Researchers have identified a "tipping point" about 2.7 million years ago when global climate conditions switched from being relatively warm and stable to cold and chaotic, as continental ice sheets expanded in the Northern Hemisphere. Following this transition, Earth's climate began swinging back and forth between warm interglacial periods and frigid ice ages, linked to slow, cyclic changes in Earth's orbit. However, glacial periods after this tipping point became far more variable, with large swings in temperature over relatively short timescales of roughly a thousand years.