The seminal paper
Ellis et al. 1978: The annual variation in the global heat balance of the Earth. J. Geophys. Res., 83, 1958-1962
provides an effective framework to assess the relative magnitudes of the global annual average radiative forcing relative to the interannual global average radiative forcing.
As evident in the figure from their paper, the variation within the year is ~27 Watts per meter squared. These number certainly could have been updated since their 1978 paper (and I welcome e-mails that provide an updated interannual top of the atmosphere radiative imbalance), but we can use to compare with estimates of the annual global average radiative imbalance predicted by the multi-decadal global model predictions.
Jim Hansen provides a succinct summary in his communication to me in 2005 (see)
Contrary to the claim of Pielke and Christy, our simulated ocean heat storage (Hansen et al., 2005) agrees closely with the observational analysis of Willis et al. (2004). All matters raised by Pielke and Christy were considered in our analysis and none of them alters our conclusions.
The Willis et al. measured heat storage of 0.62 W/m2 refers to the decadal mean for the upper 750 m of the ocean. Our simulated 1993-2003 heat storage rate was 0.6 W/m2 in the upper 750 m of the ocean. The decadal mean planetary energy imbalance, 0.75 W/m2, includes heat storage in the deeper ocean and energy used to melt ice and warm the air and land. 0.85 W/m2 is the imbalance at the end of the decade.
If we use the 0.85 W/m2 at the end of the 1990s as the estimate for the magnitude of global warming (as predicted by the GISS model), this is about 3% of variation in the global average radiative imbalance during the year. This explains why it is so difficult to skillfully measure this quantity as it such a small fraction of the variations within the year. It also explains (as everyone seems to agree with) that natural climate variations can result in large enough interannual variations in the top of the atmosphere radiative imbalance that we need to look at longer time periods.
We can do that by assessing the observed and the modeled accumulation of heat over multiple years. I have posted on this a number of times in the past; e.g. see my most recent in
Since an radiative imbalance of 0.85 Watts per meter squared corresponds to 1.38 x 10 **23 Joules per decade, as discussed in
Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335.
the global warming signal should eventually emerge even in the intrannual data.
Recent analyses, however, which present the intrannual variations in the radiative imbalance do not show a radiative imbalance of the magnitude reported by Jim Hansen, such as in the figure by Josh Willis in
Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.
Figure 1 in
R. S. Knox, David H. Douglass 2010: Recent energy balance of Earth International Journal of Geosciences, 2010, vol. 1, no. 3 (November) â€“ In press doi:10.4236/ijg2010.00000
The recent paper
C. A. Katsman and G. J. van Oldenborgh, 2011: Tracing the upper ocean’s ‘missing heat’. Geophysical Research Letters.
unfortunately, does not present the model’s intrannual variations.
My recommendations to move forward on this include:
1. The multi-decadal global modelling groups should present their intrannual variations of the global average radiative imbalance for each year of their predictions.
2. The observed intrannual global average radiative imbalance should be made available in real-time, as are other climate metrics, such as as sea ice (e.g. see), and the global average lower tropospheric temperature anomalies (see and see).
With this added information, we would be able to come closer to resolving the real magnitude of global warming over decadal and longer time scales.