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Tracing the upper ocean’s “missing heat”
 

Tracing the upper ocean’s “missing heat”

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Presentation given by Caroline Katsman at the symposium on Sea Level Rise by TU Delft Climate Institute http://bit.ly/Y5dPvY

Presentation given by Caroline Katsman at the symposium on Sea Level Rise by TU Delft Climate Institute http://bit.ly/Y5dPvY

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    Tracing the upper ocean’s “missing heat” Tracing the upper ocean’s “missing heat” Presentation Transcript

    • Tracing the upper ocean’s“missing heat”A pause in the rise inupper ocean heat content:how unusual is it, and where did the heat go?Caroline KatsmanGeert Jan van Oldenborgh Royal Netherlands Meteorological Institute KNMI - Global Climate Division Caroline.Katsman@knmi.nl
    • A warming climateincreasing greenhouse gas concentrations affectthe 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)]
    • Observed ocean heat uptake Levitus et al 2009 Argo float program (2000-present)0-700 m, global meanocean heat content
    • International Argo float networkFebruary 2012 - 3500 active floats NL = 37
    • Observed ocean heat uptake Levitus et al 20090-700 m, global meanocean heat content eXpendable BathyThermographs (XBTs) – from moving ships
    • observations – surface year=2000© National Oceanographic Data Center (NODC), USA
    • observations – 1000 m depth year=2000© National Oceanographic Data Center (NODC), USA
    • observations – 1000 m depth year=1980© National Oceanographic Data Center (NODC), USA
    • observations – 1000 m depth year=1960© National Oceanographic Data Center (NODC), USA
    • Upper ocean heat uptake upper ocean has not gained heat since 20030-700 m global mean
    • Upper ocean heat uptake “missing heat” ~ 0.3 · 1022 J/yr1. How unusual is this, in light of the ongoing greenhouse 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 greenhousegas forcing is ~0.85 ±0.15 W/m2 [Hansen et al 2005]–satellites measure incoming shortwave radiation and outgoinglongwave 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 variabilityversus forced trends
    • the ESSENCE ensemble17 coupled climate model simulations for 1950-2100analysis of Ocean Heat ContentOHC =  ρ cp Tocean dAocean dzthe large amount of data allows for a statistically robust analysis of events and processes involved
    • Upper OHC in ESSENCE forced trendOHC anomaly 0-700m
    • Upper OHC in ESSENCE forced trend measure for rangeOHC anomaly 0-700m of natural variability
    • Upper OHC in ESSENCEobservations forced trend measure for range OHC anomaly 0-700m of natural variability
    • Upper OHC in ESSENCE mean trend 1969-2000 long-term ESSENCE trends are in agreement with observation-based estimates variability model simulations encompasses observations
    • Upper OHC in ESSENCE OHC anomaly 0-700mcalculate 8-yr trends
    • Upper OHC in ESSENCE for each simulation for a 31-year period → distribution OHC anomaly 0-700mcalculate 8-yr trends
    • distribution of 8-yr trends in UOHC model: 31 yrs x 17 = 527 events
    • distribution of 8-yr trends in UOHC 3% of distribution25-30% chance of one or more (overlapping) 8-yr periods with a negative trend in upper ocean heat content
    • 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  atmosphereupper ocean continents continents   cryosphere  radiation to space deep ocean  deep ocean
    • Where did the heat go? missing heat = 2.4·1022 J atmosphere  takes much less energy toatmosphere warm one m3 of air (vol. heat capacity x 3000)  larger volume (x 20)upper ocean  ΔTatm ≈ +4.8 K
    • 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 yearsupper ocean continents  ΔTland ≈ +1.2 K (upper 50m)
    • 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 beupper ocean absorbed is much smaller  ΔTice ≈ +7.5 K (upper 100m)
    • 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
    • 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 trendupper ocean ⇔ 8-yr trends with respect to the longterm trenddeep ocean
    • 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 trendupper ocean ⇔ 8-yr trends with respect to the longterm trenddeep ocean period 1990-2020
    • 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) RadiationCAUSE: changes in cloud cover and heat uptake associated with 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 depthdeep ocean convectionmixing of surface andsubsurface watersdown 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