If we accept that greenhouse gases are warming the planet, the next concept that needs to be grasped is that it takes time, and we have not yet seen the full rise in temperature that will occur as a result of the CO2 we have already emitted. The Earth's average surface temperature has already risen by more than 0.7 degrees C since 1900. The concentration of CO2 in the atmosphere is increasing at the rate of 2 ppm per year. Scientists tell us that even if CO2 was stabilized at its current level of 390 ppm (late 2010), there is at least another 0.5 degrees "in the pipeline". If findings from a recent study of Antarctic ice cores is confirmed, the last figure will prove to be conservative . The delayed response is known as climate lag.
The reason the planet takes several decades to respond to increased CO2 is the thermal inertia of the oceans. Consider a saucepan of water placed on a gas stove. Although the flame has a temperature measured in hundreds of degrees C, the water takes a few minutes to reach boiling point. This simple analogy explains climate lag. The mass of the oceans is around 500 times that of the atmosphere. The time that it takes to warm up is measured in decades. Because of the difficulty in quantifying the rate at which the warm upper layers of the ocean mix with the cooler deeper waters, and the rate at which ice sheets disintegrate, there is significant variation in estimates of climate lag. Estimations of the time required for 60% of global warming to take place in response to increased emissions vary from 25 to 100 years. I suggest the weight of evidence suggests it is lies somewhere in the mid range at around 40 years.
In recent times, climate skeptics have been peddling a lot of nonsense about average temperatures actually cooling over the last decade. There was a brief dip around the year 2000 following the extreme El Nino event of 1998, but with greenhouse emissions causing a planetary energy imbalance of 0.85 watts per square metre , there is inevitably a continual rising trend in global temperatures. The graph below shows a clear rising trend in temperatures as well as a rising trend in sea-level.
The best estimate of 40 years for climate lag, the time between the cause (increased greenhouse gas emissions) and the effect (increased temperatures), has profound negative consequences for humanity. However, if governments can find the will to act, there are positive consequences as well.
With 40 years between cause and effect, it means that average temperatures of the last decade are a result of what we were thoughtlessly putting into the air in the 1960's. It also means that the true impact of our emissions over the last decade will not be felt until the 2040's. As men and women chosen to make decisions on behalf of current and future Australians, this should send a chill down your spine! Lately, conservative elements in both politics and the media have been playing up uncertainties in some of the more difficult to model effects of climate change, while ignoring the solid scientific understanding of the cause. If past governments had troubled themselves to understand the cause, and acted in a timely way, climate change would have been contained with minimal disruption. By refusing to acknowledge the cause, and demanding to see the effects before action is taken, past governments have brought on the current crisis. By the time they see those effects, it will too late to deal with the cause.
The positive consequence of climate lag is the opportunity for remedial action before the ocean warms to its full extent. We need to not only work towards reducing our carbon emissions to near zero by 2050, but well before then to begin removing excess CO2 from the atmosphere on an industrial scale. Biochar is one promising technology that can have an impact here. If an international agreement can be forged to provide a framework for not only limiting new emissions, but sequestering old emissions, then the full horror of the climate crisis may yet be averted.
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