ASLR,
Several times you written things like Ocean surface temperature "values appear to be being artificially suppressed by ice sheet meltwater".
It certainly makes sense to me that melted ice will cool the sea water it finds itself mixing with. I question your writing about the "artificiality" of this. To the extent ACC is artificial, this process that is integral to CC will also be artificial. But as I see CC as a natural response to ongoing anthropogenic activities, I see this melt water affect on sea surface temperatures as being natural too, and not the least bit artificial.
Am I missing something? (and if so, what - and thanks for writing about this feature of climate change)
Tor,
It is possible/probable that the word "artificial" is a poor choice of words, on my part. What I am trying to convey is that relatively thin layers of relatively fresh ocean water (due to the addition of fresh glacial meltwater) in "cool spots" in both the North Atlantic and Southern, Oceans, are temporarily (for several decades) masking the radiation of out-going longwave radiation (OLR) from warmer slightly deeper water. This reduction in OLR increases the earth energy imbalance [or global energy imbalance in panel (b) of the first attached image from Hansen et al 2016, for which panel (a) shows the consequential/associated change in global mean surface (2m) air temperature]
James Hansen, Makiko Sato, Paul Hearty, Reto Ruedy, Maxwell Kelley, Valerie Masson-Delmotte, Gary Russell, George Tselioudis, Junji Cao, Eric Rignot, Isabella Velicogna, Blair Tormey, Bailey Donovan, Evgeniya Kandiano, Karina von Schuckmann, Pushker Kharecha, Allegra N. Legrande, Michael Bauer, and Kwok-Wai Lo (2016), "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous", Atmos. Chem. Phys., 16, 3761-3812, doi:10.5194/acp-16-3761-2016
http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.htmlAbstract: "We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions."
The second two images come from the following reference and show that the Southern Ocean is already more stratified and the circumpolar deep water, CDW, is already warmer than the CMIP5 models indicate:
R. Bintanja, G. J. van Oldenborgh, S. S. Drijfhout, B. Wouters & C. A. Katsman, (2013), "Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion", Nature Geoscience, Volume: 6, 376–379, (2013), doi:10.1038/ngeo1767.
http://www.nature.com/ngeo/journal/v6/n5/full/ngeo1767.htmlNext, the linked Aquarius satellite data provides the fourth attached image of the sea surface density for April 2015, indicating how fresh both the North Atlantic and the Southern Ocean are becoming relative to the other oceans of the world; which is a clear sign that the Hansen et al (2016) ice-climate feedback mechanism has already begun:
http://aquarius.umaine.edu/cgi/gal_density.htmSo while I agree that "artificial" is not the best choice of words, nevertheless: (1) the CMIP5 (and the AR5) models do not include the influence of Hansen et al (2016)'s ice-climate feedback; and (2) while this feedback does decrease the measured GMST departures; nevertheless it results in increase climate change due to the increase in Earth Energy Imbalance, EEI, which induces such effects as: (a) accelerated ice sheet mass loss; (b) increased intensity of storm activity; and (c) a slowing of thermohaline circulation, THC, which increases surface temperatures near the equator. In this sense, rather than "artificially" reducing GMST departures, the glacial meltwater is temporarily masking the future increases in GMST departures, while currently accelerating climate change to the extent of inducing an effective ECS of about 6C. Finally, this discussion indicates that the 2C target was established without consideration of ice-climate feedback and thus it artificially creates a false sense of security in the public and policy makers with regard to climate change risk.
Best,
ASLR
