One of the critical arguments natural gas proponents make in its favor is that it is a "bridge fuel", helping our economy to transition from a carbon-intensive energy system to one much lighter on greenhouse-gas emissions. This notion remains controversial, and the subject of fierce debate.

John Vechey of PopCap Games recently joined The Motley Fool for a climate change summit. Among his guests were Stu Dalheim, vice president of shareholder advocacy at Calvert Investments, and Todd Larsen, director of corporate responsibility for Green America. In the video below, Dalheim and Larsen field a question from Motley Fool co-founder David Gardner on the merits of natural gas as a bridge fuel.

Dalheim mentions a shareholder resolution that Calvert filed with Pioneer Natural Resources (NYSE:PXD). The language on Pioneer's proxy ballot reads:

Shareholders request that Pioneer Natural Resources Company issue a report to shareholders, using quantitative and qualitative measures to describe how the Company manages the environmental and social challenges and opportunities associated with well stimulation that employs hydraulic fracturing. The report should be available by December 1, 2013, be prepared at reasonable cost, and omit proprietary information.

The votes have since come in on that resolution: It garnered a whopping 41.74% support, which is quite high. Clearly shareholders are mobilizing around this issue. Watch the video below to hear two experts' views.