It's easy to find this data, no mysteries: Which industries and activities emit the most carbon?. that links to a nice graphic, which I think may work better for some people: world greenhouse gas emissions by industry/source. Check the large version, it has neat graphics that show all the distributions.
Ag is about 25% you'll see, though of course I'm sure you can find more fine grained analysis that might take into account forest cover lost etc. Transport 15%, electricity 25%. Translated, that means OUR daily lives and consumption patterns are the primary cause, overwhelmingly. And yes, moving production of the stuff we buy out of sight to China still counts. I thought transport would be higher, closer to 25%, but I guess globally it isn't.
Here's the google search: "co2 emissions by industry" (stupid bpl forum software won't take the actual search link) so you can click around yourself and see what you find, but honestly, when I see a question like this posted, I have to scratch my head, it's not hard to type in a question to google, just phrase it in clear english and hit enter.
Methane release from ocean floor and permafrost defrosting may tilt this a bit in the coming years, I believe that's the main question now, how much and how quickly methane will get released, some of this data is 2005 vintage, and they have more data now, so you might look around more. I'm not sure how those charts are for methane, but I believe CO2 is the primary agent at this point, until we hit certain tipping points at least.
will have decent current analysis and breakdowns of various issues. There's other decent sources, but those two aren't bad because they are run by real people who actually do the work, not flakes and scoundrels.
Google works reasonably well for such questions, most of the information is public and easy to locate. You can drill down into the questions by refining your searches by adding more key words, like methane etc.
ah, this is better, that's closer to what I thought, from the EPA: Greenhouse Gas Emissions. That shows the usa, which is closer to what I thought, 40% electricity, 31% transport. That's because we consume and drive more than anyone else in the world, and live in the biggest houses that are the least efficient, the usa could easily cut its output by 50% with almost no real loss in quality of life or whatever we like to call our over-consumption patterns. I suspect ag is mixed in there with transport and industry.
Here's a cool one:
Carbon Dioxide Information Analysis Center that seems worth a look. You can look at co2 by country too. Here's epa's pie chart by gas type. That's useful because you can see ag vs your car/electricity (57% fossil fuels). here's a per capita chart with pretty colors.
Oh, oh, and here's one I did not remember:
Emissions from cement production (377 million metric tons of carbon in 2007) have more than doubled since the mid 1970s and now represent 4.5% of global CO2 releases from fossil-fuel burning and cement production. global trends cdiac.ornl.gov
Who would have thunk, cement, 5% of total fossil fuels/cement, I guess a lot of co2 gets released when they bake the lime or whatever it is they do. One could do this all day, but why bother, nobody is going to actually change their behavior anyway...
There's so much data out there really it's actually harder to avoid it than find it, as long as you look that is, of course.
Happy trails, time to sew that stealth grayish backpack I've been thinking about.