Mechanisms and Impacts of Earth System Tipping Elements. (25th February 2023) - Wang, Seaver
Abstract: Tipping elements are components of the Earth system which may respond nonlinearly to anthropogenic climate change by transitioning toward substantially different long‐term states upon passing key thresholds or "tipping points." In some cases, such changes could produce additional greenhouse gas emissions or radiative forcing that could compound global warming. Improved understanding of tipping elements is important for predicting future climate risks and their impacts. Here we review mechanisms, predictions, impacts, and knowledge gaps associated with 10 notable Earth system components proposed to be tipping elements. We evaluate which tipping elements are approaching critical thresholds and whether shifts may manifest rapidly or over longer timescales. Some tipping elements have a higher risk of crossing tipping points under middle‐of‐the‐road emissions pathways and will possibly affect major ecosystems, climate patterns, and/or carbon cycling within the 21st century. However, literature assessing different emissions scenarios indicates a strong potential to reduce impacts associated with many tipping elements through climate change mitigation. The studies synthesized in our review suggest most tipping elements do not possess the potential for abrupt future change within years, and some proposed tipping elements may not exhibit tipping behavior, rather responding more predictably and directly to the magnitude of forcing. Nevertheless, uncertainties remain associated with many tipping elements, highlighting an acute need for further research and modeling to better constrain risks. Plain Language Summary: In recent years, discussions of climate change have shown growing interest in "tipping elements" of the Earth system, also imprecisely referred to as "tipping points." This refers to Earth system components like the tropical rainforests of Amazonia or the Greenland and Antarctic ice sheets which may exhibit large‐scale, long‐term changes upon reaching critical global warming, greenhouse gas, or other thresholds. Once such thresholds are passed, some tipping elements could in turn produce additional greenhouse gas emissions or change the Earth's energy balance in ways that moderately reinforce warming. In this review, we summarize the current state of scientific knowledge on 10 systems that some have referred to as potential tipping elements of the climate system. We describe the mechanisms important to each system, highlight the response of these systems to climate change so far, and explain the dynamics of potential future changes that these systems could undergo in response to further climate change. Overall, even considering remaining scientific uncertainties, tipping elements will influence future climate change and may involve major impacts on ecosystems, climate patterns, and the carbon cycle starting later this century. Aggressive efforts to stabilize climate change could significantly reduce such impacts. Key Points: Many tipping elements have uncertain thresholds, which could be crossed this century if human emissions and impacts remain unabated Many tipping elements significant to global climate may exhibit slower onset behavior, responding to climate forcing over a century or more Emissions pathways and climate model uncertainties may dominate over tipping elements in determining overall multi‐century warming