Early Warning from Space for a Few Key Tipping Points in Physical, Biological, and Social-Ecological Systems

Abstract

In this review paper, we explore latest results concerning a few key tipping elements of the Earth system in the ocean, cryosphere, and land realms, namely the Atlantic overturning circulation and the subpolar gyre system, the marine ecosystems, the permafrost, the Greenland and Antarctic ice sheets, and in terrestrial resource use systems. All these different tipping elements share common characteristics related to their nonlinear nature. They can also interact with each other leading to synergies that can lead to cascading tipping points. Even if the probability of each tipping event is low, they can happen relatively rapidly, involve multiple variables, and have large societal impacts. Therefore, adaptation measures and management in general should extend their focus beyond slow and continuous changes, into abrupt, nonlinear, possibly cascading, high impact phenomena. Remote sensing observations are found to be decisive in the understanding and determination of early warning signals of many tipping elements. Nevertheless, considerable research still remains to properly incorporate these data in the current generation of coupled Earth system models. This is a key prerequisite to correctly develop robust decadal prediction systems that may help to assess the risk of crossing thresholds potentially crucial for society. The prediction of tipping points remains difficult, notably due to stochastic resonance, i.e. the interaction between natural variability and anthropogenic forcing, asking for large ensembles of predictions to correctly assess the risks. Furthermore, evaluating the proximity to crucial thresholds using process-based understanding of each system remains a key aspect to be developed for an improved assessment of such risks. This paper finally proposes a few research avenues concerning the use of remote sensing data and the need for combining different sources of data, and having long and precise-enough time series of the key variables needed to monitor Earth system tipping elements.

A 1150-year-long AMV reconstruction suggests early warning for a North Atlantic climate tipping point

“…The wavelet analysis hints at a recent increase in the overall spectral power of the AMV. The changes in spectral characteristic of a time series can be used as an early warning of regime shift in dynamical systems, as shown in numerous studies [50][51][52] . In particular, the AMOC is well-known as a potential tipping element of the climate system 53 and it has been…”

“…shown that an AMOC regime shift in climate models might necessitate the knowledge of hundreds of years of time series of AMOC variations 50,52 , which is prohibitive with direct observations of it at 26°N that only last for less than 20 years 54 . Here, the reconstruction of our AMV as an internal mode of variability can be related to the internal dynamics of the AMOC through its impact on heat transport and the AMV 13,14,55 .…”

“…Here, the reconstruction of our AMV as an internal mode of variability can be related to the internal dynamics of the AMOC through its impact on heat transport and the AMV 13,14,55 . Thus, the change in spectral characteristics of the AMV might be seen as a potential early warning of a regime shift [50][51][52] in the ocean circulation. It is, however, difficult to tell if the overall increase in spectral power is robust as the values for the largest periodicities are outside of the cone of influence and therefore subject to edge effects.…”

“…In terms of time series, the memory of the system can be measured using autoregressive AR1 coefficients, which are then assumed to be increasing when approaching a critical slowdown 50 . Thus, Kendall statistics are computed for the AR1 coefficients for different sliding window lengths [50][51][52] These recent changes in autocorrelation properties of the AMV towards higher values can be related to a possible approach of a tipping point in the AMV. Such an AMV tipping might reflect changes in the AMOC, subpolar gyre or the Arctic circulation, which were previously reported to have tipping points in models 15,16,53 .…”

Guest Editorial: International Space Science Institute (ISSI) Workshop on Geohazards and Risks Studied from Earth Observations

“…Indeed, the development of anthropogenic hazards can enhance or interact with already existing natural risks, thus leading to more complex effects, which in turn are more difficult to predict. Hydro-meteorological hazards such as cyclones, storms, heat waves, floods and droughts are intensifying as time goes on and some of them are becoming more frequent (e.g., heat waves and floods) (Stocker et al 2013;Yamazaki et al 2018 and references therein), and increasing the vulnerability of populations. However, the societal and economic impacts of natural and man-made hazards will differ depending on the geographical region, southern countries paying generally a heavier price in terms of human casualties and goods lost (Hyndman and Hyndman 2016).…”