Global Warming
J. Bradford DeLong
http://www.j-bradford-delong.net/
delong@econ.berkeley.edu
OK. Let's try again...
The earth's cross-section intercepts 1.762 x 10^17 watts of
solar radiation: that's 343 watts for each square meter of earth's
surface. Of that 343 watts, 34 are reflected back into space
by the land and the water, 21 are reflected back into space by
the atmosphere, and 44 are reflected back into space by the earth's
cloud cover. That leaves 240 watts per square meter of solar
radiation hitting the earth's surface and being absorbed. And
if the earth's temperature is to be constant the earth must in
turn radiate 240 watts per square meter back into space.
If we were to double the atmospheric concentration of CO2,
the CO2 would block a very large chunk of the earth's radiation
with wavelengths between 14 and 18 micrometers (our current CO2
levels block roughly half of the radiation in this range). This
is an important range of wavelengths. It is near the earth's
radiation peak: a lot of energy comes out through this band.
The physicists tell us that a doubling of CO2 would reduce radiation
from the earth back into space from 240 to 236 watts--if the
earth's temperature were to remain constant.
But if we have 240 watts coming in and 236 watts going out,
the temperature isn't going to remain constant. It will rise,
and a global temperature rise of 2.2 Fahrenheit degrees would
put us back into thermal equilibrium if nothing else were changing--if
cloud cover, the polar icecaps, water vapor, and a bunch of other
things we don't understand well don't change.
But other things will change:
--a warmer earth is a wetter earth, with more water vapor
in
the atmosphere, and water vapor is also a greenhouse
gas.
--a warmer earth has more low clouds, which tend to cool
the
earth by reflecting solar radiation before it gets
here.
--a warmer earth has more high clouds, which tend to warm
the
earth by reflecting the earth's radiation back down to
the surface.
--a warmer earth has less ice and snow, which means that
more
solar radiation would be absorbed.
--a warmer earth produced by human action is likely to have
more dust and sulfur compounds in its atmosphere, which
shade and cool the earth.
What will all this mean? We don't know. Scientists today give
estimates of the increase in global temperatures from a doubling
of CO2 (and other greenhouse gases) from pre-industrial levels
that range from 1.8 degrees Fahrenheit (Lindzen) to 4.5 degrees
Fahrenheit (Houghton) or higher.
Since December 23 a lot of people have told me that this is
"junk science" because...
...the sea level is not rising, but falling. (Doubtful, but
not yet relevant: no one's model would have predicted a noticeable
rise in the sea level yet.)
...satellite measurements of atmospheric temperatures show
not a warming but a cooling trend since 1979. (False: more recent
satellite measurements show a sustained warming trend since 1979.)
...the global warming that occurred over the past century
took place before humans had significantly raised CO2 levels.
(Sorta true. Something else must have been driving increasing
temperatures from 1900 to 1940. Global warming is a candidate
explanation only for what we have seen since 1980.)
...people who fear global warming are opposed to nuclear power.
...starting to do something about global warming would expand
the power of the government.
...any money raised in carbon taxes will be spent instantly.
...they [presumably scientists who believe in global warming]
would like to see a major human die-off.
It seems clear (to me at least) that what most people are
objecting to is not the science--the radiative physics, the thermodynamics,
and the (crude) attempts to model atmospheres and oceans--but
the politics: what they object to is not "junk science"
but "junk politics."
It also seems clear (to me at least) that calling global warming
"junk science" is extremely counterproductive for three
reasons:
First, it's mendacious.
Second, there *is* a lot of junk science out there--a lot
of lawsuits based on mendacious stupidity (of the "power
lines cause cancer" or the "smoking doesn't cause cancer"
level), and at least some juries that find themselves snowed
under. This is a problem. Our chances of doing something about
this problem will be lower if global warming is labelled "junk
science": the argument that we need to stop "junk science"
will then be countered by "yeah, well your guys think that
global warming is junk science," and my arguments and those
of the rest of the good guys will have less force.
Third, there is likely to be an enormous political battle
a decade from now as the signal that is higher global temperatures
emerges from the noise. The battle will be between those who
call for imposing a massive and destructive EPA-led command-and-control
regime on industrial civilization, and those who call for more
sensible policies--carbon taxes, bounties for carbon sinks, nuclear
energy, first world-funded transfer of clean technologies to
China and India, better dikes for Bangladesh, living with some
global temperature rise, and so forth. My side is going to be
a lot weaker if the other side can say: "yeah, a decade
ago your guys were saying that global warming was junk science."
People who call global warming "junk science" are
trying to steal the bad connotations that have been (deservedly)
attached to junk science and attach them to global warming. This
is a bad thing to do because global warming *ain't* "junk
science." And this is a bad thing to do because the blowback
might be extremely destructive.
Brad DeLong
Context:
He disputes that the warming trend is caused by CO2. But
as far as I
know no one disputes that the CO2 in the atmosphere a century
ago
warmed the earth a lot...
Brad DeLong
Brad,
I dispute it. Prove it, with logic and facts that do not
include assumptions.
My Comment:
The flux of radiant energy from the sun onto a surface of
one square meter normal to the sun at the mean distance of the
earth from the sun is some 1370 watts. But each square meter
of the Earth receives on average a quarter of this amount of
radiation: remember that the surface of the Earth has four times
the area of an earth-sized disk facing the sun. So that the average
flux of radiant energy onto a square meter of the Earth is some
343 watts.
The atmosphere scatters about 6% of this radiation back into
space before it even hits the Earth's surface. Because the earth
is not a black body, an additional 10% of this radiation gets
reflected back from the surface. Thus the average square meter
of the Earth absorbs 288 watts.
To balance this incoming energy, the Earth must radiate at
a rate of 288 watts per square meter. A body at a temperature
of -6 degrees Celsius would radiate this amount of energy. Yet
the average temperature of the Earth's surface is not -6 degrees
Celsius, but about 15 degrees Celsius. A body at a temperature
of 15 degrees Celsius radiates at a rate of not 288 watts per
square meter but 390 watts per square meter. Something is absorbing
the extra 102 watts per square meter of thermal radiation, and
so keeping the Earth in thermal equilibrium at an average surface
temperature that is comfortable 15 degrees Celsius, rather than
a chilly -6 degrees.
What is this something? Our greenhouse gases:
--H20 (water vapor) (1% of the atmosphere)
--C02 (carbon dioxide) (.036%)
--CH4 (methane) (.00018%)
--N20 (nitrous oxide) (.00003%)
--O3 (ozone) (.0005%)
Water vapor is good at absorbing radiation with a wavelength
of less than .0078 millimeters or of more than .018 millimeters
or so. Methane and nitrous oxide are good at absorbing radiation
with a wavelength between .0078 and .0083 millimeters or so.
Ozone is very good at absorbing radiation with a wavelength between
.0093 and .01 millimeters. And carbon dioxide is good at absorbing
radiation with a wavelength of between .014 and .018 millimeters.
Take away all our greenhouse gases, and the earth looks a
lot more like Mars...
Brad DeLong
Context:
I feel like I'm feeding the Troll
http://www.arn.org/currpage/ozfacts.htm
First observed by measurement 1956 by Dobson the guy who
name is
on the measurement units. I suppose he's not reliable.
My Comment:
arn.org ain't working.
But http://bsweb.nerc-bas.ac.uk/public/icd/jds/ozone/history.html
reports that:
There is an oft quoted statement that the Antarctic ozone
hole was discovered in 1956 and therefore it can't be caused
by CFCs. This remark originates from a paper by Professor G M
B Dobson, the scientist who designed the ozone spectrophotometer
which has been the standard for ozone measurements since the
1930s. The big advantage in standardising on one make of instrument
is that we can be certain that changes in ozone amount that are
measured, are changes in the atmosphere rather than changes due
to observational technique. The following is taken from Dobson's
paper in Applied Optics, March 1968, Vol 7, No3.
'One of the more interesting results on atmospheric ozone
which came out of the IGY (International Geophysical Year) was
the discovery of the peculiar annual variation of ozone at Halley
Bay (76 south, 26 west). The annual variation of ozone at Spitzbergen
was fairly well known at that time, so, assuming a six months
difference, we knew what to expect. However, when the monthly
telegrams from Halley Bay began to arrive and were plotted alongside
the Spitzbergen curve, the values for September and October 1956
were about 150 units lower than was expected. We naturally thought
that Evans has made some large mistake or that, in spite of checking
just before leaving England, the instrument had developed some
fault. In November the ozone values suddenly jumped up to those
expected from the Spitzbergen results. It was not until a year
later, when the same type of annual variation was repeated, that
we realized that the early results were indeed correct and that
Halley Bay showed a most interesting difference from other parts
of the world. It was clear that the winter vortex over the South
Pole was maintained late into the spring and that this kept the
ozone values low. When it suddenly broke up in November both
the ozone values and the stratosphere temperatures suddenly rose.'
This table shows the difference between what Dobson expected
from Spitzbergen, the normal values observed at Halley between
1956 and 1975 and the values presently observed. Mean October
ozone values have fallen by around 3% per year since 1976, while
the amount of chlorine has risen by 3% per year.
Spitz Feb Mar Apr May Jun Jul Aug Sep Oct
1956 440 470 450 400 350 320 300 280 280
Halley Aug Sep Oct Nov Dec Jan Feb Mar Apr
1956 300 300 300 330 350 320 300 280 280
1996 172 155 149 181 260 278 265 245 242
The Antarctic ozone hole is the depletion in the spring over
and above that caused by the different atmospheric circulations
in the two hemispheres. Signs can be seen in data from 1976 when
you know what to look for, but suspicion didn't really arise
until the end of the decade and the paper announcing the discovery
of ozone loss in the Antarctic was not published until 1985.
When American satellite data was reanalysed it became apparent
that it was a phenomena that covered the whole of the Antarctic
and it was given the name ozone hole. The latest data also show
ozone depletion during the summer and autumn months, in addition
to the spring- time 'hole'.
Context:
Climate is _WAY_ more complex than you are
bothering to pay any attention to. So until
the eco-nuts are willing discuss the fact
that their "statistics" are hogwash and their
"facts" are theories, and theories as full of
holes as Swiss Cheese, I'm going to keep
pounding them.
However, if you were confused by this
response, I'll keep it simple: You are
spouting political bullshit and not science.
My Comment:
Ah, once again the manners of a pig...
It's hard to be polite in response. But I will try.
First, we are making progress in this thread: we have agreement
that CO2 is being pumped into the atmosphere by human activity,
that more CO2 makes a warmer world, and that climate is complex.
Please note that this is pretty far away from where you were
a couple of days ago: now you're saying that we don't know how
much human-induced global warming is happening; then you were
saying that we had no good reason to think that human-induced
global warming was happening.
But there is one important point that you have missed: uncertainty
about the effects is not an argument for doing nothing. Uncertainty
is an argument for buying insurance against the bad things that
might happen.
The bad things that might happen from global warming over
the next century are pretty clear: the potential for a lot of
dead Bengalis as storm surges come up the Bay of Bengal, and
the loss of some species as their habitats shift north too fast.
Figuring out what kind of insurance we should buy is hard.
Please think about it. I think that we should shift some of our
tax burden away from income and sales taxes and towards greenhouse
gas-emissions taxes; I think that we need to fund a lot of research
into oceanic and atmospheric physics; I think that we should
fund a bunch of research into greenhouse gas-free sources of
energy; I think that we should fund a bunch of research into
carbon sinks.
Most important, however, we need people who are willing to
update their beliefs in response to data: to take a fresh look
at the information we have and evaluate it. So far in this thread
I have said that:
...measurements of troposphere temperatures that used to
show a
(slight) downward trend over time now show a (slight)
upward trend.
...dumping CO2 into the atmosphere will in all probability
warm
the earth.
...noisy data is still data--albeit noisy.
...we shouldn't casually act to change the earth's climate
without
thinking about what we are doing.
...there are big uncertainties.
Your response has been that I am "spouting political
bullshit and not science." There are people who are spouting
ideology--who are not looking at the data or using any more brainpower
than a snail does. But I am not among them. I am trying very
hard to mark my beliefs to market.
Please do the same.
Brad DeLong
Context:
I snipped the thing about the Ganges bull herder because
my answer is I
don't care about Ganges bull herders...
My Comment:
Adam Smith would say--did say--that human society is held
together by sympathy: an inborn propensity to think yourself
into someone else's shoes, and imagine what they feel. I don't
think he would have thought it possible for anyone sane not to
care...
|
Professor
of Economics J. Bradford DeLong, 601 Evans Hall, #3880