There may well be problems with my method for predicting Jan 2015. However, your method seems to ignore the latest data and tries to predict a whole year ahead rather than just a month.
I would be inclined to also look at whether Dec vs Nov rise was particularly large or small to improve my method rather than ignore the latest data.
Dec rise of 1.65 is above average so maybe that will tend to make the Dec to Jan smaller than typical.
I don't think it is as certain as your figures seem to suggest.
It may well not be a good idea to focus on too much detail at too short a timeframe. But if you do, I would have thought estimating a month ahead is likely to be more accurate than estimating a year ahead.
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MEI
2013 .038 -.165 -.171 .01 .108 -.242 -.436 -.586 -.175 .102 -.08 -.3
2014 -.318 -.269 -.017 .152 .932 .878 .816 .858 .5 .36 .712 .578
http://www.esrl.noaa.gov/psd/enso/mei/table.htmlPeak seems to be AprMay - JulAug, AugSep & SepOct figures are rather low and OctNov &NovDec figures just a little lower than Peak values.
It could be that the peak values are still feeding through into larger than average rises so another month of above average rise should be expected. Or maybe we have passed the peak effect and now we should get slightly below average rises? If "warmer oceans, even where they don't actually vent CO2, just don't absorb as much as they would in other years" is an important factor then I would expect quite a delay and another large rise in Jan so it is highly likely for Co2 to be over 400 in Jan 2015.