World Oxygen Sources
I have a college professor that claims trees are not as
neccasary to the atmosphere as we think because most of our oxygen
comes from bacteria in the ocean. How true is this and how much of our
oxygen comes from land plants?
It is perfectly all right to ask your professor to direct you to some
references on this topic. A discussion with him or her will also allow
you to make sure that he is not misunderstood with regard to the facts
and also their implications.
Regarding your question, it is true that most of the earth's oxygen
production, PERHAPS as much as 90%, is from the sea plants through
photosynthesis within the top 100 m of the ocean water where there is
enough sunlight for the process to take place. But the implication
that somehow trees are not necessary (to atmosphere and perhaps by
implication to life) is unwarranted. To state that, we have to fully
understand the entire ecosystem, be able to model it, validate the
model going back in time, and then cautiously applying it to predict
and verify future trends.
The ecosystem that supports life on earth is a very delicate, our
knowledge of it negligible, and we are not in a position to state what
facets of the ecosystem are necessary and which ones are not. One
approach to ecosystem management - if we can all it so - is to avoid
causing dramatic man-made changes until we understand the system
better. The other school of thought, driven mostly by ideological and
financial considerations, states that undertaking activities that
cannot be shown to cause damage is fine.
Ali Khounsary, Ph.D.
Argonne National Laboratory
Global warming (the greenhouse effect) is not well understood (that is
being kind). First, the various numersou computer models give conflicting
results because the input data are insufficient and/or not well defined. The
classic example is the very term "average global temperature". Despite its
common use, it is meaningless. The climatic condition cannot be
characterized by a single number. A better concept is a "global temperature
fingerprint", that is, some places are going to get warmer, others are going
to get colder. But no such "fingerprint" exists. Second, WATER (H2O), not
CO2, is the major "greenhouse gas" and many models do not take water into
account and so are doomed from the start. The condition of the climate
depends upon several interacting positive/negative feedback cycles (H2O,
CO2, sea ice, marine biology, terrestrial biology and hydrology, other
atmospheric chemicals e.g. methane, solar insolation, solar "events", and
other upper atmospheric effects, global lightning patterns, particulates and
gases both from human origin and 'natural' origins such as volcanoes, even
cosmic rays). Each is complex in its own domain. Some of these cycles (and
others not mentioned) humans can have an impact; on others cycles, there is
no control. See "Understanding Climate Change Feedbacks" National Research
Council report. It is accurate to say that the "burn fossil fuel-produce
CO2-increase global temperature" is so primitive a paradigm it is useless
and meaningless, despite its popular use and appeal. At present, climate
models are not even able to reconstruct climate history, much less predict
the future. Chapter 10 of Philip Ball's book "Designing the Molecular World"
gives a balanced statement of the state of affairs with respect to global
This is not to be taken as "anti-environmental" or "anti-conservation".
Take it to mean that we need to ask the right questions, identify the proper
variables, construct meaningful models. In fact, we don't need all the
scientific data and predictions to "take care of mother Earth, it's the only
one we have." We need to be honest about the state of our knowledge and
understanding, however. And that state is very uncertain. Absurdly
oversimplified models, like the "burn fossil fuel-produce CO2-increase
global temperature" one are not constructive, to put it mildly. It focuses
on only one of many interacting feedbacks that define "climate".
More follow-up on this inquiry: See Feb 2004 issue of National Geographic
for article on "Where Has the Carbon Gone?" Climate issues involve at least
3 types of events: statics (such as a mass balance); dynamics (such as
atmospheric / terrestrial changes over time -- both short and long term);
chaotic (catastrophic events that influence climate, e.g. volcanoes). The
National Geographic article is a well thought out example of a mass balance
that doesn't "add up". That does not minimalize the seriousness of the
issues, but illustrates that the science is not so easy.
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Update: June 2012