The Earth’s climate changes naturally on all timescales. At the short end of the spectrum—hours or days—it is affected by sudden events such as volcanic eruptions, which raise the atmospheric temperature directly, and also indirectly, by the addition of greenhouse gases such as water vapour and carbon dioxide. Over years, centuries, and millennia, climate is influenced by changes in ocean currents that, ultimately, are controlled by the geography of ocean basins. On scales of thousands to hundreds of thousands of years, the Earth’s orbit around the Sun is the crucial influence, producing glaciations and interglacials, such as the one in which we live. Longer still, tectonic forces operate over millions of years to produce mountain ranges like the Himalayas and continental rifts such as that in East Africa, which profoundly affect atmospheric circulation, creating deserts and monsoons. Over tens to hundreds of millions of years, plate movements gradually rearrange the continents, creating new oceans and destroying old ones, making and breaking land and sea connections, assembling and disassembling supercontinents, resulting in fundamental changes in heat transport by ocean currents. Finally, over the very long term—billions of years—climate reflects slow changes in solar luminosity as the planet heads towards a fiery Armageddon. All but two of these controls are direct or indirect consequences of plate tectonics.
Solar influence on Earth's climate