... but in any case, to aid understanding of the dynamics at...

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    ... but in any case, to aid understanding of the dynamics at play, consider the hypothetical case of an instantaneous doubling of greenhouse gas concentrations. What you would see coinciding with that is an instantaneous decrease in OLR, followed by a gradual increase over many years as the surface and oceans warm up and emit more IR, until finally OLR reaches the same level on average as it was before your GHG increase. In overview, it's a simple energy balance: if the earth emits exactly as much energy as IR as it receives from the sun, temperatures will be static; if it emits less then it will be warming and if it emits more then it will be cooling. So what matters most in determining climate change is not whether OLR is increasing or decreasing per se, but whether it's higher or lower than the rate of incoming radiation. In the former case it'll be going down only if we're emitting at a fast enough rate to be pushing the system further from equilibrium rather than just slowing its return to equilibrium, while it's the latter that actually decides whether we're warming or cooling overall.
 
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