NOAA: Scientists Find 20 Years of Deep Water Warming Leading to Sea Level Rise
Sea-level rise has the potential to reshape the coastal environment. Credit: NOAA)
Scientists analyzing measurements taken in the deep ocean around the globe over the past two decades find a warming trend that contributes to sea level rise, especially around Antarctica.
Greenhouse gases in the atmosphere, such as carbon dioxide, cause heating of the Earth. Over the past few decades, at least 80 percent of this heat energy has gone into the ocean, warming it in the process.
“Previous studies have shown that the upper ocean is warming, but our analysis determines how much additional heat the deep ocean is storing from warming observed all the way to the ocean floor,” said Sarah Purkey, an oceanographer at the University of Washington and lead author of the study.
This study shows that the deep ocean – below about 3,300 feet – is taking up about 16 percent of what the upper ocean is absorbing. The authors note that there are several possible causes for this deep warming: a shift in Southern Ocean winds, a change in the density of what is called Antarctic Bottom Water, or how quickly that bottom water is formed near the Antarctic, where it sinks to fill the deepest, coldest portions of the ocean around much of the globe.
The scientists found the strongest deep warming around Antarctica, weakening with distance from its source as it spreads around the globe. While the temperature increases are small (about 0.03°C per decade in the deep Southern Ocean, less elsewhere), the large volume of the ocean over which they are found and the high capacity of water to absorb heat means that this warming accounts for a huge amount of energy storage. If this deep ocean heating were going into the atmosphere instead – a physical impossibility – it would be warming at a rate of about 3°C (over 5°F) per decade.
“A warming Earth causes sea level rise in two ways,” said Gregory Johnson, a NOAA oceanographer at the Pacific Marine Environmental Laboratory in Seattle, and the study’s co-author. “The warming heats the ocean, causing it to expand, and melts continental ice, adding water to the ocean. The expansion and added water both cause the sea to encroach on the land.”
Sea level has been rising at around 3 mm (1/8 of a inch) per year on average since 1993, with about half of that caused by ocean thermal expansion and the other half because of additional water added to the ocean, mostly from melting continental ice. Purkey and Johnson note that deep warming of the Southern Ocean accounts for about 1.2 mm (about 1/20th of an inch) per year of the sea level rise around Antarctica in the past few decades.
The highly accurate deep-ocean temperature observations used in this study come from ship-based instruments that measure conductivity through salinity, temperature and depth. These measurements were taken on a series of hydrographic surveys of the global ocean in the 1990s through the World Ocean Circulation Experiment and in the 2000s in support of the Climate Variability program. These surveys are now coordinated by the international Global Ship-based Hydrographic Investigations Program.
The study, “Warming of Global Abyssal and Deep Southern Ocean Waters between the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise Budgets,” authored by Sarah G. Purkey and Gregory C. Johnson, will be published in an upcoming edition of the Journal of Climate.
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Here is the abstract:
2 NOAA/Pacific Marine Environmental Laboratory, Seattle WA 98115, USA
| Abstract |
|---|
We quantify abyssal global and deep Southern Ocean temperature trends between the 1990s and 2000s to assess the role of recent warming of these regions in global heat and sea level budgets. We compute warming rates with uncertainties along 28 full-depth, high-quality, hydrographic sections that have been occupied two or more times between 1980 and 2010. We divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and estimate temperature trends in the 24 sampled basins. The three southernmost basins show a strong statistically significant abyssal warming trend, with that warming signal weakening to the north in the central Pacific, western Atlantic, and eastern Indian Oceans. Eastern Atlantic and western Indian Ocean basins show statistically insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic seas, the rate of abyssal (below 4000 m) global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0.027 (±0.009) W m−2 applied over the entire surface of the Earth. Deep (1000–4000 m) warming south of the Sub-Antarctic Front of the Antarctic Circumpolar Current adds 0.068 (±0.062) W m−2. The abyssal warming produces a 0.053 (±0.017) mm yr−1 increase in global average sea level and the deep warming south of the Sub-Antarctic Front adds another 0.093 (±0.081) mm yr−1. Thus warming in these regions, ventilated primarily by Antarctic Bottom Water, accounts for a statistically significant fraction of the present global energy and sea level budgets.
Received: February 16, 2010; Revised: July 28, 2010; Revised: August 18, 2010
*Pacific Marine Environmental Laboratory Contribution Number 3524.
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Am I reading this correctly?
“Scientists analyzing measurements taken in the deep ocean around the globe over the past two decades find a warming trend that contributes to sea level rise, especially around Antarctica.”
&
“Purkey and Johnson note that deep warming of the Southern Ocean accounts for about 1.2 mm (about 1/20th of an inch) per year of the sea level rise around Antarctica in the past few decades.”
Sea-level is a local phenomena?
Dirk
both can be right, it has to do with the time scales. On the time scale from 1989-2010 there has been warming, even though in the period from 2005-2008 there was cooling. One step forward and two steps back or something.
regardless, I would not attribute causation to anything in the antarctic ocean right now, the collapse of the Ross ice shelf is big enough that it should confound anyone trying to isolate causes. Until things settle down (or our understanding of the planet increases exponentially) the significance of any change in the antarctic oceans should be tempered with the realization a dramatic event is changing the terrain.
I still have difficulty with the panic about rising sea levels. If you live by the sea, you know the defenses are at least 5m above the average sea level. That is what is needed to avoid getting flooded every time there is a bit of a storm surge at spring tides, and a few big waves. So 3mm a year means adding a brick every decade or so to the existing defenses. Does that constitute a crisis? Or is it really all in Al Gore’s imagination?
We are talking changes in sea level rise of a single millimeter a year.
One whole 25th of an inch.
OMG, we are so inundated. Prepare the sacrifice to the Goreacle.
I can comment on the statistics
0.027 (±0.009) W m−2 applied over the entire surface of the Earth.
This is according to them a 3 sigma effect. Possibly interesting, but could disappear as noise
Deep (1000–4000 m) warming south of the Sub-Antarctic Front of the Antarctic Circumpolar Current adds 0.068 (±0.062) W m−2.
This is barely 1 sigma, definitely noise.
The abyssal warming produces a 0.053 (±0.017) mm yr−1 increase in global average sea level and the deep warming south of the Sub-Antarctic Front adds another 0.093 (±0.081)
Adding noise to a weak 3 sigma putative signal , to more than double it, is not only a scientific misstep, it also betrays the authors as working on an agenda.
What sort of peer reviews are these that do not catch so elementary scientific errors ?
DCC says:
September 26, 2010 at 10:56 am
“Seems odd that this paper failed to mention an earlier conclusion that the missing heat could not be at depth else we would have noticed it in transit from the surface.”
Last I checked, Trenberth was looking for a missing .5 W m−2. This study claims to have found a fraction of that.
A bit of a difference between claiming we would have seen a bowling ball rolling down the street and we found a golf ball that we didn’t see rolling down the street.
richard111 and davidmhoffer, re sunlight penetrating only the top few mm of water.
The solar ponds show that is not the case. see e.g.
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=DD3754904F37D9B7EE92E4C803BB06FF?purl=/756432-k7Q3X9/webviewable/
and click on the pdf shown there.
“If this deep ocean heating were going into the atmosphere instead – a physical impossibility – it would be warming at a rate of about 3°C (over 5°F) per decade.”
So this would seem to imply that this warming is thus being driven by something other than the atmosphere. Conversely, couldn’t all atmospheric warming then be driven by the oceans ??? – I have done the math – it is entirely possible (given the relative heat capacity of the ocean vs atmosphere) So if this article is implying that this ocean warming is non GHG driven, then it could be concluded that it is entirely possible the that atmospheric warming is also not GHG driven
Yeah, and think what will happen when the ice comes back … It’s not a one way street.
Roger Sowell,
while it is true that UV light can penetrate water a reasonable distance, and UV light is part of sunlight, the GHC/CO2 mechanism works on the IR end of the spectrum not the UV end. Solar ponds work on the UV end of the spectrum, not the IR end.
Roger Sowell says:
richard111 and davidmhoffer, re sunlight penetrating only the top few mm of water.
The solar ponds show that is not the case.
They are talking about the long wave infrared emitted from greenhouse gases, which indeed can only penetrate a few microns past the surface, all energy used up in the phase change of evaporation, with nothing left over to heat the deeper layers.
This chart shows depth of penetration v. wavelength:
http://omlc.ogi.edu/spectra/water/gif/hale73.gif
as the chart shows, solar UV and visible radiation can penetrate to much greater depths and heat the oceans.
Well the article is behind a pay wall.
But wait, Underdog to the rescue, the author’s copy can be found here;
http://www.pmel.noaa.gov/people/gjohnson/Recent_AABW_Warming_v3.pdf
R T Barker said:
“Measure it with a micrometer, mark it with a grease pencil and cut it with an axe.”
There speaks a true engineer.
BTW I seem to remember from back in the mists of time that below the deep sound channel (1000-2000m?) the thermal structure of the ocean is essentially isothermal at +4 deg with salinity being the cause of any variations. So why are minuscule temperature variations being ascribed to CO2?
Elizabeth, above, points out that the contribution to estimated sea level rise from ground water drawdown is not considered. If the drawdown is equivalent to 283 cubic kilometers per year and the area of ocean is 335 million square kilometers then my feeble brain suggests that the purported sea level rise from “global warming” may be a negative number. Also how many cubic kilometers of sediment are washed into the oceans each year?
I thought it was already reasonably well established, or at least generally accepted, that global ocean average level is going up 2-3mm per year in last few decades and it was going up 1-2mm per year for the last few centuries or so with decreased confidence since tide gauges weren’t designed for that kind of resolution and the land itself where the tide gauge is anchored might have been subsiding or rising in the past with no real way to measure it. I also thought it was generally accepted that the rise is more or less an even split between thermal expansion and glacier melt.
It doesn’t seem like there’s any significant new information in the report.
pochas says:
September 26, 2010 at 10:25 am
………The real question is, “Why did the deep oceans get so cold?”
Cold water sinks and stays down there a long time.
On other matters, IMO ,”adiabatic heating” of the ocean bottom has to be taken into consideration in all this mess of heat budgets.
“The authors note that there are several possible causes for this deep warming: a shift in Southern Ocean winds, a change in the density of what is called Antarctic Bottom Water, or how quickly that bottom water is formed near the Antarctic, where it sinks to fill the deepest, coldest portions of the ocean around much of the globe.”
Lets take a stab at figuring out why the water may be warming from this statement. I would guess that the earths crust and mantel over time would warm the ocean water from the bottom up. What keeps the deep waters cold is that the cold water at the surface continually sinking to replace the slightly warmed water with fresh cooler water. I would imagine that melting ice would cool the surface water faster, and a decrease in melting would slow the feeding of colder water into the deep ocean, thus allowing the thermal transfer of heat from the Earths crust to the bottom water, thus warming it.
Stephen Wilde quoted DCC saying: “Nor is there any discussion of why, of all places, this phenomenon should only exist in the Antarctic “weakening with distance from its source as it spreads around the globe.”
He responded:
“I don’t have a problem with that. If the source of any ‘extra’ deep water energy is solar shortwave input from a period of active sun then the southern hemisphere being mostly water then I would expect the maximum effect south of the equator.”
But he didn’t say the ocean warmed south of the equator at any depth, except near Antarctica. Your theory would require the sun to have an effect only closer to the pole. But it makes you a great candidate for climate scientist. First the conclusion, then the supporting arguments.
simpleseekeraftertruth says:
September 26, 2010 at 11:16 am
I would start by doing some searches for variations in earth’s measured gravity, irregularities in the shape of the planet, and variations in the composition (and now temperature) of seawater. I wouldn’t expect huge differences in sea levels, but I would expect some.
DCC said:
“But he didn’t say the ocean warmed south of the equator at any depth, except near Antarctica. Your theory would require the sun to have an effect only closer to the pole. But it makes you a great candidate for climate scientist. First the conclusion, then the supporting arguments”
The article said:
“The scientists found the strongest deep warming around Antarctica, weakening with distance from its source as it spreads around the globe.”
So there clearly was southern hemisphere warming generally but it became concentrated around Antarctica which is consistent with the thermohaline transporting it there, carrying it around Antarctica and then distributing it northward.
As always the conclusion is provided by the observations. One then has to try and work out how it might be so.
and they are having meetings and panel discussions and committees on how to make their “message” more believable……………
Excuse my ignorance but at depths of 3000ft plus the pressure is such that a 0.03 oC supposed rise in temperature will expand the water by how much?
As I understand it, water heated at great pressure reacts differently to water heated at atmospheric pressures.
Just how much would one square meter of water at 15000 pounds per square inch pressure expand if it were warmed by just 0.03 oC? Maybe I am missing something here but just how could a slight atmospheric warming of around 0.5 oC over the last hundred years possibly warm the deep ocean? We know how long the deep ocean takes to recycle its water content and I didnt think it was such a short time.
“The warming heats the ocean, causing it to expand, and melts continental ice, adding water to the ocean. The expansion and added water both cause the sea to encroach on the land.”
Are the oceans warming at all depths equally? I wonder if the authors actually realise the oceans are in fact cooling not warming.
My read on sea level rise is it appears to be flattening over the past decade. An eye-ball measurement from the sea level curve suggests that over the past 5 or 6 yrs its rise has slowed to 2mm/yr. It is ridiculous to use only a linear fit as this carries your 3mm rate forward for a few decades. When the growth is zero over a few years, the linear trend over 30 years would still read some 2.8mm/yr.
simpleseekeraftertruth says:
September 26, 2010 at 11:16 am
Sea-level is a local phenomena?
to a much greater degree than the average global trend due to ocean oscillations, El Nino, La Nina, etc.
http://www.aviso.oceanobs.com/fileadmin/images/news/indic/msl/MSL_Map_MERGED_Global_IB_RWT_NoGIA_Adjust.png
There are a couple of scientists that might disagree.
If any reader thinks they would be offended by hypothermia-induced Tourettes, they should forego this video, whose disclaimer appears below.
“The following video contains language of a sort that is entirely unbecoming of any self-respecting ichthyologist, or, for that matter, any self-respecting scientist of any field or discipline. Nevertheless, in the interest of presenting an accurate portrayal of the indignities that must often be endured by scientists while in pursuit of their never-ending quest for discovery and exploration, the dialog contained in this video has not been edited in any way from its original (albeit vulgar) content.”