Archives par mot-clé : CO2

Climate Science : some principles

Dr.  Albert Jacobs, Calgary, Canada


Climate science seems to have been taken over by politicians and the media. It is therefore essential to keep the debate alive on scientific principles, rather than popular hype.

This complex amalgam of scientific disciplines, called Climate Science, is replete with uncertainties and controversies. Politicians will proclaim that “The Science is settled”, because politicians do not want to deal with uncertainties. As scientists, we know that science is never “settled”. Scientific progress thrives on challenges and debate and it is up to science organisations to foster that.

I will list a number of essential aspects …

(See also CO2 as a function of geologic times)

Le changement climatique : la règle en géologie … Le taux de CO2 atmosphérique n’a jamais été aussi faible qu’aujourd’hui et la relation température/teneur en CO2 reste encore mal comprise

par Alain Préat

Article publié ( 27 décembre 2016) sur http://revue-arguments.com

Egalement pour les commentaires, sur le site notre-planete.info


Un écheveau d’une incroyable complexité

Depuis que la Terre existe, c’est-à-dire depuis 4,567 milliards d’années [1], s’il est bien une constante c’est qu’elle n’est jamais restée figée telle quelle, et qu’elle fut sans cesse profondément modifiée de façon plutôt aléatoire. Cela concerne autant les processus internes (notamment la composition de la lithosphère et les variations des mécanismes affectant la dérive des continents) que les processus externes. Parmi ces derniers l’atmosphère n’a cessé de varier du tout au tout notamment en ce qui concerne sa composition gazeuse. L’ensemble de ces processus internes et externes se sont sans cesse ‘télescopés’ et ont entraîné des rétroactions complexes à l’origine des nombreux changements climatiques observés dans les archives géologiques. A ces paramètres s’ajoutent également ceux pilotés à l’échelle extraterrestre, parmi les plus importants citons l’activité du Soleil ou les variations des paramètres orbitaux de notre Planète (précession, obliquité, écliptique). Le résultat est une combinaison extrêmement complexe de processus cumulatifs réguliers, irréguliers, linéaires ou non, chaotiques souvent, jouant à toutes les échelles temporelles et affectant à tout moment le climat qui en constitue une réponse. Physiciens, chimistes, biologistes, géographes… géologues tentent chacun à partir de son pré-carré de démêler cet écheveau particulièrement difficile à comprendre. Les synergies entre les disciplines sont heureusement nombreuses et le système climatique est peu à peu mis à nu à travers les temps géologiques (voir figure ci-dessous pour la succession des âges géologiques).

Echelle des temps géologiques:

ChronostratChart2016-04

Climate Change : the Rule in the Geological Record (Conference)

par Alain Préat


 The first aim of paleoclimate science is to identify from observations of the geological record, the  nature of past climate changes. Paleoclimate is probably the oldest discipline in Earth science, it began in the 19th-century, and earlier with the discovery of elephant-like beast in the superficial deposits of Europe and Siberia debate about the intepretation in the 18th-century. The debate was about these surface enviroments of temperate areas shaped by the biblic flood or by glaciers [Préat, 2015 http://www.notre-planete.info/actualites/actu_4356.php]. By the middle of the 20th-century, many climate features associated with the recent ice ages have been identified. Geological processes are critical to the evolution of the climate. The most important issue pertaining the earliest evolution of the Earth’s climate is that energy emitted by the sun has progressively increased over 4.6Ga.  Recontructing climate history from the inherently incomplete geological record requires integrated analyses including geochronology, paleomagnetostratigraphy, paleobiology, paleotectonics etc.  Climate change in the geological past is the rule, it has been reconstructed using a number of key archives (including sedimentary, geochemical proxies) since billion of years. These records reveal that since its birth the Earth’s climate as a rule has been warming up or cooling down with periods of (super)greenhouse and (super)icehouse modes, on scales of thousands to hundreds of million of years. The controlling factors are both cyclic (external or astronomical) and secular (internal to the Earth) and related to plate tectonics. For more than 90 percent of its 4.6 billion-year history, Earth has been too  warm, even at the poles, for ice sheets to form. We live  in unusual times at least from the cooling at the Eocene-Oligocene boundary (± 34 Ma)  with the glaciating Antarctica. The Earth was also severely glaciated several times in its history (e.g. about 750 and 535 Ma).  As an example of the conditions prevailing in the very warm times, oxygen isotopes suggest that the Archean seawater (4.0-2.5 Ga) coud have experimented hyperthermal environments, with temperatures as high as 55-85°C [Knauth, 2005 Palaeogeography, Palaeoclimatology,  Palaeoecology, 219 : 53-69]. Considering the Precambrian as a whole (4.6-0.541 Ga), prior to about 2.2 billion years ago, the amount of oxygen in the atmosphere and surface ocean was small, concentrations of CO2 were as high as 100-1000 times modern levels, as those of CH4 which were more higher. Complex microbial eocosystems developed during this period (sulfate-reducing bacteria, autotrophic methanogens, fermenting bacteria, anoxygenic phototrophic bacteria) and could have been important contributors to the biological productivity of early Earth. Past about 2.2 Ga the productivity began to be driven by oxygen-producing (micro)organisms.