There’s a La Nina Developing — So Why is the World Still Heating Up?
4
November, 2016
ong
term, there’s no doubt what’s in control of the world’s
temperature trend. The vast belching of greenhouse gasses by fossil
fuel industry and related non-renewable based machinery has caused
atmospheric carbon levels to hit 405 ppm CO2 and 490 ppm CO2e this
year. All this added carbon has caused the world to warm by a record
1.22 C since 1880s levels during 2016 (approx). But superimposed over
this long term warming trend is the natural variability based ebb and
flow of atmospheric and surface ocean heat that is the ENSO cycle.
ENSO
— A Wave Pattern Overlying the Long Term Warming Trend
Think
of it as a smaller wave pattern that overlaps the current global
upswing in temperatures. As El Nino builds and comes into the fore,
natural forcings caused by periodic ocean surface warming in the
Equatorial Pacific push global temperatures higher. This tends to add
to the human forced global warming trend. So, often, El Nino years
are also record warm years.
(El
Nino to La Nina temperature variations create a wavy pattern in the
overall global warming trend. Note — the record warm year of 2016
is not included in this graph. Image source: NOAA.)
Conversely,
La Nina, which generates a periodic cooling in the Equatorial Pacific
tends to pull a bit against the long term warming trend. So periods
of La Nina tend to show average global atmospheric temperatures in
the annual measure drop off by about 0.2 to 0.4 C from the peak
periods of atmospheric heating during El Nino. Of course, since the
ENSO variability typically follows a range of +0.2 C to -0.2 C but
does not affect long term temperature trends, it only takes about a
decade for La Nina years to be about as warm as recent El Nino years.
Slight
Warming During Fall of 2016 Despite La Nina
During
fall of 2015 and the winter and spring of 2016 a powerful El Nino
helped to push global surface temperatures into new record high
ranges. This happened because greenhouse gasses the world over
had been loading heat into the Earth System for some time and the
strong El Nino served as a kind of trip wire that opened the flood
gates for a surge of atmospheric heat. Which is why 2016 will be
about 1.22 C hotter than 1880s temperatures (1 C hotter than NASA
20th Century baseline temps) and why the years from 2011 to 2016 will
average above 1 C hotter than 1880s values overall (0.8 C hotter than
20th Century baselines).
But
now, with the 2016 El Nino in the rear view mirror and
with a La Nina forming in the Pacific,
we would expect global temperatures to cool down somewhat. For the
most part, this has happened. Back in January and February, monthly
average temperatures were as much as 1.5 C above 1880s averages.
Since summer, the averages have dipped to around 1 to 1.1 C above
1880s values.
(Global
temperatures bottomed out at around 1 C above 1880s or 0.4 C above
the 1981 to 2010 average in this GFS based graph by Karsten
Haustein during
June then began to slowly climb through fall even as a weak La Nina
developed.)
With
La Nina continuing to form, we would expect these monthly values to
continue to fall for a bit as La Nina strengthened. But that doesn’t
appear to be happening. Instead, global atmospheric temperatures
bottomed out at around 1 to 1.1 C above 1880s levels in June, July,
August and September and now they appear to be rebounding.
Polar
Amplification Signal Shows Up as a Blip in the Global Measure
In
other words, we see a rise in the global temperature trend when we
should see a steady counter-trend decline forced by natural
variability.
Why
is this happening?
The
climate evidence points to a rather obvious set of suspects. For this
fall saw extreme warming both in the northern and southern polar
regions of the world. Today, temperature anomalies in both the Arctic
and the Antarctic were 5.84 and 4.19 C above average respectively. A
rough average between the two poles of +5 C for these high latitude
regions. As we’ve mentioned many times before, such severe warming
is an obvious signal of climate change based polar amplification
where temperatures at the poles warm faster relative to the rest of
the Earth during the first phase of greenhouse gas forced warming.
(Extreme
warming of the polar regions continued on November 4 of 2016. This
warming is pushing against the La Nina trend which would tend to cool
the world temporarily. Image source: Climate
Reanalyzer.)
By
themselves, these abnormally high temperatures at the poles would be
odd enough. But when taking into account that La Nina should still be
cooling the globe off, it starts to look like this severe polar
warming has jostled the La Nina cooling signal a bit — turning it
back toward warming by late fall. And if that is what’s really
happening, then it would imply that the natural variability signal
that is produced by ENSO is starting to be over-ridden by polar
amplification based influences. In other words, there appears to be
another signal that’s starting to intrude as a polar amplification
based temperature spike.
It’s
something that has popped up from time to time as a blip in the
observational data over the past few years. But fall of 2016 provides
one of the stronger signals so far. And it’s a signal related to a
set of feedbacks that have the potential to affect the overall pace
of planetary warming. Something to definitely keep an eye on.
:
Hat
tip to June
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