The PaleoJump database for abrupt transitions in past climates

A reliable benchmark of the last 640,000 years millennial climate variability

How often have past climates undergone abrupt transitions? While our understanding of millennial variability during the past 130,000 years is well established, with precise dates available, such information on previous climate cycles is limited. To address this question, we identified 196 abrupt transitions in the δ18O record of the well-dated Chinese composite speleothem for the last 640,000 years. These results correspond to abrupt changes in the strength of the East Asian Monsoon, which align with the Greenland stadials and interstadials observed in the North Atlantic region during the last 130,000 years before present. These precise dates of past abrupt climate changes constitute a reliable and necessary benchmark for Earth System models used to study future climate scenarios.

Analysis of a two-layer energy balance model: Long time behavior and greenhouse effect

We study a two-layer energy balance model that allows for vertical exchanges between a surface layer and the atmosphere. The evolution equations of the surface temperature and the atmospheric temperature are coupled by the emission of infrared radiation by one level, that emission being partly captured by the other layer, and the effect of all non-radiative vertical exchanges of energy. Therefore, an essential parameter is the absorptivity of the atmosphere, denoted εa. The value of εa depends critically on greenhouse gases: increasing concentrations of CO2 and CH4 lead to a more opaque atmosphere with higher values of ϵa. First, we prove that global existence of solutions of the system holds if and only if εa∈(0,2) and blow up in finite time occurs if εa>2. (Note that the physical range of values for εa is (0,1].) Next, we explain the long time dynamics for εa∈(0,2), and we prove that all solutions converge to some equilibrium point. Finally, motivated by the physical context, we study the dependence of the equilibrium points with respect to the involved parameters, and we prove, in particular, that the surface temperature increases monotonically with respect to εa. This is the key mathematical manifestation of the greenhouse effect.

A punctuated equilibrium analysis of the climate evolution of cenozoic exhibits a hierarchy of abrupt transitions

The Earth's climate has experienced numerous critical transitions during its history, which have often been accompanied by massive and rapid changes in the biosphere. Such transitions are evidenced in various proxy records covering different timescales. The goal is then to identify, date, characterize, and rank past critical transitions in terms of importance, thus possibly yielding a more thorough perspective on climatic history. To illustrate such an approach, which is inspired by the punctuated equilibrium perspective on the theory of evolution, we have analyzed 2 key high-resolution datasets: the CENOGRID marine compilation (past 66 Myr), and North Atlantic U1308 record (past 3.3 Myr). By combining recurrence analysis of the individual time series with a multivariate representation of the system based on the theory of the quasi-potential, we identify the key abrupt transitions associated with major regime changes that separate various clusters of climate variability. This allows interpreting the time-evolution of the system as a trajectory taking place in a dynamical landscape, whose multiscale features describe a hierarchy of metastable states and associated tipping points.