"As if we could change the level anyway"---we have already changed the level, increasing it by about 33% from where it was in 1800. Air bubbles trapped in glacial ice can be and have been analyzed. For as deep as the ice goes, thousands of years, CO2 has come in at about 290 parts per million. The level began to seriously move up in the 1900s. Now, it's up to over 390. Our fossil fuel use has been calculated, and it's quite sufficient to account for the observed increase. Case closed.