Energy efficiency contributes to cleaner production, reduction in carbon dioxide emission, reduction in ecological footprint, sustainable development, reduce energy poverty and increase access to quality energy.

The following are a group of possible impact of energy efficiency on the populations and on the environment:

•Health and well-being impacts. This mainly relates to the public health improvements observed as a result of improved heating and cooling of buildings and air quality from more efficient transport and power generation and less demand for both.

•Poverty alleviation: Energy affordability and access. As energy demand and bills are reduced for the poor, these households have the ability to acquire more and better energy services, as well as free up income to spend on satisfying other critical needs. In addition, as utilities (notably in developing countries) improve their supply‐side efficiency, they can provide more electricity to more households, thereby supporting increased access initiatives which is often an important stated objective of supply‐side energy efficiency activities in developing countries.

•Increased disposable income. Across all income levels, when energy efficiency improves, reduced energy bills provide increased disposable income for households, individuals, and enterprises. The effect of increased spending and investment can in turn result in positive macroeconomic effects.

•Industrial productivity and competitiveness. Benefits for industrial firms from improvements in energy efficiency improvements include reductions in resource use and pollution, improved production and capacity utilization, and less operating and maintenance, which leads to improved productivity and competitiveness.

•Energy provider and infrastructure benefits. Improved energy efficiency can help energy providers provide better energy services for their customers, reducing operating costs and improving profit margins.

•Increased asset values. There is evidence that investors are willing to pay a rental and sales premium for property with better energy performance. Some values of this premium have been estimated for commercial property.

•Job creation. Investment in energy efficiency and the increased disposable income can lead to direct and indirect job creation in energy and other sectors. This makes energy efficiency important part of governments’ green growth strategies.

•Reduced energy‐related public expenditures. The public budgetary position can be improved through lower expenditures on energy in the public sector (including by government agencies on energy consumption and state‐owned utilities on fuel purchases). In countries where fuels are imported there is a related likely positive impact on currency reserves, and in energy‐exporting countries domestic energy efficiency can free up more fuels for export. In addition, for countries with energy consumption subsidies, reduced consumption means lowered government budgetary outlays to finance these subsidies.

•Energy security. Improvements in energy efficiency leading to reduced demand for energy can improve the security of energy systems across the four dimensions of risk: fuel availability (geological), accessibility (geopolitical), affordability (economic) and acceptability (environmental and social).

•Macroeconomic effects. Energy efficiency can have positive macroeconomic impacts, including increases in GDP, and the cumulative benefits of the above‐mentioned impacts of improved trade balance (for fuel importing countries), national competitiveness, and employment support. These are mainly indirect effects resulting from increased consumer spending and economy‐wide investment in energy efficiency, as well as from lower energy expenditures.

•Reduced GHG emissions. Greenhouse gas (GHG) emissions are reduced when energy efficiency improvements result in reduced demand for fossil fuel energy. Many climate change mitigation strategies put energy efficiency measures at their core as the most cost‐effective way to reduce greenhouse gas emissions.

•Moderating energy prices. If energy demand is reduced significantly across several markets, energy prices can be reduced, particularly relative to the impact of the counter‐factual of increased energy demand. This can have implications on economic competitiveness of countries, and, for individuals across borders, improves the affordability of energy services and the availability of resources for other expenditures.

•Natural resource management. At an aggregated international level, less demand can reduce pressure on resources, with potential beneficial impacts on prices (at least for importing countries), as well as overall resource management. For example, in the context of peak oil and related supply constraints, energy efficiency can help to relieve pressure on a scarce resource. Similarly, expanding demand for oil etc., is pushing industry to increasingly challenging contexts for extraction (such as deep off‐shore and shale oil extraction), with related incremental investment costs and technological and environmental uncertainties.

•Development goals. Improved energy efficiency is important in achieving economic and social goals in developing countries, including improved access to energy services, eradicating poverty, improving environmental sustainability, and economic development. Advancing development in these countries in a sustainable way is a shared international goal with benefits for developing countries themselves and for OECD countries alike.

as long as the new energy is not available... the only way to improve our environment is by efficient use of energy.

The overall impact depends on the dynamics of consumption following the increase of efficiency, that is the rebound effect. When consumption is highly sensitive to changes in the energy price, you may expect that an increase of efficiency does not reduce the consumption of energy (as in the history of lighting technologies), but simply produces an increase in energy applications. When the demand is close to saturation, energy efficiency may be expected to reduce the consumption of energy. 

That is about the impacts on environment. Other respondents have focused on the impacts on economy, innovation, and society as well.

In terms of sustainability, the consideration depends on your ideological position. The followers of the weak sustainability consider increasing efficiency per se a positive driver for sustainability. The followers of the strong sustainability focus on the dynamics of consumption, so energy efficiency can be positive, neutral or negative (e.g. the case of diverting resources from other potential uses) for sustainability.

Article The impact of a stimulus to energy efficiency on the economy...

energy efficiency can reduce the co2 emission and climate change.