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 (e.g., in automobiles, industry, and electricity generation). If current
trends in emissions were to continue, the amount of carbon dioxide in the atmosphere would
double during the twenty-first century, with further increases thereafter. The amounts of several
other greenhouse gases would increase substantially as well.