关键词: 临界点, 级联影响, 极端事件, 气候安全, 早期预警

Abstract:

Climate warming has greatly increased the instability of the climate system, which in turn intensified the induced climate extremes. A tipping point occurs when changes in a part of the climate system become self-sustaining without the need for an external driver. Crossing tipping point of climate tipping elements will have significant and wide-ranging impacts on the planet and its inhabitants, ranging from sea level rise unprecedented on human timescales to extreme weather that is uninhabitable and beyond the current capacity to adapt. Thus, for policymakers, the key question now is not only how to mitigate climate change, but also, increasingly, how to build resilience to cope with the irreversible effects of tipping points.

Starting from the basic concept of the tipping point, this paper systematically summarizes the status and trend of tipping elements in the climate system, comprehensively analyzes the tipping points of four tipping systems with global influence, namely the Amazon Rainforest, the Atlantic Meridional Overturning Current (AMOC), the Greenland Ice Sheet (GrIS) and the Antarctica Ice Sheet (AIS), and their possible cascading effects, especially the possible effects and threaten to China’s climate security. The analysis shows that the collapse of the Amazon Rainforest has a negative impact on the wind and light resources and the stability of the cryosphere in China, mainly through affecting the temperature and precipitation over the Qinghai-Tibet Plateau (QTP), while the collapse of AMOC has an impact on food production, mainly by influencing the patterns of Asian summer monsoon rainfall, and is likely to have adverse impacts on food security and energy security by raising regional sea level, intensifying land heat waves and coastal storm surges. The collapses of the GrIS and AIS impact on China not only through contributing to global sea level rise, which has a negative impact on marine and coastal ecosystems, but also through injecting more fresh water into the Atlantic and the Southern Ocean, hence contributing to the weakening of AMOC and the lower limb of the abyssal overturning circulation around Antarctica, which in turn affects climate anomalies, sea level height and the productivity of marine ecosystems that directly or indirectly affect food availability and diversity.

It should be noted that the crossing of tipping points by some low-temperature tipping elements, together with feedbacks from some non-tipping elements may push the global mean surface temperature even higher, triggering abrupt changes in tipping elements at higher temperature levels. Without greater efforts to control the level and rate of global warming, humanity will be put in high risks of tipping. However, we are unprepared for the potentially devastating consequences of climate tipping points, and there is an urgent need to develop the capacity to provide early warning of climate tipping points and ensure climate security to build sustainable and resilient societies.

Different from the existing early warning systems, early warning of tipping points requires the establishment of a “climate security early warning system”, which provides response suggestions based on long-term climate predictions and projections, so as to better help governments and communities develop long-term climate change adaptation and mitigation strategies and development plans, and mitigate the negative impacts of abrupt changes of climate system on social and economic structures. By analyzing the early warning signals of tipping points, this study points out the strategic importance of implementing early warning of climate tipping points for ensuring China’s climate security. Combined with the current scientific understanding of tipping points, it is proposed that the QTP can be the starting point for practicing early warning for climate security in China. Taking the QTP as the starting point, on one hand, increasing the research and cognition of the tipping state of the QTP, monitoring and evaluating precursor signals of tipping, and on the other hand, studying the upstream and downstream impacts of climate abrupt change over the QTP, and conducting graded early warning according to the prediction and projection results, should be an operational approach and priority for China to establish an early warning system for climate security and ensure climate security.

On the basis of the unified understanding that the climate system is becoming more and more extreme and the climate tipping point has posed a certain threat to human security, quantifying the tipping point of the QTP and its potential cascading impacts, and monitoring the early warning signals have become the key to establishing a climate security early warning system and realizing truly sustainable development. However, the QTP itself is a complex system, and the data problems caused by sparse ground-based observations, coarse reanalysis and model grids, and limited satellite life cycle make the current scientific understanding on the drivers, interactions and feedbacks of the physical processes on the QTP, such as the hydrothermal cycle and energy balance, insufficient. As a result, the applicability of the parameterization in the climate model is limited in this region, which brings challenges to the research, operational monitoring and decision-making services for the QTP climate tipping point and early warning indicators. To this end, the study puts forward three research suggestions: first, the use of artificial intelligence technology to accelerate scientific understanding of the Earth’s climate system, a typical complex system; second, leveraging the unique role of satellite remote sensing in supplementing space coverage to detect the changing resilience of vulnerable systems and identify the tipping points of the system; third, accelerating the development of physical and AI-driven models that can identify small warning signals and build the ability to detect climate tipping points on the QTP.

Key words: Tipping point, Cascading effects, Extreme events, Climate security, Early warning