Originally Posted by
TyroPicard
there does seem to be a regular cycle between roughly 180 - 300 ppm every 100,000 years or so.
Look more carefully at the graph to see the arrow at 400 showing 'current levels'. Without doubt the level is significantly higher than for the last million years. On the other hand it has been 10x current level in the distant past - on some of theose occassions it was quite warm and others quite cold.
Who knows what the future holds - but less fuel burn and lower maintenance costs are both good things to do now.