There is little remaining doubt that human activities since the mid 19th century have played a significant role in climate change by overloading the atmosphere with carbon dioxide, hence retaining solar heat that would otherwise radiate away.

300 parts per million ( p.p.m.) is a healthy level of CO2 in the atmosphere, and measurements from ice cores show a CO2 level of 280 p.p.m. before the industrial revolution. In 2005 atmospheric levels of CO2 were 379 p.p.m., higher than at any time in the past 650,000 years. 11 of the 12 warmest years on record were in the last decade ( 1995 – 2006 ) and so the trend continues into the 21st century. The global carbon dioxide in 2006 neared 32 billion tons, equivalent to 15% of the millions of years worth of carbon locked up in the arctic ice.