Hothouse Earth (HL) (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Hothouse Earth

• Global warming is moving the Earth away from the natural glacial-interglacial cycles of the Quaternary period

  • The Quaternary period began 2.5 million years ago

  • It was characterised by alternating ice ages and warmer interglacial periods

• Natural climate changes have previously occurred over very long time periods (i.e. tens to hundreds of thousands of years)

• However, human activities are now driving unprecedented rapid changes in the climate

  • Some scientists suggest that these changes mark the beginning of the Anthropocene epoch

What is Hothouse Earth?

• The Hothouse Earth concept refers to a potential future state where the Earth’s climate becomes much hotter than the natural variability of the past

  • Scientists researching Earth's historical climate and its reaction to greenhouse gases were the first to propose this idea

  • Hothouse Earth describes a scenario where warming self-amplifies through positive feedback mechanisms

  • This leads to:

    • extreme global temperatures

    • severe climate and weather events

    • significant changes in ecosystems

  • In the Hothouse Earth climate change scenario, the Earth's average temperature rises irreversibly to 4-5°C above pre-industrial levels

The role of tipping points

• Climate tipping points are thresholds where small changes can lead to significant, irreversible shifts in the climate

  • Even an increase of just 2°C could trigger a series of positive feedback loops that intensify the global warming process

  • Once these feedbacks are triggered, they can drive further warming and climate change

  • This creates a feedback cycle that is difficult to reverse

Positive feedback mechanisms

• Positive feedback loops amplify global warming and its effects

  • Melting ice

    • As the ice melts, the Earth’s surface becomes darker, absorbing more sunlight and further increasing warming

  • Methane release

    • Warming leads to the release of methane from thawing permafrost, which is a powerful greenhouse gas

  • Reduced carbon storage

    • As temperatures rise, oceans may become less effective at absorbing carbon

    • This may lead to higher levels of greenhouse gases in the atmosphere