loop to form what has been called a
virtuous cycle—the opposite of a
vicious cycle. For example, as more and more solar modules are deployed, prices fall because of the
economies of scale, allowing the technology to become cost-competitive in new applications that in turn increase demand for more deployment.
Decarbonisation of the global energy system The emissions reductions necessary to keep global warming below 2°C will require a system-wide transformation of the way energy is produced, distributed, stored, and consumed. For a society to replace one form of energy with another, multiple technologies and behaviours in the energy system must change. For example, transitioning from oil to solar power as the energy source for cars requires the generation of solar electricity, modifications to the electrical grid to accommodate fluctuations in solar panel output or the introduction of variable battery chargers and higher overall demand, adoption of
electric cars, and networks of
electric vehicle charging facilities and repair shops. Many climate change mitigation pathways envision three main aspects of a low-carbon energy system: • The use of low-emission energy sources to produce electricity •
Electrification – that is increased use of electricity instead of directly burning fossil fuels • Accelerated adoption of energy efficiency measures Some energy-intensive technologies and processes are difficult to electrify, including aviation, shipping, and steelmaking. There are several options for reducing the emissions from these sectors: biofuels and synthetic
carbon-neutral fuels can power many vehicles that are designed to burn fossil fuels, however biofuels cannot be sustainably produced in the quantities needed and synthetic fuels are currently very expensive. For some applications, the most prominent alternative to electrification is to develop a system based on sustainably-produced
hydrogen fuel. Technologies that are relatively immature include batteries and processes to create carbon-neutral fuels. Developing new technologies requires research and development,
demonstration, and
cost reductions via deployment. The transition to a zero-carbon energy system will bring strong
co-benefits for human health: The World Health Organization estimates that efforts to limit global warming to 1.5 °C could save millions of lives each year from reductions to air pollution alone. With good planning and management, pathways exist to provide universal
access to electricity and
clean cooking by 2030 in ways that are consistent with climate goals. Historically, several countries have made rapid economic gains through coal usage. However, there remains a window of opportunity for many poor countries and regions to "
leapfrog" fossil fuel dependency by developing their energy systems based on renewables, given adequate international investment and knowledge transfer.
Integrating variable energy sources , Germany, produce more energy than they consume. They incorporate rooftop solar panels and are built for maximum energy efficiency. To deliver reliable electricity from
variable renewable energy sources such as wind and solar, electrical power systems require flexibility. Most
electrical grids were constructed for non-intermittent energy sources such as coal-fired power plants. As larger amounts of solar and wind energy are integrated into the grid, changes have to be made to the energy system to ensure that the supply of electricity is matched to demand. In 2019, these sources generated 8.5% of worldwide electricity, a share that has grown rapidly. Building overcapacity for wind and solar generation can help ensure that enough electricity is produced even during poor weather. In optimal weather, energy generation may have to be
curtailed if excess electricity cannot be used or stored. The final demand-supply mismatch may be covered by using
dispatchable energy sources such as hydropower, bioenergy, or natural gas.
Energy storage Energy storage helps overcome barriers to intermittent renewable energy and is an important aspect of a sustainable energy system. The most commonly used and available storage method is
pumped-storage hydroelectricity, which requires locations with large differences in height and access to water. Batteries typically store electricity for short periods; research is ongoing into technology with sufficient capacity to last through seasons. Pumped hydro storage and
power-to-gas (converting electricity to gas and back) with capacity for multi-month usage has been implemented in some locations. According to the International Energy Agency (IEA), global battery storage capacity is expected to increase nearly 15-fold between 2021 and 2030, driven by falling costs and increased investment in clean infrastructure.
Electrification . In contrast to oil and gas boilers, they use electricity and are highly efficient. As such, electrification of heating can significantly reduce emissions. Compared to the rest of the energy system, emissions can be reduced much faster in the electricity sector. As of 2019, 37% of global electricity is produced from low-carbon sources (renewables and nuclear energy). Fossil fuels, primarily coal, produce the rest of the electricity supply. One of the easiest and fastest ways to reduce greenhouse gas emissions is to phase out coal-fired power plants and increase renewable electricity generation. Climate change mitigation pathways envision extensive electrification—the use of electricity as a substitute for the direct burning of fossil fuels for heating buildings and for transport. Ambitious climate policy would see a doubling of energy share consumed as electricity by 2050, from 20% in 2020. One of the challenges in providing universal access to electricity is distributing power to rural areas. Off-grid and
mini-grid systems based on renewable energy, such as small solar PV installations that generate and store enough electricity for a village, are important solutions. Wider access to reliable electricity would lead to less use of
kerosene lighting and diesel generators, which are currently common in the developing world. Infrastructure for generating and storing renewable electricity requires minerals and metals, such as
cobalt and
lithium for batteries and
copper for solar panels. Recycling can meet some of this demand if product lifecycles are well-designed, however achieving net zero emissions would still require major increases in mining for 17 types of metals and minerals. Most of the world's cobalt, for instance, is
mined in the Democratic Republic of the Congo, a politically unstable region where mining is often associated with human rights risks.
Hydrogen Hydrogen gas is widely discussed as a fuel with potential to reduce greenhouse gas emissions. This requires hydrogen to be produced cleanly, in quantities to supply in sectors and applications where cheaper and more energy efficient
mitigation alternatives are limited. These applications include heavy industry and long-distance transport. Hydrogen can be deployed as an energy source in
fuel cells to produce electricity, or via combustion to generate heat. When hydrogen is consumed in fuel cells, the only emission at the point of use is water vapour. The main method of producing hydrogen is
steam methane reforming, in which hydrogen is produced from a chemical reaction between steam and
methane, the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. While carbon capture and storage (CCS) could remove a large fraction of these emissions, the overall carbon footprint of hydrogen from natural gas is difficult to assess , in part because of emissions (including
vented and
fugitive methane) created in the production of the natural gas itself. Electricity can be used to split water molecules, producing sustainable hydrogen provided the electricity was generated sustainably. However, this
electrolysis process is currently more expensive than creating hydrogen from methane without CCS and the efficiency of energy conversion is inherently low. Hydrogen can be produced when there is a surplus of
variable renewable electricity, then stored and used to generate heat or to re-generate electricity. It can be further transformed into liquid fuels such as
green ammonia and
green methanol. Innovation in
hydrogen electrolysers could make large-scale production of hydrogen from electricity
more cost-competitive. Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonisation of industry alongside other technologies, such as
electric arc furnaces for steelmaking. For steelmaking, hydrogen can function as a clean fuel and simultaneously as a low-carbon catalyst replacing coal-derived
coke. Hydrogen used to decarbonise transportation is likely to find its largest applications in shipping, aviation and to a lesser extent heavy goods vehicles. For light duty vehicles including passenger cars, hydrogen is far behind other
alternative fuel vehicles, especially compared with the rate of adoption of
battery electric vehicles, and may not play a significant role in future. Disadvantages of hydrogen as a fuel include high costs of storage and distribution due to hydrogen's explosivity, its large volume compared to other fuels, and its tendency to make pipes brittle. Transport accounts for 14% of global greenhouse gas emissions, but there are multiple ways to make transport more sustainable.
Public transport typically emits fewer greenhouse gases per passenger than personal vehicles, since trains and buses can carry many more passengers at once. Short-distance flights can be replaced by
high-speed rail, which is more efficient, especially when electrified. Promoting non-motorised transport such as walking and cycling, particularly in cities, can make transport cleaner and healthier. The
energy efficiency of cars has increased over time, but shifting to
electric vehicles is an important further step towards decarbonising transport and reducing air pollution. A large proportion of traffic-related air pollution consists of particulate matter from road dust and the wearing-down of tyres and brake pads. Substantially reducing pollution from these
non-tailpipe sources cannot be achieved by electrification; it requires measures such as making vehicles lighter and driving them less. Light-duty cars in particular are a prime candidate for decarbonization using
battery technology. 25% of the world's Carbon dioxide| emissions still originate from the transportation sector. Long-distance freight transport and aviation are difficult sectors to electrify with current technologies, mostly because of the weight of
batteries needed for long-distance travel, battery recharging times, and limited battery lifespans.
Hydrogen vehicles may be an option for larger vehicles such as lorries. Many of the techniques needed to lower emissions from shipping and aviation are still early in their development, with
ammonia (produced from hydrogen) a promising candidate for shipping fuel.
Aviation biofuel may be one of the better uses of bioenergy if emissions are captured and stored during manufacture of the fuel.
Buildings Over one-third of energy use is in buildings and their construction. To heat buildings, alternatives to burning fossil fuels and biomass include electrification through
heat pumps or
electric heaters,
geothermal energy,
central solar heating, reuse of
waste heat, and
seasonal thermal energy storage. Heat pumps provide both heat and air conditioning through a single appliance. The IEA estimates heat pumps could provide over 90% of space and water heating requirements globally. A highly efficient way to heat buildings is through
district heating, in which heat is generated in a centralized location and then distributed to multiple buildings through
insulated pipes. Traditionally, most district heating systems have used fossil fuels, but
modern and
cold district heating systems are designed to use high shares of renewable energy. features, such as these
windcatcher towers in Iran, bring cool air into buildings without any use of energy.Cooling of buildings can be made more efficient through
passive building design, planning that minimizes the
urban heat island effect, and
district cooling systems that cool multiple buildings with piped cold water.
Air conditioning requires large amounts of electricity and is not always affordable for poorer households.
Cooking are one of the most energy-efficient and safest options.In developing countries where populations suffer from
energy poverty, polluting fuels such as wood or animal dung are often used for cooking. Cooking with these fuels is generally unsustainable, because they release harmful smoke and because harvesting wood can lead to forest degradation. The universal adoption of clean cooking facilities, which are already ubiquitous in rich countries, would dramatically improve health and have minimal negative effects on climate. Clean cooking facilities, e.g. cooking facilities that produce less indoor soot, typically use natural gas,
liquefied petroleum gas (both of which consume oxygen and produce carbon-dioxide) or electricity as the energy source; biogas systems are a promising alternative in some contexts.
Improved cookstoves that burn biomass more efficiently than traditional stoves are an interim solution where transitioning to clean cooking systems is difficult.
Industry Over one-third of energy use is by industry. Most of that energy is deployed in thermal processes: generating heat, drying, and
refrigeration. The share of renewable energy in industry was 14.5% in 2017—mostly low-temperature heat supplied by bioenergy and electricity. The most energy-intensive activities in industry have the lowest shares of renewable energy, as they face limitations in generating heat at temperatures over . For some industrial processes, commercialisation of technologies that have not yet been built or operated at full scale will be needed to eliminate greenhouse gas emissions.
Steelmaking, for instance, is difficult to electrify because it traditionally uses
coke, which is derived from coal, both to create very high-temperature heat and as an ingredient in the steel itself. The production of plastic, cement, and fertilisers also requires significant amounts of energy, with limited possibilities available to decarbonise. A switch to a
circular economy would make industry more sustainable as it involves recycling more and thereby using less energy compared to investing energy to mine and refine new
raw materials. ==Government policies==