Introduction To The NODC Ocean Heat Content Anomaly Data For Depths Of 0-2000 Meters
The National Oceanographic Data Center (NODC) recently posted a new Ocean Heat Content (OHC) anomaly dataset on its website. It is available on annual and quarterlybases, along with the data for its standard and documented dataset that covers depths of 0-700 meters. I looked for but was not able to find any papers (in any state of publication) that supported the new OHC data for 0-2000 meters. We’ll just have to wait and see how the NODC intends to present this dataset.
The data for the depths of 0-700 meters is, of course, documented in the paper Levitus et al (2009) “Global ocean heat content (1955-2008) in light of recent instrumentation problems”. Refer to Manuscript. It was revised in 2010 as noted in the October 18, 2010 post Update And Changes To NODC Ocean Heat Content Data. As described in the NODC’s explanation of ocean heat content (OHC) data changes, the changes result from “data additions and data quality control,” from a switch in base climatology, and from revised Expendable Bathythermograph (XBT) bias calculations.
COMPARISON OF GLOBAL OHC ANOMALIES: 0-700 METERS VERSUS 0-2000 METERS
Figure 1 compares the quarterly NODC OHC anomaly data for the depths of 0-700 meters and 0-2000 meters on a global basis. As noted on the illustration, the most obvious divergence between the two datasets occurs during the ARGO era. This is the period when ARGO floats became the dominant means of sampling of ocean temperatures and salinity at depth.
Figure 1
If we limit the comparison to the period from 1970 to 1999, Figure 2, we can see that there is basically no difference in the linear trends. There are minor differences from year to year, but the two datasets appear to be basically the same. Why?
Figure 2
There are extremely few observations prior to the year 2000 at depths greater than 1000 meters. This is illustrated in Figure 3. (Note that NOAA Climate Prediction Center Data Distributionwebpage breaks down the temperature profiles into depths of 0-250 meters, 250-500 meters, 500-1000 meters and 1000-5000 meters. Those depths don’t agree with the depths presented by the NODC for its Ocean Heat Content anomaly data.)
Figure 3
And Animation 1 shows a series of annual maps of the locations of temperature profiles from 1979 to 2005 for the depths 1000-5000 meters. As illustrated, there is also very little spatial coverage at these depths until the introduction of the ARGO floats.
Animation 1
As a reference, Figure 4 shows the number of temperature profiles for depths of 250 to 500 meters. There were between 2000 to 5000 temperature profiles per month between the late 1970s and the late 1990s at these depths before the ARGO floats were deployed. Note that the TAO/TRITON project (red curve) shows temperature profiles that were initially for the equatorial Pacific (coordinates approximately 8S-9N, 137E-95W). Those buoys were deployed for the study of El Niño and La Niña events. The locations were later expanded to include portions of the Tropical Atlantic and Indian Oceans under the PIRATA and RAMA projects. Refer to the TAO Project Global Arraywebpage. So while there are a good number of temperature profiles for the TAO project, they are limited in their location.
Figure 4
Figure 5 illustrates the difference between the two NODC Global Ocean Heat Content (OHC) datasets, where the 0-700 meter data has been subtracted from the 0-2000 meter data. Also referring back to Figure 3, the difference between the two datasets seems to increase in concert with the number of temperature samples at depths greater than 1000 meters. It appears as though the divergence of the 0-2000 meter dataset from the 0-700 meter data since around 2000 could be caused by the increased number of samples at depth and the increased spatial coverage of the ARGO floats, as shown in the animations. The impacts on short-term and long-term trends of the increased number of samples at depths greater than 700 meters and the impact of the increased area of observations should be determined. (A study such as that is well beyond my capabilities.) Maybe it will be documented in the NODC paper that accompanies the 0-2000 meter dataset.
Figure 5
Keep in mind, before the ARGO era, there were very few ocean temperature observations at any depth in the Southern Hemisphere south of about 40S. For example, Animation 2 is a gif animation of maps that illustrate the locations of temperature profiles for depths of 0-250 meters, 250-500 meters, 500-1000 meters, and 1000-5000 meters for the year 1995.
Animation 2
And Animation 3 shows the same series of temperature profile maps but for the year 2005.
Animation 3
A COUPLE OF QUESTIONS FOR READERS
Were the Expendable Bathythermograph (XBT) probes with wire lengths of 760 meters the most commonly used XBT probes before the ARGO era? Is this the reason the NODC originally limited the depth to 700 meters for the Ocean Heat Content anomaly data? Does anyone recall a paper that presents this? I had always assumed the depth of 700 meters was selected due to the number of and locations of observations, but I have never seen it stated in a paper.
LONG-TERM TRENDS PER OCEAN BASIN
When I originally prepared the graphs for this post, I could find no reason to present the long-term trends for the individual ocean basins of the 0-2000 meter data. The reason being, in some respects, the NODC OHC data for 0-2000 meters appears to me to simply be a 0-2000 meter OHC dataset spliced onto a 0-700 meter dataset. But on further thought, my failure to present the data might be thought by some as an attempt on my part to hide something. So Figure 6 (0-2000 meters) and Figure 7 (0-700 meters) are long-term trend comparisons of the Ocean Heat Content anomalies for the individual ocean basins as presented by the NODC. The most obvious similarity is that the long-term trends of the North Atlantic Ocean Heat Content are significantly higher than other ocean basins in both datasets, and in both, the North Atlantic Ocean Heat Content peaked in 2004. After that, there are significant declines. One would think this would lead researchers to examine the effects of the Atlantic Multidecadal Oscillation and Meridional Overturning Circulation on North Atlantic Ocean Heat Content observational data, yet, as far as I know, this is an area unexplored by climate scientists.
Figure 6
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Figure 7
ARGO-ERA TRENDS PER OCEAN BASIN
The ARGO-era (2003 to present) linear trends per ocean basin for the depths of 0-2000 meters and 0-700 meters are shown in Figure 8 and 9, respectively. Like the trends for the 0-700 meter data, the South Atlantic and Indian Ocean are the only basins with significantly positive linear trends for the 0-2000 meter Ocean Heat Content data. And also like the trends 0-700 meter data, the linear trends of the 0-2000 meter Ocean Heat Content anomalies in the North Atlantic and South Pacific are negative. The linear trends for those two ocean basins are less negative for 0-2000 meter depths than they are for 0-700 meter depths, indicating that the declines at depths of 0-700 meters are greater than the increases at the 700-2000 meter depths. Considering there is less than a decade of ARGO-era data with “full” coverage, there is no need to speculate about the cause. Note also that the trend for the North Pacific OHC anomalies is basically flat for the 0-2000 meter data, and that the same holds true for the 0-700 meter data.
Figure 8
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Figure 9
CLOSING COMMENTS
The undocumented (as of this writing) NODC 0-2000 meter Ocean Heat Content dataset appears as though it was prepared to show that Global Ocean Heat Content continues to rise during the ARGO era, and that it is intended to counter the argument that Global Ocean Heat Content has flattened during the ARGO era as shown in the NODC 0-700 meter dataset.
Due to the extremely limited number of observations at depths of 1000-5000 meters (shown in Figure 3 and in the animations), the 0-2000 meter Ocean Heat Content dataset should be used with great caution. It appears to me to be an ARGO-era 0-2000 meter Ocean Heat Content dataset spliced onto a long-term 0-700 meter dataset. For this reason, I, personally, would not expend the effort to analyze the long-term (pre-ARGO era) 0-2000 meter NODC OHC data beyond what has been presented in this post.
Each time I see the claim (based on many assumptions) by anthropogenic global warming proponent scientists that the rise in ocean heat content at depth “will come back to haunt us” I wonder why those same scientists have not bothered to attempt to document how much of the rise in OHC from the 1970s to the early 2000s (0-700 meters) was caused by the deep oceans upwelling warmer anomalies from past decades, other than the fact that there’s no data for them to do so. Could they believe that multidecadal variability is limited to Sea Surface Temperatures and does not impact temperatures at depth? Or is their intent to have the unsuspecting public believe it?
Philip Bradley,
see,
http://pielkeclimatesci.wordpress.com/2011/10/21/my-recent-discussion-with-gavin-schmidt-on-real-climate/
comment of 10th October 2011 9:50pm
and
http://www.realclimate.org/index.php/archives/2011/10/global-warming-and-ocean-heat-content/comment-page-4/#comment-216643
comment 163, also 10th October 2011 9:50pm
to support Rick C’s statements.
John Eggert says: “Is it possible for the mean ocean temperature to be lower than the mean surface temperature?”
No. The oceans have their own “greenhouse effect”. They are heated by sunlight to depth but only release it at the surface, primarily through evaporation.
Bob Tisdale says:
October 25, 2011 at 2:48 am
Thanks – so I was close with the Indian ocean but off-target with the Atlantic. I guess the Atlantic ENSO complicates the picture. How’s that for a research grant application: “tracking the growth of Atlantic ENSO as the Atlantic ocean widens…”
paulhan says: “I can’t understand how all that extra energy could get down to the 700-2000m level before showing up in the 0-700m level first.”
The the most logical way, at least to me, is that the “warmer” water is being transported to depths of 700-2000 meters at high latitudes through meridional overturning circulation faster than it is being replenished at depths of 0-700 meters. The unanswerable question I now have is, is there a decadal or multidecadal component to this? The problem: There’s less than a decade of ARGO data.
Dave Springer says: “ARGO only dives to 2000 meters so displaying it on a 1000-5000 meter chart is deceiving.”
Is your statement directed to me or to NOAA? They are illustrating observations within the range of depths, not observations that cover the entire range.
“The mechanism is that a warmer atmosphere impedes evaporation and therefore warms the oceans.”
For the last 10 years at least, the thought has been that a warmer atmosphere INCREASES evaporation and humidity (that’s one of the positive feedbacks). IIRC, Dr Spencer’s work has shown that cloud cover does indeed increase at temperature rises.
Dave Springer says:
October 24, 2011 at 6:42 pm
John Eggert says:
October 24, 2011 at 5:37 pm
“I’ve been wrestling with a question over the last number of weeks. The question is: Why is the ocean so cold?”
I’ve been trying to tell people the answer to that question for a long time. The average temperature of the global ocean is 3.9C and the only possible way for it to get that way is for the average surface temperature to be 3.9C.
A period of time of oh say 100,000 years is sufficient for even slow-ass conduction to equalize the bottom temperature with the surface temperature. This gives some perspective on the earth’s average temperature over a full glacial/interglacial cycle.
I cant see how the ocean temps top to bottom will ever equilibrate, as long at there are asymmetries of heat input and output to generate currents, any more than the atmosphere could equilibrate as long as heat asymmetries generate winds. As Richard Lindzen put it a climate system at equilibrium would be “like something dead”. In such a dynamic system I doubt that it is necessary even in the long term for surface temperature to match ocean average temperature (but I dont have the maths to back this up).
Note that even 50 mllion years ago during a much warmer period, research has found evidence that there was normal ENSO cycling, implying intermittent episodes of cold upwelling in the south east Pacific of Peru, as now. Thus the warmer global climate still left cold deep water to periodically upwell.
http://wattsupwiththat.com/2011/09/19/climate-clam-chowder/
It’s fair to say that the current climate is thin skin of temporary warmth floating on a bucke of icewater. Imagine something that might disturb the mix rate between shallow surface layer (about 10% of the ocean volume has a temperature greater than 3C) such that more of that 3C frigid deep rises to the surface. Can you spell instant end to the Holocene Interglacial?
I agree entirely with this, in an ocean with strong vertical stratification with temps up to 20+ at the surface and about 3C at the bottom, ANY significant increase in vertical mixing over the whole water column, on a global scale, cannot fail to result in downward movement of heat. As Bill Illis has pointed out before, a major reason for the current glacial period in the last 20 or so million years is the isolation of Antarctica and the establishment of the strong circumpolar current, with the increase on oceanic vertical mixing this caused. The deep ocean is a cold hand from below, which can snatch away our interglacial warmth any time it chooses.
Thus changes in the extent of vertical oceanic mixing may be an important contributor to global climate swings.
“I’ve been wrestling with a question over the last number of weeks. The question is: Why is the ocean so cold?”
John, as a complete lay person I should say because the Earth, (despite the odd, brief, slightly warmer interglacial) is still in a long term ice-age.
It is many millions of years since the epoch when the world was ice-free. Hence the water at depth is still very cold.
John Eggert says:
October 24, 2011 at 7:54 pm
“Dave: What is 10 / 0.7? Why did I divide by 0.7? Hint. I was talking about mass, not pressure.”
Ah sorry. Thought you were talking about mass of the air column above the water column not mass of all the air above water or not.
The deep ocean is cool or one could say bloody cold, this missing heat of warmist fame hiding in the briny deep changing the status quo by .00poofteenth of a degree is so alarming.
This heat so near the temperature of freezing is suddenly one day going to transform itself into blistering world temperatures that set our atmosphere ablaze.
Call me stupid but I have never seen cold make things hot, this heat measured at near 4C is going to transform itself magically into atmospheric warming temperatures at some time in the near future. These people are obviously smoking some thing that is only available to government funded employees and is a national secret.
phlogiston says:
October 25, 2011 at 3:32 am
The question was: is it possible for mean ocean temperature to be 3.9C without mean surface temperature of 3.9C?
The answer is no. This doesn’t mean the ocean ever attains the same temperature from top to bottom. What it means is that a change in surface temperature will eventually be reflected in a change in bottom temperature because the top and bottom are in thermal contact. Stratification halts convection. It is physically impossible to halt conduction so while the conductivity of water is poor it isn’t non-existent and given sufficient time temperature change on the surface will be reflected by a temperature change on the bottom through conduction.
Indeed, a method of reconstructing surface temperature history over land is to bore a hole in the ground and very very precisely measure the temperature of the rocks on the way down. There are very slight changes in the temperature that depart from the constant increase in temperature due to conductivity of the rock. These slight departures reflect the change in temperature at the surface as it conducts its way down through the rock.
Bob Tisdale says:
October 25, 2011 at 3:03 am
John Eggert says: “Is it possible for the mean ocean temperature to be lower than the mean surface temperature?”
No. The oceans have their own “greenhouse effect”. They are heated by sunlight to depth but only release it at the surface, primarily through evaporation.”
That being the case then. How is it that the depths of the ocean are not warmer. The oceans move energy to space by evaporation, conduction to the air and radiation. I thouroughly understand that and can model it from first principles. But they also move heat to the depths by conduction and convection. If the surface ocean temperature has been, on average, warmer than the ocean depth, then there must be a net energy flow into the depths. Given that there is a small net heat flow into the ocean at the bottom of the ocean, the only place that surface ocean heat can go is to the atmosphere or the depths (that is, it can’t go into the crust, the crust is also a source of warming). The big picture equilibrium (yes there will be currents, etc.) temperature of the depths of the ocean should be 15C, not 4C. As with the atmosphere, warmer in some places than others, but on average 15C. As I noted, the oceans, by the insulating properties of ice should actually be warmer than the surface (in a dynamic system that freezes and thaws). The oceans are cooler than the black body equilibrium temperature of the planet. Indeed, the entire mass of surface fluid (atmosphere plus hydrosphere) is cooler than the equilibrium black body temperature. That is, there is no need for a greenhouse gas theory to explain the increased temperature of the planet because the planet isn’t warmer than an equivalalent black body radiator would be. As I said, here be dragons. For those unaware of the reference, see Dr. Curry’s sky dragons posts.
I think Argo is giving us the correct answer. There has been no warming since 2002, excepting the Indian Ocean. Additionally SL data does not support the hidden heat going into the oceans as, with out the recent continental rebound adjustments, SL is going down recently and almost flat since 2005.
Just as the land based temperature data sets are diverging ever more over the recent decade, so the SL and OHC estimates appear to be diverging ever more.
phlogiston says:
October 25, 2011 at 3:32 am
“Note that even 50 mllion years ago during a much warmer period, research has found evidence that there was normal ENSO cycling, implying intermittent episodes of cold upwelling in the south east Pacific of Peru, as now. Thus the warmer global climate still left cold deep water to periodically upwell.”
50 million years ago the earth’s mean surface temperature was only a few degrees C above today so the ocean bottom would have been 6C instead of 3C. That’s still pretty cold if it upwells into tropical surface water at 25C or more. The oceanic conveyor belt wouldn’t stop. Warm surface currents from the tropics would still travel to the pole, dump its heat, sink to the bottom, and then flow back to the tropics along the bottom.
John Eggert says: “Is it possible for the mean ocean temperature to be lower than the mean surface temperature?”
Yes, of course.
I don’t understand why someone else thinks it’s not.
The oceanic water mass is very cold, the surface water is something around 14 °C, globally averaged.
That’s a fact!
And it’s very easy to understand why the water mass is very cold while, for another reason, the surface is warm in the average. No ocean green house effect involved.
John Eggert says:
October 25, 2011 at 4:31 am
“That being the case then. How is it that the depths of the ocean are not warmer. The oceans move energy to space by evaporation, conduction to the air and radiation. I thouroughly understand that and can model it from first principles. But they also move heat to the depths by conduction and convection.”
It doesn’t move downward by convection. Tisdale is right. The greenhouse effect is primarily a result of the physics of liquid water. Shortwave energy from the penetrates to a depth of roughly 100 meters where it is eventually completely absorbed by impurities in the water. Water is quite opaque to far infrared so the solar energy absorbed below the skin layer cannot escape radiatively. That sunlight warmed water must be mechanically transported to the skin layer where it gives up the heat primarily through evaporation (70% of ocean heat loss) and secondarily (20%) radiatively. Conduction plays a role but not much of one.
So what you have is tranmission of energy into the water happening at the speed of light to a depth of 100 meters but loss of energy from the water at depth happenign at the speed of convection and conduction. Transparency to shortwave radiation and opacity to far infrared are the very properties that distinguish greenhouse gases from non-greenhouse gases. Liquid water possesses these exact same characteristics only its opacity to far infrared is complete whereas it’s only partial in greenhouse gases. We should consider liquid water and CO2 both as greenhouse fluids. Technically both are fluids and both are quite capable of producing a greenhouse effect.
Paolo M. says:
October 25, 2011 at 4:38 am
You’re talking about an instant surface temperature. We’re talking about a mean surface temperature.
Consider: the temperature of the rocks below the ocean are warmer than the ocean so the ocean cannot possibly be cooled from below. The earth is molten beneath a thin crust of solid rock. If the ocean cannot be cooled from below then it must be cooled from above. If the mean surface temperature is 16C how can that possibly cool what’s below it to 3C?
The answer is it cannot. This would violate the law of entropy also known as the second law of thermodynamics. If it were possible then perpetual motion machines would be possible.
Rick C says:
……
Maybe somebody can explain to me what mechanism would allow heat to reach 2000 meters from the less than 1 mm skin depth of infrared penetration in less than 11 days.
This is a rough outline. The paper has yet to be peer-reviewed, but will be published in full in AR5.
We will show that each water molecule in the upper layer is quantum-coupled with a water molecule in the ~2000m layer.
When an upper layer molecule absorbs photons from sunlight, its energy level is raised. This causes its quantum–coupled molecule to exist in a superposition of states, both excited and unexcited. Or neither, according to taste.
When the changed energy state of an upper molecule is detected, this collapses the probability wave and the molecule in the deep reflects this change. Recording the data from an ARGO buoy would cause this. Or perhaps Erwin’s cat or Wigner’s friend swam in the water and detected its warmth.
It follows that this instantaneous transmission of the missing heat is easily prevented; do not record any of the ARGO measurements. Or keep the cat indoors and get Wigner’s friend to stick to the pool.
Here is a discussion document that covers some of the issues being raised here as regards the role of the oceans in the global energy budget:
http://www.irishweatheronline.com/news/environment/climate-news/wilde-weather/setting-and-maintaining-of-earth%e2%80%99s-equilibrium-temperature/18931.html
I think the oceans plus solar input plus atmospheric pressure set the equilibrium temperature whilst the surface pressure distribution effects the necessary fine tuning to prevent destabilisation.
@John Eggert
“The oceans are cooler than the black body equilibrium temperature of the planet.”
Say what? The black body equilibrium temperature of the earth is usually given to be -18C with albedo assumed to be 30%.
“If the ocean cannot be cooled from below then it must be cooled from above. If the mean surface temperature is 16C how can that possibly cool what’s below it to 3C?”
As per my linked article it is atmospheric pressure that sets the net energy cost of the evaporative process. At current atmospheric pressure that value is such that the evaporation which occurs reduces the temperature of the ocean bulk (not the surface layers) to a value lower than the temperature of the rocks below and the air above.
If atmospheric pressure were higher the value of the latent heat of vapourisation would change (more energy would be needed to break the bonds between water molecules) so the temperature of the bulk ocean would rise.
If atmospheric pressure were to be lower the value of the latent heat of vapourisation would change (less energy would be required to break the bonds between water molecules) so the temperature of the bulk cean would fall further.
The net energy cost of the evaporative process changes with atmospheric pressure as witness boiling at a lower temperature at the top of Everest as compared to at sea level.
It is the net energy cost of evaporation which dictates the rate at which energy can leave the oceans and in the case of Earth’s atmospheric pressure that rate is such that given the current injection of energy from the Earth beneath and the sun above the equilibrium temperature for the ocean bulk appears to be 3.9C
GHGs cannot affect the net energy cost of evaporation (and thus the temperature of the bulk ocean) unless they affect the atmospheric pressure at the surface. They do not do so to such an extent that they alter the net energy cost of evaporation in an amount we would ever be able to measure. Instead they just alter the rate of energy flow through the system from ocean skin upwards by slightly altering the speed of the water cycle.
“Liquid water possesses these exact same characteristics only its opacity to far infrared is complete whereas it’s only partial in greenhouse gases. We should consider liquid water and CO2 both as greenhouse fluids. Technically both are fluids and both are quite capable of producing a greenhouse effect.”
Quite so:
“The Earth is known as the watery planet with 71% of the surface covered by water and in many places to a substantial depth. That water is also (in addition to the atmosphere) involved in maintaining the Earth’s temperature at a higher level than it otherwise would be.
Importantly both the atmosphere AND the oceans delay the incoming solar heat from being radiated out to space. Neither ADD new heat, both receive and store heat from the sun before it leaves the planet again. In both cases water whether in atmosphere or ocean is by far the main component in delaying the passage of heat back to space. In the atmosphere water vapour dwarfs CO2 and anything else as the main greenhouse gas. The oceans are, again, water but in a far denser form. Heat from the oceans has to be processed through the atmosphere before it can leave the planet.”
from here:
http://climaterealists.com/index.php?id=1487&linkbox=true&position=5
“The Hot Water Bottle Effect”
from July 2008
The deepest ocean temperature is just going to reflect if there is ice at the poles (whenever there is sea ice or glaciers, the deep, deep ocean is going to be around 0.0C (range of +2.0C if there is not much ice to -1.0C if there is extensive ice/ice age conditions).
As long as there is permanent ice at the poles, even the mid-level ocean is going to be about 3.0C. The immediate surface ocean might go up and down more in reaction to general surface/atmosphere temperatures but the deep ocean just reflects the weighted average temperature of the coldest, densest ocean water on the planet (the poles) over the last several thousand years.
This also means the deep ocean temperature proxies/drill cores can be used as a proxy for polar temperatures in the past. The Eocene might have been +12.0C at the poles. But polar amplification also means the global temperature average was only +6.0C. Climate scientists often taken advantage of their audience by not pointing out that global temperature change is only half that of polar temperatures. See the Eocene for an example of that as well.
@JohnEggert
I took a look at Curry’s Sky Dragon blog entry. Sure, she’s right that back radiation is real. What she misses is the difference between back radiation being absorbed by liquid water versus sold objects. Greenhouse gases operate by slowing down radiative heat loss. Land surfaces, particularly dry surfaces, lose heat primarily through radiation. The ocean however loses heat primarily through evaporation. Greenhouse gases don’t slow down the rate of evaporative heat loss therefore the insulating property they produce over land is greatly reduced over water.
“The deepest ocean temperature is just going to reflect if there is ice at the poles”
Maybe so, but weren’t we discussing the average global ocean temperature of about 3.9C and not just the deepest ocean temperature ?
The average global ocean temperature will be dependent on net energy flows in and out and in that regard the energy cost of the evaporative process is key.
If the energy cost for a given amount of evaporation changes then so will ocean equilibrium temperature and the only thing in physics that will change that energy cost is atmospheric pressure at the surface.
In theory one could alter ocean equilibrium temperature by changing the amount of evaporation but evaporation will only speed up or slow down by redistributing the surface air pressure systems. That process is a wholly negative response in the atmosphere every time the air temperature tries to diverge from sea surface temperature.
Thus changes in the rate of evaporation are always self limiting as those changes work to return surface air temperatures to match sea surface temperatures.
Thus in practice no change in the ocean bulk average temperature from changes in the rate of evaporation.
One does however see changes in the surface air pressure distribution via changes in the relative sizes and position of the permanent climate zones and that is what we perceive as climate change.
The total system energy content changes barely at all and would not do so until atmospheric pressure changes, or the sun goes to such extremes of variation that it overwhelms the water cycle thermostat.
Hence the relatively stable global temperature despite the faint sun paradox and the regular recovery of the system from asteriod strikes, supervolcanic outbreaks and the coming and going of ice ages.