I don’t agree fully with your premise of an economic downturn leading to significantly less energy consumption. There will be a reduction in gas usage as people stay at home more often, or try to save money either on gas/heating/hydro, but people will be using more energy at their homes playing on computers or game systems, watching movies, cooking at home, having fires in their fireplaces (wood burning ones do pollute a bit), etc. Laureth brings up great points as well. And of course cows farting really does contribute a non-significant amount of pollution.
Energy could be reduced by businesses going out of business, but then China might build new and more polluting factories to replace those, equaling out to more pollution overall.
Plus, the economic situation has not really surfaced yet, let alone in countries other than America.