大氣中的 CO2 濃度是有季節性起伏的，曲線像鋸齒狀 (見網頁的圖)，夏季樹木生長較多使 CO2 濃度減少，冬季則相反，所以不能單從過去幾個月升幅就代表全年平均增加率，不過從整體統計 (過去 50年數據) 而言，CO2 濃度總是有增無減，至2010 年底，平均增幅超過 400 ppm 是可預見的。
網頁有說明 CO2 clock 的 Methodology，即時鐘的跳動以 linear interpolation 方式顯示 (故此冬天時數字跳動比平均率快)，每個月開始時 CO2 clock 會 recalibrated 一次。
Clock Calculation: Continuously updated CO2 concentrations are derived from the montly data points provided by the in situ measurements, and currently are taken as a linear extrapolation of the previous two data points. Clock is recalibrated after the release of each new monthly data point. Future updates will take into account the seasonal trend variations in the forward interpolation (see Keeling curve below). Note that the number of significant digits given is for time lapse effect rather than empirical accuracy.
發表於 2009-11-4 23:18:38
發表於 2009-11-10 02:18:32
發表於 2009-11-11 13:47:00
