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Carbon & CO2

Emissions values are usually given in tonnes of carbon dioxide, but occasionally a value is given in tonnes of carbon (the giveaway is that the value looks surprisingly small). To convert a mass of carbon to carbon dioxide multiple by 3.67.

How is this number derived?

The atomic mass of carbon is 12. The atomic mass of oxygen is 16.
The ratio of CO2 to C is therefore 44/12 (1 × 12 + 2 × 16 / 12) or ~3.67.
To calculate the mass of CO2 released by burning a particular fossil fuel it is necessary to know how much carbon it contains. The additional mass comes from the oxygen.



Peat is an accumulation of partially decayed vegetation or organic matter. The IPCC classifies peat as neither a fossil fuel nor a renewable fuel, and notes that its emission characteristics are similar to fossil fuels. Wikipedia


The formation of coal takes a significant amount of time (on the order of a few million years), and the first coal-bearing rock units appeared about 290-360 million years ago, at a time known as the Carboniferous or "coal-bearing" Period. As well, there are extensive coal deposits from the Cretaceous age - about 65 to 144 million years ago. Energy Education: coal formation

Oil & Gas

70% of oil deposits existing today were formed in the Mesozoic age (252 to 66 million years ago), 20% were formed in the Cenozoic age (65 million years ago), and only 10% were formed in the Paleozoic age (541 to 252 million years ago). This is likely because the Mesozoic age was marked by a tropical climate, with large amounts of plankton in the ocean. Energy Education: oil formation


Geologic time

Paleozoic Era541-252 myaAncient life
Carboniferous Period359-299 myaIts coal beds powered the Industrial Revolution
Mesozoic Era252-66 myaAge of Reptiles and the Age of Conifers
Cretaceous Period145-66 myaFurther coal beds laid down
Cenozoic Era66 mya - presentAge of Mammals
Holocene epoch11.65 kyaInterglacial period

Human time

A rough, and disputed timeline of human evolution.

Hominini tribe separates from Gorillini8-9 myaHumans, Australopithecus, and chimpanzees separate from gorillas
Separation of the subtribes Hominina and Panina2.3-1.6 myaHumans and extinct biped ancestors separate from chimpanzees
Homo habilis4-7 myaHuman ancestor or related species
Homo erectus2 myaExtinct species of archaic human
Earliest use of fire1 myaWonderwerk Cave, South Africa
Earliest evidence of cooking.5 myaBy Homo erectus
Last Glacial Maximum (LGM)120 kyaIce sheets at their greatest extent
Younger Dryas11.7-12.9 kyaTemporary reversal of climactic warming since LGM
Holocene epoch11.65 kyaInterglacial period
First domestication of livestock10-11 kyaFertile Crescent
Domestication of cereal crops11 kyaFertile Crescent
James Watt patents his steam engine design1769Catalyses The Industrial Revolution


Emissions since when?

The IPCC calculates the rise in the global mean surface temperature (GMST) from the beginning of large-scale industrial activity. Their reference period (PDF) is 1850-1900.
Industrialisation had begun before this date, primarily in England (78% of global emissions). Dates for the Industrial Revolution in Europe and the United States are typically given as starting in 1760, and ending in 1820, or 1840, but emissions were low by comparison to today, just 4.96 billion tonnes, and were localised. Prior to this period humans had been burning wood, coal, and clearing land, but emissions were comparatively insignificant.

Cumulative emissions

YearCumulative emissions (billions of tonnes)

In 1850 cumulative global emissions were around 0.3% of what they are today.

Fuel emissions

FuelEmis­sions kgCO2/kWhEmis­sions kgCO2/GJ
Anthracite (hard coal)0.3494.6
Crude oil0.26
Natural gas0.2



SI Units: Quick reference

Energy density

You can start explaining some of the limits and possibilities of everyday life or historical progress by playing with energy densities: the more concentrated sources of energy give you many great advantages in terms of their extraction, portability, transportation and storage costs, and conversion options. Vaclav Smil (PDF)

FuelEnergy density MJ/kgEnergy density
Solar1.5 microjoules/m3
Wind0.5-50 J/m3
Lithium-ion battery0.79220-260 Wh/kg
Crude oil4435-45,000 MJ/m3
Gasoline4646 MJ/m3
Natural gas5535 MJ/m3
Hydrogen1430.01 MJ/m3
Nuclear (uranium-235)3,900,000
*Solar energy has a density over twenty quadrillion times less than oil

Power density

Power sourcePower density W/m2 range*Power density W/m2 median+
Solar PV4-96.6
Solar CSP4-109.7
Natural gas200-2,000482.1


There are numerous definitions for the value of horsepower; one metric measure is defined as,
The power needed to lift 75 kilograms by 1 metre in 1 second.
Comparing horses and humans,
A horse can reach a peak of ~11kW over a period of a few seconds.
A human can reach a peak of ~1kW over a period of a few seconds.
Over time,
A horse can perform sustained activity at a work rate of about 0.75kW.
A human can perform sustained activity at a work rate of about 0.075kW.
Everyday power requirements,
A toaster uses in the range of .8 to 1.5kW of energy.
An ordinary family salon has ~120 horsepower, and an SUV ~200 horsepower.

Human power

2000 Calories / 1 day × 1 day / 24 hours × 60 minutes × 60 seconds × 4184 Joules / 1 Calories = 96.85 J/second = 96.85W ≈ 100W


Photosynthesis is an inherently inefficient energy conversion process, and production of biomass has large space requirements. Even with an intensively cultivated plantation of fast-growing trees, a wood-burning electricity generation plant would not have power densities higher than 0.6 W/m2, and for most operations the rate would be below 0.5 W/m2. Space demand for such facilities, then, would be two to three orders of magnitude (100 to 1,000 times) greater than for coal- or gas-fired electricity generation.