The rapid rise in greenhouse gases is a problem because it is changing the climate faster than some living things may be able to adapt. Also, a new and more unpredictable climate poses unique challenges to all life.

Hosni Mubarak stepped down after 30 years as the country's president on Friday in the face of unprecedented street protests. We look back at his three decades in power.

After 18 days of protests, President Hosni Mubarak stepped down from power. A military council is now in charge of guiding Egypt through a “peaceful transition” until presidential elections provisionally scheduled to take place in September. Meanwhile,opposition players are trying to gain a foothold while protesters keep a close watch on the army government’s response to their demands.