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Climate Links: Resilient Arctic & Pacific Decadal Oscillation

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Items that caught my eye this morning on Twitter:

Scientists: Arctic Is More Resilient To Global Warming Than We Thought” Who is “We” and why did “we” think the Arctic wasn’t resilient?  The second is easier to answer: because climate scientists with bullhorns told us for years that the Arctic was “DOOMED!”  I’ve written about this topic and knew when the record low extent and volume occurred in 2012 that it was likely one bad year and not the end of the world.  I haven’t seen or heard from those same scientists who breathlessly told the public about the doomed Arctic in 2012 that they were wrong (boy, were they wrong!).  While this article makes that point today (3 years too late), I don’t expect anyone to remember it when the Arctic has another bad summer.  2013 was a good Arctic summer: cooler than recent years – and guess what? Arctic ice responded by … growing – you know, what it’s supposed to do according to physics.  Headslap.

To truly grasp what we’re doing to the planet, you need to understand this gigantic measurement”  This is an article about “giga”: what the prefix means and how people should know about it.  I disagree with it from the perspective that the explanations don’t utilize anything truly useful.  For example: a gigaton is “more than 6 million blue whales”.  Who knows how much a big whale weighs?  Can you envision 6 million of them?  The basic problem with giga is it is so big that it defies our everyday experiences.  The superficial problem is despite being written by someone who understands science, the article likely misses its intended audience and thus is not useful.

At the risk of delving too far into technical issues, this article is useful for me personally based on relevance to my geographic region’s upcoming winter weather: “Subtle Differences to Previous El Niños Key to Winter Forecast, And Why the PDO Matters“.  The PDO is the Pacific Decadal Oscillation – a low-frequency natural climate pattern that has direct and indirect influences on weather across at least the western half of the nation.  Many people in my professional community are aware that there is currently a strong El Nino in the equatorial Pacific.  I noted from recent write-ups that there are also warm sea surface temperature anomalies in the north Pacific (e.g., off the west coast of the U.S.) – in addition to the warm anomalies across the central and eastern equatorial Pacific (hallmarks of El Ninos).

The northern Pacific anomalies are an oddity and this article helps explain why they might be present.  In the late 1990s, the PDO likely entered into a cool pattern, which helps explain a couple of things.  First, El Ninos during the 2000s and 2010s had lower amplitude (cooler).  And second, global temperatures didn’t rise as quickly since 1998 as they did during the previous PDO phase (1977-1998).  This observation is also known as the global warming “hiatus” or “pause”.  A cool PDO means Pacific sea surface temperatures are cooler than average.  One effect of this is the Pacific absorbs heat from the atmosphere and keeps the atmosphere cooler than it otherwise would be.  The opposite is also true: warmer than average Pacific SSTs releases more heat to the atmosphere than is absorbed and the atmosphere warms more than average.

Which leads me to the next article: “Has the PDO Flipped to a Warming Phase?”  The PDO typically stays in a warm or cool regime for 10 to 30 years – hence the “multidecadal” characterization.  As I wrote above, the PDO moved into a cool phase in the late 1990s.  Recent positive temperature anomalies (since 2014) might indicate that the PDO is temporarily positive or it might indicate the PDO switched back to a positive or warm phase.  This has significant implications for global weather patterns until it switches back to its negative phase.  For example, I wrote above that there is currently a strong El Nino.  If the PDO switched to a positive phase, it could enhance any El Nino.  It would also do what I described above: release heat back into the atmosphere.  This means the global warming “hiatus” is, if the PDO switches, over.

Back to the Colorado forecast.  With a warmer north and equatorial Pacific (positive PDO and ENSO), what kind of winter can we expect?  The answer won’t surprise you: it’s hard to tell.  There are few similar historical examples that scientists can use to issue a reliable forecast.  They have to determine if warmer ocean temperatures persist and how the atmosphere’s jet stream responds.  Ridge and trough locations over the western US will ultimately determine when we get snow and how much snow we get during each storm.

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