||The greenhouse effect occurs naturally, providing a habitable climate. Atmospheric concentrations of some of the gases that produce the greenhouse effect are increasing due to human activity and most of the world's climate scientists consider that this is a significant part of the cause of observed climate change. The oceans are a critical part of the climate system, with vastly greater thermal capacity than the atmosphere. Most of the net energy increase in the climate system in recent decades is stored in the oceans. A small, slow increase in their temperature is significant. Over one-third of human-induced greenhouse gas emissions come from the burning of fossil fuel to generate electricity. Nuclear power plants do not emit these gases.