Based on analysis of recent data on the evolution of global temperatures, snow and ice covers, and sea level rise, the Intergovernmental Panel on Climate Change (IPCC) has recently declared that "warming of the climate system is unequivocal." Global surface temperatures, in particular, have increased during the past 50 years at twice the speed observed during the first half of the 20th century. The IPCC has also concluded that with 95 percent certainty the main drivers of the observed changes in the global climate have been anthropogenic increases in greenhouse gases (GHG). While the greenhouse effect is a natural process without which the planet would probably be too cold to support life, most of the increase in the overall concentration of GHGs observed since the industrial revolution has been the result of human activities, namely the burning of fossil fuels, changes in land use (conversion of forests into agricultural land), and agriculture (the use of nitrogen fertilizers and live stock related methane emissions).