That would be a false conclusion. The greenhouse effect may be natural, but present levels of greenhouse gasses are almost certainly caused by human activities. The concentrations of CO2 and methane have increased by 36% and 148% respectively since 1750. These levels are much higher than at any time during the last 800,000 years, the period for which reliable data has been extracted from ice cores. Less direct geological evidence indicates that CO2 values higher than this were last seen about 20 million years ago.(wikipedia) Are we ready for the climate of 20 million years ago? This would be a completely new situation for most life on Earth.