Au cours de son histoire, notre planete a connu des conditions climatiques tres diverses. Comment fonctionne la machine climatique ? Qu'est-ce que le climat global ? Pourquoi et comment a-t-il change ...au cours des temps geologiques ? Comment se situe le changement climatique en cours dans ce contexte geologique et historique ? Le rechauffement en cours est marque par des phases d'acceleration et de ralentissement, et des amplitudes differentes selon les regions. Comment faire la part des facteurs naturels et des activites humaines dans ce rechauffement recent ? A quels risques climatiques serons-nous amenes a faire face, pour les prochaines decennies, et les prochains siecles ? Les sciences du climat ont construit des methodes d'observation, d'analyse, de modelisation et de reconstitution des climats passes qui permettent de repondre a ces questions. Cet ouvrage, clair et precis, presente ainsi les acteurs du climat, leurs interactions, leurs echanges avec toutes les composantes de l'environnement terrestre, cet environnement qui est a la fois conditionne par le climat et affecte son evolution. Il en resulte un systeme qui genere sa propre variabilite, et peut produire des variations abruptes, comme en temoignent les climats passes. C'est egalement un systeme qui va reagir a des perturbations, qu'elles soient naturelles ou liees a l'influence humaine, avec des mecanismes complexes de retroactions. La modelisation du climat est donc centrale pour decrypter les causes des changements recents ou passes, et pour anticiper les futurs possibles.
During 7–12 July 2012, extreme moist and warm conditions occurred over Greenland, leading to widespread surface melt. To investigate the physical processes during the atmospheric moisture transport ...of this event, we study the water vapor isotopic composition using surface in situ observations in Bermuda Island, South Greenland coast (Ivittuut), and northwest Greenland ice sheet (NEEM), as well as remote sensing observations (Infrared Atmospheric Sounding Interferometer (IASI) instrument on board MetOp‐A), depicting propagation of similar surface and midtropospheric humidity and δD signals. Simulations using Lagrangian moisture source diagnostic and water tagging in a regional model showed that Greenland was affected by an atmospheric river transporting moisture from the western subtropical North Atlantic Ocean, which is coherent with observations of snow pit impurities deposited at NEEM. At Ivittuut, surface air temperature, humidity, and δD increases are observed. At NEEM, similar temperature increase is associated with a large and long‐lasting ∼100‰δD enrichment and ∼15‰ deuterium excess decrease, thereby reaching Ivittuut level. We assess the simulation of this event in two isotope‐enabled atmospheric general circulation models (LMDz‐iso and ECHAM5‐wiso). LMDz‐iso correctly captures the timing of propagation for this event identified in IASI data but depict too gradual variations when compared to surface data. Both models reproduce the surface meteorological and isotopic values during the event but underestimate the background deuterium excess at NEEM. Cloud liquid water content parametrization in LMDz‐iso poorly impacts the vapor isotopic composition. Our data demonstrate that during this atmospheric river event the deuterium excess signal is conserved from the moisture source to northwest Greenland.
Key Points
Water vapor isotopic fingerprint of Greenland summer 2012 atmospheric river
Surface and remote sensing observations and models depict similar patterns
Strong influence of subtropical North Atlantic moisture with low distillation
Stable water isotope records from Antarctica are key for our understanding of Quaternary climate variations. However, the exact quantitative interpretation of these important climate proxy records in ...terms of surface temperature, ice sheet height and other climatic changes is still a matter of debate. Here we report results obtained with an atmospheric general circulation model equipped with water isotopes, run at a high-spatial horizontal resolution of one-by-one degree. Comparing different glacial maximum ice sheet reconstructions, a best model data match is achieved for the PMIP3 reconstruction. Reduced West Antarctic elevation changes between 400 and 800 m lead to further improved agreement with ice core data. Our modern and glacial climate simulations support the validity of the isotopic paleothermometer approach based on the use of present-day observations and reveal that a glacial ocean state as displayed in the GLAMAP reconstruction is suitable for capturing the observed glacial isotope changes in Antarctic ice cores.
The isotopic composition of precipitation, in deuterium, oxygen 18 and oxygen 17, depends on the climatic conditions prevailing in the oceanic regions where it originates, mainly the sea surface ...temperature and the relative humidity of air. This dependency applies to present‐day precipitation but also to past records which are extracted, for example, from polar ice cores. In turn, coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air. This interpretation of isotopic measurements has largely relied on simple Rayleigh‐type isotopic models and is complemented by Lagrangian back trajectory analysis of moisture sources. It is now complemented by isotopic General Circulation Models (IGCM) in which the origin of precipitation can be tagged. We shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition. We then present experiments performed with two different IGCMs, the GISS model II and the LMDZ model. We focus our study on marine water vapor and its contribution to precipitation over Antarctica and over the Andean region of South America. We show how IGCM experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition. Such experiments support, at least qualitatively, the current interpretation of ice core isotopic data in terms of changes in sea surface temperature. Additionally, we discuss recent studies clearly showing the added value of oxygen 17 measurements.
Key Points
Link between the isotopic content of precipitation and its oceanic origin
Application of this method to polar ice cores & Andean precipitation
Potential of combining deuterium‐excess and oxygen 17‐excess
The Intergovernmental Panel on Climate Change (IPCC) is the leading international body for assessing the science related to climate change. It provides policymakers with regular assessments of the ...scientific basis of human-induced climate change, its impacts and future risks, and options for adaptation and mitigation. This IPCC Special Report on Climate Change and Land (SRCCL) is the most comprehensive and up-to-date scientific assessment of the multiple interactions between climate change and land, assessing climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems. It assesses the options for governance and decision-making across multiple scales. It serves policymakers, decision makers, stakeholders, and all interested parties with unbiased, up-to-date, policy-relevant information. This title is also available as Open Access on Cambridge Core.
Weather and climate extremes impose serious impacts on natural and human systems. In its fifth assessment report (AR5) and a special report Managing the Risks of Extreme Events and Disasters to ...Advance Climate Change Adaptation (SREX), the Intergovernmental Panel on Climate Change provided a thorough assessment of observed and projected changes in extremes in a warming climate, with evidenced scientific gaps in the understanding of these responsive changes being reported. Reviewing post-AR5 literature, this article synthesizes recent advances regarding these previous gaps with respect to detection, attribution, and projection of extremes. We focus on constraints for the assessment confidence, overlooked types and characteristics of extremes, and changes in their thermodynamic-dynamic drivers. We also stress potential misinterpretations of existing results, propose an update of earlier key findings, and identify burgeoning topics.
A record of atmospheric carbon dioxide (CO2) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO2record back to 650,000 ...years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO2lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO2remains stable throughout the six glacial cycles, suggesting that the relationship between CO2and Antarctic climate remained rather constant over this interval.
Abstract
The United Nations Framework Convention on Climate Change (UNFCCC) process agreed in Paris to limit global surface temperature rise to “well below 2°C above pre-industrial levels.” But what ...period is preindustrial? Somewhat remarkably, this is not defined within the UNFCCC’s many agreements and protocols. Nor is it defined in the IPCC’s Fifth Assessment Report (AR5) in the evaluation of when particular temperature levels might be reached because no robust definition of the period exists. Here we discuss the important factors to consider when defining a preindustrial period, based on estimates of historical radiative forcings and the availability of climate observations. There is no perfect period, but we suggest that 1720–1800 is the most suitable choice when discussing global temperature limits. We then estimate the change in global average temperature since preindustrial using a range of approaches based on observations, radiative forcings, global climate model simulations, and proxy evidence. Our assessment is that this preindustrial period was likely 0.55°–0.80°C cooler than 1986–2005 and that 2015 was likely the first year in which global average temperature was more than 1°C above preindustrial levels. We provide some recommendations for how this assessment might be improved in the future and suggest that reframing temperature limits with a modern baseline would be inherently less uncertain and more policy relevant.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
PDF
