Milankovitch, the father of paleoclimate modelling

The origin of the long-term variations of the astronomical elements used by Milankovitch are first described, followed by the value of the astronomical periods. The detailed calculations by Milankovitch of the incoming solar radiation during the astronomical and caloric half-years are summarized, stressing the originality of the caloric ones. The second original contribution of Milankovitch to paleoclimate research was without any doubt his mathematical climate. How this model allowed him to give the caloric summer and winter insolation a climatological meaning is illustrated.

Documented and Simulated Warm Extremes during the Last 600 Years over Monsoonal China

In this study, we present an analysis of warm extremes over monsoonal China (21–45° N, 106–124° E) during the last 600 years based on Chinese historical documents and simulations from the Paleoclimate Modelling Intercomparison Project Phase 3 (PMIP3) and the Coupled Model Intercomparison Project Phase 5 (CMIP5). The Chinese historical documents indicate that extreme warm records become more frequent after ~1650 CE in North China and ~1850 CE in the Yangtze River Valley. Our analyses of two threshold extreme temperature indices also illustrate that warm extremes have become more frequent since the 17th century in North China and the mid-19th century in Yangtze River Valley in good agreement with the changes in warm extremes revealed in the historical documents. This agreement suggests potential mechanisms behind the shift of periods, which should be further investigated in the future.

Dansgaard-Oeschger Tipping Events (TEs): Towards determining if IPCC-relevant models represent these TEs.

<p>Dansgaard-Oeschger (DO) events are abrupt, large climate swings that punctuated the last glacial period. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. This has implications for whether these models are also capable of simulating future TEs,  and more in general, for the delivery of accurate climate change projections. Here we present progress on possible pathways to a DO Paleoclimate Modelling Intercomparison Project (PMIP) protocol. This is broad interest to the climate community since (1), there is currently no PMIP common guidance to investigate DO events, (2) it could help carry out simulations in Earth system models under a common framework, and (3) it will help guide a more methodical search for DO events in current models. A protocol could help investigate cold-period TEs through a range of insolation-, freshwater-, green-house-gas-, and Northern Hemisphere ice sheet-related forcings, as well as evaluating the possibility of spontaneous TEs. MIS3 was a period of noticeable millennial-scale climate variability, characterised by the most regular incidence of DO events (Schulz et al., 1999). Although most abrupt DO events happened during MIS3, only few studies investigate TEs in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we therefore suggest that the MIS3 period could be the focus of such a DO-event focussed modelling protocol. Experiments performed under MIS 3 boundary conditions may help (1) explore variability under intermediate glacial conditions, (2) better understand the mechanisms behind millennial-scale TEs, (3) look for spontaneous DO-type oscillations, and (4) help answer the question: “are models too stable?”.</p>

The penultimate deglaciation: protocol for Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 transient numerical simulations between 140 and 127 ka, version 1.0

The penultimate deglaciation (PDG, ∼138–128 thousand years before present, hereafter ka) is the transition from the penultimate glacial maximum (PGM) to the Last Interglacial (LIG, ∼129–116 ka). The LIG stands out as one of the warmest interglacials of the last 800 000 years (hereafter kyr), with high-latitude temperature warmer than today and global sea level likely higher by at least 6 m. Considering the transient nature of the Earth system, the LIG climate and ice-sheet evolution were certainly influenced by the changes occurring during the penultimate deglaciation. It is thus important to investigate, with coupled atmosphere–ocean general circulation models (AOGCMs), the climate and environmental response to the large changes in boundary conditions (i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice-sheet geometry and associated meltwater fluxes) occurring during the penultimate deglaciation. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocol to perform transient simulations of the last deglaciation (19–11 ka; although the protocol covers 26–0 ka). Similar to the last deglaciation, the disintegration of continental ice sheets during the penultimate deglaciation led to significant changes in the oceanic circulation during Heinrich Stadial 11 (∼136–129 ka). However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the Past Global Changes (PAGES)-PMIP working group on Quaternary interglacials (QUIGS), we propose a protocol to perform transient simulations of the penultimate deglaciation under the auspices of PMIP4. This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice sheets as well as freshwater input from the disintegration of continental ice sheets. This experiment is designed for AOGCMs to assess the coupled response of the climate system to all forcings. Additional sensitivity experiments are proposed to evaluate the response to each forcing. Finally, a selection of paleo-records representing different parts of the climate system is presented, providing an appropriate benchmark for upcoming model–data comparisons across the penultimate deglaciation.

Mid-Holocene drylands: A multi-model analysis using Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) simulations

This study examines changes in aridity levels during the mid-Holocene (approximately 6000 cal. yr ago) using multi-model simulations from the Paleoclimate Modelling Intercomparison Project Phase III. Overall, there is little difference in the total area of drylands from the preindustrial period; global drylands are 8% wetter than during the preindustrial period as measured by an aridity index; and 16% of preindustrial drylands convert to a wetter climate subtype, double the sum of zones that are replaced by a drier category. Considerable variations are present among regions with major contractions of each dryland subtype from northern Africa to South Asia and the main expansions of arid, semiarid, and dry subhumid climates in southern hemisphere continents. The difference in precipitation is the leading factor of the aforementioned changes. The second factor is the altered potential evapotranspiration as mainly induced by relative humidity, which contributes to additional aridity changes in a same direction as precipitation does. The collective effects of precipitation and relative humidity account for more than 80% of the dryland variations. In comparison, the simulated aridity change is in reasonable agreement with reconstructions, while there are model–data discrepancies for Australia and uncertainties across proxies for southern Africa.

Análise das Simulações do PMIP3 Sobre o Nordeste Brasileiro Para o Período Pré-Industrial e Holoceno Médio

Resumo Este trabalho mostra uma analise das simulações obtidas no banco de dados do PMIP3 (Paleoclimate Modelling Intercomparison Project Phase IIII) para o período pré-industrial com os dados observados pelo CMAP (Climate Prediction Center Merged Analysis of Precipitation) e Climatic Reserch Unit (CRU) para a precipitação pluviométrica em mm/mês e os dados de reanálise do NCEP/NCAR para a temperatura do ar a 2 m acima da superfície em graus Celsius, para as região do Nordeste Brasileiro (NEB) (46° W - 34° W; 16° S - 2° S), a fim de encontrar um conjunto de modelos com representação realista do clima do presente. Em seguida, uma comparação é feita entre os resultados das simulações desses modelos para o período pré-industrial (PI) e o Holoceno médio (HM, ~6.000 anos atrás), a fim de identificar possíveis mudanças climáticas entre esses períodos sobre a América do Sul. Esses modelos do PMIP3 sugerem que houve diferenças importantes entre o clima atual e o do Holoceno Médio no que diz respeito à intensidade da monção da América do Sul (monção mais fraca no HM do que no presente).

Strengthening of the East Asian winter monsoon during the mid-Holocene

The change in the East Asian winter (December–January–February) monsoon (EAWM) during the mid-Holocene, approximately 6000 years ago, was investigated using all available experiments within the Paleoclimate Modelling Intercomparison Project (PMIP). As defined by regional-averaged meridional wind speed at 850 hPa, the mid-Holocene EAWM intensity was consistently stronger than that of the reference period in 38 out of the 42 models chosen for analysis, with an average strengthening of 14% across all models. In response to changes in the Earth’s orbital parameters and atmospheric greenhouse gas concentrations, zonal and meridional land–sea thermal contrasts and sea-level pressure gradients were enhanced between the continent and the adjacent oceans of East Asia, leading to the strengthening of the mid-Holocene EAWM. In addition, there were uncertainties regarding the EAWM reconstructions and the effect of dynamic ocean and vegetation on the EAWM change during the mid-Holocene.