The energy transition to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is one of the greatest challenges facing humanity in the 21st century. Energy use is responsible for over 70% of greenhouse gas emissions that cause climate change. Global energy demand is increasing and nearly a billion people still lack access to electricity, with over 2.5 billion relying on smoky fuels such as wood, charcoal or animal dung to cook. The Paris Agreement to limit climate change and the United Nation's Sustainable Development Goals for 2030 aim for a rapid transition to sustainable energy. Governments use several policies to achieve these goals, such as energy efficiency standards, carbon pricing and a phase-out of fossil fuel subsidies.