Peak oil means the maximum level of production that will ever be reached. Peak oil does not cause any decline, it's rather being past it that necessarily means experiencing a decline from that peak level.

Now, maybe your question was if the decline will be due to climate change or to scarcity. At the moment, I'd say hardly any decline can be attributed to climate change fighting, except in countries that have either heavily taxed carbon emission (Sweden), or strongly subsidised alternative energy production.

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi

A rule of thumb would be to look at the price spikes (ex taxes) indicating oil shocks. If we have many such price spikes, we are supply-constrained (that is, production is dropping because we cannot get more oil out of the ground). If we have few such price spikes, we are demand-constrained (that is, production is dropping because people are not allowed to consume as much oil due to global warming regulations).

An individual spike may be put down to speculators, but when you have five or ten in the space of a decade and a half, it's a trend.

- Jake

If you only spend 20 minutes of the rest of your life on economics, go spend them here.