The document discusses a pause in the rise of upper ocean heat content observed since 2003 despite ongoing greenhouse gas forcing. The summary is: 1) This pause is not unusual according to climate model simulations and can be explained by natural variability. 2) It is associated with about 45% of the "missing heat" being radiated to space and 35% entering the deep ocean layers. 3) The causes are variations in cloud cover and heat uptake related to El Nino/La Nina events and deep convection in the North Atlantic Ocean.

1. Tracing the upper ocean’s
“missing heat”
A pause in the rise in
upper ocean heat content:
how unusual is it, and where did the heat go?
Caroline Katsman
Geert Jan van Oldenborgh
Royal Netherlands Meteorological Institute
KNMI - Global Climate Division
Caroline.Katsman@knmi.nl

2. A warming climate
increasing greenhouse gas concentrations affect
the Earth’s energy budget
ocean expansion is
responsible for ±50%
of the observed global
mean sea level rise
[3 mm/yr over 1993-2003]
% energy content change
[1993-2003, data source: IPCC (2007)]

3. Observed ocean heat uptake
Levitus et al 2009
Argo float program
(2000-present)
0-700 m, global mean
ocean heat content

4. International Argo float network
February 2012 - 3500 active floats NL = 37

5. Observed ocean heat uptake
Levitus et al 2009
0-700 m, global mean
ocean heat content
eXpendable BathyThermographs
(XBTs) – from moving ships

6. observations – surface
year=2000
© National Oceanographic Data Center (NODC), USA

7. observations – 1000 m depth
year=2000
© National Oceanographic Data Center (NODC), USA

8. observations – 1000 m depth
year=1980
© National Oceanographic Data Center (NODC), USA

9. observations – 1000 m depth
year=1960
© National Oceanographic Data Center (NODC), USA

10. Upper ocean heat uptake
upper ocean has not
gained heat since 2003
0-700 m global mean

11. Upper ocean heat uptake
“missing heat”
~ 0.3 · 1022 J/yr
1. How unusual is this, in light of the ongoing
greenhouse gas forcing?
2. Where did the energy go?

12. Upper ocean heat uptake
“missing heat”
~ 0.3 · 1022 J/yr
energy budget change of
~ 0.2 W / m2
– the imbalance in the Earth’s energy budget due to greenhouse
gas forcing is ~0.85 ±0.15 W/m2 [Hansen et al 2005]
–satellites measure incoming shortwave radiation and outgoing
longwave radiation at ~0.5 to 1.0 W/m2 precision
[Trenberth et al 2010]

13. the ESSENCE ensemble
17 coupled climate
model simulations
for 1950-2100
A1B emission scenario
started from slightly
different initial
conditions
→ natural variability
versus forced trends

14. the ESSENCE ensemble
17 coupled climate
model simulations
for 1950-2100
analysis of Ocean Heat Content
OHC =  ρ cp Tocean dAocean dz
the large amount of data allows for a
statistically robust analysis of
events and processes involved

15. Upper OHC in ESSENCE
forced trend
OHC anomaly 0-700m

16. Upper OHC in ESSENCE
forced trend
measure for range
OHC anomaly 0-700m of natural variability

17. Upper OHC in ESSENCE
observations
forced trend
measure for range
OHC anomaly 0-700m of natural variability

18. Upper OHC in ESSENCE
mean trend 1969-2000
 long-term ESSENCE trends are in agreement with
observation-based estimates
 variability model simulations encompasses observations

19. Upper OHC in ESSENCE
OHC anomaly 0-700m
calculate 8-yr trends

20. Upper OHC in ESSENCE
for each simulation
for a 31-year period
→ distribution
OHC anomaly 0-700m
calculate 8-yr trends

21. distribution of 8-yr trends in UOHC
model: 31 yrs x 17 = 527 events

22. distribution of 8-yr trends in UOHC
3% of
distribution
25-30% chance of one or more (overlapping) 8-yr periods with a
negative trend in upper ocean heat content

23. Where did the heat go?
space missing heat
8 yr x 0.3 1022 J/yr =2.4·1022 J
atmosphere if absorbed in the ocean then
ΔTocean ≈ +0.02 K
cryosphere
 atmosphere
upper ocean continents
continents

 cryosphere
 radiation to space
deep ocean  deep ocean

24. Where did the heat go?
missing heat = 2.4·1022 J
atmosphere
 takes much less energy to
atmosphere warm one m3 of air
(vol. heat capacity x 3000)
 larger volume (x 20)
upper ocean  ΔTatm ≈ +4.8 K

25. Where did the heat go?
missing heat = 2.4·1022 J
continents
 takes 40% less energy to
warm one m3 of rock
(vol. heat capacity x 0.6)
 heat penetrates only over
~50m in a few years
upper ocean
continents
 ΔTland ≈ +1.2 K (upper 50m)

26. Where did the heat go?
missing heat = 2.4·1022 J
cryosphere [warming]
 takes half the energy to
cryosphere warm one m3 of ice
(vol. heat capacity x 0.5)
 volume of the ice sheets
over which heat can be
upper ocean absorbed is much smaller
 ΔTice ≈ +7.5 K (upper 100m)

27. Where did the heat go?
missing heat = 2.4·1022 J
cryosphere
 melt 7.3 ·1016 kg ice
cryosphere
 global mean SLR ≈ +0.2m
(x 8 observed)
upper ocean
 3 x current sea ice extent
Arctic Ocean

28. Where did the heat go?
space missing heat
8 yr x 0.3 1022 J/yr =2.4·1022 J
 radiation to space
 deep ocean
plateau in upper OHC:
⇔ downward trend superposed
on longterm upward trend
upper ocean ⇔ 8-yr trends with respect to
the longterm trend
deep ocean

29. Where did the heat go?
space missing heat
8 yr x 0.3 1022 J/yr =2.4·1022 J
 radiation to space
 deep ocean
plateau in upper OHC
⇔ downward trend superposed
on longterm upward trend
upper ocean ⇔ 8-yr trends with respect to
the longterm trend
deep ocean period 1990-2020

30. Top of the Atmosphere (TOA) Radiation
45% of the variation in upper OHC is associated with
a variation in the net outgoing TOA radiation
upper ocean cooling ⇔ more radiation out

31. Top of the Atmosphere (TOA) Radiation
CAUSE: changes in cloud cover and heat uptake associated
with El Nino / La Nina events (Pacific Ocean)

32. Deep Ocean Heat Content
35% of the decrease in upper OHC (0-700 m)
is associated with an increase in deep OHC (700-3000 m)

33. Deep Ocean Heat Content
UOHC trend as function of depth

34. Deep Ocean Heat Content
UOHC trend as function of depth
deep ocean convection
mixing of surface and
subsurface waters
down to 1000-2000 m
[variable process]

35. Summary
 A pause in the rise in upper Ocean Heat Content as
recently observed is not unusual in the late 20th /
early 21st century, despite greenhouse gas forcing
 Such a pause is associated with increased radiation
to space (~45%) and an increase in the deep ocean
heat content (~35%)
 The causes for these energy exchanges are two
modes of natural variability (ENSO conditions and
deep convection in the North Atlantic Ocean)

36. Summary
 A pause in the rise in upper Ocean Heat Content as
recently observed is not unusual in the late 20th /
early 21st century, despite greenhouse gas forcing
 Such a pause is associated with increased radiation
to space (~45%) and an increase in the deep ocean
heat content (~35%)
 The causes for these energy exchanges are two
modes of natural variability (ENSO conditions and
deep convection in the North Atlantic Ocean)
Katsman and van Oldenborgh (2011)

37. Latest ocean heat content observations
Katsman and van Oldenborgh (2011)

38. Latest ocean heat content observations
ocean expansion is projected to result in
10-30 cm global mean sea level rise
by the end of the century