A group of construction managers and real estate specialists at Tsinghua University, in China, has found that the unusually high number of unoccupied residential units in China’s cities is responsible for releasing massive amounts of carbon into the atmosphere.

In their study published in the journal Nature Communications, Hefan Zheng, Rongjie Zhang, XinruYin and JingWu used a variety of tools and techniques to estimate the carbon footprint of the unoccupied buildings and suggest possible ways to mitigate the problem.

Over the past several decades, the Chinese government has been pushing economic growth, leading to massive investments in infrastructure, job opportunities and building construction. One aspect of that growth has been the construction of residential buildings in urban areas to house the workers who have been migrating from rural areas to take advantage of the new opportunities. The problem is that those in the construction business have vastly overestimated the number of workers who will need living space, resulting in extremely low occupancy rates.

Prior research has shown that by 2021, approximately 17% of homes built in cities in China were unoccupied. Some in the field have suggested that the number has only grown since then, to between 20 and 65 million unoccupied units. In this new effort, the research team wondered about the ecological footprint of so many unoccupied homes.

They collected as much data as they could find from traditional sources for 56 major cities covering the year 2020 to 2021, using AI to fill in the blanks. They found that approximately 17.4% of all new residential units built between 2001 and 2018 have never been occupied. The team then attempted to make estimates of the amount of carbon released into the atmosphere due to the empty homes.

They noted such homes have two main sources of emissions. The first is derived from the footprint of the materials used to make them, such as steel and cement. Each square meter, they note, emits hundreds of kilograms of carbon dioxide.

The second source comes from heating and cooling costs. Because most of the residential units are apartment buildings with central heating and cooling, even units that are not occupied are heated and cooled, resulting in massive waste.

The total the team came up with was 55.81 million tons of carbon emissions solely due to the unoccupied housing units, which they note represent approximately 6.9% of China’s total residential emissions.

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