6.1F Quaternary period (HL) Notes

Global Warming and the End of the Quaternary Climate Rhythm

1. For the past 2.5 million years, Earth’s climate has been characterised by a repeating pattern of glacial (cold) and interglacial (warm) periods.
2. This geological time period is known as the Quaternary, and its climate cycles have been governed primarily by Milankovitch cycles, natural greenhouse gas fluctuations, and feedback loops such as the ice–albedo effect.
3. However, since the Industrial Revolution, the scale and speed of human-caused warming have begun to push the Earth beyond the natural boundaries of this cycle.
4. Anthropogenic global warming is now moving the planet toward new, hotter climatic conditions, very different from anything observed in Quaternary climate records.

Why This Warming Is Different from Natural Climate Change

1. Natural climate variations in the Quaternary occurred slowly, over tens of thousands of years.
2. The current rate of warming, approximately 1.1°C since the late 19th century, is geologically instantaneous, occurring within a few decades.
3. Atmospheric CO₂ concentrations have risen from 280 ppm (pre-industrial) to over 420 ppm today.
4. This rise is faster, larger, and more abrupt than any natural changes observed in ice-core records covering 800,000 years.

The Anthropocene Epoch

1. Because humans are now the dominant force altering atmospheric chemistry, ecosystems, and climate, many scientists propose a new geological epoch called the Anthropocene.
2. The Anthropocene is characterised by:
   1. Rapid increases in CO₂, CH₄, and N₂O
   2. Massive land-use change
   3. Plastic pollution in sediments
   4. Radioactive isotopes from nuclear testing
   5. Global biodiversity decline
3. These changes act as geological markers, meaning they will be preserved in rock layers for millions of years.

Hothouse Earth Scenario

1. Some researchers warn that Earth might be approaching a “Hothouse Earth” state if warming crosses key thresholds.
2. Features of a Hothouse Earth State:
   1. Global temperatures 4–5°C above pre-industrial levels
   2. Potential rise in sea levels by more than 1 metre
   3. Large-scale collapse of ice sheets
   4. Shift of climate zones, including expansion of deserts
   5. Intensification of heatwaves, cyclones, and floods
   6. Widespread ecosystem disruption

Why it may become irreversible

1. A Hothouse Earth is driven by self-amplifying positive feedback loops, such as:
   1. Melting ice reduces albedo, increasing absorption of heat
   2. Thawing permafrost releases methane, accelerating warming
   3. Warmer oceans release CO₂, rather than storing it
   4. Tropical forests becoming carbon sources, not sinks
2. Once triggered, these feedbacks could push Earth permanently into a hotter climate state.