Earth's energy imbalance and heat absorption by oceans

[John Nissen]

Dear Peter and Mike,

The oceans are often said to absorb a large proportion of the heat from climate forcing.  I have seen estimates up to 97%.  When I looked into the actual heat absorption, I always found it was measured in energy units  (e.g. ZJ or zettajoules) per year rather than power units (e.g. petawatts).  The EEI measurements are in power units.  So I tried a conversion for this source [1].  In the Gantt diagram* they show 200 ZJ for ocean absorption "anomaly" in 2020, relative to a baseline zero around 2000; i.e. the absorption had grown by around 200 ZJ per year in 20 years.   This 200 ZJ peer year translates into 6.34 petawatts.  This corresponds to about 12 W/m2 over the whole planet, whose surface area is 510 million km2.  But forcing from GHGs is far less than this; estimates are sometimes around 4 W/m2, but nowhere near 12 W/m2.  And there's no way that the forcing had grown as much as this over 20 years.  It seems that there's something very wrong in measurements of ocean absorption.  Or I have just stumbled on some naff science pretending to be authoritative?

BTW, their estimate of an annual growth of ~5 ZJ per year is much less than the annual growth of ~7.5 ZJ per year (300ZJ growth, 1980 to 2020) shown in the diagram.

Best wishes, John

*Source Cheng et al. 2020

[1] Mulhern (Earth.Org, 2021)

The Ocean Absorbed 20 Sextillion Joules of Heat in 2020

https://earth.org/data_visualization/the-ocean-absorbed-20-sextillion-joules-of-heat-in-2020/

[Michael MacCracken]

Hi John--A quick initial response.

When IPCC is talking about forcing, you need to remember that this is at the tropopause, not at the surface.

If you go way back to a fundamental paper in Science by Jim Hansen from 1981 (copy attached), Figure 4 shows that, at equilibrium for a CO2 doubling (you can scale down from that situation), the fluxes at the surface are several times larger than the flux levels at the tropopause--a result of how greenhouse gas effect amplifies things. In the question you pose below, you seem to not account for the different locations (surface and tropopause).

Best, Mike MacCracken

[John Nissen]

Hi Mike,

I am pretty sure it's a mistake in labelling.  The graph is of accumulated energy in the ocean.  That is why a unit of energy is used.  The straightness of the graph from 2000 to 2020 means that there was constant heat uptake, i.e. 6.3 petawatt divided by 20 equals 0.315 petawatt or ~0.6 W/m.  This is less than the excess heat power from the Earth's Energy Imbalance.  So the 90+% figure is nonsense as a proportion of energy absorbed by the oceans, unless the ZJ figures are wrong. I wonder where the truth lies.

Cheers John

[John Nissen]

Hi Mike,

I don't know whether there's something wrong with my computer, but the PDF reader didn't want to decode your attachment.  I wonder if anyone else had problems.

John

On Sun, Feb 1, 2026 at 11:08 PM Michael MacCracken <mmac...@comcast.net> wrote:

[Douglas Grandt]

John,

The file was not attached to my email 

If you go way back to a fundamental paper in Science by Jim Hansen from 1981 (copy attached), Figure 4 shows that …

Cheers,

DougG

Sent from my iPhone (audio texting)

On Feb 2, 2026, at 1:05 PM, John Nissen <johnnis...@gmail.com> wrote:



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[Michael MacCracken]

Hi Gene--Nice to see the updated analysis, but it is incorrect to say that the difference is due to albedo loss. The difference is likely mainly due to the greenhouse effect creating larger flux numbers than the forcing number that are referenced to the tropopause, as Indicated in a note that I sent to John et al.

Mike

On 2/2/26 9:09 AM, Gene Fry wrote:

John et al.,

You calculate growth in ocean heat content of 0.6 W/m^2 over 2000-2020.

From NOAA data over a slightly more recent time interval, 2006-2024, I calculated 0.68 W/^2,

from 11 ZJ heat dded per year to the oceans.

There has probably been a modest acceleration.

More important,

 from 2000-2025, the added radiative forcing from albedo loss was 2.2 times that the added forcing from greenhouse gases: 2.19 W/m^2 from albedo loss vs 1.00 W/m^2 from added GHGs.

This suggests that the difference between 12 W/m^2 and 4 W/m^2 is due to albedo loss.

Gene Fry

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[Michael MacCracken]

HI JOHN, GENE (AND ROBERT C)--YOUR COMMENT IS ONLY A SMALL PART OF THE PROBLEM WITH THE COMPARISON, IF AT ALL. THE OCEAN HEAT UPTAKE IS BASED ON ENERGY FLUXES THAT ARE OCCURRING BELOW THE GREENHOUSE GAS EFFECT THAT AMPLIFIES THE AMOUNT OF DOWNWARD  FLUX TO THE SURFACE AND THE FORCING FLUX IS ABOVE THE GHG EFFECT.

LOOK AT AN ENERGY BALANCE DIAGRAM FOR THE EARTH. ONLY 50% OF INCOMING SOLAR MAKES IT TO THE SURFACE; WHAT REALLY KEEPS THE EARTH WARM IS THAT THE DOWNWARD IR IS MORE THAN TWICE AS LARGE AS THE SOLAR THAT REACHES THE SURFACE, THE GREENHOUSE EFFECT BEING THE CAUSE OF SO MUCH HEAT AVAILABLE AT THE SURFACE.

MIKE

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[Michael MacCracken]

Hi John--It may have been downloaded quite a while ago. Here is a version downloaded from Science magazine today.

Mike

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[Gene Fry]

John et al.,

You calculate growth in ocean heat content of 0.6 W/m^2 over 2000-2020.

From NOAA data over a slightly more recent time interval, 2006-2024, I calculated 0.68 W/^2,

from 11 ZJ heat dded per year to the oceans.

There has probably been a modest acceleration.

More important,

 from 2000-2025, the added radiative forcing from albedo loss was 2.2 times that the added forcing from greenhouse gases: 2.19 W/m^2 from albedo loss vs 1.00 W/m^2 from added GHGs.

This suggests that the difference between 12 W/m^2 and 4 W/m^2 is due to albedo loss.

Gene Fry

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