From the school strikes for climate , to Extinction Rebellion protests and calls for a Green New Deal , citizens around the world are putting pressure on their governments to prevent global warming more than 2°C above pre-industrial levels.

In the U.K., these efforts have met with some success—the government has declared a “climate emergency” and promised to reduce greenhouse gas emissions to net zero by 2050. Even so, scepticism persists in some quarters: the chancellor of the exchequer, Philip Hammond, has argued that the U.K. government’s goal may be unaffordable, based on estimates that the transition to a zero-carbon economy could cost up to £1 trillion.

Of course, there is likely to be significant public money spent on renewable energy transition and carbon offsetting. The costs of assets made obsolete by climate change policy—such as unexploited fossil fuel reserves—is also potentially huge.

But the problem with perspectives like Hammond’s is that they don’t balance the cost of acting now against the cost of doing nothing. In the U.K. and around the world, people live and work in buildings that are typically powered, heated and cooled using energy from fossil fuels. If these buildings are not retrofitted with energy efficiency measures, there is a real risk they will be rendered obsolete by policies aimed at reducing greenhouse emissions.

A valuable asset

Research at Northumbria University has examined this situation in relation to international real estate. The global value of real estate is estimated at US$217 trillion—that’s roughly 2.7 times the GDP of the entire world. Of this, $162 trillion worth is residential, $29 trillion worth is commercial and $26 trillion worth is agricultural land.

A conservative estimate is that global real estate consumes 40% of global energy annually and accounts for more than 20% of international carbon emissions. So it’s hardly surprising that international agencies have identified real estate and the built environment as key contributors toward global warming and a major target of international efforts to reduce greenhouse gas emissions.

One of the most comprehensive approaches to reducing building energy use can be seen in the European Union (EU). A 2010 directive on energy performance made it mandatory for all European properties to hold an energy performance certificate and monitor energy use from heating and air conditioning. The government of England and Wales has used these energy performance certificates to enforce minimum standards of energy efficiency for privately rented family homes and commercial properties.