The
Intergovernmental Panel on Climate Change (IPCC) is the main
scientific body that studies global warming. Although it takes some
heat from the skeptical, it seems that in a broad sense the IPCC has
done two things right.
The
first thing it has done right is to avoid making only one projection
of future global warming until the year 2100. Given all the
uncertainties, it would be very dogmatic to do such a thing. Instead
of publishing only one projection, the IPCC publishes a variety of
different scenarios, which have names such as RCP8.5, RCP6.0, RCP4.5,
and RCP2.6. Some of them are shown in the graph below (from this document).
The
climate change implications of these scenarios are shown in the next
IPCC graph, which uses a color-coding scheme matching the one
used in the previous graph. So we see that the RCP 8.5 scenario
(requiring a total carbon dioxide emission of about 6000 gigatons or
more) translates into a very damaging 3.5 Centigrade increase in
global warming. But the RCP2.6 scenario and the RCP 4.5 scenario
(involving only about 3 or 4 gigatons of carbon dioxide emission) result in
a much smaller increase of between 1.5 and 2..0 Centigrade.
Now,
you could argue that the RCP 8.5 scenario will never occur, on the
grounds that we will never be extract so much carbon dioxide (6000
gigatons or more). The International Energy Agency estimates that the
total world reserves of coal are only about 892 billion tons, and
much of that is hard-to-extract coal that may never be extracted
because it is not economically feasible to extract.
But
given the IPCC's approach of providing widely different scenarios,
such an objection does not damage its credibility. For one of its
other scenarios such as RCP 2.6 or RCP 4.5 may still be valid,
despite such an objection. Given its differing scenarios allowing
such a variety of outcomes, we really can't fault the IPCC for being
too dogmatic in this regard.
There's
another thing that is good about the IPCC approach: the fact that it
uses a probability scale. The IPCC has a scale
that looks like this:
These
probability assessments are used in the IPCC's Fifth Assessment
report. So rather than the report speaking as if it was 100% certain
about everything, we are told that some things are likely, other
things are very likely, and other things are as likely as not.
The
use of such a likelihood scale is to be commended, because there is a
great deal of uncertainty in our understanding of nature. If
scientists are not sure about something, it is is good that they
state assertions in a shaded away, expressing only moderate
confidence or low confidence.
It
would be good if other sciences followed such an approach. But do we
find such a likelihood scale used in fields such as biology, physics,
neuroscience or cosmology? No, we do not.
The
general tendency in contemporary science is to follow a very different
approach. It is as if there were two big lists: the list of approved
doctrines, and the list of disapproved doctrines. All of the items
on the list of approved doctrines are pretty much taught as if they were gospel
truths. This is not too different from the way that the Catholic Church
teaches religious doctrines.
Once
some teaching somehow manages to get on this list of approved
doctrines, the doctrine has it “made in the shade.” We are then
told that there is a scientific consensus, so it's kind of
“case closed.”
But
what if a different approach was taken, an approach using a
probability scale, like the IPCC is using? The results would be
salutary. There would no more be a situation in which doctrines
could endlessly “rest on their laurels.” Each scientific teaching
would have to be graded on a probability scale. If such a
probability scale was used honestly, it would soon become apparent
that some of the theories that have chewed up the most research funding have a
not-very-high ranking on the probability scale.
It
would be best to make use of a probability scale rather different
from the one used by the IPCC. The scale below would be better suited
for grading a wide variety of scientific assertions.
Almost certain | Greater than 99% likelihood |
Very likely | Greater than 90% likelihood |
Likely | Greater than 50% likelihood |
Quite possible | Greater than 5% likelihood |
Possible | Greater than 1% likelihood |
Remotely possible | Less than 1% likelihood |
Apparently impossible | Apparently no likelihood |
I can
imagine a two-phase exercise to make use of such a scale. In the
first phase, you begin with a chart like the one below. You draw
colored lines between the items on the left and the items on the right,
using a different color of ink for each level of confidence.
So the end result might look something like this:
In
the second phase of the exercise, you would be required to justify
each case in which you had specified that one of the items on the
left had a probability of “quite possible” or higher. This would
require actually presenting observations or experiments that show
there is a basis for concluding a likelihood of at least 5%. Appeals
to current popularity or a consensus of agreement would not be
allowed.
Let
us imagine how clarifying such an exercise would be. Using such a scale in the area of physics and cosmology would
throw light on how much of modern theoretical physics is on shaky
ground. For example, there would be no basis for giving either the
theories of supersymmetry or string theory a probability grade of
higher than “remotely possible” or “possible.” The fact that
such theories are widely popular would be no basis for granting
them an assessment of “quite possible” or “likely.”
Using
such a likelihood scale sounds like a great idea, so why is such a
scale not used in fields such as cosmology, physics, and biology? I
suspect the reason is that using such a scale would involve introducing a level
of humility that today's dogmatic theoretician would prefer to avoid.
Consider
the dogmatic scientific theorist. He may advance some theory
unlikely to be true. But he would rather that people not judge his theory
based on some scale in which it is judged whether the theory is “quite
possible,” “likely” or “very likely.” Because then it
might become clear that there is no basis for concluding that the
theory is probably true. Such a theorist would prefer the current
approach, in which it is as if there is a “list of approved
doctrines,” and you are supposed to accept all the items on the
list. Having got his theory on such a list (often because of
sociological considerations), such a theorist would not want there
to be a system in which scientists use varying shades of confidence
in their assertions. It might then become apparent to all that the
theorist's pet theory is not on very firm ground.
Similarly,
an apologist for an organized religion would never want you to make
use of some exercise like the one above, in which you drew lines
specifying whether 15 assertions of his creed were “possible,”
“quite possible,” “likely,” “very likely,” or “almost
certain.” He would instead want you to accept the whole creed with
complete confidence, regarding every item in it as a certainty.
Like such a theological apologist, the modern pitchman for the "official party line" of modern science would rather that you not use probability scale ratings that might make his "standard story" look like something that is largely speculative, largely a kind of social construct in which many a predominant theory is more of a speech custom than something that has been established as a likelihood.
Like such a theological apologist, the modern pitchman for the "official party line" of modern science would rather that you not use probability scale ratings that might make his "standard story" look like something that is largely speculative, largely a kind of social construct in which many a predominant theory is more of a speech custom than something that has been established as a likelihood.
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