Mapa klimatických bodů zlomu

When warming exceeds tipping points, ecosystems, currents, and ice sheets can no longer maintain stability. While the threshold and the pace vary for each system, the resulting changes are irreversible. For humanity, this means moving beyond the stable climate that supported our civilization for millennia.

What are climate tipping points?

Imagine you are leaning over the side of a canoe to look at fish. You can lean quite far and the boat stays upright. But then at a specific point the centre of gravity shifts so much that the boat, carrying you with it, starts to inevitably flip over. No matter what happens next, the system’s own physics finish the job. Similar dynamics work in ecosystems, ice sheets or ocean currents – warming beyond a certain level pushes them out of stability.

Major climate tipping points

Ice sheets collapse

There are a few major ice sheets on Earth and each is exposed to its own dynamics. Two of them, the Greenland and West Antarctica ice sheets, are already in the state of accelerated loss and may be at or near their tipping points.

The Greenland ice sheet covers 1.7 million km², roughly 80% of Greenland, and is over 3,000 m thick. As a mountain of ice, its surface lies in high, cold air. But with global warming, the surface melts and the ice sheet gets thinner. The surface then drops into lower, warmer altitudes of the atmosphere, which causes even more melting. Once the ice sheet drops below a certain critical elevation, it can no longer grow back even if we stop emissions, because the surface is now permanently in a warm-air zone. The complete melting of the Greenland ice sheet would cause a global sea level rise of 7 m and would probably take several thousand years.¹

The West Antarctica ice sheet covers 2 million km² with ice over 2,000 m thick. Most of the ice sits on bedrock that is below sea level and even slopes downward as you go further inland. The warming ocean water melts the ice and causes it to retreat. Once the retreat reaches a downward slope in the bedrock, the loss of ice may become self-sustaining. This is because if the slopes go down toward the interior, it exposes a taller, thicker face of ice to the ocean, and thicker ice flows faster into the sea (more weight means more pressure pushing ice out to sea). The complete collapse of the West Antarctic ice sheet would raise global sea levels by up to 5 m in several thousand years.

Coral reefs die-off

Coral reefs are built on a delicate partnership: the corals provide the limestone architecture, while microscopic algae living within them provide food via photosynthesis. When the sea becomes too warm, the algae begin producing harmful chemicals, forcing the coral to expel them. This leaves the coral white and starving – a process known as bleaching – and it dies if the water doesn’t cool down quickly. These events are abrupt; a single marine heatwave can turn a vibrant reef ecosystem into a graveyard in just a few months.

Large parts of the Great Barrier Reef have recently experienced recurring bleaching events and many corals have died. Scientists estimate that at 1.5 °C of global warming, 70–90% of tropical and subtropical reefs will be lost, with near total loss by 2.0 °C. Coral collapse will eliminate one of the Earth’s richest ecosystems in biodiversity, affecting a vast marine food web, and the livelihoods of hundreds of millions of people.

The remaining tipping points — permafrost thaw, Atlantic circulation collapse, and Amazon dieback — continue on The Thresholds of Climate Tipping Risks.

Footnotes

1. Temperature thresholds, time horizons, and other details on this page are based on a thorough assessment of the tipping points by McKay, D.A. et al. (2022). Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science 377, eabn7950. DOI: 10.1126/science.abn7950. ↩