What effects of climate change can no longer be reversed?
As temperatures rise, some elements in the Earth’s climate system will undergo rapid and dramatic rather than gradual change. Scientists have identified more than a dozen such “tipping elements.” At certain temperature thresholds (which experts cannot precisely quantify yet), they will “tip” past a point of no return, making a return to their previous state practically impossible.¹
One example is the Greenland ice sheet. This sheet is currently several kilometers thick, which means the surface is at an altitude where it is significantly cooler (just like being in the mountains). As the ice sheet melts, its surface will drop into warmer layers of air and begin melting faster and faster. For the ice mass to grow again, the Earth’s temperatures would first need to fall to a level similar to that seen during the last ice age (a decrease of about four degrees Celsius compared to today, on a global average). Other tipping elements include the melting of the Antarctic ice sheet, the destruction of the Amazon rain forest, and the dying off of tropical coral reefs. Some tipping elements will further exacerbate global warming through the release of additional greenhouse gases. This applies, for example, to the thawing of permafrost, which could release huge quantities of methane or carbon dioxide.²
The speed of steps to protect the climate is therefore extremely important. To avoid passing the tipping points, we must see a rapid decrease in greenhouse gas emissions, because even if humanity were able to cool the climate back down to preindustrial levels in the distant future, it would change nothing about the loss of Greenland’s ice, the Amazon rain forest, or coral reefs, for example, or its consequences, such as a drastic rise in sea levels, mass extinction of species, etc.³
¹ Lenton et al. 2019: https://www.nature.com/articles/d41586-019-03595-0
² IPCC 2018, SR1.5, Kapitel 188.8.131.52 – https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Chapter3_L…