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The climate of the past informs our future



Future in the past

A major cause of uncertainty in climate projections is our inaccurate knowledge of how much warming will occur due to the increased amount of carbon dioxide in the atmosphere. Paleoclimate profiles have the potential to help us hone that understanding as they capture so many environmental conditions. Tierney et al. Considering recent advances in data collection, statistics and modeling could help us better understand how the increase in atmospheric carbon dioxide will affect future climate.

Science, this problem p. eaay3701

Structured summary

BACKGROUND

Man-made emissions are rapidly changing Earth’s climate, pushing it into a warmer state with no historical precedent. Although no perfect analogues exist for such disruption, Earth’s history includes past climatic states— “paleo-climates” —that is a lesson for the future of our world is warming. These periods in the Earth’s past experience a large range of temperatures, precipitation patterns, degrees of freezing, and biosphere adaptations and are increasingly relevant to enhance our understanding of how key elements of the climate system are affected by greenhouse gas levels. The proliferation of new statistical and geochemical methods, as well as improvements in the paleontological model, allows for a formal evaluation of climate models based on paleontological data. In particular, because some of the latest generation climate models are highly sensitive to doubling the amount of CO in the atmosphere.2, there is a new role for paleontological species in limiting the equilibrium climate sensitivity (ECS) and its dependence on the state of the climate.

PROGRESS

Over the past decade, more and more studies are using the epigenetic climate and CO2 estimate to infer ECS in the deep past, in both warm and cold climates. Recent studies support the model that ECS is highly state dependent, increasing as CO increases2 concentration. Simulations of past warm climates such as Eocene further highlight the role of cloud feedback in contributing to high ECS under increased CO.2 levels. Paleoclimates introduced important limitations to the assessment of future ice stability and at the same time sea level rise, including the viability of threshold processes such as sea cliff instability. . In addition to changes on a global scale, analysis of past changes in the water cycle has enhanced our understanding of the hydrodynamic factors of hydrological climates, which are highly relevant. regional climate projections and social impacts. New and extensive techniques, such as the analysis of individual foraminifera coatings, are providing sub-seasonal climatic information that can be used to study modes of change during and beyond the affected year. how by external climate pressure. Studies of transient, irregular passes in the paleontological environment from a background state such as the Paleocene-Eocene Thermal Peak provide important context for man-made aberrations, their effects with the Earth system and the recovery time scale.

Some advances have removed the “language barrier” between climate modeling and proxy data, enabling more direct use of epigenetic information to limit model performance. Direct incorporation of geochemical markers, such as water isotopes, into model simulations is increasingly common and this method has significantly improved model-proxy comparison. The development of new statistical methods derived from Bayesian inference has resulted in a more thorough quantification of the uncertainties of the post paleontological data. In addition, techniques such as data assimilation allow formal aggregation of model data and proxies into hybrid products. Such aggregations provide an overview of past climatic zones and may impose restrictions on climate variables for which we do not have a direct proxy, such as the coverage of clouds or wind speed.

OPINION

A general concern when using paleontological information as a model target is the absence of CO2 Forged objects, such as aerosols and greenhouse gases, are not well known, especially in the distant past. Although evidence to date suggests that such ablative behaviors are secondary to CO2Future improvements in both proxy localization and modeling are being made to address this issue. New and rapidly developing geochemical techniques are capable of providing improved limits to terrestrial biosphere, aerosols, and trace gases; Likewise, biochemical cycles can now be incorporated into the paleontological modeling simulation. In addition to limiting corrective behavior, it is important that proxy information is converted into quantitative estimates that account for uncertainty in the proxy system. Statistical tools have been developed to achieve this, making it easier to create powerful goals for model evaluation. With the quantitative increase in paleontological climate information, we propose that the modeling centers include simulations of past climates in their assessment and modeling performance. This practice has the potential to narrow the uncertainties surrounding climate sensitivity, ice sheets and water cycles and thereby improve future climate projections.

Past climate provides the setting for future climate scenarios.

Both past (top) and future (bottom) climates are colored by the estimated change in average annual surface temperatures globally relative to pre-industrial conditions, from green. blue (cooler) to red (warmer). The “Sustainability”, “Middle Line” and “High Emissions” represent the anomaly in 2300 global temperature estimated from the Common Socio-Economic Pathways (SSP) SSP1-2.6 , SSP2-4.5 and SSP5-8.5. In both the past and the future, a warmer climate is associated with an increase in CO2 (indicated by arrows). Ma, millions of years ago.

abstract

As the world warms, climate change projections need to be deeply improved. Although the latest Earth system models offer some unprecedented features, fundamental uncertainties continue to obscure our vision of the future. The past climate provides a unique opportunity to observe how the Earth system responds to high levels of carbon dioxide, emphasizing the fundamental role of paleontology in limiting future climate change. Here, we examine the relevance of paleontological information to climate projections and discuss the prospects of emerging methodologies for understanding more about past climates. Advances in proxy and interpretative methods pave the way for the use of past climates to evaluate models – a practice we believe should be widely applied.


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