In this section:
Wobbles in the Earth’s orbit, volcanoes and impacts with asteroids have all changed Earth’s climate in the past. The earth’s climate depends on the amount of energy that flows from the Sun to Earth, then back out into space. Anything that interferes with that flow of energy changes the climate.
When light and heat from the Sun reaches Earth it is absorbed by the land and ocean, captured and stored by plants, converted to other forms of energy like wind or waves, or radiated back into space. The Sun’s energy drives a system of biological, chemical and physical reactions that together, make up the climate. Change is constant.
Concentrations of Carbon dioxide gas rise and fall. Carbon dioxide is a gas that’s present in tiny amounts in the Earth’s atmosphere but it appears to have a powerful impact on the temperature of the planet. Investigations show that, historically, when the Earth gets hotter, carbon dioxide levels are high.
Volcanoes can blast ash and gases into the upper atmosphere where they absorb sunlight and cool the planet. In 1815 an Indonesian volcano triggered a ‘year without summer’. Crops failed and famine followed. Volcanoes can also warm the planet by releasing enough carbon dioxide to form a thick ‘blanket’ around the Earth. This layer traps heat that would otherwise be radiated into space.
Asteroids and meteorites are large rocks that share our solar system. They usually disintegrate in Earth’s atmosphere but sometimes they hit the planet. Sixty-five million years ago a very big one slammed into the Earth, throwing up enough dust and vaporised material to block out the Sun. The global fires resulting from the impact would have produced large amounts of carbon dioxide, trapping heat and raising temperatures.
The Earth wobbles as it spins on its axis, like a spinning top when it’s slowing down. The North Pole traces a circle in space every 25,800 years. This wobble determines the time of year of summer and winter. Twelve thousand years from now the Australian summer will occur in June.
The Earth also leans over on its axis, then straightens up, once every 41,000 years. This alters the regions of the Earth that receive intense energy from the sun. When the lean is greater, winter and summer seasons become extreme. Today the Earth is in the middle of the cycle so we have distinct seasons.
Earth’s orbit changes shape, moving us closer to or further from the Sun. Over a period of 100 000 years, the Earth’s orbit around the Sun changes from round to elliptical and back again. A stretched elliptical shape increases the Earth’s distance from the Sun, so temperatures fall and more ice develops. When the orbit is rounder the Earth is close to the Sun all the time so temperatures are warmer. Currently Earth’s orbit is almost a perfect circle.