About Jeff Masters
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
Are We Entering a New Period of Rapid Global Warming?
By: Bob Henson , 5:04 PM GMT on February 24, 2015
Residents of New England may understandably look back at 2015 as the year of their never-ending winter. For the planet as a whole, though, this year could stand out most for putting to rest the “hiatus”— the 15-year slowdown in atmospheric warming that gained intense scrutiny by pundits, scientists, and the public. While interesting in its own right, the hiatus garnered far more attention than it deserved as a purported sign that future global warming would be much less than expected. The slowdown was preceded by almost 20 years of dramatic global temperature rise, and with 2014 having set a new global record high, there are signs that another decade-plus period of intensified atmospheric warming may be at our doorstep.
The most compelling argument for a renewed surge in global air temperature is rooted in the Pacific Decadal Oscillation (PDO). This index tracks the fingerprint of sea surface temperature (SST) across the Pacific north of 20°N. A closely related index, the Interdecadal Pacific Oscillation (IPO), covers a larger swath of the entire Pacific. Both the PDO and IPO capture back-and-forth swings in the geography of Pacific SSTs that affect the exchange of heat between ocean and atmosphere (see Figure 1). We’ll use PDO as shorthand for both indexes in the following discussion.
The PDO typically leans toward a positive or negative state for more than a decade at a time. The positive phase, which features warmer-than-average SSTs along the U.S. West Coast, was dominant from the mid-1970s to the late 1990s. The PDO then flipped to a negative phase between about 1999 and 2013, with cooler-than-average SSTs along the West Coast. Figure 2 shows that even when a particular mode is favored, the PDO can still flip back to its opposite mode for periods of a few months or so.
Figure 1. Departures from average sea-surface temperature (degrees C) and wind (arrows) that typically prevail when the Pacific Decadal Oscillation is in its positive mode (left) and negative mode (right). Image credit: University of Washington.
It’s not clear exactly what drives the PDO, but in some ways it can be viewed as a geographically expanded version of the SST patterns created by El Niño and La Niña, averaged over a longer time period. (See Figure 2.) It’s well-established that El Niño can raise global temperature for a few months by several tenths of a degree Celsius, as warm water spreads over the eastern tropical Pacific and mixes with the overlying atmosphere. Likewise, La Niña can act to pull down global average temperature, as cooler-than-average water extends further west than usual across the tropical Pacific. The PDO mirrors these trends, but over longer periods. When the PDO is positive, there are more El Niño and fewer La Niña events, and heat stored in the ocean tends to be spread across a larger surface area, allowing it to enter the atmosphere more easily. When the PDO is negative, SSTs are below average across a larger area, and global air temperatures tend to be lower. 
Figure 2. Typical warm and cool anomalies in sea-surface temperature during positive PDO years (left) and El Niño years (right). The patterns are similar, though with differences in intensity over some regions. The anomalies are reversed for negative PDO and La Niña years. Image credit: University of Washington Climate Impacts Group.
Figure 3 shows a striking connection between favored PDO modes (top) and global air temperature anomalies (bottom). The vast majority of atmospheric warming over the last century occurred during positive PDO phases, with negative PDOs tending to result in flat temperature trends. It’s easy to see how an atmospheric warming “hiatus” could occur during a negative PDO phase.
Figure 3. PDO values (top) and global air temperature anomalies (bottom). Gray shading indicates positive PDO periods, when atmospheric warming was most evident. The NOAA PDO values shown here vary slightly from those discussed in the article, which are calculated by the University of Washington. Image credit: Jerimiah Brown, Weather Underground. Data sources:NOAA (top) and NOAA/NCDC (bottom).
From the AMS meeting
The hiatus was discussed at length in a series of talks during the annual meeting of the American Meteorological Society last month in Phoenix. Jerry Meehl, from the National Center for Atmospheric Research (my former employer), gave a whirlwind 15-minute overview of hiatus-oriented research conducted over the last six years. Meehl’s talk can be viewed online. More than 20 papers have studied the hiatus and its links to the PDO/IPO, according to Matthew England (University of New South Wales). Most of the flattening of global temperature during the hiatus can be traced to cooler-than-average conditions over the eastern tropical Pacific, which pulled down global averages. An emerging theme is that natural, or internal, variability in the tropical Pacific can explain at least half of the hiatus. NCAR’s Clara Deser presented new modeling evidence along these lines (see video online). Other factors may be involved as well, including a series of weak volcanic eruptions that could explain a small part of the hiatus, according to a recent analysis by Ben Santer (Lawrence Livermore National Laboratory).
One crucial point is that global warming didn’t “stop” during the hiatus: the world’s oceans actually gained heat at an accelerated pace. Trade winds blew more strongly from east to west across the Pacific, consistent with the tendency toward La Niña conditions, as described in this open-access article by NCAR’s Kevin Trenberth and John Fasullo. Over parts of the central tropical Pacific, trade winds averaged about 3 mph stronger during 1999-2012 compared to 1976-1988. These speeds are higher than for any previous hiatus on record, bolstering the idea that other factors may have joined this negative PDO/IPO phase. The faster trade winds encouraged upwelling of cooler water to the east and helped deepen and strengthen the warm pool to the west—enough, in fact, to raise sea level around the Philippines by as much as 8 inches. Other parts of the deep ocean warmed as well. A new study led by Dean Roemmich (Scripps Institution of Oceanography) maps the areas of greatest ocean heating from 2006 to 2013 and finds that significant warming extended to depths of greater than 6600 feet.
What next for the PDO?
The PDO index, as calculated at the University of Washington, scored positive values during every month in 2014, the first such streak since 2003. By December it reached +2.51, the largest positive value for any December in records that go back to 1900. The January value from UW was 2.45, again a monthly record. (NOAA calculates its own PDO values through a closely related methodology.)
Because the PDO can flip modes for a year or more within its longer-term cycle, we don’t yet know whether a significant shift to a positive PDO phase has begun. If trade winds weaken throughout this year, and positive PDO values persist, that’ll be strong evidence that a new cycle is indeed under way. The last time we saw a two-year streak of positive values was in 1992-93. If this occurs, and assuming no spikes in major volcanic activity, we could expect greater rises in global temperature over the next 10 to 15 years than we’ve seen during the hiatus. In addition, we should watch for El Niño to make its presence known more often.
“I am inclined to think the hiatus is over, mainly based on the PDO index change,” NCAR’s Kevin Trenberth told me. While Matthew England isn’t ready to offer such a prediction, he emphasized that any post-hiatus global temperature rise is likely to be fairly rapid. Trenberth also commented on an interesting NOAA analysis (see Figure 4): “If one takes the global mean temperature from 1970 on, everything fits a linear trend quite well except 1998.”
Figure 4. When looking at global temperature over a full PDO cycle (1970s to 2010s), the overall rise becomes evident, despite the flattening observed in the last 15 years. Image credit: NOAA.
A record-strong El Niño occurred in 1998, providing an unusually powerful boost to global temperature and fueling years of subsequent declarations that “global warming stopped in 1998.” The record warmth of 2014 made it clear that global warming has no intention of stopping, and the next few years are likely to reinforce that point. Nevertheless, snowbound New Englanders, and millions of other easterners now dealing with record cold for so late in the year, may be wondering why eastern North America has seen so much cold and snow in the past few winters--especially this one--and how long that climatic quirk might continue. Stay tuned for a separate post on that topic.
Bob Henson
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Reader Comments
Category 6™
343. LAbonbon
Is drought the new normal for Southern California?
By GEOFFREY MOHAN
FEBRUARY 23, 2015 4:11 PM
Inreased carbon dioxide in the atmosphere is altering Earth's most important atmospheric weather cell, drawing more moisture into the deep tropics and broadening areas of drought at higher latitudes, according to a new study.
The U.S. west, including Southern California, as well as swaths of subtropical Brazil that are suffering from acute drought lie in the heart of the decreased rainfall band shown in 33 climate scenarios run over a 140-year span, according to the study published online Monday in the journal Proceedings of the National Academy of Sciences.
The study shows a clear global-warming signal in the changed water cycle brought on by a "deep tropical squeeze" in the Hadley circulation, a massive convection-driven cell extending from Earth's equator toward the planet's mid-latitudes.
“We are finding the region of drying exactly coincides with the places where we are now seeing this worldwide drought and wildfire happening," said University of Maryland atmospheric scientist William Lau, lead author of the study. "That includes the western U.S., southwestern U.S., Mexico, Brazil, southwestern Australia, southern Africa, northern Africa, the mid-Mediterranean region, southern Europe — all this is at the edge of the climatological sub-tropics that are being extended.” Read Full Article
342. sar2401
I really never expect that the bulls eye will verify. It is about 50 miles west of me but the small scale of the map makes it hard to tell accurately. As I've said many times, take those numbers and "X'es" off the map. They are distracting and serve no purpose except to highlight that the WPC is making a forecast that they don't have enough skill to make. What was important about the map was Eufaula is in the deep purple contour, which is 2.50" - I think. I'm slightly color blind and have a hard time distinguishing those fine color gradients. I'm now at 1.05" since Sunday. Not bad, but another inch at least before 6:00 pm tonight is needed before I'd call it in the ballpark. Below two inches isn't really the ballpark. What I think the WPC got right (and we'll see this evening if it did) is that an area of fairly substantial rain would occur between Sunday and Thursday. There must be a better way to communicate this than what the WPC is now using. I remember the hatched plots as well. I thought they were much more readable than what we have now. Unfortunately, graphic power progresses, bright young college grads who know that stuff backwards and forwards show up, and the old stuff gets put in the archives. Life is like that.
Big increase in lightning strokes since I started typing this. Up to about 12 a minute now. over 100 a minute is what I'd expect to see from a good line of storms but at least it's a little different than yet another batch of stratiform rain.
341. Neapolitan
340. weathermanwannabe
339. jpsb
Not at all, a luke warmest knows that CO2 is a green house gas and knows that the climate has been warming and knows that mankind is responsible for some of that warming. We just do not believe the IPCC computer models nor to we believe all the doom and gloom predictions coming from the alarmist camp. There are agents other than CO2 which drive climate.
338. WaterWitch11
geez you guys didn't you see ratatouille? it was the flea...
plus wasn't the blankets and bedding an issue?
337. sar2401
336. LAbonbon
I've hit the lower end of the forecast for my area. I was going to comment on this yesterday, but you and Caleb were a bit tetchy so I held off. Here goes...I think you look at these a bit differently than I do. The 'X' you've mentioned is the maximum for that area. You are about 70 or so miles from there...it's not marking where you are...
(For reference the 1-3 day from the 22nd is below)
Your area is in the 2-2.5 range. Jedkins (I think) wrote up a comment when I was first a commenting member...where he talked about how best to interpret and use the maps. He said to not take the range I was in as gospel, especilally if the isohyets were close together. For example, I'm in the 1-1.25 range on the 3-day. However, I wouldn't have been surprised or disappointed in the forecast if I ended up in the 0.75-1 or in the 1.25-1.5 ranges. You are in the 2-2.5...using the same thought process, and looking to ranges that are relatively close to Eufala, you could easily end in the 1.75-2 or the 1.5-1.75 range.
I know this has been mentioned (by you, if memory serves), that people's eyes are drawn to the 'X'. If you viewed the QPF, w/ contours only, you would never have seen the 'X', and never focused on it. (I tried to find this map in the archives w/ contours only, but no luck.) By expecting to get the maximum, it's almost goes without saying that you will be unlikely to ever have that expectation met.
Anyway, just an explanation on how I look at these. If anything, I ignore the 'X', and focus on which contours are closest to me.
BTW, just got some thunder here. Wasn't expecting that.
335. washingtonian115
334. Storms306
I'm all for a northwest shift in the precip. Would elevate my projected totals to 8-10 inches.
333. sar2401
332. georgevandenberghe
331. georgevandenberghe
The dominant rat in the middle ages in Europe was the Black Rat, a roof and house dweller. It was displaced sometime later in the middle ages and after the Plague, by the Norway rat which is a burrowing ground and sewer dweller and thus has less close contact with humans. (From 1969 reading of Time Life science books.. why I still remember this is another question?)
330. Drakoen
The models have trended more favorablly for us this morning and I wouldn't be surprised to see a slight shift northwest with the precipitation shield if the trend continues.
329. Patrap
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328. sar2401
327. georgevandenberghe
I am also skeptical we will scrape through this one with less than an inch in DC metro. Yet another round of school delays. My hunch is a few inches of powder in College Park.
We had a rare Winter anomaly today. No school delays.
326. Xyrus2000
There's been a few papers on the subject that basically boil down to the warmer temperatures/reduced sea ice have decreased the strength of the jet, allowing it to become more like a rubber band than a wall keeping arctic air locked up.
Here's a paper on the topic: Link
324. win1gamegiantsplease
323. sar2401
322. LAbonbon
321. vis0
and helped deepen and strengthen the warm pool to the west—enough, in
fact, to raise sea level around the Philippines by as much as 8 inches." could this account for some seeing not as high water levels off the UsofA east coast as i read some WxU members described during their fishing off Florida?
(*play opening Twilight Zone music*)
II. Anyone notice a 2:1* occurrence as to these PDOs. Remember my clues as to when one see 2:1 ratios in natures' patterns, as how many fingers [sit Down SAR2401 this is not a sobriety test] of cooler vs. warmer & vice versa occur? If they happen on both ends of a specific (as in PDO) catagory to observe "sounds"/resonances/vibrations from "space" and how that affects friction of fluids within a physical dimension, its a "Law of Galacsic" but then again i'm a nut.
When science eventually "reads" "sounds"/resonances/vibrations from black holes/q-Novaes, remember not to read them as plus/minus sine waves but inward / outward (squeezing,contracting / expanding). The Physical dimension reads the contracting as the energy being taken away thus cooler and expanding energy being added thus warmer, oh i must have hit my head on something *clearing "cob webs"* why am i writing Galacsics clues i stopped this last year forgive me for posting unknown sciences.
(*play closing Twilight Zone music*)
*2:1 as .666 to .333, the remainder .001 is for "nature" & "gawd" to communicate i.e. the trigger as to when to to recycle or switch this pattern ON/OFF.
PAY ATTENTION TO SUDDEN WIND SHIFTS & weather warnings.
320. tampabaymatt
Good morning Sar. Another grey, soupy, dreary day here. When I went for my 5 AM run this morning, there was a persistent light mist the entire time, enough to bring my gauge to 0.04" for the day so far. It looks like the low is going to follow the exact same track as every other Gulf low has since November.
319. sar2401
318. win1gamegiantsplease
The geography of NC doesn't help matters either. The way it sticks out tends to affect the northeastern part of the state for longer than down here. From what I've heard they mainly had to deal with snow west of the sounds and a wintry mix for the OBX.
And this has been a tricky event for the NWS to predict. Interesting forecaster's discussion opening:
TAKING A LOOK AT THE MORNING SOUNDING...WE CAME IN A BIT WARMER
ALOFT THAN EXPECTED. HOWEVER...WE WERE DRIER AS WELL...SUGGESTING
THAT THE WET BULBING EFFECTS WILL BE CRITICAL TO THE FORECAST. THIS
IS NOTHING NEW...BUT MOST PROJECTIONS ALOFT STARTED AT ABOUT
+4...WHERE OUR SOUNDING CAME IN AT +8 AT 800MB. SINCE THERE IS
LITTLE TO NO COLD AIR ADVECTION PROCESSES TO HELP OUT THE FROZEN
PRECIP...WE WILL HAVE TO RELY COMPLETELY ON DYNAMICAL OR MECHANICAL
COOLING...THAT IS FORCING COLDER AIR ALOFT DOWNWARD THROUGH HEAVY
PRECIP PROCESSES.
OTHERWISE...THE START TIME TO THE MOISTENING IS LOOKING QUICKER THAN
EXPECTED WHICH WILL POSSIBLY NOT ALLOW ALL THAT MUCH IN THE WAY OF
SURFACE WARMING. BIG DIFFERENCE BETWEEN EET AT 35/23 AND BHM
32/22...AS BHM WOULD WET BULB SEVERAL DEGREES BELOW FREEZING AS LONG
AS ANY PRE-PRECIP WARMING IS NOT TOO DRAMATIC.
WE ARE MOVING FROM THE MODELS TO OBSERVATIONS. WE WILL LAUNCH 1 OR
2 SPECIAL BALLOON RUNS TO TRY AND ASSESS MOVING FORWARD. FORECAST
WILL REMAIN THE SAME...BUT WITH WARMER TEMPS ALOFT AND COOLER
SURFACE WET BULBING...BE EXTREMELY WEARY OF SLEET AT THE ONSET AND
POSSIBLY SLEET FOR THE DURATION IN SOME LOCATIONS ALONG THE SOUTHERN
END OF THE WARNING. MY TWO RULES FROM HERE GOING FORWARD WILL BE TO
WATCH SURFACE AND 850MB TEMPS AND DEWPOINTS...WHICH ARE BEST
ASSESSED THROUGH OBSERVATIONAL DATA.
LAST POINT...THE PRECIPITATION IS EXTREMELY HEAVY...CONVECTIVE IN
SOME CASES...SO THE DYNAMICAL PROCESSES WILL BE AMPED SIGNIFICANTLY
COMPARED TO OUR TYPICAL WINTER EVENTS. KEEP THIS IN MIND...THAT
COOLING THE COLUMN WILL OCCUR QUICKLY AND IT WILL LIKELY MODIFY ANY
FORECAST SOUNDINGS PROJECTED. USING FORECAST SOUNDINGS WILL BE A
VERY DANGEROUS PROPOSITION FROM HERE FORWARD.
317. sar2401
316. Sfloridacat5
315. Guysgal
314. NativeSun
313. vis0
312. HaoleboySurfEC
311. Sfloridacat5
310. MAweatherboy1
"The hiatus" is a real thing, at least to an extent. Air temperature warming has slowed considerably since the PDO flipped, although as mentioned the oceans continue to take in large amounts of heat. And 15 years still isn't a long enough time to make meaningful conclusions about climate. But with a cold PDO, and other natural factors like a quiet Sun supporting slightly cooler conditions, you would think we would've seen some cooling over the last decade. Obviously that hasn't happened. This is further proof that the climate forcing we have created, mainly absurd amounts of CO2 in the atmosphere, are more than powerful enough to overcome natural cycles, and that when the natural cycles go to a warmer phase, we're likely to see some pretty scary levels of warming. We're just along for the ride at this point.
309. StormTrackerScott
308. hurricanes2018
307. tampabaymatt
306. washingtonian115
MattRogers-CapitalWeatherGang
7:05 AM EST
Yeah, I think the NWS snow projections seem too low to me right now. The NAM (high and low-res ) from the 6z cycle seemed to be in the 2-4" range and the SREF mean is about 4" for DC.
305. yonzabam
Totally unconvincing argument. All rodents can carry plague. Sporadic human cases are frequently associated with marmots (prairie dogs). Neither marmots nor gerbils colonise ships in the way that rats do. All European plague outbreaks began in port cities, so it's a no brainer.
Last year, a couple of UK scientists with a book to sell, were claiming the Black Death was caused by Ebola, despite the fact that plague victim mass graves in London have recently been excavated and the RNA of the plague pathogen, Yersinia pestis, identified from teeth pulp.
304. islander101010
303. islander101010
302. LAbonbon
Morning, Matt. I think a lot of us are in for some rain today (or snow for some).
301. LAbonbon
300. tampabaymatt
Good morning Bon!
299. LAbonbon
298. tampabaymatt
295. riverat544
So the effect of solar variation (the sunspot cycle) is so small it's less than the uncertainty from other sources in climate models and I don't think they include it. But the yearly variation due to orbital eccentricity is big enough that it is accounted for in some way. (That's my understanding but I don't know for sure.)
294. yankees440
Lived in Coral Springs at the time.. Barely got much from it
293. KoritheMan
Gustav was similar to Charley in terms of extent of inland wind damage. It kind of happens with the fast-moving storms.