Another Look At Polar Amplification

Posted by invitation, from Bob Tisdale’s website – original here. Photo/caption below added by Anthony.

Guest post by Bob Tisdale

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).

THE DELETED COMMENT

Regarding the well-documented Polar Amplification, refer to RealClimate thread here:

http://www.realclimate.org/index.php/archives/2007/12/tropical-troposphere-trends

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):”

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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.

http://i33.tinypic.com/10fu8p2.jpg

http://i38.tinypic.com/w8l4c0.jpg

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]

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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.

http://i42.tinypic.com/e9b04g.jpg

Regards

UPDATE

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):

http://www.glaciology.net/Home/PDFs/Jevrejeva_grl04_-_enso_to_polar.pdf?attredirects=0

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].”

Posted by Bob Tisdale at 5:50 AM