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Saturday, June 6, 2009

Another Look At Polar Amplification

I’ve moved to WordPress.  This post can now be found at Another Look At Polar Amplification
On two occasions I’ve attempted to leave a comment at Joe Romm’s Climate Progress. I discussed the first try back in July 2008 in my post Climate Progress Posts My Comment, Returns It To Awaiting-Moderation Limbo, Then Deletes It. Yesterday, I posted a comment on the Exclusive: New NSIDC director Serreze explains the “death spiral” of Arctic ice, brushes off the “breathtaking ignorance” of blogs like WattsUpWithThat thread at Climate Progress, but was thwarted again by the moderator.

Note: The original Climate Progress title included a misspelling “breathaking” that made the quoted “breathaking ignorance” quite comical.

In the recent Climate Progress post, Joe Romm wrote, “Humans are cranking up the Arctic heat by pouring steadily increasing amounts of greenhouse gases into the atmosphere, which in turn cranks up warming in the Arctic, a very well documented phenomenon (see “What exactly is polar amplification and why does it matter?“). The linked Climate Progress explanation of Polar Amplification pertains primarily to positive feedbacks from albedo changes caused by the retreat of ice and snow, and to contradict Romm’s statement in his recent post, the term “Greenhouse gases” does not appear in Joe’s earlier explanation of Polar Amplification, nor does CO2, methane, GHG, etc.

The comment I tried to post yesterday at Climate Progress contained the quotes and illustrations from RealClimate that I used in my July 28, 2008 post on Polar Amplification and Arctic Warming. It also included an annotated RSS MSU TLT Time-Latitude Plot and Time-Series Graph from my post “RSS MSU TLT Time-Latitude Plots... ...Show Climate Responses That Cannot Be Easily Illustrated With Time-Series Graphs Alone”.

There was nothing earth shattering in my comment, no reason for it to be deleted. Here take a look. It simply illustrated cause (El Nino events) and effect (poleward heat redistribution).


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.” [My Emphasis]
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.




And for those looking for papers describing the poleward transport of heat resulting from El Nino events, the following paper can serve as a starting point. It’s Jevrejeva et al (2004) “Oceanic and atmospheric transport of multiyear El Nino–Southern Oscillation (ENSO) signatures to the polar regions” (GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L24210, doi:10.1029/2004GL020871, 2004):

Their Conclusion reads:

“We provide evidence of ENSO influence on the winter climate variability in NH during the last 150 years via signals in the 2.2, 3.5, 5.7 and 13.9 year bands. The contribution from the signals to the total variance is relatively weak, varies considerably with time, but is statistically significant. Phase relationships for the different frequency signals suggest that there are different mechanisms for distribution of the 2.2–5.7 year and the 13.9 year signals. The 2.2–5.7 year signals are most likely transmitted via the stratosphere, and the AO mediating propagation of the signals, through coupled stratospheric and tropospheric circulation variability that accounts for vertical planetary wave propagation.

“The delay of about two years in the 13.9 year signals detected in polar region can be explained by the transit time of the 13.9 year signal associated with ECW (0.13– 0.17 ms_1) propagation in the Pacific ocean, KBW (1–3 ms_1) propagation along the western margins of the Americas and by poleward-propagating of atmospheric angular momentum [Dickey et al., 2003]. This mechanism is supported by similar features in the Pacific sector of the Antarctic SST field.

“Our results highlight the importance of tropical variations for the Arctic and NA climate and probably at least the Pacific sector of the Antarctic, suggesting a global mode of interaction between atmosphere and ocean and consistent with GCM experiments of a proposed ENSO-NA link [e.g., Trenberth et al., 1998; Dong et al., 2000; Merkel and Latif, 2002].”


fred said...

That could be the cause, but there could be other causes too.

For example you could fit a line of best fit through the TLT record and describe varition from that line in terms of ENSO and volcanic eruptions.

Bob Tisdale said...

Fred: You wrote, "That could be the cause, but there could be other causes too.

"For example you could fit a line of best fit through the TLT record and describe varition from that line in terms of ENSO and volcanic eruptions."

Refer to the earlier post that I took the Time-Latitude graph from.

It discusses volcanic aerosols and the impacts of the 1986/87/88 and 1997/98 El Nino events. And why do a best fit line? The El Nino-induced step changes are obvious.


Frontiers of Faith and Science said...

What will be interesting is how Romm and his predictive powers will be treated if he is proven to have been wrong.

Bob Tisdale said...

Frontiers of Faith and Science: You wrote, "What will be interesting is how Romm and his predictive powers will be treated if he is proven to have been wrong."

If you're referring to Romm's predictions from this post...
...that this decade will the hottest on record, that's a done deal. If you're referring to Romm's prediction that this year will be the warmest on record, he should fall short. So he'll most likely be wrong on one of two predictions.


Andrew said...

It is only sure if one arbitrarily defines decades as periods between years ending in zeroes, rather than as ten year periods. After all, the ten year period of 99-08 was, I think, cooler than 98-07.

Bob Tisdale said...

Regardless, Andrew, it will be a major talking point for the alarmists as soon as 2009 is done. I doubt they'll wait for the end of 2010.


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