique to climate models.”
To create the polar amplification profile illustrated in the above figures in the GCMs, there had to be a doubling of CO2 or a 2% increase in solar irradiance. Neither happened in the last 3 to 4 decades, so what created the polar amplification profile? Real Climate provides the answer. El Nino events.
Since 1976, did we endure a string of El Nino events whose frequency and magnitude greatly outweighed La Nina events? Most assuredly.
And when did polar amplification become evident in the Northern high latitudes? Immediately after the 1997/98 El Nino. It's very visible in the RSS MSU Time-Latitude plot. I'll make it easier to see with a time-series graph along side.
Thanks for sharing Mr. Tisdale, very interesting. Do you have any idea, how is PDO/Nino connected with AMO? Because the climate in Europe is well related to AMO, even Alpine glacier growth/retreat.
From this chart, there is obvious some 20-year long lag between PDO and AMO.
Juraj V: You asked, “Do you have any idea, how is PDO/Nino connected with AMO?”
Since you have combined ENSO and PDO above, I’ll assume you are aware of this. But for those who are not…
The PDO is misrepresented and misunderstood. First, it is not a measure of the SST of the North Pacific. It is only an indication of the pattern of SST anomalies (positive PDO = warm in east and cool in central and west). Second, the PDO is an aftereffect of ENSO. I discussed this here:
To answer your question, there are direct effects of ENSO on North Atlantic SST:
And AMOC is inversely related to ENSO. That is, an increase in NINO3.4 SST anomalies tends to slow AMOC:
And as I understand, there is supposed to be feedback from the North Atlantic SST anomalies to the eastern tropical Pacific SST anomalies, but I have not researched it.
You wrote, “From this chart, there is obvious some 20-year long lag between PDO and AMO.”
I don’t know that I’d call it a lag. They very well could be independent cycles that influence one another. Have you plotted the two on the same graph? Smooth both datasets with a 121-month filter.
Over the years I have read many of your interesting contributions on other blogs and because of that have not been here before. Because of the severe winter now raging across europe I have a bit of time to spare tonight.
firstly, thanks for sharing your work. This particular piece is really quite thought provoking and one of those is that I noted that the transport / tranfer of el niño heat seems to be more efficient than la niña. Any thoughts from you?
Stephen Richards: You wrote, "...the transport / tranfer of el niño heat seems to be more efficient than la niña."
If the following doesn't address what you're referring to, would you expand on your statement?
An El Nino is the anomalous state in the tropical Pacific. Trade winds can reverse direction, the equatorial countercurrent expands and transports water from below the surface of the Pacific Warm Pool to the eastern tropical Pacific, etc. But a La Nina is simply an exaggeration of the "normal" state.
Great paper! Thank you.
You may wish to have a look at the relationship between TLT and CO2.
My paper is posted at
The attached Excel spreadsheet ("CO2 vs T") shows that variations in atmospheric CO2 concentration lag (occur after) variations in Earth's Surface Temperature by ~9 months (Figures 2, 3 and 4).
For the time period of this analysis, variations in ST lead (occur before) variations in both LT and dCO2/dt, by ~1 month. The integral of dCO2/dt is the atmospheric concentration of CO2 ("CO2") (Figures 3 and 4).
My work was done using global average ST and LT (your "TLT").
It might be fun to determine if there is a better correlation, and a greater lead-lag, using Tropics TLT.
I'm busy now so hope someone else will have the time.
Happy New Year!
Allan M R MacRae
That was truncated - try this:
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