4.2 The natural causes of climate change

Milankovitch cycles are three separate but inter-connected cycles of Earth's orbit. Sometimes, the Earth orbits further from the sun, cooling the global temperature. Sometimes, Earth orbits closer to the sun, increasing the global temperature.

• Eccentricity refers to the shape of Earth's orbit around the Sun. Over a cycle of about 100,000 years, the orbit changes from more circular to more elliptical (oval). When the orbit is more elliptical, the distance between the Earth and the Sun varies more throughout the year, which can lead to variations in the seasons and global climate.

• Axial Tilt is the angle between Earth's rotational axis and its orbital plane. It changes between 21.5° and 24.5° over a cycle of approximately 41,000 years. The tilt influences the severity of seasons – a greater tilt means more extreme seasons, while a lesser tilt means milder seasons. This can affect the distribution of solar energy across the planet.

• Precession is the wobble in Earth's spin axis, occurring over a cycle of around 26,000 years. This wobble changes the timing of the seasons in relation to Earth's position in its orbit. It can alter the contrast between seasons in each hemisphere and can influence when seasons occur.

• Sunspots are dark patches on the Sun that correspond with regions of lower temperature and are often associated with magnetic storms. They follow an 11-year cycle from a solar minimum to a solar maximum and back. When there are more sunspots, the Sun can emit more solar energy, which can slightly increase Earth's temperatures.

• Solar Flares are sudden eruptions of high-energy radiation from the Sun's surface, which can also increase the amount of solar energy reaching Earth, affecting the climate.

• Volcanic Ash ejected into the atmosphere can block sunlight, leading to short-term cooling. This can last for days to years, depending on the size of the eruption and the extent of the ash cloud.

• Sulphur Dioxide released during eruptions can form sulphuric acid, which reflects sunlight away from Earth. This can have a cooling effect on the climate that can last for several years after large eruptions, contributing to longer-term climate variability.

Misconception 1: Human activities are the only cause of climate change.

• Reality: While human activities significantly impact climate change, natural phenomena like Milankovitch cycles, solar activity, and volcanic eruptions also play a pivotal role.

Misconception 2: The sun has a constant and consistent effect on Earth's climate.

• Reality: Solar activity varies due to the number of sunspots and solar flares, influencing climate in varying patterns over approximately 11 years.