Lake Vostok does indeed give evidence of changing climate over millennia.  However this lake is some distance beneath glacial ice so it has been recording these changes over many years including when Antarctica was further north than it is now.  It is also a matter of the degree of evidence.  More recent evidence gathered from ice closer to the surface shows that carbon dioxide (CO2) has also always been there but its concentration has increased exponentially over the last 70 years.  So for COMMON SENSE follow the logic:  1. It has been proven that CO2 is a 'greenhouse' gas.  2. Since hydrocarbons contain carbon and the atmosphere contains oxygen the burning of hydrocarbons (fossil fuels) produces CO2 and water (H2O) (human activity).  3. All fires including wild fires (many caused by humans) produce CO2 as well since trees are carboniferous materials.  That said it is also worthwhile to mention that water readily absorbs CO2 creating carbonic acid thus acidifying the oceans.  No hoax.