The Eurasian ice sheet reinforces the East Asian summer monsoon during the interglacial 500 000 years ago

Deep-sea and ice-core records show that interglacial periods were overall less "warm" before about 420 000 years ago than after, with relatively higher ice volume and lower greenhouse gases concentration. This is particularly the case for the interglacial Marine Isotope Stage 13 which occurred about 500 000 years ago. However, by contrast, the loess and other proxy records from China suggest an exceptionally active East Asian summer monsoon during this interglacial. A three-dimension Earth system Model of Intermediate complexity was used to understand this seeming paradox. The astronomical forcing and the remnant ice sheets present in Eurasia and North America were taken into account in a series of sensitivity experiments. Expectedly, the seasonal contrast is larger and the East Asian summer monsoon is reinforced compared to Pre-Industrial time when Northern Hemisphere summer is at perihelion. Surprisingly, the presence of the Eurasian ice sheet was found to reinforce monsoon, too, through a south-eastwards perturbation planetary wave. The trajectory of this wave is influenced by the Tibetan plateau

Unraveling the forcings controlling the vegetation and climate of the best orbital analogues for the present interglacial in SW Europe

The suitability of MIS 11c and MIS 19c as analogues of our present interglacial and its natural evolution is still debated. Here we examine the regional expression of the Holocene and its orbital analogues over SW Iberia using a model-data comparison approach. Regional tree fraction and climate based on snapshot and transient experiments using the LOVECLIM model are evaluated against the terrestrial-marine profiles from Site U1385 documenting the regional vegetation and climatic changes. The pollen-based reconstructions show a larger forest optimum during the Holocene compared to MIS 11c and MIS 19c, putting into question their analogy in SW Europe. Pollen-based and model results indicate reduced MIS 11c forest cover compared to the Holocene primarily driven by lower winter precipitation, which is critical for Mediterranean forest development. Decreased precipitation was possibly induced by the amplified MIS 11c latitudinal insolation and temperature gradient that shifted the westerlies northwards. In contrast, the reconstructed lower forest optimum at MIS 19c is not reproduced by the simulations probably due to the lack of Eurasian ice sheets and its related feedbacks in the model. Transient experiments with time-varying insolation and CO2 reveal that the SW Iberian forest dynamics over the interglacials are mostly coupled to changes in winter precipitation mainly controlled by precession, CO2 playing a negligible role. Model simulations reproduce the observed persistent vegetation changes at millennial time scales in SW Iberia and the strong forest reductions marking the end of the interglacial "optimum".SFRH/BD/9079/2012, SFRH/BPD/108712/2015, SFRH/BPD/108600/2015info:eu-repo/semantics/publishedVersio

Interglacials in China before 400 kyrs ago

The vermiculated red soil (VRS) in southern China is widely distributed in the region south of the Yangtze River, covering an area of about 2.2 × 106 km2. Chronological studies consistently indicate a mid-Pleistocene age of the VRS, correlative to the S4 and S5 soil units in the Loess Plateau in northern China and to marine 18O stages 11, 13, and 15. Soil micromorphological, mineralogical and chemical characteristics of the VRS indicate an extremely strong East Asian summer monsoon in mid-Pleistocene. What might be the origin of these strong monsoons climate documented by VRS, S4 and S5 soils? Prell and Kutzbach (1987) concluded that under interglacial conditions, increased northern hemisphere solar radiation produce strong East Asian summer monsoon. It is remarkable that around the peak of MIS-11, -13 and -15, such maxima also occur. For example for these three MIS, at 60°N in June, insolation is 34, 48 and 55 Wm-2 above the present-day value of 476 Wm-2. Does it mean that the conclusion of Prell and Kutzbach offering an astronomical origin to the strong East Asia monsoon may be extrapolated to the interglacials MIS-11 to MIS-15? Apparently not. Deep-sea records reveal indeed that MIS-13 and -15 are more glaciated than the following interglacials MIS-11 to -1. Moreover, ice-records from EPICA document a lower-than-average temperature for the Southern Hemisphere during these interglacials, opposite to the warm extreme reflected by the northern hemispheric soils in China. The CO2 concentration during MIS-13 and MIS-15 is also lower than during the other interglacials. Actually, the amplitude of the glacial-interglacial cycles is significantly reduced before MIS-11 in all these cores with cool interglacials and cold glacials. The great warmth and humidity of VRS, S4, S5-1 and S5-3 soils cannot therefore be easily related to global ice-volume variations as they appear to be exceptional, especially S5-1, whereas the interglacials are on the contrary much less pronounced. Although it remains to demonstrate from modeling experiments whether insolation changes can trigger a so intense East Asian monsoon during MIS-11,-13 and -15, Guo et al. (1998) suggested that other factors , as the ocean circulation, might have operated during the formation of S4,S5-1 and S5-3 soils. This kind of climate extreme has indeed clear counterparts in marine δ13C records , suggesting possible relationships with the strength of Deep Water (NADW) production in the North Atlantic. Moreover, the cooler MIS-13 in the Southern Hemisphere, as evidenced by the EPICA records, supports the explanation by the NADW strength. Stronger NADW would bring more heat from the equator and the Southern Hemisphere to the Northern Hemisphere, leading to a cooler Southern Hemisphere and a warmer Northern Hemisphere. A warmer Northern Hemisphere would possibly lead in turn to stronger monsoons

Le climat exceptionnel de 2015, conforme aux analyses paléoclimatiques

Please find the full article at http://dailyscience.be/2016/03/17/le-climat-exceptionnel-de-2015-conforme-aux-analyses-paleoclimatiques

Understanding the warm climates from past interglacials to the future

Given the predicted future warming and that we presently live in an interglacial (the Holocene), past interglacials are of particular interest to understand better the climate processes characterizing the warm climate conditions. In my study, the climate response to insolation and CO2 during the interglacials of the past 800,000 years are investigated by using climate models. My simulations show that the relative contributions of insolation and CO2 to the intensity and duration of each interglacial vary from one interglacial to another. They also show that CO2 plays a dominant role on the variations of the global annual mean temperature and of the climate in the Southern high latitudes, whereas, insolation plays a dominant role on the variations of monsoon precipitation, vegetation and the climate in the Northern high latitudes. Compared to the projected future climate, the past interglacials are cooler during boreal winter, but are warmer over the continents during boreal summer due to their much higher summer insolation. This suggests that the sensitivity of climate to the latitudinal and seasonal distribution of insolation must be kept in mind for the climatic projection at the century-millennium time scales. My results underline the diversity of the warm climates of the last million years and therefore the potential but also the difficulty to find exact analogues for our interglacial and its future. They show that the best analogue to the Holocene and its future depends critically upon the criteria used to select such an analogue

Understanding the warm climates from past interglacials to the future

Given the predicted future warming and that we presently live in an interglacial (the Holocene), past interglacials are of particular interest to understand better the climate processes characterizing the warm climate conditions. In my study, the climate response to insolation and CO2 during the interglacials of the past 800,000 years are investigated by using climate models. My simulations show that the relative contributions of insolation and CO2 to the intensity and duration of each interglacial vary from one interglacial to another. They also show that CO2 plays a dominant role on the variations of the global annual mean temperature and of the climate in the Southern high latitudes, whereas, insolation plays a dominant role on the variations of monsoon precipitation, vegetation and the climate in the Northern high latitudes. Compared to the projected future climate, the past interglacials are cooler during boreal winter, but are warmer over the continents during boreal summer due to their much higher summer insolation. This suggests that the sensitivity of climate to the latitudinal and seasonal distribution of insolation must be kept in mind for the climatic projection at the centurymillennium time scales. My results underline the diversity of the warm climates of the last million years and therefore the potential but also the difficulty to find exact analogues for our interglacial and its future. They show that the best analogue to the Holocene and its future depends critically upon the criteria used to select such an analogue

Relative importance of insolation and CO2 on the interglacial climates of the past 800,000 years

The individual contributions of insolation and greenhouse gases (GHG) to the interglacial climates of the past 800,000 years are quantified through simulations with a model of reduced complexity LOVECLIM and using the factor separation technique. The interglacials are compared in terms of their forcings and responses of surface air temperature, vegetation and sea ice. The results show that the relative magnitude of the simulated interglacials is in reasonable agreement with proxy data. GHG plays a dominant role on the variations of the annual mean temperature of both the Globe and the southern high latitudes, whereas, insolation plays a dominant role on the variations of tree fraction, precipitation and of the northern high latitude temperature and sea ice. The Mid-Brunhes Event (MBE) appears to be significant only in GHG and climate variables dominated by it. The results also show that the relative importance of GHG and insolation on the warmth intensity varies from one interglacial to another. For the warmest (MIS-9 and MIS-5) and coolest (MIS-17 and MIS-13) interglacials, GHG and insolation reinforce each other. MIS-11 (MIS-15) is a warm (cool) interglacial due to its high (low) GHG concentration, its insolation contributing to a cooling (warming). MIS-7, although with high GHG concentrations, can not be classified as a warm interglacial due to it large insolation-induced cooling. Related to these two forcings, MIS-19 appears to be the best analogue for MIS-1. In the response to insolation, the annual mean temperatures averaged over the globe and over southern high latitudes are highly linearly correlated with obliquity. However, precession becomes important in the temperature of the northern high latitudes and controls the tree fraction globally. Over the polar oceans, the response during the local winters, although the available energy is small, is larger than during the local summers due to the summer remnant effect

Exceptional East Asian summer monsoons during interglacials 400 kyrs ago and before

The vermiculated red soil (VRS) in southern China is widely distributed in the region south of the Yangtze River, covering an area of about 2.2 × 106 km2. Chronological studies consistently indicate a mid-Pleistocene age of the VRS, correlative to the S4 and S5 soil units in the Loess Plateau in northern China and to marine 18O stages 11, 13, and 15. Soil micromorphological, mineralogical and chemical characteristics of the VRS indicate an extremely strong East Asian summer monsoon in mid-Pleistocene. What might be the origin of these strong monsoons climate documented by VRS, S4 and S5 soils? Prell and Kutzbach (1987) concluded that under interglacial conditions, increased northern hemisphere solar radiation produce strong East Asian summer monsoon. It is remarkable that around the peak of MIS-11, -13 and -15, such maxima also occur. For example for these three MIS, at 60°N in June, insolation is 34, 48 and 55 Wm-2 above the present-day value of 476 Wm-2. Does it mean that the conclusion of Prell and Kutzbach offering an astronomical origin to the strong East Asia monsoon may be extrapolated to the interglacials MIS-11 to MIS-15? Apparently not. Deep-sea records reveal indeed that MIS-13 and -15 are more glaciated than the following interglacials MIS-11 to -1. Moreover, ice-records from EPICA document a lower-than-average temperature for the Southern Hemisphere during these interglacials, opposite to the warm extreme reflected by the northern hemispheric soils in China. The CO2 concentration during MIS-13 and MIS-15 is also lower than during the other interglacials. Actually, the amplitude of the glacial-interglacial cycles is significantly reduced before MIS-11 in all these cores with cool interglacials and cold glacials. The great warmth and humidity of VRS, S4, S5-1 and S5-3 soils cannot therefore be easily related to global ice-volume variations as they appear to be exceptional, especially S5-1, whereas the interglacials are on the contrary much less pronounced. Although it remains to demonstrate from modeling experiments whether insolation changes can trigger a so intense East Asian monsoon during MIS-11,-13 and -15, Guo et al. (1998) suggested that other factors , as the ocean circulation, might have operated during the formation of S4,S5-1 and S5-3 soils. This kind of climate extreme has indeed clear counterparts in marine δ13C records , suggesting possible relationships with the strength of Deep Water (NADW) production in the North Atlantic. Moreover, the cooler MIS-13 in the Southern Hemisphere, as evidenced by the EPICA records, supports the explanation by the NADW strength. Stronger NADW would bring more heat from the equator and the Southern Hemisphere to the Northern Hemisphere, leading to a cooler Southern Hemisphere and a warmer Northern Hemisphere. A warmer Northern Hemisphere would possibly lead in turn to stronger monsoons