Actualité climatique du mois passé dans laquelle j'entrepose pêle-mêle les articles que j'ai trouvés intéressants (mais j'ai pu, et dû, en louper un certain nombre) ; comme je n'ai pas toute la journée à dédier à la tenue de ce blog je me dispenserai de traduire les articles en français, à chacun donc de se débrouiller avec la langue de Shakespeare en fonction de ses capacités (il y a au demeurant des outils de traduction en ligne assez performants...)
Comme je ne ferai aucun commentaire (sauf pour les dessins humoristiques), me contentant de reprendre quelques extraits ou graphiques des articles en question, les lecteurs qui m'accuseraient de cherry-picking verraient leur prose automatiquement envoyée à la
poubelle sans forcément une explication de ma part ; je donnerai à chaque fois les liens donc toute personne n'ayant pas de poil dans la main sera capable d'aller consulter les sources dans leur totalité.
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Le 12/12/2017 : Arctic Report Card: Lowest Sea Ice on Record, 2nd Warmest Year
Climate scientists say the magnitude and rate of sea ice loss this century is unprecedented in 1,500 years and issue a warning on the impacts of a changing climate.
Arctic shows no sign of returning to reliably frozen region of recent past decades
Despite relatively cool summer temperatures, observations in 2017 continue to indicate that the Arctic environmental system has reached a 'new normal', characterized by long-term losses in the extent and thickness of the sea ice cover, the extent and duration of the winter snow cover and the mass of ice in the Greenland Ice Sheet and Arctic glaciers, and warming sea surface and permafrost temperatures.
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Le 8/12/2017 : Changes in temperature extremes over China under 1.5 °C and 2 °C global warming targets
Abstract
The long-term goal of the 2015 Paris Agreement is to limit global warming to well below 2 °C above pre-industrial levels and to pursue efforts to limit it to 1.5 °C. However, for climate mitigation and adaption efforts, further studies are still needed to understand the regional consequences between the two global warming limits. Here we provide an assessment of changes in temperature extremes over China (relative to 1986‒2005) at 1.5 °C and 2 °C warming levels (relative to 1861‒1900) by using the 5th phase of the Coupled Model Intercomparison Project (CMIP5) models under three RCP scenarios (RCP2.6, RCP4.5, RCP8.5). Results show that the increases in mean temperature and temperature extremes over China are greater than that in global mean temperature. With respect to 1986‒2005, the temperature of hottest day (TXx) and coldest night (TNn) are projected to increase about 1/1.6 °C and 1.1/1.8 °C, whereas warm days (TX90p) and warm spell duration (WSDI) will increase about 7.5 %/13.8 % and 15/30 d for the 1.5 °C/2 °C global warming target, respectively. Under an additional 0.5 °C global warming, the projected increases of temperature in warmest day/night and coldest day/night are both more than 0.5 °C across almost the whole China. In Northwest China, Northeast China and the Tibetan Plateau, the projected changes are particularly sensitive to the additional 0.5 °C global warming, for example, multi-model mean increase in coldest day (TXn) and coldest night (TNn) will be about 2 times higher than a change of 0.5 °C global warming. Although the area-averaged changes in temperature extremes are very similar for different scenarios, spatial hotspot still exists, such as in Northwest China and North China, the increases in temperatures are apparently larger in RCP8.5 than that in RCP4.5.
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Le 13/12/2017 : North American Snow Cover on the Decline
As the world warms, the overall area of North America covered by snow is decreasing. One reason is because an increasing percentage of winter precipitation is falling as rain instead of snow in many locations. A Climate Central
report found that between sea level and 5,000 feet in elevation across the Western U.S., a smaller percentage of winter precipitation is falling as snow.
However, the relationship is more complex at each local level. Rising temperatures can cause some individual storms to produce more snow, where temperatures are still well enough below freezing. That’s because for every 1°F rise in temperature, the atmosphere can hold 4 percent more water vapor. In turn, more water is available to fall as snow or rain.
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| Moyenne de l'enneigement Nord Américain en millions de miles carrés. |
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ENSO
La Niña strengthened in November, and there is now a greater than 80% chance that it will continue through the winter. The event is predicted to be a weak-to-moderate strength one. The strength of an event isn't strongly linked to the strength of the impacts in the U.S., but strength does increase the likelihood that at least some level of the typical impacts will be felt. The next update will be on January 11.
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| Visualisation du phénomène ENSO sur le Pacifique Est en novembre 2017. |
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GISS L-OTI anomalies de températures vs 1951-1980
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Note: Gray areas signify missing data.
Note: Ocean data are not used over land nor within 100km of a reporting land station. |
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| Anomalies de températures à fin novembre 2017 selon la latitude. |
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Data Snapshots
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| Contenu de la chaleur océanique en 2016 (Colors on the map show where instruments detected more or less heat energy in the top 2,300 feet of water than the long-term average annual heat content. Orange areas show where heat content was higher than the long-term average. Blue areas show where heat content was lower than the long-term average. The darker the shade of blue or orange, the larger the heat-content difference from the long-term average.) source climate.gov/maps-data/data-snapshots/heatcontentanomaly-annual-ncei-2016-00-00 |
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Coral Reef Watch
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Climate Prediction Center
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| Global Tropics Benefits/Hazards |
| Last Updated: 12.26.17 | Valid: 12.27.17 - 01.09.18 |
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The CPC velocity potential and RMM-based MJO indices both exhibited a weakening signal during the past few days as the enhanced phase of the intraseasonal signal began propagating over the East Pacific and Western Hemisphere. The upper-level velocity potential anomaly field, usually a good indicator of MJO activity, has remained fairly disorganized since around 8 December. A large contributor to the weakened amplitude of the MJO is destructive interference from the La Nina base state, which favors enhanced (suppressed) convection in regions co-located with the recent positions of the suppressed (enhanced) MJO envelopes. Low-level tropical easterly anomalies weakened or reversed sign across the Pacific basin in recent days, and a divergent pattern aloft emerged over the East Pacific as the intraseasonal signal managed to overcome the base state to some extent. Dynamical model MJO index forecasts quite consistently show a re-amplification of the MJO signal as it enters the Indian Ocean, moving away from peak destructive interference with the La Nina signal. Should this occur, Indian Ocean MJO events teleconnect well with the North American midlatitude circulation, and the MJO may therefore help effect a pattern change in the late Week-2 or Week-3/4 period.
Typhoon Tembin formed on 20 December and is currently passing just south of Vietnam at tropical storm intensity. Further weakening is anticipated, but the tropical cyclone or its remnants will likely contribute to enhanced convection over Southeast Asia and the Bay of Bengal during the next several days. Elsewhere, recent satellite imagery does not reveal any areas of imminent risk for tropical cyclone development. Dynamical models highlight three regions for development during Week-1: the southwestern Indian Ocean (moderate confidence), Australia's Kimberley Coast (moderate confidence), and the Northwest Pacific between Guam and the Philippines (high confidence). There is less model predictability in Week-2, which precludes additional shapes on the outlook, but if tropical cyclone development does not occur over the southwestern Indian Ocean in Week-1, the area favored for development shifts westward towards Madagascar and the Mozambique Channel.
Forecasts for above- and below-average rainfall were made using the consensus among dynamical model forecasts and composites showing canonical patterns associated with MJO and La Nina activity. During Week-1, suppressed convection is favored across the central Maritime Continent as the MJO suppressed phase continues to interfere with the base state. Suppressed convection is also favored across much of the western and central Pacific, as the enhanced phase of the MJO crosses the Western Hemisphere and the suppressed phase and La Nina signal begin to constructively interfere. Areas of enhanced convection were indicated by dynamical model guidance across parts of the Indian Ocean basin and Western Australia, partly due to potential tropical cyclone activity. Across the Western Hemisphere, enhanced (suppressed) convection is favored over the tropical Atlantic, northern South America, Paraguay, and southern Brazil (southeastern Brazil).
The region of highest confidence during Week-2 is the Pacific Basin, where suppressed convection is favored as the suppressed phase of the MJO is anticipated to constructively interact with the La Nina signal. Unlike most other dynamical models, the CFS does not depict widespread enhanced convection across the Indian Ocean, so MJO composites and the ECMWF were favored. The ECMWF did depict enhanced convection over the Indian Ocean, but the region was primarily limited to a region south of the Equator. Elsewhere, the CFS and ECMWF both depicted enhanced convection over the East Pacific, and a reversal of the wet-dry dipole across eastern South America.
Forecasts over Africa are made in consultation with CPCs international desk, and can represent local-scale conditions in addition to global-scale variability. |
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Polar Science Center
Average Arctic sea ice volume in October 2017 was 6100 km3 a 1100 km3 above the record of 2012 ( 5000 km3) and almost the same as 2010. October 2017 volume was 65% below the maximum October ice volume in 1979, 50% below the 1979-2016 mean, and very close to the long term trend line. While 2017 started well below prior years and remained so through May, ice loss during June through October was less than previous years with July and August accounting for most of the “catch up”. This is shown in Fig 8 which compares daily ice volume anomalies for several recent years (base period 1979-2016). The difference between 2012 (the previous record) is notable. While 2017 started out with much lower sea ice volume, 2012 had a much more rapid sea ice loss through May and June. Both 2012 and 2017 have very similar anomaly progression through July. August and September 2017 by comparison was a months of reprieve relative to 2012.
Average ice thickness in October 2017 over the PIOMAS domain increase a bit relative to September and is 10 cm above to the lowest on record (Fig 4.). Note that the interpretation of average ice thickness needs to take into account that only areas with ice thickness greater than 15 cm are included so that years with less total volume can have a greater ice thickness. That’s why the average ice thickness can increase late in the year as thin regrown sea ice is added into the average.
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| Fig 8 Comparison of Daily Sea Ice Volume Anomalies relative to 1979-2016. |
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| Fig 4.Average Arctic sea ice thickness over the ice-covered regions from PIOMAS for a selection of years. The average thickness is calculated for the PIOMAS domain by only including locations where ice is thicker than .15 m. |
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| Fig.1 Arctic sea ice volume anomaly from PIOMAS updated once a month. Daily Sea Ice volume anomalies for each day are computed relative to the 1979 to 2016 average for that day of the year. Tickmarks on time axis refer to 1st day of year. The trend for the period 1979- present is shown in blue. Shaded areas show one and two standard deviations from the trend. Error bars indicate the uncertainty of the monthly anomaly plotted once per year. |
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| Fig. 2 Total Arctic sea ice volume from PIOMAS showing the volume of the mean annual cycle, and from 2010-2017. Shaded areas indicate one and two standard deviations from the mean. |
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| Fig.3 Monthly Sea Ice Volume from PIOMAS for April and Sep. |
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| Fig 6. PIOMAS Ice Thickness Anomaly for October 2017 relative to 2000-2015. |
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Arctic Data archive system (ADS)
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| Arctic sea ice extent. |
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| Antarctic sea ice extent. |
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| On pourrait écrire politi-sized... |
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| Dialogue de sourds. |
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| En hommage à tous les neuneus qui évoquent la vague de froid actuelle en Amérique du Nord. |
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| Ce genre d'affiche marche aussi très bien avec la Californie... |
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| Allez, encore un hommage aux mêmes neuneus qui parlent de vague de froid. |
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