This year marks the first-ever Buildings Day at the annual climate talks. At COP21 in Paris, leaders from around the world and all sectors will launch a new Global Alliance for Buildings and Construction and discuss how to transform the buildings sector to become part of the low-carbon urban economy of the future. One-third of global greenhouse gas emissions are due to energy use in buildings, and building-related emissions are expected to double or even triple by 2050 without action.

In part, this is due to rapid urbanization: We are adding 250,000 people to our cities each day. In India alone, more than half of the buildings that will exist in 2030 did not exist in 2010. Unless we are deliberate in the way we design, construct and renovate buildings, we could lock-in our cities to inefficient energy use for decades to come. Energy waste by buildings burdens our citizens with higher energy bills, air pollution and carbon emissions.

What’s the challenge? We must act now, yet most countries have not focused on energy waste by buildings. A review of building efficiency in countries’ national climate plans (known as INDCs) finds fewer than 50 countries provided details on how they would tackle building energy efficiency. It’s time to turn our attention not only to the important issues of energy supply, but also to the equally critical need to ensure that every kilowatt hour delivered is used efficiently. Energy waste in buildings is something no country or city can afford.

The IEA estimates that an additional $220 billion is needed by 2020 – an almost 50 percentincrease on 2014 investment in energy efficient buildings.

The good news? We have options. Technologies and practices commercially available today can shift our emissions trajectory.

Global change on building efficiency requires local action and a broad coalition of city regulators, businesses and financing institutions. From Bogota to Bangkok, cities are poised to move forward. ICLEI’s recent review of the commitments made by 608 subnational jurisdictions in the carbonn® Climate Registry found that roughly half of the 1,293 commitments are supported by actions in the building sector. To speed and scale action, cities are reaching out seeking technical support, looking for trusted advisors and working with the private sector to deliver change.

In support of this agenda, The Global Environment Facility, in partnership with the World Resources Institute (WRI) and the UN Environment Programme (UNEP), announced today the expansion of the Building Efficiency Accelerator (BEA). This commitment of new funding will catalyze an increase in energy efficient buildings in developing country cities.

The BEA is working in partnership with the UN Sustainable Energy for All Energy Efficiency Platform and the Global Alliance for Buildings and Construction. It will engage 50 cities on issues of policy implementation, most importantly building codes, but also project development, and tracking and monitoring of building efficiency. Of those, six cities will work with the partnership in a more intensive, multi-stakeholder process to help align policies and markets. Interventions will focus on codes and standards; targets; certifications; financial mechanisms; government leadership; and benchmarking and disclosure.

Each of the 30 cities that joins the Building Efficiency Accelerator will:

1) Commit to implement a new policy or update existing policies; 2) Undertake a project such as retrofits or construction of efficient new buildings; and 3) Measure and communicate its progress against energy and climate goals.

Mayor Mancera of Mexico City, for example, announced at Buildings Day that it is moving forward to integrate building energy performance in local construction codes, retrofitting hospitals with solar hot water and efficiency measures, and auditing and retrofitting municipal buildings. More than 100 stakeholders have participated in WRI Ross Center for Sustainable Cities’ workshops and working groups to provide input and recommendations on how to implement local codes and advance retrofits. The goal? To help meet their ambitious climate targets and improve the performance and competitiveness of the city.

We are proud these activities will support the new Global Alliance for Buildings and Construction as we shine a spotlight on the potential for real change that can help improve buildings and the lives of people in cities around the world.

How we plan and design our future cities can have major impacts. This is an important reason why the GEF recently launched a $1.5 billion sustainable cities project to support city planning, initially in 23 cities in 11 developing countries.

With the build-out of our cities we must act now to create a culture of urban efficiency around the world.