payback period, but building‐mounted types may take 20 years or more. For solar photovoltaic, estimates are between five and ten years. Wind turbines require periodic maintenance, although solar operating and maintenance costs are negligible (Carbon Trust, 2012, 8 and 44).

Local government dedication of capital to low carbon assets may appear to impact a small portion of a city’s carbon footprint, but local governments “lead by example,” signaling market opportunities through their analyses and investments (USEPA, 2014, 62). In the US, 58% of green energy purchases have been made by government, yet the capital assets of government and private industry are similar enough to benefit from the same types of carbon reducing improvements (USEPA, 2009, 62). The financial projections of capital, operating, and maintenance costs estimated by governments in the capital investment planning process signal to the community the economic returns possible from various low carbon investments. Businesses may perceive a payback period of more than two or three years to be too long to justify energy saving capital investments, and overcoming this hurdle involves demonstrating how the government achieved returns for the same types of investments. Local government plans that lack the time horizon and metrics necessary to convey the business case for low carbon investment miss this opportunity (Koh et al., 2011, 2050).

# _Measuring carbon to reduce carbon_

Greenhouse gas inventories originated from the need to determine whether or not – and to what extent – anthropogenic emissions contribute to observed patterns of rising global temperature. Having unequivocally served that purpose, greenhouse gas inventories have since become one of several steps governments, commercial entities, and communities may take in order to reverse the causal trend of rising temperature from rising emissions. Emissions are measured today – or in reference to a meaningful point in history, such as the 1990 numbers cited in the Kyoto Protocol – to form a baseline from which local governments and nation‐states can then measure change over time. If local governments can associate changes in emissions over time with specific policy and investment actions, they can begin to manage greenhouse gas emissions.

City networks such as Local Governments for Sustainability (ICLEI) and C40 Cities Climate Leadership Group (C40) are promoting the creation of greenhouse gas emission inventories at the local level. Additionally, many mayors have already signed climate agreements to reduce their city’s carbon footprint based on the merits of climate change science, or to promote the “green” image of their city for branding purposes. Regardless of the catalyzing rationale, the technical information created through these inventories can prove useful to local governments in addressing climate change. Inventories create opportunities to set targets for greenhouse gas reductions, and then help local governments track their progress toward these goals. Capital investment plans are developed at a critical juncture, when determining which investments will be made in infrastructure goods and services, all of which raise implications for carbon emissions. Just as greenhouse gas inventories back‐cast carbon emissions, capital investment plans present opportunities to forecast the carbon emissions anticipated from proposed projects.

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