There's a fascinating post on the Sustainable Buildings Centre blog that outlines how the world energy community has tended to stop using "energy conservation" and to use "energy efficiency" instead.
According to the blog post, after the 1970s oil crisis, in the framework of the Organization for Economic Co-operation and Development (OECD) the International Energy Agency (IEA) was established by the International Energy Program agreement, which was amended in September 2008. Neither the original agreement or the later revison mention “energy efficiency”, but fo refer to “energy conservation” and the goal of reducing the growth of energy consumption:
exchange of national experiences and information on energy conservation; ways and means for reducing the growth of energy consumption through conservation.
The author of the post then did some research on Google and compiled some fascinating statistics on the number of mentions of the two terms in books indexed by Google. The results showed that the use of "energy conservation" in books increased exponentially in the 1970s, but then dramatically dropped in the early 1980s. "Energy efficiency" on the other hand had a much slower rise in the 1970s, but surpassed "energy conservation" by the middle of the 1980s.
After further research, it turned up that the Shared Goals of the IEA adopted at the IEA Ministers meeting in Paris in June 1993, was the first official mention of “energy efficiency” in the context of the IEA.
Improved energy efficiency can promote both environmental protection and energy security in a cost-effective manner. There are significant opportunities for greater energy efficiency at all stages of the energy cycle from production to consumption. Strong efforts by governments and all energy users are needed to realise these opportunities.
The author of the post notes that ”reducing the growth of energy consumption” disappeared along with "energy conservation". Apparently, the energy community decided to replace the concept of “energy conservation” with “energy efficiency” which as the the author of the post points out is not the same thing. Energy efficiency is the ratio between the energy service delivered and the energy consumed to deliver said service. In other words, doing the same with less. Energy conservation involves reducing overall energy consumption in addition to improving energy efficiency.
This may have to do with the different emissions goals of the developed world and the developing world, principally China, but also India, Brazil, and others, in reducing emissons. China's goal is to reduce its energy intensity, the amount of energy required to produce a unit of GDP, because China will not agree to halt its economic development (China's per capita emissions are much less than the United States) and so its emissions will continue to grow, but not as rapidly. The developed world, especially the EU, has tended to set goals to reduce the absolute level of emissions.