It is not at all trivial to make precise measurements of greenhouse gas concentrations in the atmosphere, but exactly this is needed when assessing climate change impacts from human emissions. Only when present concentrations are known as accurately as possible can long-term trends be identified and seasonal variability be studied. The three most important greenhouse gases in the atmosphere are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Several clean air measuring stations around the world, with Mauna Loa the most well known, form a global network to monitor atmospheric concentrations. One of these stations is Baring Head, close to Wellington in New Zealand....