World energy resources and consumption

The remaining world energy resources are large, compared to world energy consumption. To make it easier to compare the numbers, this article uses SI units and prefixes and measures energy rate (or power) in watts (W) and amounts of energy in joules (J).

In 2004, the worldwide energy consumption of the human race was 15 TW (= 1.5 x 1013 W) with 86.5% from burning fossil fuels.[1] This is equivalent to 0.5 ZJ (= 5 x 1020 J) per year, although there is at least 10% uncertainty in the world's energy consumption. Not all of the world's economies track their energy consumption with the same rigor, and the exact energy content of a barrel of oil or a ton of coal will vary with quality.

Most of the world energy resources are from the sun's rays hitting earth - some of that energy has been preserved as fossil energy, some is directly or indirectly usable e.g. via wind, hydro or wave power. The term solar constant is the amount of incoming solar electromagnetic radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays. The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1366 watts per square meter, though it fluctuates by about 6.9% during a year - from 1412 W/m2 in early January to 1321 W/m2 in early July, due to the earth's varying distance from the sun, and by a few parts per thousand from day to day. For the whole Earth, with a cross section of 127,400,000 km², the power is 1.740×1017 W, plus or minus 3.5%.

By comparing this contribution by the sun to that contributed by human energy consumption, it can be readily understood that the direct human contribution to earth's heating is a very small fraction: the ratio of 1.5×1013 watts / 1.740×1017 watts is less than 1/10,000th (0.01%). Direct heating of the earth by humans is thus negligible. The earth has been warming recently, however, and mankind's contribution is understandably under close review. Global warming theories that do focus on mankind's contribution point towards the important side-effects of human energy consumption, such as greenhouse gases added to the earth's atmosphere.

The remaining worldwide energy resources are large, with the remaining fossil fuels totaling an estimated 0.4 YJ (1 YJ = 1024J) and the available nuclear fuel such as uranium exceeding 2.5 YJ. Fossil fuel range from 0.6-3 YJ if estimates of reserves of methane clathrates are accurate and become technically extractable. Mostly thanks to the Sun, the world also has a renewable usable energy flux that exceeds 120 PW (8,000 times 2004 total usage), or 3.8 YJ/yr, dwarfing all non-renewable resources. Even that amount is also only a minute amount of the sun's total energy output, due to the small solid angle the earth's outline makes with the sun.