麻豆淫院

The Arctic is warming almost four times faster than the rest of the planet. High temperatures are already causing the permanently frozen ground, known as permafrost, to thaw. The carbon contained in this soil is then released into the atmosphere as carbon dioxide or methane, further exacerbating global warming.

Scientists have suggested that permafrost is a so-called "tipping element"鈥攁 part of the climate system that shifts to another state when a critical temperature threshold is reached. But what exactly does this mean in the case of permafrost?

In a review paper in the journal Surveys in Geophysics, researchers from the Max Planck Institute for Meteorology (MPI-M) along with their international colleagues have investigated whether the processes in the Arctic are abrupt on the one hand and irreversible on the other鈥攖wo typical criteria for a tipping point.

They concluded that large-scale thawing of permafrost occurs gradually with increasing temperatures. "We don't see a sudden tipping in our climate models," says Victor Brovkin, researcher at MPI-M and lead author of the study.

However, the loss of permafrost carbon is still irreversible: Once the soil thaws, the decomposition of the carbon it contains continues, even if global temperatures stabilize. Therefore, a tipping is still possible at a later time.

Local tipping

At the local level, irreversible changes can also occur abruptly. The team presents the example of thermokarst landscapes, which are formed when permafrost collapses and lakes form in the depressions. These lakes transport thermal energy deep into the ground, which accelerates the thawing of the permafrost and the decomposition of the carbon it contains.

Sometimes sudden changes can also be triggered by extreme events, such as heat waves or flooding. This can cause an ecosystem to tip locally or regionally. However, this does not necessarily lead to a chain reaction that affects the entire Arctic.

As the researchers demonstrate, many of these changes can be detected through Earth observation. For instance, satellite instruments can measure sudden subsidence and changes in water levels from space. The researchers are pursuing various approaches to extract possible early warning signals from this data indicating a tipping. These efforts may be aided by new satellite products, such as those provided by the recently launched Sentinel-1C operated by the European Space Agency ESA.

The global perspective

According to the researchers, the impact of changing hydrology on the global climate has been overlooked in the discussions about whether permafrost is a tipping element. "Whether the Arctic becomes wetter or drier has consequences for cloud formation, which in turn affects the planet's energy balance," explains Philipp de Vrese, researcher at the MPI-M and co-author of the study. These changes could impact other regions of Earth, including the Amazon region and the Sahel, which are also considered to be possible tipping elements.

Overall, there is no clear evidence that permafrost is a tipping element, but the possibility can't be excluded either. "Either way, the current changes we see in the Arctic are alarming," says Brovkin. As a next step, the researchers will participate in the Tipping Point Modeling Intercomparison Project (TIPMIP) led by Ricarda Winkelmann, Director at the Max Planck Institute for Geoanthropology, which aims to better understand the role of permafrost and other potential tipping elements.