Opinion: Distribute paleoscience information across the next Intergovernmental Panel on Climate Change reports

In this opinion piece, we evaluate two approaches for incorporating paleoscience information into future assessment reports by the Intergovernmental Panel on Climate Change (IPCC). One approach advocates for a dedicated paleoclimate chapter, while the other supports the continued integration of paleoscience along with other lines of evidence across multiple sections of the report, as done in the most recent assessment cycle. We address the merits and challenges of these two approaches. We argue that paleoscience expertise is most effectively deployed where it leads to integration of paleoscience knowledge and demonstration of its policy relevance, and we suggest opportunities for expanding paleoscience contributions in future IPCC reports, regardless of the approach chosen.</p

Réchauffement climatique : état des connaissances scientifiques, enjeux, risques et options d’action

This article takes stock of climate change, based on three special IPCC reports published in 2018 and 2019. These reports provide integrated assessments across different scientific disciplines, and for the first time are written by scientists from different disciplines in each chapter. They provide an update on observed changes and their causes, future opportunities and risks, depending on the evolution of greenhouse gas emissions, socio-economic development choices, and shed light on solutions for climate action and for sustainable development, preserving biodiversity and enabling everyone to live in dignity.The first SR15 Special Report (October 2018) focuses on the impacts associated with a global warming of 1.5 °C, as well as compatible greenhouse gas emission trajectories, in the context of strengthening the response to climate change, sustainable development and efforts to eradicate poverty: www.ipcc.ch/report/SR15.The second SRCCL Special Report (August 2019) focuses on climate change and land use, particularly desertification and land degradation, sustainable land management, food security and greenhouse gas flows in terrestrial ecosystems: www.ipcc.ch/report/SRCCL. It addresses the challenges of both adaptation and mitigation.The third SROCC Special Report (September 2019) focuses on the ocean and cryosphere in an changing climate. It focuses on how climate change is affecting the ocean and the cryosphere, ecosystems and human societies, in high mountain areas, the regions polar, for the coastline, which is linked to the ocean, including via extreme and abrupt events. The mitigation options are not part of this assessment, except for “blue carbon” (the potential for carbon sinks linked to coastal marine ecosystems). This report highlights the challenges of action to building resilience: www.ipcc.ch/report/SROCC.This summary takes stock of the trends observed, their causes, the projections of future changes, in particular with regard to their impacts and risks, depending on the future greenhouse gas emission trajectories, and our collective choices

Réchauffement climatique : état des connaissances scientifiques, enjeux, risques et options d’action

This article takes stock of climate change, based on three special IPCC reports published in 2018 and 2019. These reports provide integrated assessments across different scientific disciplines, and for the first time are written by scientists from different disciplines in each chapter. They provide an update on observed changes and their causes, future opportunities and risks, depending on the evolution of greenhouse gas emissions, socio-economic development choices, and shed light on solutions for climate action and for sustainable development, preserving biodiversity and enabling everyone to live in dignity.The first SR15 Special Report (October 2018) focuses on the impacts associated with a global warming of 1.5 °C, as well as compatible greenhouse gas emission trajectories, in the context of strengthening the response to climate change, sustainable development and efforts to eradicate poverty: www.ipcc.ch/report/SR15.The second SRCCL Special Report (August 2019) focuses on climate change and land use, particularly desertification and land degradation, sustainable land management, food security and greenhouse gas flows in terrestrial ecosystems: www.ipcc.ch/report/SRCCL. It addresses the challenges of both adaptation and mitigation.The third SROCC Special Report (September 2019) focuses on the ocean and cryosphere in an changing climate. It focuses on how climate change is affecting the ocean and the cryosphere, ecosystems and human societies, in high mountain areas, the regions polar, for the coastline, which is linked to the ocean, including via extreme and abrupt events. The mitigation options are not part of this assessment, except for “blue carbon” (the potential for carbon sinks linked to coastal marine ecosystems). This report highlights the challenges of action to building resilience: www.ipcc.ch/report/SROCC.This summary takes stock of the trends observed, their causes, the projections of future changes, in particular with regard to their impacts and risks, depending on the future greenhouse gas emission trajectories, and our collective choices

Possible different calibration of moisture source temperatures from water isotopes in the Dome Fuji ice core

第33回極域気水圏シンポジウムポスター発

Precipitation Water Stable Isotopes in the South Tibetan Plateau: Observations and Modeling

International audienceMeasurements of precipitation isotopic composition have been conducted on a daily basis for 1 yr at Bomi, in the southeast Tibetan Plateau, an area affected by the interaction of the southwest monsoon, the westerlies, and Tibetan high pressure systems, as well as at Lhasa, situated west of Bomi. The measured isotope signals are analyzed both on an event basis and on a seasonal scale using available meteorological information and airmass trajectories. The processes driving daily and seasonal isotopic variability are investigated using multidecadal climate simulations forced by twentieth-century boundary conditions and conducted with two different isotopic atmospheric general circulation models [the isotopic version of the Laboratoire de Meteorologie Dynamique GCM (LMDZiso) and the ECHAM4iso model]. Both models use specific nudging techniques to mimic observed atmospheric circulation fields. The models simulate a wet and cold bias on the Tibetan Plateau together with a dry bias in its southern part. A zoomed LMDZ simulation conducted with similar to 50-km local spatial resolution dramatically improves the simulation of isotopic compositions of precipitation on the Tibetan Plateau. Simulated water isotope fields are compared with new data and with previous observations, and regional differences in moisture origins are analyzed using back-trajectories. Here, the focus is on relationships between the water isotopes and climate variables on an event and seasonal scale and in terms of spatial and altitudinal isotopic gradients. Enhancing the spatial resolution is crucial for improving the simulation of the precipitation isotopic composition

Understanding the O-17 excess glacial-interglacial variations in Vostok precipitation

International audienceCombined measurements of delta O-18, delta O-17, and delta D in ice cores, leading to d excess and O-17 excess, are expected to provide new constraints on the water cycle and past climates. We explore different processes, both in the source regions and during the poleward transport, that could explain the O-17 excess increase by 20 per meg observed from the Last Glacial Maximum (LGM) to Early Holocene (EH) at the Vostok station. Using a single-column model over tropical and subtropical oceans, we show that the relative humidity at the surface is the main factor controlling O-17 excess in source regions. Then, using a Rayleigh-type model, we show that the O-17 excess signal from the source region is preserved in the polar snowfall, contrary to d excess. Evaporative recharge over mid and high latitudes and delta O-18 seasonality in polar regions can also affect the Vostok O-17 excess but cannot account for most of the 20 per meg deglacial increase from LGM to EH. On the other hand, a decrease of the relative humidity at the surface (rh(s)) by 8 to 22% would explain the observed change in O-17 excess. Such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity, if the surface thermodynamic disequilibrium decreased by 4 degrees C. Such a change in rh(s) would affect source and polar temperatures reconstructions from delta O-18 and d excess measurements, strengthening the interest of O-17 excess measurements to better constrain such changes

Temporal and spatial structure of multi‐millennial temperature changes at high latitudes during the Last Interglacial

The Last Interglacial (LIG, 129–116 thousand of years BP, ka) represents a test bed for climate model feedbacks in warmer-than-present high latitude regions. However, mainly because aligning different palaeoclimatic archives and from different parts of the world is not trivial, a spatio-temporal picture of LIG temperature changes is difficult to obtain. Here, we have selected 47 polar ice core and sub-polar marine sediment records and developed a strategy to align them onto the recent AICC2012 ice core chronology. We provide the first compilation of high-latitude temperature changes across the LIG associated with a coherent temporal framework built between ice core and marine sediment records. Our new data synthesis highlights non-synchronous maximum temperature changes between the two hemispheres with the Southern Ocean and Antarctica records showing an early warming compared to North Atlantic records. We also observe warmer than present-day conditions that occur for a longer time period in southern high latitudes than in northern high latitudes. Finally, the amplitude of temperature changes at high northern latitudes is larger compared to high southern latitude temperature changes recorded at the onset and the demise of the LIG. We have also compiled four data-based time slices with temperature anomalies (compared to present-day conditions) at 115 ka, 120 ka, 125 ka and 130 ka and quantitatively estimated temperature uncertainties that include relative dating errors. This provides an improved benchmark for performing more robust model-data comparison. The surface temperature simulated by two General Circulation Models (CCSM3 and HadCM3) for 130 ka and 125 ka is compared to the corresponding time slice data synthesis. This comparison shows that the models predict warmer than present conditions earlier than documented in the North Atlantic, while neither model is able to produce the reconstructed early Southern Ocean and Antarctic warming. Our results highlight the importance of producing a sequence of time slices rather than one single time slice averaging the LIG climate conditions

How warm was Greenland during the last interglacial period?

The last interglacial period (LIG, ~ 129–116 thousand years ago) provides the most recent case study for multi-millennial polar warming above pre-industrial level and a respective response of the Greenland and Antarctic ice sheets to this warming, as well as a test bed for climate and ice sheet models. Past changes in Greenland ice sheet thickness and surface temperature during this period were recently derived from the NEEM ice core records, North-West Greenland. The NEEM paradox has emerged from an estimated large local warming above pre-industrial level (7.5 ± 1.8 °C at the deposition site 126 ka ago without correction for any overall ice sheet altitude changes between the LIG and pre-industrial) based on water isotopes, together with limited local ice thinning, suggesting more resilience of the real Greenland ice sheet than shown in some ice sheet models. Here, we provide an independent assessment of the average LIG Greenland surface warming using ice core air isotopic composition (δ15N) and relationships between accumulation rate and temperature. The LIG surface temperature at the upstream NEEM deposition site without ice sheet altitude correction is estimated to be warmer by +7 to +11 °C (+8 °C being the most likely estimate according to constraints on past accumulation rate) compared to the pre-industrial period. This temperature estimate is consistent with the 7.5 ± 1.8 °C warming initially determined from NEEM water isotopes. Moreover, we show that under such warm temperatures, melting of snow probably led to a significant firn shrinking by ~ 15 m. Climate simulations performed with present day ice sheet topography lead to much smaller warming but larger amplitudes (up to 5 °C) can be obtained from changes in sea ice extent and ice sheet topography. Still, ice sheet simulations forced by 5 °C surface warming lead to large ice sheet decay that are not compatible with existing data. Our new, independent temperature constrain therefore reinforces the NEEM paradox

What controls the isotopic composition of Greenland surface snow?

International audienceWater stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (d18O, dD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor d18O and air temperature (0.85 ± 0.11‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with d18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5-day periods between precipitation events, our data demonstrate parallel changes of d18O and d-excess in surface snow and near-surface vapor. The changes in d18O of the vapor are similar or larger than those of the snow d18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model-data comparisons, and call for further process studies. © Author(s) 2014