Achieving energy efficiency across all domains of economic activity is an imperative for climate change mitigation. Energy efficiency can be understood as a wide range of efforts that aim to reduce total energy use without reducing the total amount of energy services provided. While some of these efforts are purely technology-related, others require behavioural change among individuals and entire societies, or even infrastructure investment to facilitate these changes. There are dozens of energy efficiency measures across different sectors. They include: deep energy retrofit of buildings, technical measures that increase the use of excess heat in certain industries, energy efficient lighting technologies, vehicle emission standards, energy efficiency of electric appliances and etc. Each entails different costs and pay-back times, different systemic effects. More variables enter when considering energy efficiency potentials depending on climates and geographies, different national energy mixes, industrial and economic development levels, available infrastructure, financial capabilities of societies.
Although achieving the needed climate change mitigation levels may take more than just energy efficiency measures, but nevertheless energy efficiency plays a key role in the long term goal of building a low-carbon economy. One of the European Union climate change policy aims is to achieve a 20 per cent increase in energy efficiency by 2020.
Energy efficiency is usually discussed in the context of energy security and climate change, but its systemic effects span beyond that. Previously climate stabilization on a global level has been viewed primarily as a gigantic and unaffordable cost to take for the benefit of distant future generations. Now the discourse is changing. In tackling climate change effectively and investing in decarbonization of economies we may also achieve several other objectives. Implemented energy efficiency measures have synergistic effects on the economy, society and the environment. Therefore, energy efficiency policies are part of the recipe in the transition towards a green or low-carbon economy.

The COMBI research project aims to bring some of the usually unseen and unconsidered co-benefits of energy efficiency into the light and to the decision-making table. Some of those anticipated benefits include:
- reduced air pollution emissions and mitigation of negative air pollution effects on ecosystems, human health and built environment;
- social welfare as a result of reduced morbidity and mortality, increase in comfort and increased disposable income for those potentially affected by energy poverty;
- positive effects on energy security via reduced energy imports, effects on energy supply and distribution,
- positive macroeconomic impacts on job creation, public budgets, income;
- reduced energy and material consumption.
This is not a finite list and the COMBI researchers will stay open-minded to any potential additions as well as any negative aspects/outcomes of energy efficiency.
Previously there have been studies assessing the co-benefits of some of the energy efficiency measures in separate countries. The effort of COMBI is wide in geographical and sectoral terms. The geographical scope of the research project is the EU-28, and covers the co-benefits of selected energy efficiency measures in multiple sectors of the economy: residential, commercial, industrial and transport sectors. From methods point of view, this research project is a venture into unknown terrain. Methodologies currently used in similar studies will be reviewed and refined for separate energy efficiency measures. New methodological approaches will be developed to tackle the accounting of multiple benefits stemming from multiple energy efficiency measures. At the end, the project team plans to prepare policy recommendations and to create an on-line visualization tool to present the results to the decision-makers and the wider audience.
The COMBI research consortium includes the University of Manchester (UK), Wuppertal Institute (Germany), Copenhagen Economics (Denmark), University of Antwerp (Belgium) and Advanced Building and Urban Design (Hungary). The University of Manchester holds two work packages in this project – one on air pollution related co-benefits of energy efficiency and another on social welfare related co-benefits of energy efficiency.