The Keeling curve is a 55-year record of atmospheric CO2 measured at the Mauna Loa site which documents with unbiased accuracy the daily, seasonal and annual change in concentration of critical gaseous components of the atmosphere from a height which is not influenced by surface-level conditions. Budget constraints and limitations have placed continuous operation for this unbroken research record in jeopardy, which can be read about in more depth at the following URL:
http://www.nature.com/news/budget-crunch-hits-keeling-s-curves-1.14206