Climate Defense is a single-player tower defense game that tasks the player with preventing global warming by absorbing carbon dioxide (CO2) before it builds up in the atmosphere. Towers, representing set quantities of trees that could be grown to absorb carbon dioxide, can be constructed by the player to destroy CO2 clouds that march along pathways from the surface of the earth to the atmosphere in waves. As the average global temperature increases, impacts are presented to the player, detailing the expected results of global temperature increases predicted by scientists and economists. Players can also approach the problem by decreasing CO2 emissions or increasing the efficiency of energy consumption to decrease the size of the CO2 waves that the trees must deal with.
Climate change occurs when changes in Earth's climate system result in new weather patterns that remain in place for an extended period of time. This length of time can be as short as a few decades to as long as millions of years. Scientists have identified many episodes of climate change during Earth's geological history; more recently since the industrial revolution the climate has increasingly been affected by human activities driving global warming, and the terms are commonly used interchangeably in that context. The climate system receives nearly all of its energy from the sun. The climate system also gives off energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.