Has the world actually been cooling since 2002?

[wolfpup]

@Sam_Stone

It also opens the question as to whether even a 100 year trend means anything in this regard. The Vostok ice core temperature reconstructions show that we’re still well below the peak temperature other intra-glacial periods hit before the next ice age kicked in, and the data shows variance much greater than the difference in temperature we’ve measured in the last 100 years, and that variance is over much longer periods. .

A few points of clarification, or maybe “perspective” would be a better word.

The fact that other inter-glacial periods hit higher peak temperatures than we have today might lead someone to conclude that we were due for higher temps all along, and that this is just a natural series of events.

I would first of all ask if you question this basic approximation of CO2 forcing. I hope not, because it’s basic physics, and the present net effects have been fairly well assessed.

Now given the strength of CO2 forcing and understanding that it’s the primary driver of glaciation and its termination, we need to understand that the maximum CO2 levels of interglacials have been around 280 ppm – and never more than 300 ppm – and that the transition from a low of 180 ppm to a high of around 280 takes around ten thousand years, and thousands more to reach equilibrium temperature. We are now at 400 ppm and we’ve achieved that in just a couple of hundred years – the graph looks like this and it’s even worse than that – CO2 is increasing so fast that it’s already outdated even on the rough scale just because it’s six years old.

We’ve increased the atmosphere’s CO2 level more in the past couple of hundred years than natural glacial terminations do in ten thousand years, and moreover, we’ve introduced this increment *on top of * what had been a normal interglacial level of 280 ppm at the beginning of industrialization. Climatically, this puts us in an entirely new climate era never before seen in human history, and indeed never seen before at all since the onset of rapid glaciation at the mid-Pliocene transition 1.2 million years ago, with CO2 levels possibly already the highest in 15 million years and no end in sight.

Hopefully that helps introduce a more realistic perspective. The 100-year trend isn’t the “proof” of what we’re doing to the climate; it’s the first emergent empirical evidence of the consequences of the measured forcings that we know are occurring, and which have a very long way to go to equilibrium even if we stopped all GHG emissions tomorrow.