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
The professor may have meant what he/she said. The short response to
the assertion is, "Please, show me your data." The data (in the most
generous appraisal) is confounding, because no one knows. Climate
change is (call it the greenhouse effect if you want) has become
highly politicized. On the one hand, there is the grossly
oversimplified position: Fossil fuels when burned produce CO2;
CO2 is a greenhouse gas; therefore the average temperature of Earth
will increase with disastrous consequences. On the other hand, there
is the unsubstantiated "no problem" position characteristic of the
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 science.
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".
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Update: June 2012