The international treaty intended to provide a unified response in which the nations of the world would take collective responsibility to reduce global emissions of greenhouse gases is

I believe the answer is Kyto protocol.
Kyoto protocol is an international treaty that enacted in 1992 to address the climate change issues in the world.
One of the solution that they created is to reduce Total emission from each nations with 192 nations are committed to the program.

The Kyoto Protocol was an international treaty intended to unify the world's nations in order to take collective responsibility for climate change to work toward reduce global emission of greenhouse gases.