I'd say a refillable lighter using butane would be close to ideal. Use some old newspapers to help set the wood to fire, instead of trying to ignite wood directly with a lighter. If it runs out of butane, refill it. If it breaks, dispose of it properly. Some might suggest that butane is made from non-renewable resources. That's not an issue. The lighter is used only for starting a fire, with the fire itself using some other fuels like wood, that are ideally sustainable and renewable.
If you absolutely loathe plastic and butane because they are made from non-renewable resources, I have some good news for you:
- Butane can be made from trees
- Even plastics can be made from trees!
The little amount of plastics and butane needed is so trivial that if every lighter made in this planet was made from trees, the amount of forest used would be minuscule. (In comparison, if all gasoline and diesel used in cars and heavy trucks was made from trees, we would soon run out of forest.)
Unfortunately, you cannot purchase butane or plastics made from trees today, because the demand for such a niche product would be low in bulk quantities, and even lower when specifically used to make lighters. So I don't think we'll soon see 100% eco-friendly lighters that use only butane and plastics made from sustainably managed forests.
I'd say the environmental impact of fire is mainly caused by:
- The fuel being used, is it sustainable, is it renewable?
- The particulate matter produced by the fire that can actually be a real issue in densely populated areas even if the fuel is sustainable and renewable
Just consider how much wood a fire needs, and how little butane is used by the lighter.
If you want to minimize the environmental impacts of you starting a fire, turn your attention to the main fuel of the fire and forget the environmental impact of the fire-starting method.