The Approximate 40 Year 'Climate Lag' is Caused Mainly by the Thermal Inertia of the Oceans

The reason the Earth takes several decades to fully respond to increased CO2 is the thermal inertia of the oceans due to the fact that mass of the oceans is around 500 times that of the atmosphere. Just as it takes time for a cup of coffee to release heat into the air, so to it takes time for the ocean to release its heat into the atmosphere. This simple analogy explains what climate scientists refer to as climate lag.

Climate science has difficulty in quantifying the rate at which the warm upper layers of the ocean mix with the cooler deeper waters so there is significant variation in estimates of climate lag. One paper by James Hansen and others estimates the time required for 60% of global warming to take place in response to increased emissions to be in the range of 40 years. Kevin Trenberth, of the US National Center for Atmospheric Research.wrote in the journal Geophysical Research Letters, "Global warming is continuing but it's being manifested in somewhat different ways. Warming can go, for instance, to the air, water, land or to melting ice and snow." Adding that, "Warmth is spreading to ever deeper ocean levels, recent warming rates of the waters below 700 metres appear to be unprecedented causing pauses in surface warming could last 15 - 20 years.

Climate lag is one of the most important of climate science's many uncertainties. Trenberth mentions that some of the trapped thermal energy is is embedded in the water, land, melting ice and snow as well as the air. All ice on land from Antarctic ice sheets to glaciers has to warm from [in some places] -40C to 0C before it changes state from solid to liquid and makes a contribution to rising sea levels. It does this transformation by soaking up energy throughout its mass slowly when one ice crystal passes thermal energy onto its next door neighbors. Consequently countless billions of joules of energy are locked into the slow process of state change and just like deep ocean circulation exchange we have very little way of accurately accounting for this energy.

The Keeling Curve shows that an uncertain mixture of our industrial consumer culture's emissions, natural sources and the uncertainty of positive and negative feedbacks are together constantly adding CO2 into our atmosphere. With approximately 40 years between rising carbon pollution and its effect, it means that average temperatures of the last few years are the results of conditions in the early 70's. It also means that the true impact of our emissions over the last decade will probably not be felt until the 2050’s if the 'consensus' opinion of climate science is correct.

But no one really knows the future and just as climate change could turn out less catastrophic than the 'consensus' opinion it could just as easily turn out far worse which is in fact what many of the present indicators show. More on that in the next Mud Report as we explore how and why so many climate scientists are purposely underestimating their climate change projections.