tracing the upper ocean’s “missing heat”
DESCRIPTION
Presentation given by Caroline Katsman at the symposium on Sea Level Rise by TU Delft Climate Institute http://bit.ly/Y5dPvYTRANSCRIPT
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A pause in the rise in upper ocean heat content:how unusual is it, and where did the heat go?
Caroline KatsmanGeert Jan van Oldenborgh
Royal Netherlands Meteorological InstituteKNMI - Global Climate Division
Tracing the upper ocean’s“missing heat”
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A warming climate
% energy content change
[1993-2003, data source: IPCC (2007)]
increasing greenhouse gas concentrations affect the Earth’s energy budget
ocean expansion isresponsible for ±50%of the observed global mean sea level rise
[3 mm/yr over 1993-2003]
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Observed ocean heat uptake
Levitus et al 2009
0-700 m, global meanocean heat content
Argo float program(2000-present)
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International Argo float network
February 2012 - 3500 active floats NL = 37
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Observed ocean heat uptake
Levitus et al 2009
0-700 m, global meanocean heat content
eXpendable BathyThermographs(XBTs) – from moving ships
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observations – surface
© National Oceanographic Data Center (NODC), USA
year=2000
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observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=2000
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observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=1980
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observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=1960
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Upper ocean heat uptake
0-700 m global mean
upper ocean has notgained heat since 2003
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Upper ocean heat uptake
“missing heat”~ 0.3 · 1022 J/yr
1. How unusual is this, in light of the ongoinggreenhouse gas forcing?
2. Where did the energy go?
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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]
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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
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the ESSENCE ensemble
17 coupled climate model simulations for 1950-2100
analysis of Ocean Heat ContentOHC = ρ cp Tocean dAocean dz
the large amount of data allows for a statistically robust analysis of events and processes involved
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Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
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Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
measure for rangeof natural variability
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Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
measure for rangeof natural variability
observations
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Upper OHC in ESSENCE
mean trend 1969-2000
long-term ESSENCE trends are in agreement withobservation-based estimates
variability model simulations encompasses observations
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Upper OHC in ESSENCE
OHC anomaly 0-700m
calculate 8-yr trends
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Upper OHC in ESSENCE
OHC anomaly 0-700m
calculate 8-yr trends
for each simulationfor a 31-year period
→ distribution
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distribution of 8-yr trends in UOHC
model: 31 yrs x 17 = 527 events
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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
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Where did the heat go?
missing heat8 yr x 0.3 1022 J/yr =2.4·1022 J
if absorbed in the ocean thenΔTocean ≈ +0.02 K
atmosphere continents cryosphere radiation to space deep ocean
upper ocean
deep ocean
atmosphere
cryosphere
con
tin
en
ts
space
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Where did the heat go?
missing heat = 2.4·1022 J
atmosphere takes much less energy to
warm one m3 of air (vol. heat capacity x 3000)
larger volume (x 20)
ΔTatm≈ +4.8 K upper ocean
atmosphere
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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
ΔTland≈ +1.2 K (upper 50m)
upper oceanco
nti
nen
ts
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Where did the heat go?
missing heat = 2.4·1022 J
cryosphere [warming] takes half the energy to
warm one m3 of ice (vol. heat capacity x 0.5)
volume of the ice sheets over which heat can be absorbed is much smaller
ΔTice≈ +7.5 K (upper 100m)
upper ocean
cryosphere
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Where did the heat go?
missing heat = 2.4·1022 J
cryosphere melt 7.3 ·1016 kg ice
global mean SLR ≈ +0.2m(x 8 observed)
3 x current sea ice extent Arctic Ocean
upper ocean
cryosphere
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Where did the heat go?
missing heat8 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 ⇔ 8-yr trends with respect to
the longterm trend
upper ocean
deep ocean
space
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Where did the heat go?
missing heat8 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 ⇔ 8-yr trends with respect to
the longterm trend
period 1990-2020
upper ocean
deep ocean
space
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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
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Top of the Atmosphere (TOA) Radiation
CAUSE: changes in cloud cover and heat uptake associatedwith El Nino / La Nina events (Pacific Ocean)
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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)
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Deep Ocean Heat Content
UOHC trend as function of depth
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Deep Ocean Heat Content
UOHC trend as function of depth
deep ocean convectionmixing of surface and subsurface waters down to 1000-2000 m[variable process]
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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)
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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)
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Latest ocean heat content observations
Katsman and van Oldenborgh (2011)
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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