Let us see one by one the natural causes.
Solar Activity or Solar Variability
The first and foremost important natural cause is the solar activity or solar variability. The sun’s energy appears to be constant but undergoes small little changes over an extended period of time. There are different types of solar activities such as sunspots (A temporary, dark, relatively cool patch on the solar surface, caused by intense magnetic activity) and solar flares (A sudden, brief eruption of high-energy radiation from the sun’s surface). The sunspots are relatively cool, dark spots appearing periodically in groups on the surface of the sun, while solar flares or storms are eruptions of hot gases from the surface of the sun. So these sunspots and solar flares influence the solar output or solar activity, and that can consequently impact the earth’s climate (NASA 2024).
The sun goes through roughly 11-year-long periodic variations in the frequency of sunspots, solar flares, and other solar activity. During this period, the sun goes through a solar maximum and a solar minimum. During a solar maximum, the sun has the maximum number of sunspots and solar flares, and it gives off more energy. The reverse is true in case of the solar minimum wherein the sun has only fewer sunspots and solar flares. So in case of solar minimum, it gives off less energy, but in case of solar maximum, the solar output and solar activity will be much higher, and that can influence the earth’s climate (WMO 2025; NASA 2024).
The solar activity affects the earth’s climate. We have many examples in the past. For instance, between 1650 and 1850, the Little Ice Age occurred, believed to be triggered, in part, by reduced solar activity called the “Maunder Minimum” (NASA 2024). About 3 billion years ago, the solar radiance was only about 80 percent of the present value—atmospheric CO₂ (carbon dioxide, the chief greenhouse gas) was much higher, maintaining warmth despite the fainter Sun (IPCC AR6 2023).
The “solar constant” (average energy output of the Sun reaching the top of Earth’s atmosphere) exhibits small periodic variations (about 1 Watt/m², or less than 0.1% of total output, during an 11-year cycle). These cyclic variations (sunspot cycles) average 11 years; longer cycles include the 22-year Hale magnetic cycle and the 88-year Gleissberg cycle (NASA 2024). A persistent anomaly of one percent in the solar constant could change Earth’s average temperature by up to 0.6°C, if all other factors stayed the same, but scientific consensus shows recent global warming is ~270 times greater from human-caused greenhouse gases than from solar variability since 1750 (IPCC/NASA 2024).
Orbital Variations (Milankovitch Oscillations)
The second important factor is orbital variations, popularly called Milankovitch oscillations (Long-term, cyclic changes in Earth’s orbit, tilt, and wobble, driving major shifts in climate like ice ages), proposed by Milutin Milankovitch. These define Earth’s periodic cycles in its orbit around the Sun, affecting how much sunlight reaches Earth and its distribution by latitude and season; examples include the shape of the orbit (“eccentricity,” changing every ~100,000 years), tilt angle (“obliquity,” ~41,000-year cycle, varies from 22.1°–24.5°, currently 23.4°), and the “precession,” a wobble with a cycle of ~23,000 years (NASA/NOAA 2025).
Tectonic Processes
The third important natural cause is tectonic processes (The movement of Earth’s lithospheric plates resulting in formation or destruction of continents, mountains, and ocean basins). Mountain ranges like the Himalayas, Rockies, or Andes, as well as Atlantic mid-ocean ridges, have formed due to movements of large sections of Earth’s crust (“plates”). Over millions of years, the location and size of continents and oceans have shifted (“plate tectonics”), profoundly influencing ocean and atmosphere circulation, climate zones, and sometimes even triggering ice ages or desert formation (IPCC AR6 2023).
Volcanic Eruption
The next important natural driver is volcanic eruption. Volcanic eruptions eject large amounts of sulfur dioxide, water vapor, ash, and dust into the atmosphere. Water vapor is the most abundant greenhouse gas, but volcanic aerosols (tiny ash/dust particles) reflect solar energy, causing a short-lived cooling of the planet (IPCC AR6 2023).
Large eruptions, especially in equatorial regions, spread aerosols globally (tiny particles suspended in air), often resulting in hemispheric or global cooling of between 0.5°C and 1°C in the years following eruptions—e.g., the 1991 eruption of Mount Pinatubo led to a global cooling of about 0.6°C for nearly two years (NASA/IPCC). Aerosols from eruptions are preserved as layers in Antarctic or Greenland ice sheets, serving as historical indicators of past climate (IPCC AR6 2023).
