Responsible for an estimated 75 percent of global energy-related carbon dioxide emissions, cities represent the greatest opportunity to combat climate change. The first step for cities to realize their potential is to identify and measure where their emissions come from – you can't reduce what you don't count. The GHG Protocol seeks to provide cities with the standards and tools they need to measure emissions, create more effective emission reduction strategies, set measurable and more ambitious emission reduction targets, and track their progress more accurately and comprehensively. GHG for cities, which is formally known as  Global Protocol for the Inventory of Greenhouse Gas Emissions at the Community Level (GPC).  The GPC provides a robust framework for city-wide accounting and reporting of greenhouse gas emissions. It tries to:

• Help cities develop a comprehensive and robust greenhouse gas inventory to support climate action planning
• Help cities create a baseline year emissions inventory, set reduction targets and track performance
• Ensure consistent and transparent measurement and reporting of greenhouse gas emissions between cities according to internationally recognized principles of accounting and reporting of greenhouse gases
• Enable the aggregation of urban inventories at the subnational and national level
• Showcase the important role cities play in the fight against climate change and facilitate insight by comparing – and aggregating – comparable data (ghgprotocol.org)