Milankovitch cycles and natural climate change

Earth's climate has changed naturally throughout its history, on time scales from years to hundreds of millions of years, and scientists reconstruct past climates from proxies such as ice cores, ocean sediments, tree rings, and fossils. Over tens of thousands of years, small, regular changes in Earth's orbit and axis, called Milankovitch cycles, change how sunlight is spread across seasons and latitudes: the shape of Earth's orbit (eccentricity) changes over about 100,000 years, the tilt of Earth's axis (obliquity) varies between about 22.1 and 24.5 degrees over about 41,000 years, and the wobble of the axis (precession) cycles over about 23,000 years. These cycles pace the ice ages of the last few million years, and feedbacks amplify them: Antarctic ice cores show that temperature and carbon dioxide rose and fell together, with carbon dioxide between about 180 parts per million in glacial periods and about 280 parts per million in warm interglacials over the past 800,000 years. Over millions of years, climate also changes as plate tectonics moves continents toward or away from the poles, opens or closes ocean passages that redirect currents, and raises mountains whose weathering draws down carbon dioxide. Shorter natural swings come from changes in solar output, large volcanic eruptions, and ocean patterns like El Niño. These natural causes cannot explain today's rapid warming: carbon dioxide is now above 420 parts per million, higher than at any time in at least 800,000 years, and orbital changes act over tens of thousands of years and, if anything, currently favor very slow cooling.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report