Levitus rewarmedRichard Treadgold | April 28, 2012
Yes, the ocean has warmed; no, it’s not ‘global warming’
And warm water does not sink
Oceanographer Dr Willem de Lange has referred us to a really clear treatment of ocean warming and ocean-atmosphere interaction in an article by a noted oceanographer (now deceased). It appeared in 21st Century Science & Technology magazine in 2000 and carried the “Yes, the ocean has warmed” headline you see above. Though written 12 years ago, it makes a solid rebuttal to the substance of the modern warming scare, emphasizing, as though marine scientists needed to be told, that warm water cannot sink.
The author was Dr. Robert E. Stevenson, an oceanography consultant, who trained NASA astronauts in oceanography and marine meteorology, was Secretary General of the International Association for the Physical Science of the Oceans from 1987 to 1995 and was an oceanographer for the U.S. Office of Naval Research for 20 years.
Here’s the article’s original introduction:
Contrary to recent press reports that the oceans hold the still-undetected global atmospheric warming predicted by climate models, ocean warming occurs in 100-year cycles, independent of both radiative and human influences.
Which echoes today’s headlines about ocean heat content trying to explain why climate models don’t predict the climate. For example:
- Search For ‘Missing Heat’ Confirms More Global Warming ‘In The Pipeline’ (19 Feb 2012)
- Has the Earth’s Missing Heat Been Found? (10 Feb 2012)
- Global warming: ‘Missing’ heat found deep in the ocean (18 Sep 2011)
- Global Warming: Why Aren’t Temperatures Even Higher? (20 Apr 2010)
Stevenson’s article in 2000 was prompted by a paper published in Science magazine that year which found warming to a depth of nearly 10,000 feet in the Atlantic, Pacific and Indian Oceans since the late 1940s. In each ocean basin, substantial temperature changes were occurring and much deeper than previously thought.
In an eery forecast of an identical period since his article, Robert Stevenson said that for 15 years, modellers had tried to explain their lack of success in predicting global warming. The climate models had predicted a global temperature increase of 1.5°C by the year 2000, six times more than occurred. Undiscouraged, the modellers argued that the heat generated by their claimed “greenhouse warming effect” was being stored in the deep oceans, and that it would emerge at some time. They had no observational evidence to support that contention until the Levitus article.
Stevenson quotes two people drumming up support for the new paper. Science news writer Richard A. Kerr claimed “The ocean-induced delay in global warming also suggests to some climatologists that future temperature increases will be toward the top end of the models’ range of prediction.”
Then the ever-faithful Dr. James Hansen, of the Goddard Institute for Space Studies, enthused: “Now the ocean-warming data imply that climate sensitivity [to the greenhouse effect] is not at the low end of the spectrum.”
One can imagine those worthy spokesmen thinking, “Ok, so 15 years of no warming is a hard sell, but not impossible; we’ll brazen it through.” Neither of them guessed yet another 15 years lay ahead.
Calculating the heat in the world’s oceans
In their paper, Syd Levitus and colleagues from NOAA’s Ocean Climate Laboratory attempt to quantify the heat content in the top 3000 metres of the world ocean from 1948 to 1998. They calculated an increase of about 2 x 1023 joules from 1955 to 1995, computing a mean warming of 0.06°C. The increased heat content indicates a warming rate of 0.3 watts/m2 over the Earth’s surface.
They concluded that substantial changes in heat content took place in the 300-metre to 1,000-metre layers of each ocean, and at depths even greater than 1,000 metres in the North Atlantic. From these changes, they determined that in the upper layer (0-300 metres), the mean temperature of the global ocean had increased by 0.31°C during the last half century…
The authors reported: “We compared the range of upper-ocean heat content with the range of the climatological annual cycle of heat content for the Northern Hemisphere” (Levitus and Antonov 1997). They determined that “there is relatively little contribution to the climatological range of heat content from depths below 300 metres.”
Deep water doesn’t contribute to weather? Hardly surprising. However:
The Levitus group looked particularly at the data for the deep waters of the North Atlantic, choosing to address a depth of 1,750 metres. They learned that that ocean had warmed in the period between 1955 and 1974, and again between 1974 and 1988. The warming was not uniform, horizontally or vertically, but they determined that the changes were not small, and could have made appreciable contributions to the Earth’s heat balance on decadal time scales. Maximum heat storage was at depths greater than 300 metres.
This confirms that heat does indeed penetrate downwards, but not far. This is less than 10% of the average ocean depth of 4000 metres — and it’s caused by moving currents; it’s not a result of warm water just sinking, which is impossible.
So, we have the added knowledge that the heat content of the North Atlantic is substantial at depths below 300 metres… Regarding the World Ocean, they reported: “The Pacific and Atlantic have been warming since the 1950s, and the Indian since the 1960s. The delay in the Indian Ocean may be caused by the sparsity of data before 1960.”
- The world ocean has exhibited coherent changes of heat content during the past 50 years, resulting in a net warming.
- There is no determination whether the observed warming is caused by natural variability or anthropogenic (man-induced) forcing.
- The warming supports the contentions of global-climate modellers that the planetary radiative disequilibrium, for the period of 1979 to 1996, may be the result of “excess heat accumulating in the ocean.”
- Sea-surface temperatures have had two distinct warming periods over the past century; from 1920 to 1940, then a cooling period until the second warming began in the 1970s.
- In each period of warming, an increase in the ocean’s heat content preceded the observed warming of the sea-surface temperatures. The NOAA scientists concluded that it could be the result of natural variability, or anthropogenic effects, or more likely both.
- It was speculated that the extreme warmth of the world ocean during the mid-1990s was caused by (a) the multi-decadal warming of the Atlantic and Indian oceans, and (b) a positive polarity in a possible bidecadal oscillation of the Pacific Ocean heat content.
- And a final point, regarding the large change in Atlantic heat storage at depths exceeding 300 metres: The convection in the Labrador Sea, by mixing the ocean through a 2,000-metre-deep water column, may keep sea-surface temperature changes relatively small, despite a large heat flux from ocean to atmosphere. Such convection must be addressed, especially when anthropogenic forcing is being considered.
It sometimes seems as if I’m living in a “time-warp” in which some people, and scientists, are unaware that rational life existed before their birth—or before they got out of the sixth grade. Yet, we marine scientists did not enter the second half of the 20th century without a fair bit of understanding of the thermal ocean.
For example, Prof. Hubert H. Lamb, the premier European climatologist of the 20th century, wrote in 1977 that “there has been a general warming of sea temperatures, by 0.5–1.0°C, from 1880 to 1965, defined from widely scattered points around the oceans of the world.”
Stevenson describes how he took sea water temperature readings during the 1950s,
“learning to deploy Nansen water bottles and reversing thermometers for deep-sea sampling.” He concludes: “Those of us who obtained the data are not going to be snowed by the claims of the great precision of “historical data found stored in some musty archives.”
Basic marine climatology
The basics of these interactions start where oceans and atmosphere meet. The atmosphere cannot warm until the underlying surface warms first. The lower atmosphere is transparent to direct solar radiation, preventing it from being significantly warmed by sunlight alone. The surface atmosphere thus gets its warmth in three ways: from direct contact with the oceans; from infrared radiation off the ocean surface; and from the removal of latent heat from the ocean by evaporation. Consequently, the temperature of the lower atmosphere is largely determined by the temperature of the ocean.
We would do well to remember the simple fact that heat rises, and that the warmer gas or fluid rises above the colder. For all the talk of the radiative effects of greenhouse gases interrupting the escape of long-wave thermal energy from oceans, land and clouds, the re-heating of ocean and land caused by that radiation is minuscule. As we see shortly, long-wave infra-red penetrates only a few microns into the ocean. Coupled with the fact that as soon as water warms up a little at the surface, it evaporates, thus immediately cooling, it’s impossible for this process to cause significant warming of the water.
How the oceans get warm
Warming the ocean is not a simple matter, not like heating a small glass of water. The first thing to remember is that the ocean is not warmed by the overlying air.
Let’s begin with radiant energy from two sources: sunlight and infrared radiation — the latter emitted from the “greenhouse” gases (water vapor, carbon dioxide, methane and various others) in the lower atmosphere. Sunlight penetrates the water surface readily, and directly heats the ocean up to a certain depth. Around 3 percent of the radiation from the Sun reaches a depth of about 100 metres.
The top layer of the ocean to that depth warms up easily under sunlight. Below 100 metres, however, little radiant energy remains. The ocean becomes progressively darker and colder as the depth increases. (It is typical for the ocean temperature in Hawaii to be 26°C (78°F) at the surface, and 15°C (59°F) at a depth of 150 metres.
The infrared radiation penetrates but a few millimetres into the ocean [Dr de Lange maintains this distance is actually in the tens of micrometres (microns). Confirmed at Real Climate, strangely -- though the discussion there of why the tiny thermal effect of that OLR (outgoing longwave radiation) on the "skin layer" warms the whole ocean is oddly complex and unconvincing. – RT]. This means that the greenhouse radiation from the atmosphere affects only the top few [microns] of the ocean. Water just a few [millimetres] deep receives none of the direct effect of the infrared thermal energy from the atmosphere. Further, it is in those top few millimetres in which evaporation takes place. So whatever infrared energy may reach the ocean as a result of the greenhouse effect is soon dissipated.
The warmists hope that heat could get into the deep water, since it might hide there for a long time. Stevenson says there have been a number of studies of this process (Nakamura 1997; Tanimoto 1993; Trenberth 1994; Watanabi 1994; and White 1998), and says it is clear that solar-related variations in mixed-layer temperatures penetrate to between 80 and 160 metres, the average depth of the main pycnocline (density discontinuity) in the global ocean. “Below these depths, temperature fluctuations become uncorrelated with solar signals, deeper penetration being restrained by the stratified barrier of the pycnocline.”
Consequently, he says, anomalous heat associated with changing solar irradiance is stored in the upper 100 metres. The heat balance is maintained by heat loss to the atmosphere, not to the deep ocean as the warmists keep hoping.
What about Thermohaline Circulation?
The fact that the surface ocean can become denser than the underlying waters, thereby sinking to depths of “density equilibrium,” has been discussed since surveys of the physical ocean began in the second half of the 19th century… Thermohaline circulation is responsible for the formation of the bottom-water masses in all the world’s oceans.
Stevenson explains that modellers who “need” to get warm surface waters into the deep ocean and remain there for long periods hope (or claim) that there can be occasions when salinity, rather than temperature, is the prime determining factor in the density of the surface waters. Then, warm water made dense by a higher salt content would sink.
It does not happen!
The primary physical factor in determining the density of sea water is the temperature (Sverdrup, Johnson, and Fleming, 1943). In the open ocean, top or bottom, salinity differences are measured in a few parts per thousand. Thermohaline circulation takes place where the surface waters become colder than the waters beneath. The large vertical movements occur in polar seas, where accelerated radiation makes the surface waters greatly colder than the deeper waters.
Note that the radiation he mentions is from the frigid atmosphere sucking heat from the water, entirely dwarfing any trivial infra-red radiation from airborne greenhouse gases to the water.
In [polar] waters, surface water temperatures are about -1.9°C, the normal salinity of the water keeping it from freezing into ice. The deep waters, being warmer than such surface waters, rise to the surface, as the upper layers sink slowly into the dark ocean depths. Because only very cold surface water is able to sink, it is simple to understand that the deep ocean can never warm up, regardless of how warm the surface ocean around the world may become. No deep lying “thermal lag” is going to take place. It is clear that there’ll be no Phoenix rising as a haunting spectre.
There we have it. If the surface water warms by any means, it doesn’t sink. If it gets into a current, it may move about in the top 100 metres or so, but no further because of the density boundary at the pycnocline. Claims of thermal energy “hiding” much deeper in the oceans are speculation and no mechanism is known to cause it. Further, when surface water warms it frequently evaporates, taking energy from the surface water and the lower atmosphere, thus cooling them, then rises rapidly by convection, taking its heat far above the ocean, since water vapour is only about 63% of the density of air.
The only way the ocean water warms is by the sun. The only way the lower atmosphere warms is by the water (and a little from the land).
The Big, Deep, Blue Sea
Stevenson says the oceans are the dominant influence on our climate because of their enormous density and heat-storage capacity. The energy that flows in and out of the oceans determines the mean temperature of the global atmosphere. These interactions, plus evaporation, are quite capable of cancelling the slight effect of man-produced CO2.
Robert Stevenson, in 1987, became Secretary General of the International Association for the Physical Science of the Oceans (IAPSO), part of the International Union of Geodesy and Geophysics (IUGG). In 1991, the IUGG met in Vienna to discuss a programme to forward to the International Commission of Scientific Unions (ICSU) for consideration at the 1992 Rio de Janeiro Conference. But Stevenson and his colleagues decided not to prepare any programmes for the Rio conference.
In their joint statement, they said: “To single out one variable, namely radiation through the atmosphere and the associated ‘greenhouse effect,’ as being the primary driving force of atmospheric and oceanic climate, is a simplistic and absurd way to view the complex interaction of forces between the land, ocean, atmosphere and outer space.”
Furthermore, they stated: “climate modelling has been concentrated on the atmosphere with only a primitive representation of the ocean.” Actually, Stevenson says some of the early models depicted the oceans as nearly stagnant. The logical approach would have been to model the oceans first (there were some reasonable ocean models at the time), then add the atmospheric factors.
ICSU and the United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO) simply proceeded to evolve climate models from early weather models. Stevenson gives a fascinating insight into climate science by commenting: “That has imposed an entirely atmospheric perspective on processes which are actually heavily dominated by the ocean.”
This changes nothing — why write the paper?
Mentioning he was at first somewhat put off by the headlines about “missing warming,” after reading the Levitus paper Stevenson is left aghast by its general folly, contradicting as it did so much evident knowledge, saying: “here I sit in the middle of the Pacific Ocean [he lived in Hawaii], surrounded by papers (peer-reviewed, I guess I should add) which conclude:”
- For the past two decades at least, and possibly for the past seven decades, the Earth’s true surface air temperature has likely experienced no net change; [while]
- there should have been a sizable CO2-induced increase in atmospheric radiative forcing during that time, but there wasn’t. That must mean that a suite of compensatory feedbacks overwhelmed the “greenhouse” impetus for warming; implying, therefore,
- that the planet will not warm from any man-produced increases in CO2; indicating
- that any increases in temperature will likely fit the global trend of +0.048°C/decade, that is, about 0.5°C this century — the rate of warming that has existed since the Little Ice Age, centered around 1750 in Europe, South America and China; suggesting
- that the heat storage in the upper ocean takes place in the upper 100 metres, and the magnitude provides a rise in temperature at those depths of 0.5°C in the past 50 years (in those parts of the ocean for which we have data); [and]
- this global warming (and cooling) of the ocean occurs on biennial, ENSO, decadal and interdecadal period scales; thence,
- the ocean thermal changes on centennial-period scales, which appear as the warming trend through the past 50 to 100 years, can be explained by means of intrinsic internal modes of the Earth going through their normal cycle of warming and cooling, independent of both radiative and anthropogenic influences.
I guess what I’m really wondering is “Why did Syd Levitus and his associates write their paper in the first place?”
I encourage readers to sample Stevenson’s entire article, for I have omitted much of interest.
Regrettably, Robert Stevenson passed away in August, 2001, aged 80.