[M-IS14] Paleoclimatology and paleoceanography

[MIS14-16] Current status of the global climate and carbon cycle predictions and modeling perspective

★Invited Papers

*Hiroaki Tatebe¹ (1.Japan Agency for Marine-Earth Science and Technology)

For the international community, domestic local governments, and private companies to consider specific mitigation and adaptation policy to climate change that should be taken in the future, scientifically based information on climate change projections is necessary. One of the scientific tools for giving such information is a computer program called a climate model. Climate simulations using this tool can describe the nonlinear behavior of the climate system as a solution based on physical and biogeochemical laws, which is useful for understanding phenomena for which observation data are sparse in time and space. It is also possible to diagnose the climate response under assumptions that cannot be set in a real climate. Based on the results of these virtual simulations, IPCC assessment reports conclude that there is no doubt that global warming over recent decades is attributable to an increase in anthropogenic greenhouse gases. Along with long-term warming due to anthropogenic influences, there are self-excited variations in the climate system at various spatio-temporal scales. In particular, the El Niño Southern Oscillation and the Interdecadal Pacific Oscillation are thought to have contributed to the temporary slowdown of the global warming in the 2000s (so-called Hiatus), the consecutive La Niña around 2020, and the record high temperature observed in 2024, which exceeded the 1.5-degree target of the Paris Agreement. Simulation studies are underway to elucidate the mechanism of these self-excited oscillations. In addition, future predictions utilizing climate models and Earth System Models (ESMs) that take into account the global carbon cycle are also used to establish specific numerical targets for mitigating global warming, to verify their feasibility, and to evaluate the effectiveness of mitigation measures if they are realized.
Climate models and ESMs used in climate and carbon cycle prediction research are based on universal physical and biogeochemical laws, making them useful tools not only for climate research from pre-industrial era to the future, but also for paleoclimate research extending back tens of thousands of years or more from the present. Paleoclimate research has a socially important role in providing knowledge to predict present and future climate change by understanding the Earth's intrinsic climate variability. At the same time, in contrast to researches related to the anthropogenic global warming, which visualizes the crisis facing human society and thus arouses serious concerns about the future, paleoclimatic research is also important for understanding the geological evolution of the global environment on a very long-term scale, abrupt climate changes such as Younger Dryas, and changes in the distribution areas of species, including human beings, that may accompany these changes, stimulating people's scientific curiosity, as is the case with other natural science research such as astronomy and astrophysics. In this presentation, representative examples of anthropogenic and natural climate changes observed since the industrial revolution and the mechanisms that could explain them will be introduced as well as climate and carbon cycle prediction research, with a view to contributing to the 7th Coupled Model Intercomparison Project, the next IPCC report, and the Global Stocktaking. Long-term perspective for the development of climate models and ESMs, including the coupled model development of polar ice sheet models and ESMs that include ocean ice shelf elements will be also shown.