mardi 28 novembre 2017

Climactualités - novembre 2017

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.


Le 7/11/2017 : pnas
Assessing the present and future probability of Hurricane Harvey’s rainfall (Kerry Emanuel)

We estimate, for current and future climates, the annual probability of a really averaged hurricane rain of Hurricane Harvey’s magnitude by downscaling large numbers of tropical cyclones from three climate reanalyses and six climate models. For the state of Texas, we estimate that the annual probability of 500 mm of area-integrated rainfall was about 1% in the period 1981–2000 and will increase to 18% over the period 2081–2100 under Intergovernmental Panel on Climate Change (IPCC) AR5 representative concentration pathway 8.5. If the frequency of such event is increasingly linearly between these two periods, then in 2017 the annual probability would be 6%, a sixfold increase since the late 20th century.
Fig. 1.
Storm total rainfall (millimeters) from a simulated tropical cyclone driven by climate analysis data over the period 1980–2016. This simulated event took place in August and September 2006. The track of the storm center is indicated by the back curve; it approached Texas from the southeast, moved slowly around a counterclockwise path in coastal Texas, and exited toward the southeast
Fig. 2.
Return periods of hurricane total rainfall (millimeters) at the single point of Houston, Texas, based on 3,700 simulated events each from three global climate analyses over the period 1980–2016. The dots show the three-climate-set mean and the shading shows 1 SD in storm frequency, remapped into return periods.


Le 8/11/2017 : advances.sciencemag
Snowball Earth climate dynamics and Cryogenian geology-geobiology

Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and ≥5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO2 was 102 PAL (present atmospheric level) at the younger termination, consistent with a global ice cover. Sturtian glaciation followed breakup of a tropical supercontinent, and its onset coincided with the equatorial emplacement of a large igneous province. Modeling shows that the small thermal inertia of a globally frozen surface reverses the annual mean tropical atmospheric circulation, producing an equatorial desert and net snow and frost accumulation elsewhere. Oceanic ice thickens, forming a sea glacier that flows gravitationally toward the equator, sustained by the hydrologic cycle and by basal freezing and melting. Tropical ice sheets flow faster as CO2 rises but lose mass and become sensitive to orbital changes. Equatorial dust accumulation engenders supraglacial oligotrophic meltwater ecosystems, favorable for cyanobacteria and certain eukaryotes. Meltwater flushing through cracks enables organic burial and submarine deposition of airborne volcanic ash. The subglacial ocean is turbulent and well mixed, in response to geothermal heating and heat loss through the ice cover, increasing with latitude. Terminal carbonate deposits, unique to Cryogenian glaciations, are products of intense weathering and ocean stratification. Whole-ocean warming and collapsing peripheral bulges allow marine coastal flooding to continue long after ice-sheet disappearance. The evolutionary legacy of Snowball Earth is perceptible in fossils and living organisms.
Fig. 28 Bar graph of peer-reviewed papers on Cryogenian glaciation by discipline and year, 1982 to 2016.
Papers are assigned to one of four disciplinary categories. Note the relative growth of geophysical and geochemical papers after 1996 and geobiological papers after 2002. From the 1870s through the 1980s, research on “eo-Cambrian” glaciation was almost exclusively geological (55). The 70 chapters by various authors in the work of Arnaud et al. (175) are not tallied here. Forward modeling papers (in all categories) account for only ~25% of the current total.


Le 20/11/2017 : nature
Recently amplified arctic warming has contributed to a continual global warming trend

The existence and magnitude of the recently suggested global warming hiatus, or slowdown, have been strongly debated1,2,3. Although various physical processes4,5,6,7,8 have been examined to elucidate this phenomenon, the accuracy and completeness of observational data that comprise global average surface air temperature (SAT) datasets is a concern9,10. In particular, these datasets lack either complete geographic coverage or in situ observations over the Arctic, owing to the sparse observational network in this area9. As a consequence, the contribution of Arctic warming to global SAT changes may have been underestimated, leading to an uncertainty in the hiatus debate. Here, we constructed a new Arctic SAT dataset using the most recently updated global SATs2 and a drifting buoys based Arctic SAT dataset11 through employing the ‘data interpolating empirical orthogonal functions’ method12. Our estimate of global SAT rate of increase is around 0.112 °C per decade, instead of 0.05 °C per decade from IPCC AR51, for 1998–2012. Analysis of this dataset shows that the amplified Arctic warming over the past decade has significantly contributed to a continual global warming trend, rather than a hiatus or slowdown.

Fig. 2: Annual mean SAT anomalies relative to 1979–2004 climatology and their linear trends over 1998–2012.
a,b, The Arctic region (60–90° N, a) and the globe (b). a, Black solid lines are from Kriging interpolation; the red solid lines are the mean of two DINEOF reconstructions with the blue shading representing their range. b, The black solid lines are from Annual K2015; and the red lines and blue shading are the same as in a but for the globe. The dashed lines show trends over 1998–2012 and the numbers show the warming rates over this period (°C per decade). The errors indicate the range of the two reconstructed trends relative to their mean.

Le 23/11/2017 : sciencedaily
Climate change could increase volcano eruptions

A new study, led by the University of Leeds, has found that there was less volcanic activity in Iceland when glacier cover was more extensive and as the glaciers melted volcanic eruptions increased due to subsequent changes in surface pressure.

Climatic control on Icelandic volcanic activity during the mid-Holocene

Human-induced climate change is causing rapid melting of ice in many volcanically active regions. Over glacial-interglacial time scales changes in surface loading exerted by large variations in glacier size affect the rates of volcanic activity. Numerical models suggest that smaller changes in ice volume over shorter time scales may also influence rates of mantle melt generation. However, this effect has not been verified in the geological record. Furthermore, the time lag between climatic forcing and a resultant change in the frequency of volcanic eruptions is unknown. We present empirical evidence that the frequency of volcanic eruptions in Iceland was affected by glacial extent, modulated by climate, on multicentennial time scales during the Holocene. We examine the frequency of volcanic ash deposition over northern Europe and compare this with Icelandic eruptions. We identify a period of markedly reduced volcanic activity centered on 5.5–4.5 ka that was preceded by a major change in atmospheric circulation patterns, expressed in the North Atlantic as a deepening of the Icelandic Low, favoring glacial advance on Iceland. We calculate an apparent time lag of ~600 yr between the climate event and change in eruption frequency. Given the time lag identified here, increase in volcanic eruptions due to ongoing deglaciation since the end of the Little Ice Age may not become apparent for hundreds of years.


9/11/2017 :
La Niña is underway, with a 65-75% chance that it will continue at least through the winter. Similar to last winter, the event is predicted to be relatively weak. During a weak event, the typical U.S. impacts associated with La Niña are still possible, but they become less likely. The next update will be on December 7.


Coral Reef Watch
28/11/2017 :
This figure shows the regions currently experiencing high levels of heat stress that can cause coral bleaching.
This figure shows the distribution of the lowest heat stress levels predicted by at least 60% of the model ensemble members. In other words, there is a 60% chance that the displayed heat stress levels will occur.
NOAA Coral Reef Watch's satellite Coral Bleaching Alert Area below shows the maximum heat stress during the Third Global Coral Bleaching Event. Regions that experienced the high heat stress that can cause coral bleaching, from June 1, 2014 to May 31, 2017, are displayed. Alert Level 2 heat stress indicates widespread coral bleaching and significant mortality. Alert Level 1 heat stress indicates significant coral bleaching. Lower levels of stress may have caused some bleaching as well. More than 70% of coral reefs around the world experienced the heat stress that can cause bleaching and/or mortality during the three-year long global event.


Climate Prediction Center
28/11/2017 :
Global Tropics Benefits/Hazards 
Last Updated: 11.24.17 Valid: 11.25.17 - 12.05.17
A weak intraseasonal signal continues to be centered over the Maritime Continent region, as indicated by both CPC's velocity potential based index and the RMM index. Dynamical model MJO forecasts display substantial differences in both the predicted amplitude and degree of eastward propagation of this signal during the next two weeks. The NCEP GEFS depicts the emergence of an intraseasonal signal across the eastern Indian Ocean (phase 3) which acquires high amplitude rather quickly during Week-1, then propagates eastward while deamplifying across phases 4 and 5 (Maritime Continent) before eventually moving back inside the unit circle on the RMM plot. The Canadian RMM diagram indicates a rapidly amplifying signal into phase 4 during Week-1, only to deamplify just as rapidly across phases 4 and 5 during Week-2. The ECMWF solution maintains a MJO signal with eastward propagation to Phase 6 (west Pacific) late in Week-2. Finally, the CFSv2 ensemble RMM plot deviates significantly from the other solutions, keeping the intraseasonal signal well inside the unit circle during the two-week period on the side of the RMM diagram that includes phases 3,4,5 and 6 (eastern Indian Ocean through the Western Pacific).

Tropical Cyclone (TC) development within the Friday update's reduced domain appears to be very limited, with one possible exception. The deterministic GFS runs initialized at 0z, 6z, and 12z, and the deterministic ECMWF run initialized at 0z, forecast the possibility of a TC forming over the Western Pacific, somewhere near 10N/140E, which then tracks towards the Philippines and South China Sea during the Nov 29 to Dec 5 period.

The Week-1 and Week-2 rainfall outlooks were adjusted based on the latest precipitation guidance from the ECMWF, GFS, and CFS models.


Polar Science Center
28/11/2017 :
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.
Fig 8 Comparison of Daily Sea Ice Volume Anomalies relative to 1979-2016.
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.
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.
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.
Fig.3 Monthly Sea Ice Volume from PIOMAS for April and Sep.
Fig 6. PIOMAS Ice Thickness Anomaly for October 2017 relative to 2000-2015.


Arctic Data archive system (ADS)
xx/11/2017 :
Arctic sea ice extent.
Antarctic sea ice extent.


C'est si vrai, en riant avec What on earth? comics !

Peut-être creuse-t-on la tombe réservée à Fred Singer qui avait réussi à s'échapper de celle de gauche (les zombies sont à la mode, winter is coming isn't it?)
Si seulement ça pouvait marcher comme ça...

Une petite pensée pour Rittaud, Gérondeau et Prud'hommes (entre autres)
Oui, que peut-on répondre à ça...? La bêtise laisse souvent sans voix, elle peut même provoquer des lésions au front.

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