From Nick Thomas, Revelstoke, British Columbia, Canada
Michael Marshall reports proposals for converting carbon dioxide into useful products (17 March, p 34). I am sceptical.
Let's start with converting CO2 to synthetic fuel. In reversing the combustion process you need to put in at least as much energy as you once got out. In practice, given inefficiencies, you need far more. You could use renewable energy resources, but there are almost certainly better ways of using them.
And as for making carbonates by reacting CO2 with calcium oxide: this is made by thermal decomposition of carbonates – releasing CO2. Doing this in the cement industry produces …