This week in Doha, Qatar, world leaders are struggling with how to reduce greenhouse gas emissions fast enough, and in amounts great enough, to protect people from the droughts, food shortages, rising sea levels, and severe weather events that climate change is likely to bring.

Leaders are debating a range of solutions including carbon sequestration and policies and practices to help people prepare for the effects of climate change (“adaptation”). In fact, world leaders have been meeting to discuss possible solutions to climate change for 20 years. Yet the cheapest, cleanest, and fastest resource the world has for reducing greenhouse gas emissions remains vastly underused: energy efficiency.

Energy efficiency means better practices and technological innovations that reduce energy consumption while getting the same or better results. Airtight houses that keep people comfortable. Cities with clean, fast public transit, light bulbs that produce the same amount of light for a fraction of the energy—these practices and technologies have been around for decades, yet they still aren’t the norm. (See results of ACEEE International Scorecard where the highest score awarded for any country was just 67 out of 100.) The question that should concern leaders is, Why?

A new analysis by ECOFYS and commissioned by Philips for the United Nations Climate Change Conference estimates that energy efficiency can generate over a third of the emissions reductions we need by 2020. An ACEEE analysis found that in the United States the potential savings are even greater. Meanwhile, vast amounts of energy are wasted through outdated and inefficient practices while the greenhouse gases emitted by fossil fuels used to power these practices continue to billow into the sky.

If the world is going to address climate change in a meaningful way, world leaders must look beyond present policies that cling to old, outdated practices and technologies and instead adopt policies that will shape a future we all want to live in. Energy efficiency will help us get there.