Thus, we take 4.5 °C as our best estimate for LGM cooling, implying an amplification of surface temperature change by a factor of two relative to
deep ocean temperature change for this climate interval.
In fact, Bova et al. (2016) conclude that
deep ocean temperature changes for the last 200 years are apparently so negligible they are «below the detection limits».
Not exact matches
For as much as atmospheric
temperatures are rising, the amount of energy being absorbed by the planet is even more striking when one looks into the
deep oceans and the
change in the global heat content (Figure 4).
I am also interested in how long is required
for the surface temp to «achieve» 95 % of the ECS
change: e.g. if climate sensitivity is 2K, how much time is required
for the surface temp to increase by 1.9 K; and then how much longer
for the
deep oceans to increase by 1.9 K (or whatever 95 % of the projected increase in
deep ocean temperature works out to.)
Gavin Schmidt says: «The
deep ocean is really massive and even
for the large
changes in OHC we are discussing the impact on the
deep temperature is small (I would guess less than 0.1 deg C or so).
For as much as atmospheric
temperatures are rising, the amount of energy being absorbed by the planet is even more striking when one looks into the
deep oceans and the
change in the global heat content (Figure 4).
The surface
temperature response, T, to a given
change in atmospheric CO2 is calculated from an energy balance equation
for the surface, with heat removed either by a radiative damping term or by diffusion into the
deep ocean.
For seasonal
temperature changes, that gives about 5 ppmv / °C, mainly from NH extra-tropical vegetation
For year to year variability (1 - 3 years), that gives 4 - 5 ppmv / °C, mainly from tropical vegetation
For very long term
changes (MWP - LIA, glacial - interglacial
changes), that gives ~ 8 ppmv / °C, mainly from the
deep oceans.
If there is
deep - water formation in the final steady state as in the present day, the
ocean will eventually warm up fairly uniformly by the amount of the global average surface
temperature change (Stouffer and Manabe, 2003), which would result in about 0.5 m of thermal expansion per degree celsius of warming, calculated from observed climatology; the EMICs in Figure 10.34 indicate 0.2 to 0.6 m °C — 1
for their final steady state (year 3000) relative to 2000.
HS12 assume that
deep ocean temperature change was similar to global mean surface
temperature change for Cenozoic climates warmer than today, but this relationship does not hold true
for colder climates.
Fortunately, sufficient information is available on surface
temperature change in the Pliocene and Pleistocene to allow us to scale the
deep ocean temperature change by appropriate factors, thus retaining the temporal variations in the δ18O while also having a realistic magnitude
for the total
temperature change over these epochs.
The total
deep ocean temperature change of 6 °C
for the
change of δ18O from 1.75 to 4.75 is then divided two - thirds (4 °C)
for the δ18O range 1.75 — 3.25 and 2 °C
for the δ18O range 3.25 — 4.75.
The 800 years is
for the reaction of the
deep oceans on glacial - interglacial transitions, but the reverse reaction needs several thousands of years, while small
changes (< 1 K) like the MWP - LIA transition have only a lag of ~ 50 years and some 6 ppmv CO2 drop after the
temperature drop:
In the letter, Clement also expressed
deep concern
for other victims of climate
change impacts, such as the recent set of devastating hurricanes, more frequent and severe flooding, marine life die - offs as a result of warmer
ocean temperatures, forests at risk from invasive insects, and so on.
The internally imposed structural
changes to the climate system include the injection of the non-condensing greenhouse gases (CO2, CH4, N2O, CFCs, etc), volcanic and anthropogenic aerosols, and episodic contact to the
deep ocean cold
temperature reservoir (this is responsible
for the «natural», «internally forced», or «unforced» variability of the climate system).
I am also interested in how long is required
for the surface temp to «achieve» 95 % of the ECS
change: e.g. if climate sensitivity is 2K, how much time is required
for the surface temp to increase by 1.9 K; and then how much longer
for the
deep oceans to increase by 1.9 K (or whatever 95 % of the projected increase in
deep ocean temperature works out to.)
Obviously the
deep ocean > 700 meters is the most difficult place to sample
temperature changes (and to drill
for oil).
More succinctly, if
deep ocean temperatures can naturally rise by 1 °C in 100 years without any
change in CO2, then attributing
changes in
ocean temperature that are already «below the detection limit»
for the last 200 years (or just ~ 0.1 °C since 1955) to anthropogenic CO2 forcing is highly presumptuous at best.
The
temperature record is less complete
for the
deep ocean, and its massive volume and separation from the surface subdues its response to climatic
changes.
The long term
changes may involve the
deeper ocean temperatures and / or flows, which gives larger
changes of CO2
for a similar
temperature change.
This is a quite rapid process (
for the upper
oceans), but much slower
for deep ocean temperature changes, which results in the above differences in ratios
for short term and long term
temperature variations...
Even in the ARGO era (2003 --RRB-, the error bars and uncertainty ranges
for our educated guesses (that's what they are) about
deep ocean heat are 10 times greater (and more) than the suggested
temperature changes (hundredths of a degree) themselves.
That indeed are very long - term averages and probably involve the
deep oceans, which is not the case
for current (2 - 4 ppmv / °C)
temperature changes.