Human activities can also change the climate. The atmospheric amounts of many greenhouse gases are increasing, especially that of carbon dioxide, which has increased by 30% over the last 200 years, primarily as a result of changes in land use (e.g. deforestation) and of burning coal, oil and natural gas (in automobiles industry and electricity generation) . If current trends in emissions were to continue, the amount of co2 in the atmosphere would double during the twenty-first century with further increase thereafter . The amounts of several other greenhouse gases would increase substantially as well