As we undergo the fourth industrial revolution, companies are uniquely positioned to partner with governments to address some of the world's greatest challenges. Urbanization continues to spread globally, with 70% of the world's population expected to live in cities by 2030. This trend brings with it the urgent need for more efficient use of energy, cleaner energy generation and cost effective energy storage. While the public-sector must lead, it should work closely with the private-sector to rapidly implement best practice policies, programs and projects that will improve urban efficiency and sustainability.

Buildings are responsible for up to a third of greenhouse gas emissions globally. The most cost effective time to reduce energy consumption in buildings is before construction where integrated designs and off-the-shelf building technologies available today can yield up to a fifty percent reduction in energy use and positive returns on investments. For existing buildings, energy efficiency retrofits using these same principles can deliver 15-40 percent savings that pay for themselves over time through energy cost savings.

Best practices for improving building energy efficiency in cities include: 1) adopting and enforcing building codes and appliance standards, 2) setting reduction targets and adopting sustainable construction and leasing policies, 3) establishing retrofit programs for public and private-sector buildings, 4) introducing certification, benchmarking and transparency programs, 5) accepting innovative financial models and programs and 6) coordinating efforts with local utilities. While results are promising, very few cities globally have implemented a comprehensive set of these elements.

To help cities, the World Resources Institute (WRI), the United Nations Environment Programme (UNEP) and the Global Environment Facility announced the expansion of the Building Efficiency Accelerator1 during Paris COP-21. The Building Efficiency Accelerator is a partnership between WRI, the UN Sustainable Energy for All (SE4ALL) initiative and other organizations and industry partners including ICLEI, Global Green Growth Forum, Johnson Controls and Ingersoll-Rand. This program focused on doubling the rate of global energy efficiency improvement emerged from an initial dialog at the 2014 Annual Meeting in Davos.

One early engagement of the Building Efficiency Accelerator is in Mexico City. Mayor Mancera of Mexico City announced at Buildings Day during COP-21 that it plans to integrate building energy performance in local construction codes, retrofitting hospitals with solar hot water and efficiency measures, and auditing and retrofitting municipal buildings. A launch event in March included over 100 participants from city and federal government and the private sector. The engagement is now being supported by four working groups chaired by Mexico City staff and managed by WRI/CTS EMBARQ.

While buildings represent a great opportunity to improve demand-side urban efficiency, district energy systems are seeing a resurgence of interest in urban sustainability on the supply-side. Modern district energy systems provide centralized heating and cooling to urban areas with efficiency gains of up to 80-90 percent over conventional solutions.

Paris initially developed a district heating system in 1927 to reduce air pollution from burning coal. Today, renewables provide over 50% of co-generated heat to the equivalent of 500,000 households. Paris also developed Europe's first and largest district cooling system using water from River Seine while improving energy efficiency by 35 percent.

The UN SE4ALL District Energy Accelerator builds upon the success of the UNEP District Energy in Cities2 initiative which has documented best practices from 65 cities around the world. The District Energy Accelerator includes many institutional and industry partners including ICLEI, UN Habitat, Danfoss and Veolia.

In Dubai, air conditioning represents 70 percent of electricity consumption. The city is developing the world's largest district cooling network which will cut this electricity use in half while also reducing its consumption of fresh water through use of treated sewage effluent. The city of Anshan, China is integrating isolated boilers into their district heating network and capturing waste heat resulting in a 1.2 million ton reduction in annual coal use. Finally, Tokyo is capturing waste heat from buildings and metro stations, heat pumps connected to local water sources and solar thermal energy

Stanford University has implemented an innovative strategy for building energy efficiency and modern district energy technology. Driven by aggressive State of California goals to reduce greenhouse gas emissions and water consumption, the university developed a plan to reduce building energy use up to 30% less than code, increase renewable energy generation to 73 MW, decommission an existing natural gas fired combined heat and power plant and build a new water and energy efficient central energy system3. The new energy system provides 90% of campus heating needs from heat recovery chillers and reduces water consumption by 15%. The design includes chilled and hot water storage systems managed by sophisticated predictive control algorithms that forecast weather conditions, campus energy requirements and energy costs ten days in advance.

Increasing urban efficiency must be a priority for leaders at all levels as we collectively strive to promote the quality of life for city residents and address the great challenges of global climate change, energy security and economic development. A number of global partnerships are helping build capability and capacity through increased collaboration between the public and private sectors. With a record numbers of cities, businesses and institutions making ambitious commitments during Paris COP-21, now is the time to leverage the experience, resources and solutions of the private-sector combined with the leadership of local governments to accelerate action toward urban efficiency and sustainability.

The author is CEO of Johnson Controls.