Why the cause of global warming doesn't matter

A lot of debate has come from the debate about the source of global warming. It primarily boils down to every scientist that reviews the evidence comes to the conclusion that global warming is a man made phenomenon. The main exceptions are those scientists on the payroll of businesses with an interest in the public believing otherwise. This is not universally true, as a number of scientists not connected with oil companies have come forward and voiced their skepticism. However, I posit that when it comes to planning our future, the cause of global warming is immeterial.
To begin, let's posit that global warming is caused by human activity, namely the release of the so called greenhouse gases into the atmosphere. The corrective action to this would be to reduce the amount of greenhouse gases that we emit. Indeed, we should go further and try to reverse the damage already caused by to repopulate the plant and tree population on our planet.
So let's posit that global warming is part of the natural trends of heating up and cooling down. Would that mean we no longer have to worry about the pollution we are producing? Absolutely not! Our current life style still needs to be changed for other reasons. There is no debate surrounding whether or not we are the cause of mass extinction, the pollutions of our waterways and ocean in ways that threatens our food and water supply, without which we cannot survive as a species. It is also a fact that the availability of oil is limited. Sooner or later we must find an alternative energy source.
The green movement does not need a belief in man made global warming to have legitimacy. Man made global warming is only one part of the green argument, a part that can be easily removed without compromising its legitimacy.