The Burning Sun

It is true that the levels of carbon dioxide have fluctuated beyond what we believe to be the normal threshold. I do not deny this fact as i do not deny that it is possible, though not likely, that this has come from human activity, such as the burning of fossil fuels. I still believe however, that there must be more data collected and observations made before we can truly say that human activity is the primary cause of global warming. It is known that the temperature of the earth has risen over the last few hundred years, in the last decade in particular, but there is no way for us to know that this is a direct result of only human activity. The natural cycles in Earth's orbit can alter the planets exposure to the sun which could cause the increase in temperature and carbon dioxide level. It is also not as likely that only human activity caused global warming to the degree that people say it does. About 450 million years ago the carbon dioxide levels were over ten times what they are now but the planet was at one of it's coldest periods in history. At the moment it is way to possible that this is just a time when the Earth is naturally more susceptible to the heat from the sun. If people really want others to believe global warming is caused by human activity then they should get more hard evidence first. Because without evidence this is just another empty claim like that of an oncoming ice age from the 1970's.