For climate change, this is time of urgency, big ideas, and hope. 2015 will be a year of decisions – in Paris at the 21st Conference of Parties to the United Nations Framework Convention on Climate Change and elsewhere – decisions that set the agenda for action, agreement, and accountability for years to come.Human energy use accounts for three quarters of greenhouse gas emissions globally and an even higher share in the United States. Transitioning to a new “low carbon” and “climate resilient” energy system lies at the core of any response to climate change. This new system will need to sustain prosperity in many countries and lift many out of poverty around the world by supporting sustainable development.