My review of Broecker and Kunzig’s book Fixing Climate drew attention to the work of Klaus Lackner, a physicist at Columbia University who has been working on ways of scrubbing CO2 out of the atmosphere for sequestration. Lackner considers sequestration the harder problem of the two and believes that the only method adequate in the long-term is mineral sequestration, achieved by hurrying along the natural process geochemical weathering whereby rocks react with CO2, removing it from the air to form limestone and other carbonates.