*Please*, only answer this question if you *don't* know the answer?

Well I do know that most of the atmosphere is made up of Nitrogen and the %. The next main constituent is Oxygen. I also know the %, which leaves not a lot for all the trace gases, so on that basis CO2 makes up a very small part of that remaining %. Never thought about it that way before, so well done. Very interesting! Keeping faith with your question, and wishes, I deliberately did not put in the actual percentages and I didn't know the % of CO2 in the atmosphere, still don't, although I now have a much better idea.

i knew the anwser once, but can't quite figure out what it was. anyway, people shouldn;t be so worried about the percetnage of co2 in the atmosphere, sure it helps the global warming, but not nearly as much as H2 does, and humans have hardley put any at all of that gas in the atmosphere!! so we shouldn't be s worried about it, what we do with co2 is not as bad as they make it sound. and it's about time people stopped spreading fairytales and started learning the truth, it's not so difficult, it takes like 5 minutes to find and maybe another 5 to understand if you havn't had biology or if you're quite thick. so let's put some effort in learning the truth and stop scaring each other!!!

-.-% (--- ppm) and increasing at about -.-ppm per year, with seasonal fluctuations.

Throughout my teaching career the figure quoted was always -.-% so, although it sounds like a small amount, there has been a --% increase over the last 30 years. Prior to that the figure had been pretty stable for 100 years or more.

Actual data available on request or from the website below. I, too, would be interested to read laymen's estimates.

OK, well as you asked..I've really no idea.

I don't understand why some people think global-warming is all scare-mongering though. Don't you think there are many large corporations and governments who have a strong vested interest in wanting you to believe its all scare-mongering? Then they can keep exploiting our planet. My cousin is a geologist and I have heard the whole its-all-scaremongering arguments. I don't buy it though.

I don't need to know the % of C0 2 in the atmosphere, I just open my eyes and use my common sense to see that we are stuffing up our planet.

I'm guessing you don't want people who know the true figure to post here because you don't want anyone with a clue to rain on your little global warming denialist parade you've got going on here.

Let me guess - you reveal the true figure to be a small fraction of 1% and then 'ta-da'! You've debunked the global warming 'myth'.

Small numbers only equate to insignifigance in the minds of simpletons. People with actual knowledge of climate science know better.

Now let's all play Global Warming Skeptic Bingo!

http://timlambert.org/2005/04/gwsbingo/

Yeah - broadly speaking I know the answer too - and am watching the answers coming up with interest. Good question.

p.s. cows produce methane not Co2

But percentage or no; the actualy amount of increase is scarily significant. Just look at the current changes and incidents to out weather patterns.

3%

But it is a pointless exersise, because we don't know what percentage will spell disaster. Like it may only be 3% of the atmostpher, but if disaster occurs at 3.2% then that is a big deal. If disaster only occurs when CO2 is 20% then 3% is nothing.

I haven't looked at all, and i probably will be way out... but no doubt some smart-alic nob will post the real thing pretending he didn't know...

my guess woud have to be quite low as it is poisonous to us... so i'd have to guess at something like 0.5%.. however i'd also say that as you went higher into the air into the different atmospheres i think there'd be more, as there is less O2 up there...

As far as I can remember N2 + O2 = 99%, so the percentage of CO2 is less than 1 %, I guess.

I remember from school that nitrogen is about 76%, O2 is about 20% and all the other gases make up whats left, but I dont know what percent is CO2.