Home -- Wissenschaften/Sciences -- Literature -- Globale Erwärmung/Global Warming -- Residence Time of Carbon Dioxide in the Atmosphere
"... estimates of the characteristic 'residence time' of a molecule of carbon dioxide in the atmosphere involve a complicated mélange of factors, leading to the conclusion that
This is why the residence time of such molecules is generally characterized as a century."
Source: Robert M. May (Former President of the Royal Society (2000-2005), Chief Scientific Adviser to the British Government (1995-2000), Oxford, England), How Long Will They Stay (in cache) -in repsonse to Freeman Dyson, "The Question of Global Warming", New York Review of Books (NYBooks), Volume 55, Number 15, October 9, 2008 (in cache).
You can get a rough estimate of the lifetime of a carbon dioxide molecule in the atmosphere by dividing the total mass of carbon in the atmosphere by the mass that is absorbed in photosynthesis by land vegetation each year. I do not know the exact numbers. Roughly,
giving a lifetime of about twelve years. This is the average time that a carbon dioxide molecule spends in the atmosphere before it is absorbed by a land plant. I used this lifetime to estimate how long it would take for a major change in the land vegetation to produce a major change in the atmosphere.
- the total atmospheric carbon is eight hundred gigatons and
- photosynthesis absorbs seventy gigatons of carbon per year,
This calculation completely ignores the ocean. In reality the flow of carbon dioxide into the ocean is about twice as large as the flow into land vegetation. So the lifetime of a carbon dioxide molecule in the atmosphere is really only about five years. Between two jumps into the land vegetation, an average molecule jumps twice into and out of the ocean.
I ignored the ocean in my estimate because I was considering only land management and not ocean management as a way of controlling carbon dioxide in the atmosphere. It is possible that ocean management may turn out to be technically more effective, but land management is politically easier because each country owns its own land.
Princeton physicist Freeman Dyson has been roundly criticized for insisting global warming is not an urgent problem, with many climate scientists dismissing him as woefully ill-informed. In an interview with Yale Environment 360, Dyson explains his iconoclastic views and why he believes they have stirred such controversy.
Ruddiman doesn't contradict global warming problems. Rather he interprets data over the past four ice ages to try to explain why we are not 2000 - 4000 years into the next one. He argues, based on isotopic data and concentration data for CO2 and methane, that human activities over the last 6000 - 8000 years (the development and spread of agriculture) have prolonged the interglacial period we are in.
If Ruddiman's model is approximately correct, then after the hydrocarbon era we are in is over (approx. 200 years) and the oceans have scavenged the greenhouse gases (hundreds to thousands of years), it might be possible to drop directly into another ice age and return to the program already supposed to be 4000 - 5000 years in progress.
Ruddiman widerspricht den Problemen der globalen Erwärmung nicht. Eher interpretiert er die Daten im Zeitraum der letzten 4 Eiszeiten, mit dem Versuch, zu erklären, warum wir nicht schon seit 2000 - 4000 Jahren in der nächsten Eiszeit sind. Er argumentiert, auf der Basis von Isotopen Daten und Konzentrationsdaten für CO2 und Methan, daß menschliche Aktivitäten während der letzten 6000 - 8000 Jahren (der Entwicklung und Verbreitung der Landwirtschaft) die zwischeneiszeitliche Periode verlängert haben, in der wir sind.
Jedenfalls, wenn Ruddimans Modell in etwa zutreffend ist, dann könnte es möglich sein, direkt in eine weitere Eiszeit zu fallen und zum Programm zurückzukehren, das schon 4000 - 5000 Jahre in Gang sein sollte, nachdem das Kohlenwasserstoff-Zeitalter, in dem wir sind, vorbei ist (etwa 200 Jahre) und die Ozeane die Klimagase aufgenommen haben (einige hunderte bis tausende von Jahren).