In the past 66 million years, large dinosaurs have been extinct, angiosperms, mammals and birds have flourished, which is the Cenozoic era in geological history. In the early Cenozoic, there was no ice sheet at the poles, but large-scale ice sheets appeared in the late Cenozoic. The concentration of greenhouse gases was more than 2000 ppmv at one time, but less than 200 ppmv in the last glacial period. Paleoclimatologists have been hoping to obtain the records of climate change since Cenozoic to understand the evolution law and development trend of modern earth climate. < p > < p > exactly 100 years ago, Milankovitch proposed that the changes of earth’s orbital parameters, including eccentricity, inclination and precession, affect the latitude and seasonal distribution of solar radiation obtained on the earth’s surface, and drive the quasi periodic changes of the earth’s climate (Milankovitch, 1920). In the past 50 years, the Milankovitch hypothesis has not only become a theoretical paradigm for paleoclimate research, but also provided an astronomical dating method for paleoclimate research. Since the mid-1980s, paleoclimatologists have integrated the carbon and oxygen isotopic records of deep-sea sediments to reconstruct the Cenozoic climate history. So far, the most influential integration curve is the paper published on science by Jim zachos, a professor of paleoceanography at UCSC in 2001 (zachos et al. , 2001a)。 This paper, to a great extent, has laid a solid foundation for the overall understanding of the Cenozoic climate evolution. However, at that time, the astronomical dating time scale had just reached the Paleogene threshold (zachos et al. The time scale of the early Cenozoic mainly depends on biostratigraphy and magnetostratigraphy, and there are many differences. < / P > < p > in the past 20 years, the newly acquired deep-sea sedimentary boreholes in the world have greatly made up for these deficiencies (Fig. 1), and the astronomical time scale has gradually crossed the Cenozoic Era and extended to the Paleozoic era. A new integration curve is imminent. < p > < p > they selected 14 boreholes out of more than 1000 deep-sea sedimentary boreholes, carefully checked and corrected the splicing mode of these cores, and selected oxygen and carbon isotope records of two long-lived foraminifera genera cibicidoides and nuttallides to reconstruct the climate history. According to the preliminary time scale, some samples from late Miocene to early Eocene have been tested to ensure sufficient time resolution. They collected all the existing astronomical time scales, and adjusted these time scales to la2010b orbit scheme, and finally obtained a zenogrid (Cenozoic global reference benthic for aminifer carbon and oxygen isotope dataset) (Fig. 2). < / P > < p > the data set consists of 23629 data points. The time resolution is up to 2kA since Oligocene, 4.4ka in Paleocene and Eocene. The estimated time error is 100000 years for Paleocene Eocene, 50000 years for Oligocene Miocene and 10000 years for late Miocene Pleistocene. This is the first high-resolution isotope stratigraphic reference curve covering the Cenozoic in the world. The global climate is a complex dynamic system, and the quasi periodic astronomical forcing has complex nonlinear response on the scale of 10000 to 1000000 years. In order to study the temporal characteristics of cenogrid, the research team conducted a recurrence analysis (also known as recursive analysis). Reappearance analysis can reveal the nonlinear dynamic process of the system and the information of nonlinear interaction. The recurrence diagram is the visualization of the internal structure and predictability of time series. < / P > < p > cenogrid oxygen isotope reproduction maps reveal four distinct block regions (Fig. 3). Each square corresponds to the repeated cycles of climate in a particular state. The Cenozoic climate can be divided into four states: hot chamber, greenhouse, cold chamber and ice chamber. The state of the hot chamber lasted from 56 Ma to 47 Ma, and the temperature was 10 degrees higher than that at present. There was also an extremely hot event in which oxygen and carbon isotopes were simultaneously negative drifted. The greenhouse state has two periods, 66 Ma to 56 Ma and 47 Ma to 34 ma. The temperature of the two greenhouse States is similar, but the carbon isotope value and carbon dioxide concentration are different. The Eocene Oligocene world line around 34 Ma is the most significant transition event in Cenozoic. The cold chamber state lasted from 34 Ma to 3.3 Ma and could be divided into two stages at 13.9 ma. After 3.3 Ma, it is an ice chamber state, and the earth’s climate is controlled by the rise and fall of the northern hemisphere ice sheet. The classification of these four states is consistent with the previous understanding of the Cenozoic climate history, but the recurrence map provides the objective evidence of statistical robustness for the first time. < p > < p > Evolution spectrum shows that before 13.9 Ma, including the first stage of the earth’s hot chamber, greenhouse and cold chamber, the climate cycle is dominated by eccentricity, which means that the low latitude process drives the climate evolution. It is speculated that the eccentricity regulates the precession, affects the seasonal node of monsoon precipitation, and then acts on the global water vapor and energy distribution. However, the tilt period is not significant in the warm chamber and the first stage cold chamber, which may be due to the small scale of the ice sheet at that time and the lack of amplification effect of high latitude. With the cooling of high latitude and the growth of ice sheet, the signal of the earth’s axis tilt gradually increases after 13.9 Ma, and becomes the dominant cycle of the ice chamber earth climate system at 3.3 ma. < / P > < p > the authors also calculated the certainty of the recurrence analysis of the cenogrid curve (Figure 5), which quantitatively describes the predictability of the system. When the certainty is close to 0, the system is random and unpredictable, and close to 1 indicates that the system is deterministic. The results show that greenhouse and hot chamber earth are more predictable than cold chamber and ice chamber earth. When the Antarctic ice sheet appeared at 34 Ma, the deterministic parameters decreased significantly, and the nonlinear degree of the earth’s climate system was greatly enhanced. In the first stage of the cold chamber earth, the Antarctic ice content is relatively less 25-14 Ma, and the certainty is relatively high. Compared with the carbon and oxygen isotopes, before 6 Ma, the Arctic ice increased, and the carbon isotope certainty was higher than that of the oxygen isotope. The main reason may be that the carbon isotope was mainly controlled by the low latitude process and was less affected by the polar ice amount. It was not until 6 Ma that the cryosphere had a profound impact on the carbon cycle. After 3.3 Ma, the oxygen isotope shows a strong eccentricity period, and the certainty is enhanced. Compared with the greenhouse earth, the hot chamber earth is more difficult to predict than the greenhouse earth. The main reason is that the extreme heat event shows a strong nonlinear process and magnifies the astronomical forcing. In addition, it should be noted that after 47 Ma, the deterministic fluctuation became larger and larger, until 34 Ma reached the critical point and became unpredictable. Based on this, the authors speculate that the amount of ice at the poles not only defines the basic climate state of the earth, but also affects the predictability of the response of the climate system to astronomical radiation. < / P > < p > the cenogrid team also made public its prediction of the future climate: the current rate of man-made global warming far exceeds the natural climate fluctuation at any time in the Cenozoic era, and it is possible to push the earth’s climate from the current ice chamber to the hot chamber state (Fig. 6). “The projected anthropogenic warming will be much greater than that, and the IPCC predicts that if ‘business as usual’, global temperatures will reach their highest levels in 50 million years in 2300.” The iPhone 12 keynote has been recorded in Apple park

By ibmwl