Letters : Football crazy
Ashwood, Australia
Close study of chaos theory may be assisting English football managers
(“Chaos pitch”, 8 June, p 24), but I wonder how many Australian football coaches
consider the behaviour of atomic bonds in a crystal lattice when developing
their game plan?
In our Australian rules game, successful attacking teams consistently exploit
a pattern of play where the ball is moved quickly up the wing from the back line
to goal-scoring positions. They try to develop an unbroken running chain of
passes, either by kicking or handball. When this approach works perfectly, the
opposing defenders, despite all their efforts, end up watching the ball sail
past each of them in turn.
The first player in this chain initiates the pattern by hesitating slightly
in his run off the back line. This feigned indecision “draws” a defender towards
him, thus leaving the next attacker unmarked and ready to receive the pass. Now,
if everything goes right, just as a discontinuity propagates through a plane of
crystals, the gap into which each successive attacker can move to receive the
ball propagates up the field.
Obviously this attacking style of play demands a high skill level and
involves considerable risk, but it can be very effective indeed, and wins by 10
or 20 goals are not uncommon, since our game doesn’t have an offside rule.
Letters : Methane mix-up
Cheltenham, Gloucestershire
G. J. Faichney provides a very muddled argument concerning global warming
potential (GWP) and methane (Letters, 29 June, p 52). GWPs compare the estimated
radiative forcings of various gases to that of carbon dioxide, which has a GWP
of 1.
He begins by asserting that the Intergovernmental Panel on Climate Change
(IPCC) determines the methane GWP to be 25 (that is, 25 times that of carbon
dioxide) by integrating over 100 years. The IPCC’s most recent assessments of
GWPs are in their controversial Climate Change 1995: The Science of Climate
Change, published in June 1996. It lists methane GWPs integrated over 20
years, 100 years and 500 years, and the respective values are 56, 21 and
6.5.
He then asserts that the GWP calculations are wrong to assume that “all
methane has the same effect regardless of its source”. But this assumption is
correct. Radiative forcing is a physical effect. A molecule of methane absorbs
and emits radiation according to physical laws which are not affected by the
molecule’s previous history. Indeed, the molecule does not know from where it
was once emitted so it cannot adjust its behaviour on this basis.
He continues by claiming that “fossil-fuel related methane鈥an be
considered to add new carbon to the carbon cycle” but all “methane emitted from
the biosphere鈥epresents a redistribution of methane already in the
cycle”. This is partly true. The carbon in the cycle can be in a variety of
forms, for example as carbon dioxide or methane in the air. And the carbon can
be in different components of the carbon cycle, for example as plant tissues or
methane in the air. The total carbon in the cycle may be almost constant but the
amount of methane in the air may vary. Changes to agriculture and land use
affect the amount of methane in the air. Methane GWP is a measure of the methane
concentration in the air.
He concludes by asserting that: “As the biosphere contributes some 70 to 80
per cent of the methane now entering the atmosphere, the IPCC’s value鈥or
the GWP of methane significantly overestimates its contribution to the enhanced
greenhouse effect.”
This is wrong. GWP compares the relative physical effects resulting from the
radiative properties of gas molecules and how long they stay in the atmosphere.
If methane GWP should be reduced in proportion to its ratio of “human” to
“natural” emissions, then carbon dioxide GWP should be similarly adjusted. The
net effect of this would be an immense increase in methane GWP. Human activities
contribute a tiny proportion of the many large “natural” emissions of carbon
dioxide. For example, natural forest fires emit as much carbon dioxide as all
human activity of all kinds. And each summer the oceans release more than ten
times as much carbon dioxide as all human activity of all kinds.
Letters : Persistent plants
Edinburgh
Ian Anderson’s piece about ryegrass resistance to glyphosate (This Week, 6
July, p 6) simply provokes the question: so what’s surprising? Darwin assured us
long ago that living organisms undergo natural selection. Offer any plant a
recurrent chemical insult and it will, sooner or later, develop resistance to
it. Recall, for instance, that elegant work of years ago about grasses that
withstood toxic metals on mine tips. If all those clever chemists at Monsanto
had just looked around, they might have noticed ivy, which in my experience is
unkillable. And if ivy survives, plenty of other plants must do so too. Why
should Monsanto chemists expect universal and permanent effectiveness?
Letters : Gaia's benefits
Oxford
The plants of the Colombian paramo described by Brian Homewood (“High and dry
in Colombia”, 29 June, p 34) are very like the black and white daisies of James
Lovelock’s model for Gaia. In the paramo, the espeletia (a daisy, as it happens)
makes the local world better for itself through collecting water from clouds and
also better for its ensemble since together the plants build a peaty sponge. By
releasing excess water slowly, the sponge improves the world for plants and
people down in the valley. Unfortunately, as Homewood shows, the beneficiaries
don’t always reciprocate.
This serves to highlight the main problem with Gaia. No one has yet shown why
a mobile and/or distant agent should evolve to repay beneficially. The
whole Gaia idea of evolved stability thus depends on an unstated proposition
that distant influences and mobile agents have a meagre overall influence on
local environments compared to local effects. The fact that it seems to be much
easier to get local people to protect the paramo than it is to get the
government in Bogot谩 to do so is entirely consistent with this
reasoning.
The same principle of local human involvement is being applied successfully
in a quite opposite kind of wetland on the same continent. As Homewood makes
clear, not all the water of the moors and snows of the great Andean arc trickles
to the Amazon, but a lot does, and most of this passes eventually into a certain
spongy patch of flooded forest in western Brazil.
Here the Mamirau谩 Project based in Tef茅 motivates and organises
the local people, who are dependent on the floods and the forest, to protect
their own against outsiders. The principle is again working well.
However, even if local effects can be made to predominate over distant ones,
major questions about the capabilities of such multi-species ensembles remain.
How cooperative are the paramo plants鈥攄o they really help each other to
construct a sponge which then helps everyone? Though powerless against
bulldozers, can they nevertheless鈥攑hysically by their peat construction,
long-term by their evolution鈥攔esist uncooperative and damaging outsider
species?
These questions have not yet had the attention they deserve from ecologists.
Understanding these kinds of superorganism, if they are such, will be crucial to
the possibility of a real science of Gaia as opposed to a myth. It may prove
crucial to the future of humanity in our super-mobile world鈥攁nd even
whether we have one.
Letters : Time after time
Tuart Hill, Western Australia
While I share Phil Bagnall’s gut feeling that time travel is impossible
(Forum, 6 July, p 45) his arguments against wormhole-based time machines are
seriously flawed. According to the models currently being studied by
relativists, no travellers from the future could arrive until the wormhole in
question has been created, so the entire era prior to the invention of wormhole
technology will remain forever out of reach. And in David Deutsch’s
multiple-worlds treatment of time travel, if there are 100 parallel worlds there
would only be 50 travellers鈥攅ach one kills their “potential” grandfather
in one of the other 50 worlds鈥攃utting the total number of time-travelling
grandsons ever born down to 50 rather than 100, an entirely unparadoxical
outcome
Letters : . . .
Clifton, York
Phil Bagnall dismisses the common refutation of the grandfather paradox by
saying that it does not involve time travel, but travelling between parallel
universes. I think he might not have understood the basis of the argument, which
is that if your actions in the past cause something to happen which would then
change the fact of your time travel (hence causing you not to do the thing which
caused the problem in the first place, which is a paradox) then what actually
happens is that a new parallel universe is created.
In this universe you succeed in whatever you did and you (the one in the
future) never went back in time (possibly because you didn’t exist) and there
are then two of you, one in that universe and one in your original one (in which
the action failed鈥攆or example, if you shot your grandfather but he ducked,
or the gun misfired鈥攁nd history wasn’t changed), but both of you originate
from the same universe.
Some people would feel that this argument carries a lot of metaphysical
baggage (the parallel universes) and it is possible to say that any action which
would cause a paradox cannot occur. The two arguments are the same from the
point of view of the original universe.
Letters : . . .
London
I think Phil Bagnall missed a key point. If a person had built a time machine
and set it to go one day forward, he would expect to arrive at his position 24
hours later.
The problem is that while our brave inventor travelled through time, the
Earth has also spun above its axis, moved several million kilometres around the
Sun, and the whole Solar System has also moved in space. So when he popped into
existence a day later, he would find himself in the murky void looking at a
rapidly departing Earth.
Letters : Whale count
Winden, Germany
Your article about the recent meeting of the International Whaling Commission
(IWC) and its scientific committee (This Week, June 29, p 4) refers to a working
paper of mine as “criticising the committee for not doing enough computer
simulations”. The issue was somewhat more complex.
There were two procedures on the table for estimating the abundance of minke
whales in the North Atlantic, one developed at the Norwegian Computing Centre
(NCC) and one developed here at the Centre for Ecosystem Management Studies
(CEMS). For reasons still to be elucidated, the NCC program estimates
considerably higher numbers of whales than does ours, although comparable
estimates are not yet available from the most recent (1995) survey.
The committee developed quite an extensive set of simulation tests, but only
the CEMS program could be put through them all because the NCC program is very
complicated and needed too much computer time to perform the tests. Despite
this, the committee opted for the NCC system. It was the logic behind this
decision that I questioned in my working paper.
The IWC has a formula, called the Revised Management Procedure (RMP), for
determining the allowable catch (“Blood on the water”, June 22, p 12). The
abundance estimate is put into this formula. Since the RMP formula has an
inbuilt margin of safety, use of an overestimate of abundance will not endanger
the whale population in the short term as long as the error is recognised and
corrected before too long. The committee could therefore agree on using the
higher estimate in the RMP. The committee also inserted a new provision into the
RMP rules which allows abundance estimates to be revised retrospectively if they
are subsequently found to be wrong.
Estimating the numbers of whales is a difficult but ultimately soluble
problem. Unfortunately, the politicisation of the issue has not made its
resolution easier. There is concern that to allow any scientific discussion of
this matter could be interpreted as an admission that the accepted estimates are
less than final: in such an atmosphere progress will inevitably be slow.
Letters : . . .
Trondheim, Norway
In the editorial of 29 June a poem was the editor’s last argument in the
whale debate鈥攚hich, so far, has been remarkably objective in your
journal.
Being honest in admitting that any data or population estimates (that is, as
a scientific basis for “resource management”) are without interest, this poetic
argument comes as a relief to all.
Letters : . . .
Correction: In “Analysis of Variance” (Inside Science 91, 8 June) the
quantity s12 was incorrectly defined (page 2, column 3, line 13). It
is the sum of squared differences divided by the number of degrees of freedom.
The calculated t-value (page 3, column 1) should therefore be 2.68. This remains
insignificant at the 99% level but would be significant at the 95% level.