Possible tipping points
- Physical break-up of land-bound Greenland and/or West Antarctic ice sheets. These sheets are 3 kilometres thick and cover more than 2 million square kilometres each. Melting either would raise sea levels by 6 or more metres. Some climate models say 1.7ºC of warming could trigger an unstoppable disintegration of the Greenland ice sheet.
- Die-back of the Amazon rainforest – from heat, drought and fires. This would release CO2 and warm the planet further, possibly destabilizing other forests, causing more warming, as well as meaning we lose one of the planet’s most important carbon sinks and unique sources of biodiversity.
- Release of billions of tonnes of methane gas trapped in permafrost. Methane is a greenhouse gas, so this would add to warming. Researchers have implicated methane releases as triggering sudden global warming episodes in the past.
- Breakdown of ocean circulation system, causing major climate changes including a radically cooling Europe and possible failure of the Asian monsoon. The monsoon’s regular and predictable onset is crucial for water supplies and food production in most of Asia, the world’s most populous continent.
We KNOW that past natural change in climate often happened abruptly.
For instance, much of the warming at the end of the last ice age 10,000 years ago happened within a few decades.
The current risks of runaway change are not yet fully quantified by scientists. But they are real. One recent study put the chances of a breakdown in the ocean circulation this century at perhaps as high as 1 in 3.
In any event, the uncertainty is a cause for concern rather than complacency.
It underlines the need for frequent scientific reviews to make sure climate negotiators know the latest science.