Study suggests that in the last 60 years up to half the observed warming and associated sea level rise in low- and mid- latitudes of the Atlantic Ocean is due to changes in ocean circulation.
Over the past century, increased greenhouse gas emissions have given rise to an excess of energy in the Earth system. More than 90% of this excess energy has been absorbed by the ocean, leading to increased ocean temperatures and associated sea level rise, while moderating surface warming.
The multi-disciplinary team of scientists have published estimates in PNAS, that global warming of the oceans of 436 x 1021 Joules has occurred from 1871 to present (roughly 1000 times annual worldwide human primary energy consumption) and that comparable warming happened over the periods 1920-1945 and 1990-2015.
The estimates support evidence that the oceans are absorbing most of the excess energy in the climate system arising from greenhouse gases emitted by human activities.
Prof Laure Zanna (Physics), who led the international team of researchers said: ‘Our reconstruction is in line with other direct estimates and provides evidence for ocean warming before the 1950s.’
The researchers’ technique to reconstruct ocean warming is based on a mathematical approach originally developed by Prof Samar Khatiwala (Earth Sciences) to reconstruct manmade CO2 uptake by the ocean.
Prof Khatiwala said: ‘Our approach is akin to “painting” different bits of the ocean surface with dyes of different colors and monitoring how they spread into the interior over time. We can then apply that information to anything else – for example manmade carbon or heat anomalies – that is transported by ocean circulation. If we know what the sea surface temperature anomaly was in 1870 in the North Atlantic Ocean we can figure out how much it contributes to the warming in, say, the deep Indian Ocean in 2018. The idea goes back nearly 200 years to the English mathematician George Green.’
The new estimate suggests that in the last 60 years up to half the observed warming and associated sea level rise in low- and mid- latitudes of the Atlantic Ocean is due to changes in ocean circulation. During this period, more heat has accumulated at lower latitudes than would have if circulation were not changing.
While a change in ocean circulation is identified, the researchers cannot attribute it solely to human-induced changes.
Much work remains to be done to validate the method and provide a better uncertainty estimate, particularly in the earlier part of the reconstruction. However the consistency of the new estimate with direct temperature measurements gives the team confidence in their approach.
Prof Zanna said: ‘Strictly speaking, the technique is only applicable to tracers like manmade carbon that are passively transported by ocean circulation. However, heat does not behave in this manner as it affects circulation by changing the density of seawater. We were pleasantly surprised how well the approach works. It opens up an exciting new way to study ocean warming in addition to using direct measurements.’
This work offers an answer to an important gap in knowledge of ocean warming, but is only a first step. It is important to understand the cause of the ocean circulation changes to help predict future patterns of warming and sea level rise.
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Via Eurekalert
Full paper title: Zanna, L., Khatiwala, S., Gregory, J., Ison, J. and Heimbach, P. (2019) Global reconstruction of historical ocean heat storage and transport. Proceedings of the National Academy of Sciences of the United States of America (PNAS); doi/10.1073/pnas.1808838115
https://www.pnas.org/content/early/2019/01/04/1808838115
(open access)
Abstract:
Most of the excess energy stored in the climate system due to anthropogenic greenhouse gas emissions has been taken up by the oceans, leading to thermal expansion and sea level rise. The oceans thus have an important role in the Earth’s energy imbalance. Observational constraints on future anthropogenic warming critically depend on accurate estimates of past ocean heat content (OHC) change. We present a novel reconstruction of OHC since 1871, with global coverage of the full ocean depth. Our estimates combine timeseries of observed sea surface temperatures, with much longer historical coverage than those in the ocean interior, together with a representation (a Green’s function) of time-independent ocean transport processes. For 1955-2017, our estimates are comparable to direct estimates made by infilling the available 3D time-dependent ocean temperature observations. We find that the global ocean absorbed heat during this period at a rate of 0.30 ± 0.06 W/m2 in the upper 2000 m and 0.028 ± 0.026 W/m2 below 2000 m, with large decadal fluctuations. The total OHC change since 1871 is estimated at 436 ±91 × 1021 J, with an increase during 1921-1946 (145 ± 62× 1021 J) that is as large as during 1990-2015. By comparing with direct estimates, we also infer that, during 1955-2017, up to half of the Atlantic Ocean warming and thermosteric sea level rise at low-to-mid latitudes emerged due to heat convergence from changes in ocean transport.
Cumulative heat uptake from 1871 to 2017 (joules per year) shown for each patch (numbered here and shown in SI Appendix, Fig. S1), contributing to the integrated passive heat storage (A) globally and (B) in the Atlantic Ocean. Note the different scales for the two panels.
“Most of the excess energy stored in the climate system due to anthropogenic greenhouse gas emissions has been taken up by the oceans, leading to thermal expansion and sea level rise. ”
WR: The higher SST that have led to figure 2 could have been caused by less wind over the oceans. There is a high variability in wind speed / wind stress over the oceans. Less wind results in less mixing of the upper layers (warming) and in less deep oceanic upwelling (less cooling of the surface, also resulting in warming).
In that case the assumption that “Most of the excess energy stored in the climate system [is] due to anthropogenic greenhouse gas emissions ” is wrong. Then more stored energy would be due to warmer surface waters that were caused by less wind. Not anthropogenic greenhouse gas emissions.
And possibly there would not have been an extra energy uptake at all. After all no mechanism is known by which energy from above the surface could be taken up by the oceans.
The whole study could be a construct of assumptions.
They start off assuming what they will study, and then (magically) they find what they assumed was true.
It’s pure pseudoscience taken to an art form.
Hey, after 1960, aka “The Magic Year,” anything can happen. After all, in 1960, treemometers magically turned into NOT treemometers. How does that even happen? No one knows. It’s magic.
And it’s not just 1960. The same thing happens at the beginning and end of glaciation cycles. Something magical occurs 600-1000 years after the switch from glaciation to inter-glacial, something I’ll call FsubU, which stops whatever it was doing that caused those first few centuries of melting, and then mysteriously and lazily thing turns over the job of melting the rest of the ice (and there’s still a lot of it) to CO2. FsubU then simply vanishes! poof, like a pot of Leprechaun’s gold. What (or WHO) is/was FsubU? Where did FsubU go? No one knows. It’s a little frickin’ miracle. Then, thousands of years later, the ice is gone, nature is kicking along just fine in a nice warm world with lots of land not covered by ice, and then just as mysteriously, FsubU magically winks back into existence, has a cup of coffee and turns OFF the ability of CO2 to keep things warm, because while CO2 is at or near it’s highest peak, FsubU (or his cousin) makes the temperature start going down again even with much CO2 in the air! The ice starts coming back. I didn’t even think it was possible. How can a greenhouse gas NOT keep the planet warm when it already melted all that ice for centuries (minus 800 yrs) ? Color me amazed. Whatever this FsubU magical force is, it clearly has some PoWerZ that I don’t understand. It may even haz SKILLZ! It’s either very long-lived or more probably, immortal. Maybe it’s God? Maybe it’s Brian? Maybe it’s The Dude, since it was sort of lazy to force CO2 to do all those thousands of years of hard work, while it was taking a nap or gallivanting around the Universe doing whatever. It’s a real mystery. Want to know more? Ask the high priests at RealClimate to tell you. But don’t tell them you don’t believe in magic. Don’t them them that an effect cannot precede it’s cause. That just shows how weak in the ways of science you are. After all, it’s after 1960, so anything is possible.
Agreed! Not the least of which is that Green’s theorem, which applies only to circulation expressible as an analytic function, can explain the vagaries of real-world turbulent flow. There’s no end to what rank oceanographic novices imagine is happening in the oceans.
First of all, relatively accurate and comprehensive coverage of ocean temperature data wasn’t available until ARGO ocean buoy data went online in 2007…
Prior to ARGO data, ocean temperature data of the roughly 1.35 BILLION KM^3 of the world’s ocean volume was near zero%…
Second, there are many ocean warming factors other than CO2 to account for any ocean warming we’ve enjoyed following the end of the Little Ice Age in 1850: LIA recovery, El Nino events, PDO/AMO/NAO 30-year warm cycles, the 1933~1996 Grand Solar Maximum (strongest in 11,400 years), natural variation, natural changes of ocean currents, etc.
Third, oceans are one gigantic 1.35 billion KM^3 heat sink. According to Levitus et al 2011, the top 2,000 meters of oceans have only increased 0.09C between 1950~2010…. Oh, the humanity…
I’m sick and tired of CAGW alarmists using gigajoules to measure OHC to make the minuscule amount of actual ocean warming look catastrophic..
To assume CO2 is the ONLY major cause of ocean warming is simply the logical fallacies of argumentum petitio principii, and post hoc ergo propter hoc.
Let’s see what happens to ocean temps after 2021 when: The PDO/AMO/NAO are all in their respective 30-year ocean cool cycles, and when a 50-year Grand Solar Minimum event starts…
Can’t we just wait 5 years to see what changes these natural cooling phenomena have on global atmospheric and ocean temperatures before wasting $122 Trillion (2018 IPCC estimate) on this stupid CAGW hoax?
B-B-But by then it will be too late and we’re all DOOMED! You know, just like the last three times we have only “had [x number of] years to ACT to prevent [the human-induced climate catastrophe that never develops even though we DON’T “do” what they say we “must”/”save” the planet].
Prof Humlum @ur momisugly climate4you->clouds->oceans shows how a reduction in cloud cover over the tropics (15N – 15S, that is mostly ocean) from 1983 – 2000 of about 5% is inversely correlated to the topical sea surface temperature and global surface temperature.
When you must resort to models and guess work you do not ‘know’ in any meaningful way.
And the author’s the advantage and problem when it comes to oceans is the same thing, given it scale there is very little actual measurements so a great deal can be claimed to ‘hidden’ in it, such has cities, space ships or heat , without fear of other others showing its not there at all.
Fiddling around with a duff hypothesis and a wish list of assumptions can hardly be considered productive. Mind you – Rich pickings in the grant area.
These scientists are destroying scientific reputation.
“More than 90% of this excess energy has been absorbed by the ocean,”
So all od the excess energy over the ocean drops down into the ocean, plus 20% of the excess energy over land travels sideways to the ocean, then drops down into the ocean.
Only 10% of the excess energy goes up. I didn’t know that about heat.
“Our reconstruction, which agrees with other estimates for the well-observed period, demonstrates that the ocean absorbed as much heat during 1921–1946 as during 1990–2015.”
AMO driven reductions in low cloud cover. And the AMO is normally warm during a solar minimum. Nice negative feedback.