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
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”
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]
Observed ocean heat uptake
Levitus et al 2009
0-700 m, global meanocean heat content
Argo float program(2000-present)
International Argo float network
February 2012 - 3500 active floats NL = 37
Observed ocean heat uptake
Levitus et al 2009
0-700 m, global meanocean heat content
eXpendable BathyThermographs(XBTs) – from moving ships
observations – surface
© National Oceanographic Data Center (NODC), USA
year=2000
observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=2000
observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=1980
observations – 1000 m depth
© National Oceanographic Data Center (NODC), USA
year=1960
Upper ocean heat uptake
0-700 m global mean
upper ocean has notgained heat since 2003
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?
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]
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
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
Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
measure for rangeof natural variability
Upper OHC in ESSENCE
OHC anomaly 0-700m
forced trend
measure for rangeof natural variability
observations
Upper OHC in ESSENCE
mean trend 1969-2000
long-term ESSENCE trends are in agreement withobservation-based estimates
variability model simulations encompasses observations
Upper OHC in ESSENCE
OHC anomaly 0-700m
calculate 8-yr trends
Upper OHC in ESSENCE
OHC anomaly 0-700m
calculate 8-yr trends
for each simulationfor a 31-year period
→ distribution
distribution of 8-yr trends in UOHC
model: 31 yrs x 17 = 527 events
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
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
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
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
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
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
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
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
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
Top of the Atmosphere (TOA) Radiation
CAUSE: changes in cloud cover and heat uptake associatedwith El Nino / La Nina events (Pacific Ocean)
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)
Deep Ocean Heat Content
UOHC trend as function of depth
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]
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)
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)
Latest ocean heat content observations
Katsman and van Oldenborgh (2011)
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