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As a Titanic El Nino Begins to Fade, What Fresh Trouble Will a Record Warm World Bring?
26
February, 2016
Today
the globe is feeling quite a bit of backlash from a human-warmed sea
surface and atmosphere. As it ends up, Dr.
Kevin Trenberth was right.
Deep ocean warming set off by heat-trapping fossil fuel emissions and
building up through the first two decades of the 21st Century did
re-surge from the depths to haunt us in 2014, 2015 and 2016. In that
wrenching global climate system shift to the hot side of natural
variability, a titanic El Nino emerged. It was one of the top three
strongest such events in the modern record. One that by NOAA’s
measure appears to
have tied the extreme event of 1998 at its peak intensity.
(Sea
surface temperature departure from average in the benchmark Nino 3.4
zone shows surface ocean heat anomalies for the 2015-2016 El Nino
equaled peak 1997-1998 values. Image source:NOAA/CPC.)
Expected
Heat, Drought, and Storms Together With a Few Ominous Surprises
This
event did push the world into extreme warmth even as predicted
related severe weather flared in some of the typical regions. Annual
average global temperatures rocketed to about 1.06 C above 1880s
baselines during 2015 even as monthly departures hit 1.2 to 1.3 C or
more higher than the same benchmark during December and January.
Amidst
this great upheaval of global heat, the world also experienced yet
one more wave of freak droughts (this time over Northern South
America, the Caribbean, large swaths of Africa and Southeast
Asia), heat-related
mass casualty events, floods, and
strongest hurricanes on record. Arctic
and global sea ice measures are once again plunging to new record
lows. A
global coral bleaching event, perhaps the worst such instance ever
experienced, was also set in motion.
The
predicted patterns and potential worse-case events (such as heatwave
mass casualties, coral bleaching, and sea ice loss) were also
contrasted by a number of surprises. The first and perhaps most
ominous was the failure of El Nino to bust the California drought.
Though the West Coast of the US did experience a number of storms,
the pattern was more typical of normal Winter moisture for the
Northwestern US even as drought continued throughout the Southwest.
Moisture instead tended to split fire-hose fashion — with storms
either cycling northward into Alaska, the Aleutians, or the Bering
Sea, or south over Southern Mexico or Central America, up across the
Gulf and on out into a particularly severe storm zone forming in the
North Atlantic.
(Over
the last 30 days the southwest drought re-emerged as a blocking
pattern again began to take hold over Western North America and the
Eastern Pacific. Image source: NOAA/CPC.)
This
continued loss of moisture for the US Southwest despite a record El
Nino is particularly apparentin
the Climate Prediction Center’s most recent precipitation anomaly
measure for the last 30 days.
Here we find that large parts of Central and Southern California have
received just 10 to 50 percent of typical rainfall for this
period. Coupled
with 1-3 C above average temperatures for the month,
this loss of rainfall during what would typically be California’s
wettest period has come as a disappointment to many who were hoping a
strong El Nino would help break the state out of a crippling drought.
Now, the window for late Winter and early Spring rains is starting to
close even as the blocking pattern appears to be strongly
re-established in both the present weather pattern and in the
forecast model runs.
But
perhaps the biggest surprise coming from this El Nino year was a set
of weather events in the North Atlantic that were likely more related
to climate change.
There,
severe storms hammered a flood-beleaguered UK as
a greatly distorted Jet Stream heaved Equatorial heat and moisture
northward — rushing it up over a ridiculously warm and apparently
backed-up Gulf Stream before slamming it on into a likely Greenland
ice melt-outflow related cool pool. There the heat and moisture
collided with cold to produce the epic storms that then vented their
fury upon the UK.
(December
29th saw temperatures rise above freezing at the North Pole — the
first time temperatures have warmed so much for this high Arctic
region so late in the year. Image source: Earth
Nullschool.)
During
one such event, a daisy chain of heavy-hitting North Atlantic lows
hurled high winds, heavy rains and epic surf at the UK even as the
meridional flow set up by these powerful beasts shoved above-freezing
temperatures all the way to the North Pole during late December.
Yet one more unprecedented and unexpected event during a record warm
year. One that looks more like a human forced warming which has
overcome the traditional influences of El Nino, rather than an El
Nino related impact in itself.
As
El Nino Fades, Equatorial Heat Tends to Move Pole-ward
Though
we may see these two events — the failure of El Nino to provide
heavy rains to the US West Coast, and the massive northward pulses of
storms, heat and moisture hitting the North Atlantic — as
unrelated, the
twain patterns appear to be linked to an ongoing polar amplification.
Overall, heat within the Arctic has tended to weaken the Northern
Hemisphere Jet Stream over these two zones. And even during El Nino,
when the Jet would have typically strengthened, we have continued to
see high amplitude wave patterns forming over these regions.
But
as El Nino weakens and the Equator cools, the Jet Stream would tend
to slow even more. Such an atmospheric state would tend to further
exaggerate already significant Jet Stream wave patterns —
transferring still more low-Latitude heat poleward. In addition, the
ocean gyres tend to speed up as El Nino fades or transitions to La
Nina. The result is an amplified pulse of warmer waters emerging from
southern Latitudes and entering the Arctic.
It’s
for these combined reasons — tendency to amplify south to north
atmospheric heat transfer into the Arctic post El Nino and tendency
to flush warmer waters toward Arctic Ocean zones during the same
period that it appears we are entering a high risk time for potential
new sea ice melts and possible related Greenland land ice melts
during 2016 and 2017.
(Northeastern
Pacific Hot Blob remains at high intensity even as its size is
predicted to expand through July. Meanwhile, very warm sea surface
temperatures are predicted to remain in place off the Eastern
Seaboard. The net effect of these two hot blobs may be to shove the
Jet Stream far northward over North America during the summer of 2016
— potentially increasing the risk of widespread and potentially
record heat and drought. Predicted very warm sea surfaces in the
region of the Barents and Greenland seas — in excess of 3 C above
average for a large region — is also cause for concern. This is not
only due to risk for sea ice loss through this zone, but also due to
its potential to set off blocking pattern and heat dome formation
over Eastern Europe and Western Russia. Image source:NOAA/CFS.)
In
addition, we are at serious risk of seeing the high amplitude blocks
and wave patterns re-establish and persist, especially in the zone
over Western North America were a related Northeastern Pacific Hot
Blob is expected to restrengthen as El Nino fades. In fact, large
regions of the US may fall under record to near record heat and
drought this summer due
to the combined influences of two very warm ocean zones surrounding
her shores. Models
now indicate a particular late spring drought risk for the Great
Lakes region as
well as an extended period of far
above average temperatures for pretty much all of the Continental
US during
summer. Meanwhile, predicted above average spring-time precipitation
for the Southwest appears less and less likely to emerge.
Finally, extreme
above average sea surface temperatures are predicted to intensify
over the Barents and Greenland seas through to end of Summer 2016.
This is an area to watch. The added ocean heat would tend to pull the
Jet Stream northward over Eastern Europe and Western Russia —
generating risk of heatwaves and drought for this region even as
Central Asia fell under risk of floods. Long
range CFS precipitation and temperature model runs for Europe have
not yet picked up this risk.
However, given the intensity of heat predicted for Barents sea
surfaces and the related tendency of warmth over oceans and in the
far north to influence the formation of blocking patterns, heat
domes, and high amplitude troughs, it’s worth keeping a weather eye
on the situation.
El
Nino to Weaken and Then Return; or is a Shift to La Nina Now Under
Way?
Related
to a polar and ocean warming-enhanced tendency to generate high
amplitude Jet Stream waves — as well as associated persistent
heatwaves, droughts, and floods — is the heat balance of the
Equatorial Pacific. Strong El Ninos, or even a tendency to remain in
or near an El Nino state, has historically aided in the breaking of
new record global high temperatures when linking up to the greenhouse
gas warming trend. Meanwhile, the shift toward La Nina has tended to
enhance a range of global heating related issues including record
rainfall events and large injections of heat toward the poles in the
drop off from El Nino to La Nina.
The
cause for increased risk of major precipitation events is due to the
fact that El Nino is providing a massive moisture bleed into the
atmosphere at times of peak intensity. With the current El Nino
topping out near record levels and with global temperatures at above
1 C higher than 1880s averages, global atmospheric moisture levels
are hitting new record highs at this time. If global temperatures
subsequently drop by around 0.1 to 0.2 C during a transition into La
Nina (into a range about 0.9 to 0.8 C hotter than 1880s values) then
the atmosphere will be unable to keep a larger portion of that extra
moisture in suspension and it will fall out as precipitation —
primarily wringing out where the major trough zones tend to set up.
We should be very clear here in saying that the drought risk related
to a global warming intensification of ridge and heat dome formation
is not reduced during such instances — just that the risk of
extreme precipitation events is enhanced.
(During
2011, as the 2010 El Nino faded into La Nina conditions, a high
amplitude wave in the Jet Stream set off record heat, drought and
wildfires over Russia even as Pakistan was hit by a month-long deluge
that was the worst rainfall event for the region in the last 1,000
years. La Nina’s tendency to wring excess water out of the
atmosphere can enhance the risk for such events to occur in a warming
climate state. Image source: NASA.)
As
for risks to sea ice, we’ve provided some of the explanation above.
However, it’s also worth noting that the mobility of heat poleward
tends to be enhanced during the periods when El Nino drops off toward
La Nina. During these times, Equatorial heat tends to propagate in
wave fashion toward the Poles — especially toward the Northern
Hemisphere Pole which has already lost its strong Jet Stream
protection warding away warm air invasions.
These
two factors are major issues when considering whether La Nina or an
ENSO Nuetral state will appear post El Nino during 2016. But there is
a third — rate of global temperature rise. Though the primary
driver of global warming is a massive human fossil fuel emission, the
response of the world ocean system can significantly wag the rate of
atmospheric temperature increases on a decadal time scale. If the
ocean tendency is for La Nina, this would tend to somewhat suppress
the overall decadal rate of temperature increase — and we saw this
during the 2000s. But if the ocean tendency is to produce El Ninos
(in a switch to a positive Pacific Decadal Oscillation, as appears to
be happening now), then the overall pace of global atmospheric
temperature increase would tend to be enhanced.
(
IRI/CPC consensus model runs show a drop off to a weak La Nina by
late in the year. However, CFS model runs [image below] have shown a
tendency to predict a resurgence of El Nino conditions by Fall. Image
source: NOAA/CPC.)
To
this point we find that the official
model forecast consensus published by NOAA (IRI/CPC
figure above) shows a transition to ENSO neutral states by May, June,
and July which then proceeds on to a very weak La Nina by Fall. In
such a drop off, we would likely still see record global high
temperatures during the period of 2016 (in the range of 1.03 to 1.15
C above 1880s values).
However,
the late 2016 and 2017 tendency for temperatures to recede from new
record highs would be somewhat enhanced (likely dropping below the 1
C above 1880s mark in 2017 or 2018 before again making a challenge to
the 2015-2016 record with the potential formation of a new El Nino in
the 3-5 year time-frame of 2019 through 2021). It’s worth noting
that this scenario shows an increased risk of a stronger warm air
pulse heading toward the Northern Polar zone together with added fuel
for extreme precipitation events as global temperatures would tend to
drop off more swiftly from late 2015 and early 2016 peaks.
(CFSv2
model run — shows El Nino continuing on through the end of 2016.
Over recent months, the CFSv2 series has shown a high accuracy.
However, NOAA’s current forecast preference is for the IRI model
set predictions [previous image above]. Image source: NOAA/CPC.)
In
contrast, the CFSv2 model forecast from NOAA (above image) shows El
Nino only weakening through to July and then re-strengthening in the
October-November time-frame. This CFS model scenario would result in
higher atmospheric temperatures in 2016 — practically guaranteeing
a lock on an unprecedented three back-to-back-to-back record warm
years for 2014, 2015, and 2016. But such a scenario — implying that
the Pacific Ocean had entered a new period of El Nino tendency —
would also tend to keep atmospheric temperatures nearer to the newly
established record highs.
Under
the CFSv2 scenario, we may expect annual average global temperatures
to rise as high as 1.08 to 1.2 C above 1880s values during 2016 (a
very extreme departure and one uncomfortably close to the 1.5 C
warming mark). These extreme values would, perhaps, recede to around
between 0.9 and 1.1 C during 2017 so long as the second El Nino pulse
did not remain in place for too long. However, if the bounce back
toward El Nino conditions was strong enough in late 2016, there would
be an outside chance that the globe may experience not 3, but an
absolutely obnoxious 4 back-to-back record warm years.
(During
2015 global annual temperature rocketed to above 1 C hotter than
1880s values. There’s at least an even chance that 2016 will be
hotter still. Considering the considerable heating tendency imposed
by a fossil fuel-forced warming of the world, how much worse can it
get during the 21st Century’s second decade? Image source: NASA
GISS.)
Meanwhile,
the warm air pulse heading toward the poles may be somewhat muted
under this scenario. A statement that should be qualified by the fact
that we’ve already seen a substantial amount of El Nino heat
heading poleward during the present event. In addition, potentially
heavy rainfall events may not receive the added oomph of a decent
global temperature drop to wring out more moisture. A statement that
requires the further qualification that overall atmospheric moisture
loading is enhanced by rising global temperatures — so
comparatively less heavy rainfall is a relative term here.
At
this time, NOAA
favors a transition to La Nina forecast stating:
“A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016, with a possible transition to La Nina conditions by fall.”
However,
it’s worth re-iterating that the CFSv2 model forecasts have been
quite accurate in predicting the path of the current record El Nino
to date.
Links:
Hat
tip to Caroline
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