Yup, I also tend to like "anthropogenic change" a lot more than a simplistic "warming". I voted option 2 - in my studies of ecology of land-ecosystems, that is a fact, not a theory. Humans have changed the face of this planet for thousands of years, beginning on a large scale at the same time as our civilization and written records start. Our largest effects were long in the soil layer of the planet, but atmospheric changes have been caused from the times of the metal smelters of the Romans at the very least.
http://findarticles.com/p/articles/mi_h ... n29051107/
(not taking a stance on mr. Keys otherwise here)
"How Rome polluted the world: we tend to think of industrial pollution as a modern phenomenon but, as David Keys reveals, the ancient Romans were already contaminating the air, land and sea with toxic metals two millennia ago"
"Then, when the ore was smelted, large quantities of waste material escaped from the operation as very fine dust and were lifted into the atmosphere by the heat generated by the smelting furnaces. The techniques the Romans used to smelt the metal resulted in emissions of ultra-fine-dust pollution that were at least ten times higher than those seen in 19th-century Europe; the smelting pollution rate for copper was extraordinarily high--15 per cent--while that for lead was five per cent.
The main metal mined in Wadi Faynan was copper, and estimates suggest that up to 2,300 tonnes of the metal were released into the atmosphere each year. The major production centres for lead were in Spain, with smaller ones located in Greece, the Balkans and Britain. The combined emissions from these operations could have been as high as 4,000 tonnes per year.
Some of this material found its way into the middle troposphere--about six kilometres up--and then fell to Earth hundreds, or even thousands, of kilometres away. French researchers studying ice cores from Greenland estimate that something in the region of 800 tonnes of Roman copper and 400 tonnes of lead 'rained' down on Greenland in the form of polluted snow between 500 BC and 300 AD."
(and that doesn't say that aliens couldn't have genetically engineered humans and have had Atlantises and Lemurias here too...)
Eventually, given enough time, plate tectonics will tidy up whats left of ours, as well...