Slash-and-burn deforestation accounts for about 15% of global CO2 emissions. Despite activists' efforts, forests have been disappearing at the rate of about 34 million acres a year for the last two decades. Globally, Indonesia and Brazil are the third- and fourth-largest emitters respectively of greenhouse gases, after China and the U.S., because of their breakneck pace of forest destruction. Saving the Amazon, Earth's largest tropical jungle, can be a cheaper and faster way to avoid greenhouse gas emissions than replacing coal-fired power plants with renewable energy or switching to electric cars -- although all such measures are considered necessary by climate experts.