altering the environment

In a recent Question of the Day over at the Zeray Gazette, John asked, Do you think that anthropogenic global warming is real?

The majority or respondents said no for various reasons, most of which sound specious to me. Today I want to address one curious claim that a few people mentioned, the idea that we as human beings don't really have as big of an impact as we want to believe.

Now I'll grant that human beings, as a species, have an inflated sense of our importance within the universe. Still, if we look at our history, we can see many ways in which human beings have made significant changes to our world, for better or worse.

• We've created the domestic dog, a subspecies of wolves, and further refined it into hundreds of breeds.
  
• We've eradicated the smallpox virus globally through effective vaccination
  
• We've reduced the effects of flooding through numerous Army Corps of Engineers projects, and created lakes where none existed before
  
• With large-scale dams we've brought water to formerly dry areas, and have dried up rivers
  
• Factory pollution has created rain with the acidity of vinegar, capable of destroying all life in lakes into which it drains
  
• Enough oil was dumped into the Cuyahoga River that the river caught on fire several times between 1936 and 1969
  
• We've sent tons of chlorofluorocarbons (CFCs) into the stratosphere, where they are steadily depleting the protective layer of ozone
  
• We've introduced invasive species into new environments where they have displaced or threatened native species
  
• We've disrupted entire ecosystems by eliminating one or more species deemed to be pests
  
• Through deforestation in tropical rainforests we've sent thousands of species to extinction
  

It's a big world, but we've managed to alter our environment in many ways. Is it really so hard to believe that the burning of fossil fuels, which at current levels produces 21.3 billion tons of carbon dioxide a year, also has an effect on this fragile earth?