Climate Crisis

Fossil fuels provide 85% of the world's energy consumption, and the energy system is responsible for 76% of global greenhouse gas emissions. Around 790 million people in developing countries lack access to electricity, and 2.6 billion rely on polluting fuels such as wood or charcoal to cook. Reducing greenhouse gas emissions to levels consistent with the 2015 Paris Agreement will require a system-wide transformation of the way energy is produced, distributed, stored, and consumed.

Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Most definitions of sustainable energy include considerations of environmental aspects such as greenhouse gas emissions and social and economic aspects such as energy poverty.

Renewable energy sources are essential to sustainable energy, as they generally strengthen energy security and emit far fewer greenhouse gases than fossil fuels.

• Hydropower - Hydroelectric plants convert the energy of moving water into electricity. Hydropower is the largest source of renewable electricity while solar and wind energy are growing rapidly. In 2020, hydropower supplied 17% of the world's electricity, down from a high of nearly 20% in the mid-to-late 20th century.
• Solar - In 2019, solar power provided around 3% of global electricity, mostly through solar panels based on photovoltaic cells (PV). Solar PV is expected to be the electricity source with the largest installed capacity worldwide by 2027.
• Wind - Wind has been an important driver of development over millennia, providing mechanical energy for industrial processes, water pumps, and sailing ships. Modern wind turbines are used to generate electricity and provided approximately 6% of global electricity in 2019. Electricity from onshore wind farms is often cheaper than existing coal plants and competitive with natural gas and nuclear. Wind turbines can also be placed offshore, where winds are steadier and stronger than on land but construction and maintenance costs are higher.
• Geothermal - Geothermal energy is produced by tapping into deep underground heat and harnessing it to generate electricity or to heat water and buildings. Power is produced from the steam created in underground reservoirs. Geothermal energy provided less than 1% of global energy consumption in 2020.
• Biomass/Bioenergy - Biomass is renewable organic material that comes from plants and animals. It can either be burned to produce heat and electricity or be converted into biofuels such as biodiesel and ethanol, which can be used to power vehicles.

Non-renewable energy comes from sources that will run out or will not be replenished in our lifetimes—or even in many, many lifetimes. In order to reduce greenhouse gases, and reach our climate goals, we must eliminate burning fossil-fuels, especially coal. However, non-renewable energy sources have many complicated counter-productive characteristics. 

• Natural Gas - Switching from coal to natural gas has advantages in terms of sustainability. Burning natural gas produces around half the emissions of coal when used to generate electricity and around two-thirds the emissions of coal when used to produce heat. Natural gas combustion also produces less air pollution than coal. However, natural gas is a potent greenhouse gas in itself, and leaks during extraction and transportation can negate the advantages of switching away from coal. Switching from coal to natural gas reduces emissions in the short term and thus contributes to climate change mitigation. However, in the long term it does not provide a path to net-zero emissions.
• Nuclear - Nuclear power has been used since the 1950s as a low-carbon source of baseload electricity. Nuclear power plants in over 30 countries generate about 10% of global electricity. As of 2019, nuclear generated over a quarter of all low-carbon energy, making it the second largest source after hydropower. Nuclear power's lifecycle greenhouse gas emissions (including the mining and processing of uranium) are similar to the emissions from renewable energy sources. Nuclear power uses little land per unit of energy produced, compared to the major renewables. Climate change mitigation pathways consistent with ambitious goals typically see an increase in power supply from nuclear. There is controversy over whether nuclear power is sustainable, in part due to concerns around nuclear waste, nuclear weapon proliferation, and accidents. Radioactive nuclear waste must be managed for thousands of years.