Changes to Earth’s climate over long periods are caused by the natural variations in intensity and distribution of solar radiation that reaches the planet.
Today, when the Milankovitch Cycles are taken into consideration, Earth should have been slowly cooling over the past 9,000 years. Instead, we’re warming, delaying the next glacial epoch by at least 50,000 years(Fig. 1 & Video 2).
This gradual warming was because people developed agriculture. On balance, the climate remained relatively stable until the Industrial Revolution in the 1800s when we started burning huge amounts of fossil fuels. This rapid anthropogenic (man-maded) forcing rapidly outweighed the gradual cooling effects from the Milankovitch Cycles.
These cycles are because Earth’s orbit around the Sun is eccentric (Fig. 2), it’s axis is tilted (Fig. 3), and it wobbles (Fig. 4), each over different time frames or cycles (Fig. 5).
The cycles are named after the geophysicist and astronomer Milutin Milanković, who developed James Croll’s theory that these cycles were the main climate change forcings (Video 1).
Changes to Earth’s climate over long periods are caused by the natural variations in intensity and distribution of solar radiation that reaches the planet.
Today, when the Milankovitch Cycles are taken into consideration, Earth should have been slowly cooling over the past 9,000 years. Instead, we’re warming, delaying the next glacial epoch by at least 50,000 years(Fig. 1 & Video 2).
This gradual warming was because people developed agriculture. On balance, the climate remained relatively stable until the Industrial Revolution in the 1800s when we started burning huge amounts of fossil fuels. This rapid anthropogenic (man-maded) forcing rapidly outweighed the gradual cooling effects from the Milankovitch Cycles.
These cycles are because Earth’s orbit around the Sun is eccentric (Fig. 2), it’s axis is tilted (Fig. 3), and it wobbles (Fig. 4), each over different time frames or cycles (Fig. 5).
The cycles are named after the geophysicist and astronomer Milutin Milanković, who developed James Croll’s theory that these cycles were the main climate change forcings (Video 1).
The dark grey line shows the observed temperature changes for the past 125 years, while the pale blue line shows Earth’s orbital changes. The cooling influence of the Milankovitch Cyles over the past 9,000 is hardly noticeable in this short time frame. Image Bloomberg
Fig. 2: Earth’s eccentric orbit around the sun (100,000 year cycle). When Earth is further away from the sun it receives less solar energy and therefore less warmth.
Fig. 3: Earth is slightly tilted (40,000 year cycle). As most of the land mass is now in the Northern Hemisphere (see the link in the menu ‘How to start an ice age’), when less of that hemisphere is facing the sun in winter, it receives less warmth.
Fig. 4: Precession (26,000 year cycle). This wobble can either add to the cooling or warming depending on which phases of the other two cycles that Earth is in (Figures 1 and 2).
Fig. 5: Each cycle occurs over different time frames. When they coincide, the effects are multiplied. Factors such as plate tectonics (see Video 1) and the balance of the carbon cycle can exaggerate, reduce, or cancel the effects of the Milankovitch Cycles over thousands or millions of year. Image: The Nature Education Project
Video 1: The Milankovitch Cycles are changes in the Earth’s orbit and rotation that cause the Earth’s climate to change over hundreds of thousands of years.
The term ‘climate forcing’ comes from ‘radiative forcing’ or RF, which is the difference between the amount of solar energy reaching Earth’s atmosphere and the amount that escapes. If more solar energy escapes than arrives, the planet cools. Conversely, if less energy escapes than gets in, the planet warms.
Fossil fuels are literally the carbon in plants and animals that died millions of years ago. As the conditions that made them no longer exist, they cannot be replaced (at least in anything remotely relevant to human lifespans), so they are non-renewable.
Take coal for example. This comes from trees that grew in vast lowland swamp forests during the (appropriately named) Carboniferous Period, 358.9 million years ago (Mya), to 298.9 Mya. The high levels of carbon dioxide and even higher levels of oxygen in the atmosphere during that period plus the collision of continents that created low lying land and a hot wet climate, were the perfect conditions over millions of years for dead trees to fall into swampy ground. Here, they couldn’t be decomposed through normal processes. Instead, they turned into peat and eventually became the ‘fossil’ fuel coal. (See the carbon cycle on this website for more details and how oil and gas was made).
Today, burning this coal is releasing the carbon back into the atmosphere as carbon dioxide (CO2).
2013: IPPC Chapter 8: Anthropogenic and Natural Radiative Forcingin: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
The dark grey line shows the observed temperature changes for the past 125 years, while the pale blue line shows Earth’s orbital changes. The cooling influence of the Milankovitch Cyles over the past 9,000 is hardly noticeable in this short time frame. Image Bloomberg
