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Causes of the Rapid Warming of the North Atlantic Ocean in the Mid-1990s

April 9, 2020

By Paul Homewood


Most of us are probably familiar with the pattern of Arctic sea ice decline between 1979 and 2007, followed by a period of relative stability. Most of the decline took place after the mid 1990s.

The decline is nearly always explained away as the result of global warming, but a couple of old studies show this not to be the case.

In 2011, Robson & Sutton found that the sub polar gyre underwent remarkable and rapid warming in the mid 1990s, and that this was linked to changes in the North Atlantic Oscillation:



A gyre is simply a system of rotating ocean currents:

This is the key chart in their paper:



Graphs a) and b) compare sea surface temperatures, and show just how radically seas warmed between the two decades in the N Atlantic.

Perhaps even more remarkable are the temperatures for the oceans down to 500m, shown in c) and d).

There is no physical basis for such enormous changes to have been caused by greenhouse gases, because the heat capacity of the oceans is far too massive. The explanation must lie elsewhere.


The Robson study fits in with an earlier one from NASA in 2007, which linked climatic changes in the Arctic to the Arctic Oscillation:


PASADENA, Calif. – A team of NASA and university scientists has detected an ongoing reversal in Arctic Ocean circulation triggered by atmospheric circulation changes that vary on decade-long time scales. The results suggest not all the large changes seen in Arctic climate in recent years are a result of long-term trends associated with global warming.
The team, led by James Morison of the University of Washington’s Polar Science Center Applied Physics Laboratory, Seattle, used data from an Earth-observing satellite and from deep-sea pressure gauges to monitor Arctic Ocean circulation from 2002 to 2006. They measured changes in the weight of columns of Arctic Ocean water, from the surface to the ocean bottom. That weight is influenced by factors such as the height of the ocean’s surface, and its salinity. A saltier ocean is heavier and circulates differently than one with less salt.
The very precise deep-sea gauges were developed with help from the National Oceanic and Atmospheric Administration; the satellite is NASA’s Gravity Recovery and Climate Experiment (Grace). The team of scientists found a 10-millibar decrease in water pressure at the bottom of the ocean at the North Pole between 2002 and 2006, equal to removing the weight of 10 centimeters (four inches) of water from the ocean. The distribution and size of the decrease suggest that Arctic Ocean circulation changed from the counterclockwise pattern it exhibited in the 1990s to the clockwise pattern that was dominant prior to 1990.
Reporting in Geophysical Research Letters, the authors attribute the reversal to a weakened Arctic Oscillation, a major atmospheric circulation pattern in the northern hemisphere. The weakening reduced the salinity of the upper ocean near the North Pole, decreasing its weight and changing its circulation.
"Our study confirms many changes seen in upper Arctic Ocean circulation in the 1990s were mostly decadal in nature, rather than trends caused by global warming," said Morison.
"While some 1990s climate trends, such as declines in Arctic sea ice extent, have continued, these results suggest at least for the ‘wet’ part of the Arctic — the Arctic Ocean — circulation reverted to conditions like those prevalent before the 1990s," he added.
The Arctic Oscillation was fairly stable until about 1970, but then varied on more or less decadal time scales, with signs of an underlying upward trend, until the late 1990s, when it again stabilized. During its strong counterclockwise phase in the 1990s, the Arctic environment changed markedly, with the upper Arctic Ocean undergoing major changes that persisted into this century. Many scientists viewed the changes as evidence of an ongoing climate shift, raising concerns about the effects of global warming on the Arctic.
Morison said data gathered by Grace and the bottom pressure gauges since publication of the paper earlier this year highlight how short-lived the ocean circulation changes can be. The newer data indicate the bottom pressure has increased back toward its 2002 level. "The winter of 2006-2007 was another high Arctic Oscillation year and summer sea ice extent reached a new minimum," he said. "It is too early to say, but it looks as though the Arctic Ocean is ready to start swinging back to the counterclockwise circulation pattern of the 1990s again."



The Arctic Oscillation is closely linked to the NAO, and is said to be “negative” when high pressure dominates the pole:


According to NSIDC:

The Arctic Oscillation primarily affects sea ice through winds that cause changes in where the sea ice drifts.” When the Arctic Oscillation is in its negative mode, he said, the winds and ice tend to flow in a clockwise direction, generally keeping more of the older, thicker ice in the middle of the Arctic. In the positive phase, that old ice tends to get pushed out of the Arctic along the Greenland coast. Meier said, “This means that the sea ice tends to be younger and thinner and more prone to melt after a winter with a strong positive Arctic Oscillation

The unusually positive AO is evident in the late 1990s, since when it has been more stable.

Note also positive AO during the 1920s, when the Arctic underwent similar warming.




The exact mechanisms are complex and still not well understood by scientists. But both of these studies point to natural, decadal atmospheric changes as being responsible for Arctic sea ice trends since the 1990s, which include the self evident stabilisation of sea ice extent since 2007.

  1. jack broughton permalink
    April 9, 2020 12:31 pm

    It is not easy to put the measurements into a meaningful context: 10 cm water in about 1000m depth implies an accuracy of 0.01%, the gravitational noise is much higher than that. It seems to agree with the tidal gauge measured increase in ocean depth over the period reasonably though.

  2. Gamecock permalink
    April 9, 2020 1:56 pm

    ‘Most of us are probably familiar with the pattern of Arctic sea ice decline between 1979 and 2007, followed by a period of relative stability. Most of the decline took place after the mid 1990s.’

    How many people died from this?

  3. April 9, 2020 3:24 pm

    Reblogged this on Tallbloke's Talkshop and commented:
    Pointing to any natural factors is frowned on by climate alarmists. But these factors have always been in play and always will be, and some researchers at least will find and discuss them.

  4. Ulric Lyons permalink
    April 9, 2020 5:06 pm

    This is nonsense. The NAO was in a negative regime 1995-1999, and positive NAO years 2013-2015 and 2017-2018 have driven AMO cooling episodes, remember the cool blob?

    • April 9, 2020 6:57 pm

      You have not read it properly, Ulric

      In the mid-1990s, the subpolar gyre of the North Atlantic underwent a remarkable rapid warming, with sea surface temperatures increasing by around 1°C in just 2 yr. This rapid warming followed a prolonged positive phase of the North Atlantic Oscillation (NAO) but also coincided with an unusually negative NAO index in the winter of 1995/96

      That proplongued positive phase can be seen on your graphs between 1989 and 1995, followed by prolongued negative phase from 1995 to 1999.

    • Ulric Lyons permalink
      April 13, 2020 10:56 pm

      Claiming that the post 1995 warming of the AMO is a delayed response to the previous positive NAO regime is the nonsense, it’s a direct response to the negative NAO regime 1995-1999.

      • April 14, 2020 10:26 am

        Evidence please?

      • Ulric Lyons permalink
        April 16, 2020 8:32 pm

        All the positive NAO episodes are associated with colder AMO anomalies, the early to mid 1970’s, the mid 1980’s, the early 1990’s, relative AMO cooling around the last two sunspot cycle maxima 2000-2002 and 2014-2015 (the cool blob), and through 2017-2018. And the corollary for negative NAO episodes.

  5. April 9, 2020 7:25 pm

    Reblogged this on WeatherAction News and commented:
    Excellent work and something to keep an eye on in the years ahead.

  6. April 9, 2020 8:59 pm

    Hi Paul. Pleased to see that the 2007 NASA study came in handy.

    Curious (2 items) – Re: the temp anomaly maps. Would be curious to see the next (2006 forward) decadal period.

    2nd. Pretty easy to see a rather flat trend in the Sept Arctic sea ice extent from roughly 1991-2000+. That would be inspire of the ‘rapid warming of the mid-1990’s?

    Not to mention the step-up warming cycle on the other side, when the PDO flipped phase in about 1976


  7. Jonathan Drake permalink
    April 9, 2020 9:16 pm

    “… Arctic sea ice decline between 1979 and 2007, followed by a period of relative stability”. This pattern can be explained by the switch from satellites with significant orbital decay to ones with well controlled orbits:

  8. April 9, 2020 9:18 pm

    “… Arctic sea ice decline between 1979 and 2007, followed by a period of relative stability”. This pattern can be explained by the switch from satellites with significant orbital decay to ones with well controlled orbits:

  9. Michael Olsen permalink
    April 10, 2020 1:14 am

    Somewhat surprisingly, the Canadian government (Natural Resources Canada) acknowledges that the main cause of reductions in ice thickness and late summer ice extent in the Arctic was not atmospheric warming, but an increased export of sea ice via Fram Strait during 1989-2003.

    It also acknowledges that the summer sea ice extent in the Canadian archipelago today is similar to that recorded in “the much cooler mid-nineteenth century”.

    Several scientific studies are referenced in support of these statements, but alarmists take no notice.

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