jai,
Thanks for opening a new thread on this topic, which begs such questions as: (a) what is the true Equilibrium Climate Sensitivity, ECS; (b) what is the Planetary Heat Budget; (c) when and how did/does heat get into both the upper, and lower, ocean; and (d) how quickly might slow response feedback mechanisms kick-in to contribute to temperature rise this century?
You mentioned previously that aerosols might contribute to some of the "global-warming hiatus", but this negative feedback from aerosols certainly cannot account for the heat going into the upper ocean over more than three decades that Durack et al (2014) have documented. Clearly, this heat in the upper ocean indicates that the ECS is higher than the CMIP5 projections have assumed and that the excess heat has been making its way into the ocean via both PDO (see Tollefson (2014) and attached image) and AMO (see Mann et al 2014) related pathways. However, from a Planetary Heat Budget point of view, we should not forget the heat going into the deep ocean as discussed by Llovel et al (2014). Finally, I point-out that Lovejoy et al (2014) have proven that the "global-warming hiatus" must be natural variability and if so global warming will accelerate soon:
Jeff Tollefson, (2014), "Climate change: The case of the missing heat - Sixteen years into the mysterious ‘global-warming hiatus’, scientists are piecing together an explanation", Nature, 505, 276–278, doi:10.1038/505276a
http://www.nature.com/news/climate-change-the-case-of-the-missing-heat-1.14525http://www.nature.com/polopoly_fs/1.14525!/menu/main/topColumns/topLeftColumn/pdf/505276a.pdf
Mann, M. E., B. A. Steinman, and S. K. Miller (2014), On forced temperature changes, internal variability, and the AMO, Geophys. Res. Lett., 41, 3211–3219, doi:10.1002/2014GL059233.
http://onlinelibrary.wiley.com/doi/10.1002/2014GL059233/abstractAbstract: "We estimate the low-frequency internal variability of Northern Hemisphere (NH) mean temperature using observed temperature variations, which include both forced and internal variability components, and several alternative model simulations of the (natural + anthropogenic) forced component alone. We then generate an ensemble of alternative historical temperature histories based on the statistics of the estimated internal variability. Using this ensemble, we show, first, that recent NH mean temperatures fall within the range of expected multidecadal variability. Using the synthetic temperature histories, we also show that certain procedures used in past studies to estimate internal variability, and in particular, an internal multidecadal oscillation termed the “Atlantic Multidecadal Oscillation” or “AMO”, fail to isolate the true internal variability when it is a priori known. Such procedures yield an AMO signal with an inflated amplitude and biased phase, attributing some of the recent NH mean temperature rise to the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming. Claims of multidecadal “stadium wave” patterns of variation across multiple climate indices are also shown to likely be an artifact of this flawed procedure for isolating putative climate oscillations."
W. Llovel, J. K. Willis, F. W. Landerer & I. Fukumori, (2014), "Deep-ocean contribution to sea level and energy budget not detectable over the past decade", Nature Climate Change, doi:10.1038/nclimate2387
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2387.htmlAbstract: "As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth’s energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000 m depth explain about 32% of the observed annual rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 ± 0.28 mm yr−1 in sea-level rise and agree with the upper-ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2,000 m) contributes −0.13 ± 0.72 mm yr−1 to global sea-level rise and −0.08 ± 0.43 W m−2 to Earth’s energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 ± 0.44 W m−2 from 2005 to 2013."
Lovejoy, S. (2014), Return periods of global climate fluctuations and the pause, Geophys. Res. Lett., 41, 4704–4710, doi:10.1002/2014GL060478.
http://onlinelibrary.wiley.com/doi/10.1002/2014GL060478/abstractAbstract: "An approach complementary to General Circulation Models (GCMs), using the anthropogenic CO2 radiative forcing as a linear surrogate for all anthropogenic forcings [Lovejoy, 2014], was recently developed for quantifying human impacts. Using preindustrial multiproxy series and scaling arguments, the probabilities of natural fluctuations at time lags up to 125 years were determined. The hypothesis that the industrial epoch warming was a giant natural fluctuation was rejected with 99.9% confidence. In this paper, this method is extended to the determination of event return times. Over the period 1880–2013, the largest 32 year event is expected to be 0.47 K, effectively explaining the postwar cooling (amplitude 0.42–0.47 K). Similarly, the “pause” since 1998 (0.28–0.37 K) has a return period of 20–50 years (not so unusual). It is nearly cancelled by the pre-pause warming event (1992–1998, return period 30–40 years); the pause is no more than natural variability."
Best,
ASLR