And 21 young people in the United States have sued the Obama Administration over climate change. The federal lawsuit argues climate change violates the public trust doctrine, which requires the government to protect resources essential to the survival of future generations. In the suit, the 21 youths demand the court order federal agencies to develop a plan to decrease concentrations of carbon in the atmosphere to 350 parts per million by the year 2100. Renowned climate scientist James Hansen, who is a co-plaintiff on the suit, argues that it is essential to reduce carbon levels to this target in order to avoid the most catastrophic impacts of climate change.