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).

Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0)

Simulations of climate over the Last Millennium (850–1850 CE) have been incorporated into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). The drivers of climate over this period are chiefly orbital, solar, volcanic, changes in land use/land cover and some variation in greenhouse gas levels. While some of these effects can be easily defined, the reconstructions of solar, volcanic and land use-related forcing are more uncertain. We describe here the approach taken in defining the scenarios used in PMIP3, document the forcing reconstructions and discuss likely implications.

Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0)

Simulations of climate over the Last Millennium (850–1850 CE) have been incorporated into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). The drivers of climate over this period are chiefly orbital, solar, volcanic, changes in land use/land cover and some variation in greenhouse gas levels. While some of these effects can be easily defined, the reconstructions of solar, volcanic and land use-related forcing are more uncertain. We describe here the approach taken in defining the scenarios used in PMIP3, document the forcing reconstructions and discuss likely implications.

Estudo comparativo de simulações paleoclimáticas na região do Atlântico Sul

Neste estudo são comparadas diferentes simulações de modelos paleoclimáticos para duas épocas distintas, o Último Máximo Glacial (UMG) e o Presente. Esta comparação visa elucidar as principais diferenças nos processos físicos e dinâmicos do sistema oceano-atmosfera na região do oceano Atlântico Sul entre estes dois períodos. Foram analisadas as variações na climatologia anual entre estas épocas para os seguintes parâmetros: temperatura do ar (TA), precipitação (PPT) e pressão ao nível do mar (PNM). As simulações numéricas analisadas são do projeto PMIP (Paleoclimate Modelling Intercomparison Project) e do modelo numérico acoplado NCAR (National Center for Atmospheric Research) CCSM (Comunnity Climate System Model) versão 1.4 nos dois períodos de interesse. Os resultados mostram uma intensificação do presente em relação ao UMG em todas as variáveis analisadas. As diferentes simulações atmosféricas do PMIP apresentaram padrões consistentes com os apresentados no modelo NCAR CCSM, sendo observados baixos valores de EQM (Erro Quadrático Médio) para grande parte da região de estudo.