Part of the Pacific Ocean Is Not Warming as Expected. Why?

by |June 24, 2019

State-of-the-art climate models predict that as a result of human-induced climate change, the surface of the Pacific Ocean should be warming — some parts more, some less, but all warming nonetheless. Indeed, most regions are acting as expected, with one key exception: what scientists call the equatorial cold tongue. This is a strip of relatively cool water stretching along the equator from Peru into the western Pacific, across quarter of the earth’s circumference. It is produced by equatorial trade winds that blow from east to west, piling up warm surface water in the west Pacific, and also pushing surface water away from the equator itself. This makes way for colder waters to well up from the depths, creating the cold tongue.

Climate models of global warming — computerized simulations of what various parts of the earth are expected to do in reaction to rising greenhouse gases — say that the equatorial cold tongue, along with other regions, should have started warming decades ago, and should still be warming now. But the cold tongue has remained stubbornly cold.

This troubles many scientists, because the cold tongue plays a key role in global climate. For example, it affects the El Niño-Southern Oscillation, a natural cyclic strengthening and weakening of the trade winds that causes cooling and warming of the eastern Pacific surface every two to seven years. ENSO is the world’s master weather maker; depending on which part of the cycle it is in, its echoes in the atmosphere may bring heavy rains or drought across much of the Americas, east Asia and east Africa. Whether the cold tongue warms will likely affect weather across huge regions. Resulting shifts could affect world food supplies and outbreaks of dangerous weather. But our predictions of those shifts rest on climate models.

Richard Seager, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory, has long suspected that climate models get the cold tongue wrong. In 1997, he and colleagues published a paper suggesting that it had not warmed at all during the 20th century. At the time, most scientists assumed that any discrepancy between real-world temperatures and those predicted by climate models were due to natural variability. We should just wait; eventually the signal of cold tongue warming would emerge. Now, two decades later, with more modern satellite data in hand, real-world observations are veering ever more obviously from the models. It is time to reconsider, says Seager.

In a new paper in the journal Nature Climate Change, he and colleagues use simplified models that isolate the fundamental dynamics of the tropical Pacific atmosphere-ocean system. These, they say, comport with the cold tongue’s actual behavior — and show that it is consistent with rising greenhouse gases.

We recently spoke with Seager about climate models, the intricate workings of the Pacific climate system, and the wider implications for the world.

In general, how well do climate models match real-world observations?

The mismatch between observed changes in cold tongue temperature over past decades and the models is quite striking. There are scores of simulations with multiple models from research groups across the world. While these models are all forced by the same histories of greenhouse gases, volcanoes, solar radiation and other forces, they generate their own internal variability. Hence they create a range of estimates of climate history. For changes in cold-tongue temperature, the observed changes are at the far cold end or outside the model range. The average or median model says the cold tongue should have warmed by 0.8 degrees C or more over the past six decades, but the real value is only 0.4 degrees or less.

The tropical Pacific Ocean (Australia and South America in gray, left and right). Top map shows what climate models say sea-surface temperatures should be doing in response to rising greenhouse gases, including pronounced warming of waters along the equator. Bottom map shows what the waters are actually doing; the equatorial waters are remaining relatively cool. (Seager et al., Nature Climate Change 2019)

map showing pacific ocean cold tongueWhy are the state-of-the-art climate models out of line with what we are seeing?

Well, they’ve been out of line for decades. This is not a new problem. In this paper, we think we’ve finally found out the reason why. Through multiple model generations, climate models have simulated cold tongues that are too cold and which extend too far west. There is also spuriously warm water immediately to the south of the model cold tongues, instead of cool waters that extend all the way to the cold coastal upwelling regions west of Peru and Chile. These over-developed cold tongues in the models lead to equatorial environments that have too high relative humidity and too low wind speeds. These make the sea surface temperature very sensitive to rising greenhouse gases. Hence the model cold tongues warm a lot over the past decades. In the real world, the sensitivity is lower and, in fact, some of heat added by rising greenhouse gases is offset by the upwelling of cool water from below. Thus the real-world cold tongue warms less than the waters over the tropical west Pacific or off the equator to the north and south. This pattern of sea-surface temperature change then causes the trade winds to strengthen, which lifts the cold subsurface water upward, further cooling the cold tongue.

What do your models do that the more widely used ones don’t?

Our models actually date back to the early 1980s, when people were first trying to use models to explain phenomena like the El Niño-Southern Oscillation. It was common then to make the problem simpler by assuming within the model the climatological mean state and simply simulating perturbations from that. We used that approach. By doing so, we were able to show within our one simple model that, if we assume the real-world climatological state, the response to rising greenhouse gases is warming everywhere, but not in the cold tongue. In contrast, if we assume the biased climatological state in the complex state-of-the-art models, the response to rising greenhouse gases has enhanced warming in the cold tongue. Hence this trip down modeling memory lane allows us to diagnose what is wrong with the complex models currently being used for climate projections and impact assessments.

If your ideas are correct, how might projections of ENSO’s future behavior change?

Short answer, we don’t know. One thing at a time! However, we do know that ENSO behavior depends on the mean state around which it is perturbing things. If we are right that the tropical Pacific is moving to a state where the waters are warming everywhere but not in the cold tongue, and cold subsurface waters are being lifted closer to the surface, then ENSO will almost certainly change in amplitude, frequency and other ways. We need to find out.

What are the implications for people?

They are many. The sea-surface temperature of the equatorial Pacific influences climate and its variability worldwide. Generally, warming of the atmosphere increases the amount of moisture the air can hold, and intensifies moisture transport. This tends to make subtropical dry zones drier and tropical and mid-latitude wet zones wetter. But on top of those changes there will be regional changes. If the cold tongue warms as the complex models say it should, analogous to an El Niño event, it will create a wet tendency in some regions, to offset subtropical drying in southwest North America and South America. It will also create a wetting tendency in east Africa, but a drying tendency in equatorial South America and the Sahel. If, instead, we are right and the cold tongue will not warm as much, then drying in southwest North America, subtropical South America and east Africa could be more severe than the complex models project. At the same time, equatorial South America and the Sahel might see wetter conditions. In developing climate impact assessments, scenarios should not be limited to the complex models. They should also consider the case in which the cold tongue continues to not warm. The implication for modelers is that they must find out why their models have biases, and fix them.

The study was coauthored by Lamont-Doherty researchers Mark Cane, Naomi Henderson, Dong-Eun Lee, Ryan Abernathey and Honghai Zhang. Funding: World Surf League and the U.S. National Science Foundation.


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John Moriarty
John Moriarty
3 years ago

Can micro plastic particles in the oceans absorb more heat than surrounding water and have an affect on temperature measurements and even ice formation?

Steve
2 years ago

It would probably help if anybody could properly model clouds.

frankebe
frankebe
2 years ago

The real “model” for understanding any climate change is… history. Climatologists should read some history. I suggest the 2016 THE GREAT TRANSITION—Climate, Disease and Society in the Lat-Medieval World by Bruce M.S. Campbell.

Alan Lowey
Alan Lowey
2 years ago

Post-Einstein gravity theory allows extra heat to move from the equator towards the poles. The equatorial waters are cooling.

grindupBaker
grindupBaker
2 years ago

ENSO appears to have “strengthened” since 1995 due to Pacific trade winds (Easterlies) having started increasing in average speed since 1995 and now 1 m/s faster than before 1995. This was the main cause of the “hiatus” or “pause” between 1997/98 huge El Nino and very large 2015/16 El Nino.
—————-
Quote: “Atlantic warming turbocharges Pacific trade winds Date:August 3, 2014 Source:University of New South Wales. New research has found rapid warming of the Atlantic Ocean, likely caused by global warming, has turbocharged Pacific Equatorial trade winds. Currently the winds are at a level never before seen on observed records, which extend back to the 1860s. The increase in these winds has caused eastern tropical Pacific cooling, amplified the Californian drought, accelerated sea level rise three times faster than the global average in the Western Pacific and has slowed the rise of global average surface temperatures since 2001. It may even be responsible for making El Nino events less common over the past decade due to its cooling impact on ocean surface temperatures in the eastern Pacific. “We were surprised to find the main cause of the Pacific climate trends of the past 20 years had its origin in the Atlantic Ocean,” said co-lead author Dr Shayne McGregor from the ARC Centre of Excellence for Climate System Science (ARCCSS) at the University of New South Wales.”
—————-
The Pacific Ocean easterly trade winds started increasing in 1995 AD. Caused by the rapid warming of the Atlantic Ocean surface due to global warming (1995 AD is 25 years after the carbon burn rate started increasing and also after Clean Air Acts reduced “global dimming” air pollution a bit).
—————-
Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus
Nature Climate Change 4, 222–227 (2014) doi:10.1038/nclimate2106 Received 11 September 2013 Accepted 18 December 2013 Published online 09 February 2014 Corrected online 14 February 2014
Matthew H. England, Shayne McGregor, Paul Spence, Gerald A. Meehl, Axel Timmermann, Wenju Cai, Alex Sen Gupta, Michael J. McPhaden, Ariaan Purich & Agus Santoso Affiliations
Quote: “Here we show that a pronounced strengthening in Pacific trade winds over the past two decades—unprecedented in observations/reanalysis data and not captured by climate models—is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake.”
—————-
Aside note: There’s an Aussie talk about Antarctic changes by the Matthew H. England above at https://www.youtube.com/watch?v=Ck8u1-XS9rM
—————-
Quote: “The record-breaking increase in Pacific Equatorial trade winds over the past 20 years had, until now, baffled researchers. Originally, this trade wind intensification was considered to be a response to Pacific decadal variability. However, the strength of the winds was much more powerful than expected due to the changes in Pacific sea surface temperature. Another riddle was that previous research indicated that under global warming scenarios Pacific Equatorial Trade winds would slow down over the coming century. The solution was found in the rapid warming of the Atlantic Ocean basin, which has created unexpected pressure differences between the Atlantic and Pacific. This has produced wind anomalies that have given Pacific Equatorial trade winds an additional big push. “The rapid warming of the Atlantic Ocean created high pressure zones in the upper atmosphere over that basin and low pressure zones close to the surface of the ocean,” says Professor Axel Timmermann, co-lead and corresponding author from the University of Hawaii. “The rising air parcels, over the Atlantic eventually sink over the eastern tropical Pacific, thus creating higher surface pressure there. The enormous pressure see-saw with high pressure in the Pacific and low pressure in the Atlantic gave the Pacific trade winds an extra kick, amplifying their strength. It’s like giving a playground roundabout an extra push as it spins past.” Many climate models appear to have underestimated the magnitude of the coupling between the two ocean basins, which may explain why they struggled to produce the recent increase in Pacific Equatorial trade wind trends. While active, the stronger Equatorial trade winds have caused far greater overturning of ocean water in the West Pacific, pushing more atmospheric heat into the ocean, as shown by co-author and ARCCSS Chief Investigator Professor Matthew England earlier this year. This increased overturning appears to explain much of the recent slowdown in the rise of global average surface temperatures. Importantly, the researchers don’t expect the current pressure difference between the two ocean basins to last. When it does end, they expect to see some rapid changes, including a sudden acceleration of global average surface temperatures. “It will be difficult to predict when the Pacific cooling trend and its contribution to the global hiatus in surface temperatures will come to an end,” Professor England says.”
—————-Here’s the sequence of events, some definitely linked and others possibly linked:
– 1995 AD the start. Pacific Ocean easterly trade winds began increasing.
– Pacific Ocean easterly trade winds have increased 30% (1 m/s) since 1995 AD.
– The ocean heat content (OHC) anomaly rate DOUBLED at ~1999 AD (ocean started warming twice as fast as before ~1998 AD
).
– Huge 1997/98 El Nino started soon after 1995 AD
.
– Arctic Ocean summer sea ice extent loss rate massively increased at 1997.5 AD as seen in a plot at 9:15 at https://www.youtube.com/watch?v=sCEawfpDoD0&t=42s
– GMST increase slowed. ENSO change caused the “pause” or “hiatus” (that’s why global warming” is 0.11 degrees less than in models).
– GMST ==El Nino years== started pulling ahead of La Nina faster at +0.23 degrees / decade vs +0.165 degrees / decade.
– Sea level change rise (SLR) of the ==western== equatorial Pacific Ocean has been much higher than the global average because the stronger Pacific Equatorial trade winds are pushing the water westwards harder than pre-1995 AD
– Greenland ice sheet (GrIS) mass loss more than doubled in 1997 AD,
– Arctic region warming at latitude 67N 1958-2019 sped up to +0.94 degrees / decade from a lower earlier rate ~1996-1998
– Southern westerlies strengthened & tightened on Antarctica soon after (perhaps the Antarctic circumpolar westerlies began strengthening & tightening then but I haven’t pinned ENSO as the cause yet).
– Actual “global warming” is 0.11 degrees less than model global warming because the WG1 climate scientists didn’t replicate that Pacific Ocean – Atlantic Ocean wind coupling effect in the CMIP models. I don’t know whether they’ve corrected that in CMIP6.
– Almost certainly has affected the Indian Ocean dipole with this additional wind push westward so will likely increase drought in Australia due to moving the warm rising air more often further to the west than before.
—————–
All happened soon after 1995 AD
when the tropical Pacific Ocean easterly trade winds started having higher average speed and boosting the ENSO.
—————-
The Tropical Atlantic Ocean surface has warmed and has increased the intensity of the Tropical Pacific Ocean trade winds by 50% in under 30 years because the atmospheric circulation is coupled between the Tropical Atlantic Ocean and the Tropical Pacific Ocean, but the Tropical Atlantic Ocean and the Tropical Pacific Ocean aren’t coupled because there’s land in the way
ENSO is a massive feature of Earth’s climate and the GMST trends have been:
+0.13 degrees / decade: UAH lower troposphere 1979-2017
+0.17 degrees / decade: RSS lower troposphere 1979-2017
+0.165 degrees / decade: Surface La Nina & ENSO-neutral years 1970-2014 (me from GISTEMP)
+0.20 degrees / decade: Surface El Nino years 1966-1995 (me from GISTEMP)
+0.23 degrees / decade: Surface El Nino years 1995-2014 (me from GISTEMP, high uncertainty, sparse & varied data points)
+0.18 degrees / decade: Surface average 1966-2014 (GISTEMP)
+0.11 degrees / decade: Ocean surface 1966-2014 (GISTEMP)
+0.047 degrees / decade: Ocean 0-300M depth 1966-2010 89 / 432 = 0.206 (me from various, Hadley, ORAS4, talk plots etc.)
+0.030 degrees / decade: Ocean 300-700M depth 1966-2010 76 / 576 = 0.132 (me from various, Hadley, ORAS4, talk plots etc.)
+0.026 degrees / decade: Ocean 700-1000M depth 1966-2010 (me from various, Hadley, ORAS4, talk plots etc.)
+0.15 degrees total increase: Ocean 0-1000M depth (me from various, Hadley, ORAS4, Matthew England talk plots etc.)
—————-
+0.009 degrees / decade: Ocean 700-2000M depth 1966-2010 77 / 1872 = 0.0411 (me from various, Hadley, ORAS4, talk plots etc.)
Note the +0.23 degrees / decade for El Nino years since 1995 and only +0.165 degrees / decade for La Nina & ENSO-neutral years. A big difference.

Alan Lowey
Alan Lowey
Reply to  grindupBaker
2 years ago

“Importantly, the researchers don’t expect the current pressure difference between the two ocean basins to last. When it does end, they expect to see some rapid changes, including a sudden acceleration of global average surface temperatures. “It will be difficult to predict when the Pacific cooling trend and its contribution to the global hiatus in surface temperatures will come to an end,” Professor England says.”
My model predicts that the equatorial Pacific ocean cooling will continue due to additional tidal energy transporting heat towards the polar regions.
This effect can even be seen in the IPCC report AR5 for policy makers, which shows a global heat map with vast chunks of the equatorial region blanked out with white squares. This indicates to me that the data didn’t show what was anticipated and so was omitted. Similarly, it’s only the mid-latitudes which show a confident increase in warming on the global map, with the polar regions again being left blank. This data is consistent with my hypothesis that a natural change in gravity causes climate change and not manmade CO2 emissions.
https://www.express.co.uk/news/science/1308437/dark-matter-news-scientist-moon-core-theory-newton-einstein

Walter Clark
Walter Clark
1 month ago

If the Pacific Ocean is not warming as expected, it could cause a permanent La Nina. If the Pacific Ocean is not warming up, that would make El Ninos that make the Pacific Ocean warm the thing of the past.