This is a guest post by Tom Murphy. Tom is an associate professor of physics at the University of California, San Diego. This post originally appeared on Tom's blog Do the Math.

Ever wonder how efficient it is to heat water? Of course you have! Ever measured it? Whoa, mister, now you’ve gone too far!

I recently devised a laser-phototransistor gauge to monitor my natural gas meter dial—like ya do. As a side benefit, I acquired good data on how much energy goes into various domestic uses of natural gas. Using this, I was able to figure out how much energy it takes to heat water on the stove, cook something in the oven, or heat water for a shower. Together with the knowledge of the heat capacity of water, I can compute heating efficiency from my measurements. What could be more fun? I’ll share the results here, some of which surprised me.

David Cameron describes the economic downturn as "no normal recession" UK Prime Minister David Cameron to party conference, 5th October 2011.

This is the fourth post in the series following the oil price, markets and general health of the global economy examining the simple theory that OECD recession may result from annual average oil price exceeding $100 / bbl.

The annual average price (AAP) of Brent went through $100 on around 16th August 2011 and the AAP stood at $105.3 on 12th October. The AAP high point in the 2008 price spike was $104.8 on 9th October that year.

Below the fold are observations and commentary on debt, economic growth, interest rates, commodities prices and government policy. This is not intended to be quantitative analysis but instead is intended to provide a platform for discussion in the comments.

This is a guest post by Roger Fouquet, Ikerbasque Research Professor at the Basque Center for Climate Change best known for his book Heat, Power, and Light: Revolutions in Energy Services. The post builds upon Fouquet, R. 2011a. Divergences in the Long Run Trends in the Price of Energy and of Energy Services. Review of Environmental Economics and Policy 5(2). 186-218.

His research shows that it is not the price of energy input (depletion) which matters for the economy, but the cost of energy input per unit of output (depletion + technology). Something which seems obvious but is often forgotten in the energy discussion. Also at The Oil Drum we often erroneously talk about effects of the oil price on the economy, and not the cost of an oil or energy service delivered to the economy. The latter not being affected just by energy prices, but by all inputs and the efficiency and cost.

Energy prices have risen considerably since the beginning of the twenty-first century. It is valuable to place these price rises within a historical context. Many peaks preceded the price hike of 2008, and there will, no doubt, be many more. However, if future trends follow past ones, then it is tempting to conclude that the long-run trend in individual and average energy prices will be generally stable or downwards.

This note also highlights the tendency for long-run trends in the price of energy and of energy services to diverge. That is, since the Industrial Revolution, energy efficiency improvements have led the price of energy services to fall far more than the decline in the price of energy. This is an important distinction because commentators have a tendency to focus on energy prices, even though consumers are ultimately interested in the services that energy provide, such as space and water heating or cooling, powering of appliances, illumination and transportation (Goldemberg et al. 1985). This divergence in the long-run has major implications for forecasts of future energy use and carbon dioxide emissions, welfare improvements and the evolution of economies.

This is a guest post by Cameron Murray, an Australian economist who currently works for a regulatory authority. Cameron has a blog that he calls Observations of an Economist Environmentalist.

The word efficiency carries a meaning immersed in all things positive – you never hear that being more efficient could possibly be detrimental. In fact, if you can bear the evangelical fervour, you may have read about achieving ‘Factor Four’ or ‘Factor Five’ gains in energy efficiency, as part of a ‘Natural Capital’ revolution comprising a ‘decoupling’ economic growth from a growth in the consumption of exhaustible resources – also known as ‘sustainability’. You may even have heard about the equation I=PAT or I = P x A x T, where environmental impact (I) is a function of population (P), affluence (A) and technology (T), and that becoming more efficient will enable a desired level of affluence with far less environmental cost.

Historical experience shows that these claims are untrue, and indeed the facts suggest greater energy efficiency is counterproductive to the stated aims of curbing resource use and decreasing negative environmental externalities.