1 Dwalin: Luik at thu way ye stopped thoose orcs 'n' ridduced thu solid granite o' thu toonel entrance tae nought but a molten slaghipp. {translation: Look at the way you stopped those orcs and reduced the solid granite of the tunnel entrance to nothing but a molten slagheap.}
2 Dwalin: We dwarves culd use a wizard the likes o' ye, Kyros, ye ken. {translation: We dwarves could use a wizard like you, Kyros, you know.}
3 Kyros: As a battle mage?
4 Dwalin: Nae. As a smelter. {translation: No. As a smelter.}

Smelting is the process of extracting metal from ore by the use of material containing carbon, such as coal or charcoal, and intense heat. This results in a chemical reaction in which oxygen atoms bound to the metal atoms in the ore transfer to the carbon, to produce carbon dioxide and monoxide gas plus the raw metal. The leftover material from the ore which cannot be converted to metal is called slag.

Dwarves are of course known for their metalworking skills, and would appreciate anyone who can reduce rock to a molten mass.

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2018-09-13 Rerun commentary: Looking at this again now, in the context of carbon dioxide emission and climate change, I started wondering how much carbon dioxide does metal smelting produce?

A quick web search revealed that aluminium is by far the worst offender in terms of CO₂ emissions per unit of smelted metal. The Australian Aluminium Council reports that CO₂ emissions from aluminium smelting have reduced over time with improved efficiency, but tapering off to a level of 15.6 tonnes of CO₂ per tonne of aluminium smelted, as of 2011. The Global Carbon Capture and Storage Institute reports that the value for iron/steel smelting varies from 1.25 to 3.8 tonnes of CO₂ per tonne of iron, depending on country.

Global aluminium production is currently about 5 million tonnes per month. Multiplying gives about 80 million tonnes of CO₂ per month.

However, global steel production is currently about 150 million tonnes per month. Multiplying by let's say 2 gives about 300 million tonnes of CO₂ per month. So steel wins on sheer volume of metal smelted.

Adding a bit more for all the other metals, we're looking at somewhere in the order of 500 million tonnes of CO₂ per month produced globally by the smelting of metal.

The total global CO₂ emission from all human sources is about 3000 million tonnes per month^[1].

So, assuming my references and calculations are correct, this means that metal smelting is responsible for about a sixth of humanity's total CO₂ emissions. That's quite a bit.

[1] The quoted annual value of 9.995 gigatonnes of carbon multiplied by the conversion to CO₂ factor of 3.67 below the table, divided by 12 months.