1
|
Trauth MH, Asrat A, Fischer ML, Hopcroft PO, Foerster V, Kaboth-Bahr S, Kindermann K, Lamb HF, Marwan N, Maslin MA, Schaebitz F, Valdes PJ. Early warning signals of the termination of the African Humid Period(s). Nat Commun 2024; 15:3697. [PMID: 38714681 PMCID: PMC11076281 DOI: 10.1038/s41467-024-47921-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 04/12/2024] [Indexed: 05/10/2024] Open
Abstract
The transition from a humid green Sahara to today's hyperarid conditions in northern Africa ~5.5 thousand years ago shows the dramatic environmental change to which human societies were exposed and had to adapt to. In this work, we show that in the 620,000-year environmental record from the Chew Bahir basin in the southern Ethiopian Rift, with its decadal resolution, this one thousand year long transition is particularly well documented, along with 20-80 year long droughts, recurring every ~160 years, as possible early warnings. Together with events of extreme wetness at the end of the transition, these droughts form a pronounced climate "flickering", which can be simulated in climate models and is also present in earlier climate transitions in the Chew Bahir environmental record, indicating that transitions with flickering are characteristic of this region.
Collapse
Affiliation(s)
- Martin H Trauth
- University of Potsdam, Institute of Geosciences, Potsdam, Germany.
| | - Asfawossen Asrat
- Botswana University of Science and Technology, Department of Mining and Geological Engineering, Palapye, Botswana
- Addis Ababa University, School of Earth Sciences, Addis Ababa, Ethiopia
| | - Markus L Fischer
- University of Potsdam, Institute of Geosciences, Potsdam, Germany
| | - Peter O Hopcroft
- University of Birmingham, School of Geography, Earth & Environmental Sciences, Birmingham, United Kingdom
| | - Verena Foerster
- University of Cologne, Institute of Geography Education, Cologne, Germany
| | | | - Karin Kindermann
- University of Cologne, Institute of Prehistoric Archaeology, Cologne, Germany
| | - Henry F Lamb
- Aberystwyth University, Department of Geography and Earth Sciences, Aberystwyth, UK
- Trinity College Dublin, Botany Department, School of Natural Sciences, Dublin, Ireland
| | - Norbert Marwan
- Potsdam Institute for Climate Impact Research, Member of the Leibniz Association, Potsdam, Germany
| | - Mark A Maslin
- University College London, Geography Department, London, UK
| | - Frank Schaebitz
- University of Cologne, Institute of Geography Education, Cologne, Germany
| | - Paul J Valdes
- University of Bristol, Bristol Research Initiative for the Dynamic Global Environment, School of Geographical Sciences, Bristol, UK
| |
Collapse
|
2
|
Armstrong E, Tallavaara M, Hopcroft PO, Valdes PJ. North African humid periods over the past 800,000 years. Nat Commun 2023; 14:5549. [PMID: 37684244 PMCID: PMC10491769 DOI: 10.1038/s41467-023-41219-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Accepted: 08/24/2023] [Indexed: 09/10/2023] Open
Abstract
The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the intensity of the African monsoon system. However, most climate models cannot reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we utilise a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800 kyr which have good agreement with NAHPs identified in proxy data. Our results show that precession determines NAHP pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacial periods, enhanced ice-albedo driven cooling suppresses NAHP amplitude at precession minima, when humid conditions would otherwise be expected. This highlights the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.
Collapse
Affiliation(s)
- Edward Armstrong
- Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland.
| | - Miikka Tallavaara
- Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
| | - Peter O Hopcroft
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Paul J Valdes
- School of Geographical Sciences, University of Bristol, Bristol, UK
- Cabot Institute, University of Bristol, Bristol, UK
| |
Collapse
|
3
|
Bastiaansen R, Ashwin P, von der Heydt AS. Climate response and sensitivity: time scales and late tipping points. Proc Math Phys Eng Sci 2023. [DOI: 10.1098/rspa.2022.0483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Climate response metrics are used to quantify the Earth’s climate response to anthropogenic changes of atmospheric
CO
2
. Equilibrium climate sensitivity (ECS) is one such metric that measures the equilibrium response to
CO
2
doubling. However, both in their estimation and their usage, such metrics make assumptions on the linearity of climate response, although it is known that, especially for larger forcing levels, response can be nonlinear. Such nonlinear responses may become visible immediately in response to a larger perturbation, or may only become apparent after a long transient period. In this paper, we illustrate some potential problems and caveats when estimating ECS from transient simulations. We highlight ways that very slow time scales may lead to poor estimation of ECS even if there is seemingly good fit to linear response over moderate time scales. Moreover, such slow processes might lead to late abrupt responses (late tipping points) associated with a system’s nonlinearities. We illustrate these ideas using simulations on a global energy balance model with dynamic albedo. We also discuss the implications for estimating ECS for global climate models, highlighting that it is likely to remain difficult to make definitive statements about the simulation times needed to reach an equilibrium.
Collapse
Affiliation(s)
- Robbin Bastiaansen
- Department of Physics and IMAU, Utrecht University, Utrecht, The Netherlands
- Mathematical Institute, Utrecht University, Utrecht, The Netherlands
| | - Peter Ashwin
- Department of Mathematics and Statistics, University of Exeter, Exeter EX4 4QF, UK
| | | |
Collapse
|
4
|
Armstrong McKay DI, Staal A, Abrams JF, Winkelmann R, Sakschewski B, Loriani S, Fetzer I, Cornell SE, Rockström J, Lenton TM. Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science 2022; 377:eabn7950. [PMID: 36074831 DOI: 10.1126/science.abn7950] [Citation(s) in RCA: 278] [Impact Index Per Article: 139.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a warming threshold, leading to substantial Earth system impacts. Synthesizing paleoclimate, observational, and model-based studies, we provide a revised shortlist of global "core" tipping elements and regional "impact" tipping elements and their temperature thresholds. Current global warming of ~1.1°C above preindustrial temperatures already lies within the lower end of some tipping point uncertainty ranges. Several tipping points may be triggered in the Paris Agreement range of 1.5 to <2°C global warming, with many more likely at the 2 to 3°C of warming expected on current policy trajectories. This strengthens the evidence base for urgent action to mitigate climate change and to develop improved tipping point risk assessment, early warning capability, and adaptation strategies.
Collapse
Affiliation(s)
- David I Armstrong McKay
- Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden.,Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.,Global Systems Institute, University of Exeter, Exeter, UK.,Georesilience Analytics, Leatherhead, UK
| | - Arie Staal
- Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden.,Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.,Copernicus Institute of Sustainable Development, Utrecht University, Utrecht, Netherlands
| | - Jesse F Abrams
- Global Systems Institute, University of Exeter, Exeter, UK
| | | | | | - Sina Loriani
- Potsdam Institute for Climate Impact Research, Potsdam, Germany
| | - Ingo Fetzer
- Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden.,Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
| | - Sarah E Cornell
- Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden.,Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
| | - Johan Rockström
- Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden.,Potsdam Institute for Climate Impact Research, Potsdam, Germany
| | | |
Collapse
|
5
|
Paleoclimate-conditioning reveals a North Africa land-atmosphere tipping point. Proc Natl Acad Sci U S A 2021; 118:2108783118. [PMID: 34725155 PMCID: PMC8609301 DOI: 10.1073/pnas.2108783118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 08/30/2021] [Indexed: 11/18/2022] Open
Abstract
While paleoclimate records show that the Earth System is characterized by several different tipping points, their representation within Earth System models (ESMs) remains poorly constrained. This is because historical observations do not encompass variations large enough to provoke such regime changes, and paleoclimate conditions are rarely used to help develop and tune ESMs, which potentially ignores a rich source of information on abrupt climate change. A critical example is the early to mid-Holocene "greening" and subsequent rapid desertification of the Sahara, which most ESMs fail to reproduce, casting doubt on the representation of land-atmosphere coupling and monsoon dynamics. Here, we show that this greening and abrupt termination can be successfully simulated with one ESM after optimizing uncertain model components using both present-day observations and crucially mid-Holocene (6,000 y before present) reconstructions. The optimized model displays abrupt threshold behavior, which shows excellent agreement with long paleoclimate records that were not used in the original optimization. These results suggest that in order to realistically capture climate-system thresholds, ESMs first need to be conditioned with appropriate paleoclimate information.
Collapse
|