i'm not sure if i'm imagining things but in the 25 years i've been caving, it seems to be more-so in recent years that we've been getting CO2 related problems in caves causing pretty much nil access to some of them during the peak of summer months when it's at its worst. I was reading something earlier than may be a load of rubbish but might be interesting reading about how the earth and seas are sucking more co2 and wondered if this might be relevant. Would be interested in any more sciency person's views on this.

http://www.theregister.co.uk/2012/08/02/co2_absorption_doubled_since_1960/

estelle said:

....it seems to be more-so in recent years that we've been getting CO2 related problems in caves causing pretty much nil access to some of them during the peak of summer months when it's at its worst.....

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I thought we were just getting softer.

Perhaps you are, Rob, but I doubt it; around ten years ago the CO2 problems on Mendip were worserer than they have been in the last two or three; I remember Swildon's and GB (the latter was closed because the levels were so high) being very poor, Manor Farm Swallet and Tyning's Barrow Swallet being unpassable beyond the entrance sections, Cuckoo Cleeves, Honeymead, Maesbury, White Pit, Little Crapnell et al being desperate etc., far more so than now.

There have been many suggestions about the possible causes, all of which may indeed be interplaying in numerous combinations! - warm(er) winters and the lesser resultant air refreshment effect from the Cold Trap Theory, increased frequency of vigorous rainfall, changes to farming practices, increased footfall in popular caves etc. etc..

Since the various dynamics and the resultant mathematics is probably heinous, I doubt it'll get much further than being a "who knows?" hunch... we keep an eye out for sites where the problem is serious and the Regional Council can take radical access steps if things become desperate. Meanwhile,... game on. Wheeze on.

Possibly the problems with "bad air" were always coming and going but nowadays it is easier to get hold of meters to measure gas levels and with the coming of the Internet news spreads a lot faster?

estelle said:

http://www.theregister.co.uk/2012/08/02/co2_absorption_doubled_since_1960/

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Think this was relating to global heating rather than unsavoury conditions in caves. 
The oceans have long been known as good absorbers of CO2, so as we've been pumping out more, they've been sucking (some of) it up.
Maybe there's some new finding that this has been working slightly faster than previously thought.
Doesn't mean we're off the hook re climate change, though - the price for cleaning up CO2 is higher ocean acidity: eventually shellfish will be unable to keep their shells from dissolving - and what will do for paella then ??

The change in CO2 levels in the general atmosphere is of the order of a hundred parts per million up to around 400ppm or 0.04%.  I think Cap 'n Chris has suggested more likely causes.  Also whilst nice electronics are now more easily available, simple means such as candles, carbide lights and gas lighters have provided indicators of higher levels of CO2 (at the few % level) for many decades.  As well as the not so reliable ease of breathing.

cap 'n chris said:

.....  around ten years ago the CO2 problems on Mendip were worserer than they have been in the last two or three; .........f ar more so than now.

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Some of the caves Chris mentions normally have active streams which, I believe, help to minimise the CO2, either by absorption or the movement of water causing airflow.
I measured high levels in Swildons (2.5% between the 20' and 40' pots) when there was no stream flowing. This year the wet summer has kept the air clear in that area.