I used to hear in the 1960's that it was Carbon Monoxide (CO) from car exhaust that was causing the worst damage to the environment. Then during the Mount St Helens eruption, I heard that MSH belched more CO in one week than all the cars in the history of the world. This isn't even counting Vesuvius, Krakatoa, and Pintaubo.
Now they say that its methane from cow belches, and Carbon Dioxide (from people breathing?). People eat too much meat, and have too many babies, but there's not much of a chance that anyone can legislate China and India into "cutting back". They're burning coal without exhaust filters as fast as they can.
As far as the oceans level, The north pole is a big floating pancake of ice with 90% of it underwater. Water is bigger when its frozen (ever split a milk jug when freezing water?) so if it melts, the level will be the same. Ice on land (Antarctica, Greenland, Canada, Russia) will run into the ocean, but if everything is hotter, there will be more vapor in the atmosphere, so level stays the same. I imagine there will be more rain and hurricanes from the increased atmospheric moisture. I recommend avoiding the purchase of property in New Orleans that is 17 feet below the sea level.
The K-T Boundary is the thin layer between the "giant dinosaur" era and the small animal era. It is rich in meteoric iron and volcanic ash. The bubbles in petrified tree resin called "amber" show the pevious atmosphere was over 30% oxygen. Trillions of hot iron meteorites raining through the atmosphere pulled O2 levels (rust, the oceans floors are covered with meteoric rust) down to 21% making it hard for the big dinos to breathe, the volcanic ash from a giant asteroid strikes (Yucatan, Antartica, etc...) blocked out the sun for months, killing much plant life, killing giant herbivores, which denied giant carnivores of viable prey.
There were thick lush forests in Alaska/Siberia which were neccessary to feed enormous herds of Mammoth elephants. It was so warm there was coral in the water there. Then it then got so cold, there was a ridiculously thick glacier covering most of North America.
The Earth is going through a warming cycle, but man is not the cause. I hadn't heard before about CO2 being scrubbed by the ocean and being converted to calcium carbonate, but there is more CO2-to-O2 conversion going on by oceanic plankton than by trees (those camera whores!)
I haven't seen any published measurements of Methane and CO2 concentrations in the atmosphere, and I suspect its because you can't fake an easy to replicate measurement. Mars and Venus are warming at exactly the same rate as the Earth, so its not people.
Right now oil-drillers and low-pressure helium reactor builders will bend over backwards to be clean, but the environmental lobby is using the Endangered Species Act ("spotted owl, tiger salamander, gnatcatcher", etc...) to stop all developement. The only thing that can bypass it is a presidential order during a "national emergency", and when that happens, it's going to get very messy.
Solar desalinated sea water will be expensive, and so will syn-fuels from tar-sands and shale-oil. Learn everything you can about self-sufficiency, because its coming.
