Science, Vol 309, Issue 5732, 284-287, 8 July 2005
Penetration of Human-Induced Warming into the World's Oceans
Abstract: "A warming signal has penetrated into the world's oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences. Changes in advection combine with surface forcing to give the overall warming pattern. The implications of this study suggest that society needs to seriously consider model predictions of future climate change."
Earth's Energy Imbalance: Confirmation and Implications
Abstract: "Our climate model, driven mainly by increasing human-made greenhouse gases and aerosols, among other forcings, calculates that Earth is now absorbing 0.85 ± 0.15 watts per square meter more energy from the Sun than it is emitting to space. This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years. Implications include (i) the expectation of additional global warming of about 0.6°C without further change of atmospheric composition; (ii) the confirmation of the climate system's lag in responding to forcings, implying the need for anticipatory actions to avoid any specified level of climate change; and (iii) the likelihood of acceleration of ice sheet disintegration and sea level rise."
http://pubs.giss.nasa.gov/docs/2005/2005_HansenNazarenkoR.pdf
"A caveat accompanying our analysis concerns the uncertainty in climate forcings. A good fit of observed and modeled temperatures (Fig. 1) also could be attained with smaller forcing and larger climate sensitivity, or with the converse. If climate sensitivity were higher (and forcings smaller), the rate of ocean heat storage and warming ‘‘in the pipeline’’ or ‘‘committed’’ would be greater, e.g., models with a sensitivity of 4.2- to 4.5-C for doubled CO2 yield È1-C ‘‘committed’’ global warming (3, 4). Conversely, smaller sensitivity and larger forcing yield lesser committed warming and ocean heat storage. The agreement between modeled and observed heat storage (Fig. 2) favors an intermediate climate sensitivity, as in our model. This test provided by ocean heat storage will become more useful as the period with large energy imbalance continues."
"What does this imply? Firstly, as surface temperatures and the ocean heat content are rising together, it almost certainly rules out intrinsic variability of the climate system as a major cause for the recent warming (since internal climate changes (ENSO, thermohaline variability, etc.) are related to transfers of heat around the system, atmospheric warming would only occur with energy from somewhere else (i.e. the ocean) which would then need to be cooling)."
"Secondly, since the ocean warming is shown to be consistent with the land surface changes, this helps validate the surface temperature record, which is then unlikely to be purely an artifact of urban biases etc. Thirdly, since the current unrealised warming "in the pipeline" is related to the net imbalance, 0.85+/-0.15 W/m2 implies an further warming of around 0.5-0.7 C, regardless of future emission increases. This implications are similar to the conclusions discussed recently by Wigely and Meehl et al.. Many different models have now demonstrated that our understanding of current forcings, long-term observations of the land surface and ocean temperature changes and the canonical estimates of climate forcing are all consistent within the uncertainties. Thus since we are reasonably confident in what has happened in the recent past, projections of these same models under plausible future scenarios need to be considered seriously."