With time stakeholder pressure on organizations has been increasing to act on climate change. It is a widely recognized fact that government action in itself is not sufficient to deal with carbon change impacts and more so in reversing the temperature rise.
Therefore in addition to compliance mechanism like CDM, other regional ETS and Carbon Tax mechanisms, corporate and individuals are taking it upon themselves to contribute and create tangible impacts in the global fight with Global Warming and Climate Change. Hence the term voluntary as they are not mandated under any law to reduce or neutralize their emissions.
In addition some certification standards like Gold Standard Foundation (GS) and Global Carbon Council (GCC) also map, track, verify and certify additional impacts created by the projects with respect to Sustainable Development Goals (SDGs).