geological carbon dioxide sinks. Since the industrial revolution, humanity has been adding to greenhouse gases by emitting CO2 from fossil fuel combustion, changing land use through deforestation, and has further altered the climate with aerosols (particulate matter in the atmosphere), release of trace gases (e.g. nitrogen oxides, carbon monoxide, or methane). Other factors, including land use, ozone depletion, animal husbandry (ruminant animals such as cattle produce methane), and deforestation, also play a role. The US Geological Survey estimates are that volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes. The annual amount put out by human activities may be greater than the amount released by supereruptions, the most recent of which was the Toba eruption in Indonesia 74,000 years ago. Orbital variations Slight variations in Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of kinematic change are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods, their correlation with the advance and retreat of the Sahara, and for their appearance in the stratigraphic record. During the glacial cycles, there was a high correlation between concentrations and temperatures. Early studies indicated that concentrations lagged temperatures, but it has become clear that this isn't always the case. When ocean temperatures increase, the solubility of decreases so that it is released from the ocean. The exchange of between the air and the ocean can also be impacted by further aspects of climatic change. These and other self-reinforcing processes allow small changes in Earth's motion to have a large effect on climate. Solar output The Sun is the predominant source of energy input to the Earth's climate system. Other sources include geothermal energy from the Earth's core, tidal energy from the Moon and heat from the decay of radioactive compounds. Both long term variations in solar intensity are known to affect global climate. Solar output varies on shorter time scales, including the 11-year solar cycle and