Climate change triggers numerous biological and physical mechanisms that further increase global warming. A research team has now compiled the most extensive list of such feedback loops to date. Among them are 26 reinforcing feedbacks, seven feedbacks with a mitigating effect and eight whose effects are not yet clear. Since some of the mechanisms are not sufficiently captured in previous climate models, the authors assume that measures to limit CO2 emissions are even more urgent than previously assumed.
Numerous climate change-related changes can in turn further increase warming. One of the best-known examples of such positive feedbacks is the melting of the ice sheets at the Earth's poles. Since water reflects less sunlight than ice, the less ice that remains, the more the earth warms up. In addition, large amounts of CO2 are stored in the permafrost. If this permanently frozen ground in the arctic regions thaws, the greenhouse gas is released. The thawing of the permafrost thus represents a tipping point: once it has been exceeded, the harmful effects can no longer be reversed.
Little considered effects
While feedbacks such as these are already being incorporated into current climate models, numerous others have not yet been researched and hardly taken into account. A team led by William Ripple from Oregon State University has now compiled a list of 41 feedback loops to be expected, including 26 amplifying, seven attenuating and eight with an ambiguous effect. "As far as we know, this is the most comprehensive list of climate feedback loops in existence, and not all are fully accounted for in the climate models," says Ripple's colleague Christopher Wolf.
According to the authors, many of the physical feedbacks are at least partially accounted for in the current IPCC models. In the case of the biological feedback mechanisms in particular, however, many have only recently been identified or have not yet been adequately researched. This includes, for example, the expansion of deserts, which affects both the reflection of sunlight and the mass of plants that can absorb CO2. Overall, the authors assume that the desert area will increase and thus exacerbate climate change.
Another ecological effect that has so far been little considered is that a warmer climate increases the risk of insect pests, which can destroy many trees and thus reduce the capacity for CO2 absorption. One of the mitigating feedbacks, on the other hand, is that increased levels of CO2 in the atmosphere encourage plant growth, thereby helping vegetation absorb a little more of this greenhouse gas. Compared to the numerous reinforcing feedbacks, however, the mitigating ones only have a smaller effect. For other factors, including the changing ocean circulation due to climate change, the effect on the climate is still unclear.
limit the damage
"What we urgently need is more research and modeling and accelerated reduction of emissions," says Wolf. In their scientific commentary, the authors call on political decision-makers to act quickly. “Further small increases in near-term warming pose a large risk given how badly we already suffer from climate catastrophes such as wildfires, violent storms, coastal flooding, thawing of permafrost and extreme weather events associated with an average global warming of only 1.1 to 1.2 degrees Celsius have occurred,” they write. In addition, it is important to slow down long-term warming in order to prevent tipping points from being exceeded.
“Transformative, socially just changes in global energy and transport, air pollution, food production, conservation and international economy, as well as education and equality-based population policies are required to meet these challenges in both the short and long term,” Ripple said. In addition, coordinated research efforts are important to better understand the importance of feedback loops and tipping points and to be able to estimate more reliably how quickly we need to net-zero our CO2 emissions in order to avoid major climate catastrophes.
"It is too late to fully prevent the consequences of climate change as the severe impacts are already being felt," the authors write. "However, if we better understand the feedback loops, make the necessary changes soon, and put basic human needs first, it might still be possible to limit the damage."
Source: William Ripple (Oregon State University, Corvallis, USA) et al., One Earth, doi: 10.1016/j.oneear.2023.01.004