IB Environmental systems and societies 6.1F Quaternary Period Notes

Global Warming and the End of the Quaternary Climate Rhythm

1. For the past 2.5 million years, Earth's climate has cycled between glacial (cold) and interglacial (warm) periods.
2. This period is the Quaternary, and its cycles have been governed by Milankovitch cycles, natural greenhouse gas fluctuations, and feedbacks such as the ice–albedo effect.
3. Since the Industrial Revolution, human-caused warming has begun to push Earth beyond the natural limits of this cycle.
4. Anthropogenic warming is now moving the planet toward new, hotter conditions unlike anything in Quaternary records.

Why This Warming Is Different from Natural Climate Change

1. Natural Quaternary changes happened slowly, over tens of thousands of years.
2. Current warming of about 1.1°C since the late 19th century is geologically instantaneous.
3. Atmospheric CO₂ has risen from 280 ppm (pre-industrial) to over 420 ppm today.
4. This rise is faster and larger than any natural change in ice-core records covering 800,000 years.

The Anthropocene Epoch

1. Because humans now dominate changes to atmospheric chemistry, ecosystems, and climate, many scientists propose a new epoch called the Anthropocene.
2. It is marked 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. and global biodiversity decline.
3. These act as geological markers that will remain in rock layers for millions of years.

The Hothouse Earth Scenario

1. Some researchers warn Earth could approach 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. sea-level rise of more than 1 metre,