Ordinarily, wood is a relatively temporary storehouse for carbon. While trees absorb it when growing, they re-release it when they burn or rot. A company called Titan Wood is seeking to enhance the sequestration potential of wood by chemically altering it. In so doing, they increase the span of time for which the carbon will be bound up in a solid form; by making the wood stronger (converting soft woods like pine into a form comparable to tropical hardwoods), they also allow wood to be used in a wider variety of applications, displacing more carbon-intensive building options like concrete, metal, and plastic:

Instead of deforesting tropical rainforests for the highest quality hardwoods, we can essentially make them from trees that grow in northern climates. Wood that is grown via sustainable forestry practices and modified with our acetylation process provides a far more sustainable model for producing high-performance lumber. If the wood is both grown and used locally, so much the better.

Unlike woods treated with existing processes (such as Chromated Copper Arsenate), the resulting material is non-toxic.

In the Netherlands, a heavy traffic road bridge is being constructed from this processed wood (the commercial name for it is Accoya). All the wood being used for the construction is from source-certified sustainable species.

This all strikes me as a neat idea, and a potentially good way to store some carbon in the medium term while transitioning towards more sustainable building materials.