Discussion Topic |
|
This thread has been locked |
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 25, 2010 - 11:45pm PT
|
The three pieces of evidence that the extra CO2 is anthropogenic. It is hard to come up with an alternative explanation that explains all three facts.
1. The ice core measurements of CO2 in the bubbles show that preindustrial CO2 never got above 270 ppm in the 450 thousand (not million) years that comprised the original Vostok core, until the Industrial Revolution. CO2 concentration today is about 370 ppm, an increase of 37%. Since the Mauna Lea and South Pole records started in 1958, CO2 rise has averaged about half a percent per year. If the cause is not anthropogenic, perhaps the situation is even scarier.
2. In the Northern Hemisphere, you see a distinct annual cycle because the land biosphere draws down CO2 in the spring and summer, because of enhanced photosynthesis, and then releases it in respiration. The South Pole data show less of an annual cycle because the ocean biosphere has less seasonal variability (although it has some). If you compare the South Pole and Mauna Lea data, however, you see a 1.5-2 year time lag between concentrations at Mauna Lea and the South Pole, indicating that the excess CO2 comes mainly from the Northern Hemisphere (where most of the people are).
See the Keeling graph . The line with the squiggles is Mauna Lea; the red is the South Pole, and you see the time lag. You also see that the South Pole has a small annual cycle.
3. Finally, the Seuss ratio (the amount of carbon-14 in the atmosphere divided by the amount of the normal isotope C-12) has declined as the CO2 concentration has risen. Therefore the extra CO2 is coming from a source that is depleted in C-14. C-14 has a half-life of about 5700 years, so coal and oil, whose carbon was photosynthesized from the atmosphere millions of years ago, have essentially zero C-14. If the extra CO2 were coming from some other source, like the ocean burping, we would not see a decline in the Seuss ratio.
In all this debate, it is important to recognize the contributions that Dave Keeling made. The issue of CO2 from fossil fuels was recognized in the 1890s by Arrhenius, but we had thought that the ocean would take up the extra. In the 1950s, Roger Revelle and others began to realize that ocean chemistry was more complicated than they thought. Keeling realized that CO2 would be well mixed in the atmosphere, and that a few locations for long-term measurements would be valuable. Since then, we measure CO2 at many more locations, but the Mauna Lea and South Pole data form one of the most important time series about climate.
Dave Keeling passed away in 2005 at the age of 77; he had a heart attack while hiking. Scripps has a website about him:
http://scrippsco2.ucsd.edu/
|
|
corniss chopper
Mountain climber
san jose, ca
|
|
|
Jul 26, 2010 - 12:14am PT
|
Uh-oh!!! AGW faithful lose several points in the Climategate sweepstakes
with this directive. What are they trying to hide?
IPCC warns its scientists to avoid the media
IPCC head Rajendra Pachauri says the UN panel's next report must make sure 'errors of any kind are completely eliminated'
Scientists have reacted with dismay at a letter sent out by the Intergovernmental Panel on Climate Change (IPCC) advising them not to talk to journalists.
http://www.guardian.co.uk/environment/2010/jul/19/ipcc-scientists-media
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 26, 2010 - 12:28am PT
|
But look at points 2 & 3 in my post. The idea is that there are multiple lines of evidence for the anthropogenic source, not just one.
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 26, 2010 - 12:49am PT
|
Chief - Yes. There is lots of work on diffusion of gases in the atmosphere, and the 1.5-2 year time lag is consistent with atmospheric circulation. The point is that an alternative mechanism must explain all three features of the data, not just one. I think Sherlock Holmes made similar statements!
Climate Change and the Integrity of Science is a letter in May signed by 256 members of the National Academy of Sciences. It's worth a read.
The discouraging aspect of this thread is that there are true uncertainties that we are ignoring -- regional climate, precipitation, aerosols, and ice sheet behavior -- while we battle acrimoniously about stuff that has been demonstrated by multiple lines of evidence.
I will continue to post, though.
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 26, 2010 - 07:30am PT
|
Correlation does not mean causation.
This statement has been posted many times, perhaps even by me. It's true, but I want to clarify some ways in which correlation and causation are related.
1. If we have a hypothesis about a cause (for example, the source of the extra CO2 accumulating in the atmosphere), then the hypothesis leads to some predictions, either about specific values of some variables or about a pattern that would be observed. Perhaps the most famous example in science is Einstein’s 1915 prediction from general relativity that light passing near the sun would be bent, and in 1919 Eddington’s observation of stars during a solar eclipse (the only time you can see stars at similar viewing geometry as the sun) confirmed that the stars indeed appeared to have shifted position. In the case of the extra carbon, if our hypothesis is that most of the extra carbon comes from fossil fuels (most, not all, as some is from biomass burning), then we should observe the three features I noted in my earlier post: coincident in time with the Industrial Revolution, slightly higher concentration in areas where most of the combustion occurs (only slightly because CO2 is well mixed and long lived in the atmosphere), and evidence that the extra carbon is old (i.e., the Suess ratio). You can credibly doubt an explanation only if you have an alternative mechanism, and the other major candidate is the ocean, which has nearly 40,000 gigatonnes of carbon, compared to something like 760 in the atmosphere and 600 in the vegetation. In the ocean’s mixing zone (the thermocline) the turnover is measured in years, not centuries, so if the extra carbon were coming from the ocean, that carbon would not be old (i.e., the Suess ratio would not be declining). And probably we would not see the slight spatial trend between the northern and southern hemispheres.
2. A second relationship is that correlation might imply causation. Therefore, if we observe a correlation, then we want to examine potential causes and thereby help us develop better understanding of process. In climate, probably the best example of this is that observed correlation between El Niño events and weather patterns in different parts of the Earth have led to improvement in the knowledge about the relationship between the ocean and atmospheric circulation. The climate models do not generate El Niños now (yet), but they do generate the atmospheric features that accompany them if you put the El Niño sea-surface temperatures into the model.
So when does correlation not imply causation? One case is when the causation goes in the other direction. Climate scientists agree that the decline in atmospheric CO2 during the Ice Ages was not the cause of the glaciation, but the other way round – the increased ice cover shut down much of the terrestrial biosphere, and it appears the extra CO2 went into the ocean. The Ice Ages were also dustier, and it is hypothesized that the dust added nutrients to the ocean that enabled assimilation of the CO2. The climate changes during the Ice Ages most likely resulted from orbital variability, which is not the cause of the current warming, and we probably ought to not continue to post the Vostok graph.
Another case is when the two correlated variables are both caused by something else. An example from my own work: over the years scientific papers propose a relationship between snow density and snow albedo. Indeed, if you make measurements of density and albedo throughout a snow season, you will see a correlation – as density increases, albedo decreases. However, radiative transfer theory says that density will not affect albedo until you get to about 500-600 kg per cubic m. And in experiments where we artificially compact snow, say by stomping on it with our skis, the before-and-after albedo measurements are the same. So what’s happening? Grain growth from snow metamorphism causes snow albedo to decline (because of the longer path of the photons as they pass through the grains), and at the same time the snow grains sinter and compact. Thus the same process is causing both densification and a decreasing albedo and so you see a statistical correlation.
A third case is spurious, random correlation. Statistics tell us the rare events happen in accordance with their expected probabilities. If you take a coin out of your pocket, flip it 10 times, and get all heads, you probably suspect something might be wrong with the coin (maybe both sides are heads). The probability that you get all heads in 10 flips is 2 to the minus 10, about 1/1000. But in a stadium with 100,000 people, if you ask everyone to take a coin from their pockets and flip them 10 times, about 100 people will get all heads and about 100 will get all tails, consistent with the 1/1000 probabilities. Similarly, if you correlate temperature with time for all the weather stations on Earth, you will get some with clear upward trends and some with clear downward trends. Therefore, you cannot use a single weather station to either support or argue against global warming.
Concluding remark: The proposition that climate change has a substantial anthropogenic cause is supported by a "preponderance of evidence," the legal standard used in civil cases. The proposition that most of the increasing carbon is coming from fossil fuels meets the legal standard for criminal cases, "beyond reasonable doubt."
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 26, 2010 - 09:36am PT
|
our level of ignorance of the climate system is still enormous and our policymakers need to know that.
 John Christy
Although I disagree with John Christy’s assessment of the nature and magnitude of uncertainties, let’s say for the sake of argument that I agree with the quote above. In terms of the policy implications, I assert that the quote is a strong argument that we ought to reduce emissions of greenhouse gases, with the goals to first slow down the rate, then level it off, then reduce it.
On the one hand, Christy and the Climate Change Denial folk say that we don’t know enough about climate to do anything, and on the other, they say that we ought to plunge ahead with the largest-scale global experiment in human history. At 370 ppm, atmospheric CO2 concentration is already above that at any time in Earth’s history unless you go back to times when the continents were in different places and therefore ocean circulation was completely different. But we’re only 37% above the preindustrial value, and now some want to go ahead and raise the concentration to 450, then 600, then 900 ppm, with the idea that some undefined, unverified negative feedback mechanism will reduce temperatures and also not allow ocean acidity. At those CO2 levels, we have no paleoclimatic conditions we can examine to give us a clue about the distributions of temperature and precipitation, and our only recourse is to rely on models. And the models do indeed become less certain the further away we get from current conditions.
In short, the Deniers are saying, “We don’t know what we’re doing, but let’s keep doing it.” I think you can understand the inconsistency of this logic without needing to know about the details of infrared absorption by carbon dioxide, water vapor feedback mechanisms, sea ice, ice sheets, and so forth. Usually, when I don’t know what I’m doing, I stop.
|
|
dirtbag
climber
|
|
|
Jul 26, 2010 - 09:46am PT
|
|
|
JEleazarian
Trad climber
Fresno CA
|
|
|
Jul 26, 2010 - 01:39pm PT
|
In terms of the policy implications, I assert that the quote is a strong argument that we ought to reduce emissions of greenhouse gases, with the goals to first slow down the rate, then level it off, then reduce it.
That, Dr. Deeg, forms the crux of the issue for most people. The current state of knowledge, including its uncertainty, still has policy implications. The idea that we do nothing while we wait to know more has no a priori economic merit.
Ultimately, the issue you address is one of economics, not climate science. Climate science can tell us the likely range of outcomes from any given set of actions, but ultimately people need to determine which combination of actions and possible outcomes optimizes their well-being.
My personal feeling is like yours. I'm risk averse to large changes, and there is ample evidence that trends in carbon emission risk (as opposed to are certain to cause) large, possibly irreversible change. Even though attempting to measure cost and benefit has proven elusive, we must make do with what we have until we know more.
John
|
|
bobinc
Trad climber
Portland, Or
|
|
|
Jul 26, 2010 - 03:03pm PT
|
something that seems to have gotten buried a bit in this thread is a shift in emphasis (or, at least, terminology) in this debate. "Global warming" has been replaced with "climate change", at least in some quarters. This is a useful re-designation given that researchers such as Hansen have tried to emphasize the troublesome nature of "chaotic" weather (vs just focusing on a warming planet). For example, most of the models I have looked at do predict more precipitation in temperate climates. In winter, this can mean more snow. Last year's big East Coast snow storms, which provided good fodder for global warming sketpics, could have been a good example of this. More precipitation, falling during a time of year when it is still cold enough to snow, means record-breaking snow accumulations. This seems counter to an overall warming trend but if the overall warming has so far been slight, it does make sense. If weather does get more chaotic, regardless of time of year, it will create more problems for agriculture, for the billions who live close to sea level, and for water-storage systems that rely on seasonal runoff from snowpacks (to give one example).
|
|
k-man
Gym climber
SCruz
|
|
|
Topic Author's Reply - Jul 26, 2010 - 11:13pm PT
|
Hey Chief! Just wondering, you have a lot of information and I am wondering how you are involved in the Climate Change Debate.
Sorry if you've already stated this above somewhere, but we know Ed's involvement and DrDeeg has clearly stated how he is involved. Just curious, are you a scientist, a researcher, of just an interested party?
I'm not trying to draw any conclusions, just curious because you've obviously done a bit of research on the subject.
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 28, 2010 - 11:41pm PT
|
The climate modelers do include the various semi-regular forcings (e.g. ENSO, PDO, NAO, sunspots, etc). The problem that Hansen et al 2007 identify is that the climate models do not generate these forcings themselves very well. And of course solar variability is an external forcing - the Sun does not respond to anything happening on Earth! We still do not know what triggers El Niño, but the models can put one in and simulate the result. Hence the question of whether there would be more frequent or less frequent El Niños in a warmer climate is answered only speculatively at this time.
Judith Lean's Living with a Variable Sun is a paper that is intended for a general audience and is quite readable. In it, she calculates the temperature increases from solar varibility, volcanic eruptions (El Chichón, Pinatubo), El Niño, and a secular trend from CO2. If you include all of these, you get a match to temperature observations over the past 25 years (I think she did not go further back because of the consistent solar dataset since 1980). In this period, the largest forcing is the CO2.
See her Figure 3.
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
|
Jul 28, 2010 - 11:45pm PT
|
An interesting observation, and perhaps illuminating why the models don't do precipitation well, is that the precipitation response in the southern Sierra Nevada to El Niño is perhaps chaotic. Since 1925 we have had six big El Niños, where I am defining "big" as a Southern Oscillation Index less than -2. The SOI is the normalized pressure difference between Darwin and Tahiti. Four of these big El Niños were wet in the southern Sierra, two were dry. The 1993 and 1998 El Niños had about the same strength. In the Tuolumne R drainage, the 1998 snow year was nearly at the 90th percentile (greater than or equal to 90% of the years) and 1993 was at the 15th.
[BTW: By the year, I mean the "water year" which goes from October 1 thru September 30, so 1993 = 10/1/92 - 9/30/93.]
The way one tests for chaos in a model is to tweak the input variables very slightly and see how the results change. In fact, the original 1965 Lorenz paper that spawned chaos theory came from Ed Lorenz's attempts to model convective precipitation. He found that when running the model (a set of three coupled ordinary differential equations) with slightly different inputs, the results tracked each other for a while, and then one would jump to a different domain. So over time, the models would sometimes match one another and sometimes be quite different. See chaoscope.org.
Phil Duffy (formerly at LLNL) experimented with a regional climate model's chaotic response to the 1993 El Niño. I recall that in his 10 simulations with only slightly different inputs, two were dry. The models do not show temperature to have a chaotic response.
|
|
Two Pack Jack
climber
The hills
|
|
In response to the above comment:
If you include all of these, you get a match to temperature observations over the past 25 years (I think she did not go further back because of the consistent solar dataset since 1980). In this period, the largest forcing is the CO2.
From the 'physics today' paper quoted above and given here as a link:
http://climateknowledge.org/figures/Rood_Climate_Change_AOSS480_Documents/Lean_Solar_Variability_Physics_Today_2005.pdf
A major enigma is that general circulation climate models predict an immutable climate in response to decadal solar variability, whereas surface temperatures, cloud cover, drought, rainfall, tropical cyclones, and forest fires show a definite correlation with solar activity.For example, when responses to the observed 11-year cycle in total radiative output are modeled, the resulting surface-temperature changes at Earth are a factor of five smaller than those deduced from empirical deconstruction of the surface-temperature record (figure 3)...In contrast, general circulation models of the coupled thermosphere and ionosphere predict dramatic responses to changing solar energy inputs (figure 4), but a lack of global datasets precludes comprehensive validation.
also:
Identifying and quantifying the diverse causes of contemporary change throughout the Sun–Earth system are ongoing challenges.
This is a pretty good paper to read, if you haven't gotten a hold of it yet. I tend to agree with that paper mostly, beside its statements on mass flux events over various magnetospheric boundaries and effect on heating. I also do NOT agree how, in the second or so last paragraph, she states with virtually NO evidence on the side of CO2 that it is a larger source of warming than radiative transfer from the sun. It is very important to note that in this statement not only does she give NO evidence on the side of CO2, but she also does NOT include particle heating caused by sun reconnection or dynamic pressure causing mass flux over (various) boundaries of the magnetosphere and inner boundaries (This is still a topic of wide debate in the realm of physicists, and may turn out to be a substantial source of heating). It is curious that she makes this seemingly misplaced CO2 comment where she states previously in this paper that solar output has strong and significant correlation to heating and heat triggered events.
This paper effectively states that the sun earth system is fundamentally a chaotic and extremely complex system. I agree with this, and would add that anyone who says that they truly understand the source of climate change is perhaps getting ahead of themselves.
If you want to really get educated on the subject, take a thermodynamics and meterology, perhaps a solar plasma class and pick up a James Lovelock book for fun.
It seems to me IMHO, that if you talk to the modelers that people seem to be quoting here... and I've had conversations with a few... that they are far less likely than many laymen to give a point source to climate change. As far as I'm concerned the verdict is still out, be we will know a lot more in the next 10 years or so as our understanding of the thermodynamics of the atmosphere and the sun increase through the sun's next cycle.
I'd be happy to suggest some reading for anyone who is interested in the solar cycle. The sun sure is cool! (in some senses I suppose)
|
|
DrDeeg
Mountain climber
Mammoth Lakes, CA
|
|
The sun indeed has an effect, and Judith Lean's data and reconstruction of the solar 'constant' (a poor term for exoatmospheric solar irradiance) since 1880 are used in Hansen's model (and those of others). The issue is that the variability of the sun in the whole century is ~2 Watts per sq m. Divide that by 4 (to account for the area of a sphere vs the area of the disk of the same radius), multiply that result by 0.7 to account for albedo, and then deal with the fact that much of the variable solar irradiance is at short wavelengths and is absorbed way high in the atmosphere, as the post above notes. The result in Hansen's model is that the solar forcing is ~0.2 Watts per sq m.
The effect of atmospheric CO2 on absorption of radiation emitted from Earth's surface is well studied -- in the lab, in measurements, and in models. Doubling CO2 from the preindustrial value of 270 ppm to 540 ppm causes 2-3 Watts per sq m of atmospheric absorption, with the variation depending on atmospheric profile, season, and latitude (and without water vapor feedback). You can do the calculation yourself at
http://geoflop.uchicago.edu/forecast/docs/Projects/modtran.html
Finally, the CERES (Cloud-Earth Radiant Energy System) instrument is showing that Earth is currently emitting ~1.8 Watts per sq m less than it is absorbing. The extra energy has to go somewhere, in this case probably heating the ocean. In steady state, absorption must equal emission, but Earth is in a transient state.
|
|
k-man
Gym climber
SCruz
|
|
|
Topic Author's Reply - Aug 17, 2010 - 08:57pm PT
|
Yes Bluey, it's so obvious and true. The degraded sensor on the NOAA satellite is causing wild fires in Russia, floods in Pakistan, record temps in Pakistan, record temps here in the US, and [on and on and on].
|
|
dirtbag
climber
|
|
|
Aug 31, 2010 - 07:37pm PT
|
Well, well, well.
With scientific data piling up showing that the world has reached its hottest-ever point in recorded history, global-warming skeptics are facing a high-profile defection from their ranks. Bjorn Lomborg, author of the influential tract "The Skeptical Environmentalist," has reversed course on the urgency of global warming, and is now calling for action on "a challenge humanity must confront."
In a book to be published this year, Lomborg calls global warming "undoubtedly one of the chief concerns facing the world today" and calls for the world's governments to invest tens of billions of dollars annually to fight climate change.
http://news.yahoo.com/s/yblog_upshot/20100831/sc_yblog_upshot/noted-anti-global-warming-scientist-reverses-course
|
|
Chiloe
Trad climber
Lee, NH
|
|
|
Aug 31, 2010 - 08:57pm PT
|
And meanwhile, in the physical world (as seen from space):
Over the period of satellite observation, and probably much longer, Arctic sea ice area reached record lows in 2007, 2008, and 2009. A few days ago, this year's area dropped below the 2009 mark to become the 3rd-lowest ever observed. With several weeks left in the melt season, it's still heading down.
Predictions that global temperatures would drop as El Nino ended, and baseless claims that global warming trends are an artifact of poorly-sited weather stations, have found no comfort in the continuing high lower-troposphere temperature anomalies seen by satellite. August monthly summaries aren't out yet but the daily feed from AQUA AMSU-A channel 5 sure looks hot:
I think both graphs I just linked to should continue to update.
Sources:
Sea ice area from IARC-JAXA Information Systems (IJIS),
http://www.ijis.iarc.uaf.edu/seaice/extent/AMSRE_Sea_Ice_Area.png
Daily satellite temperature plots from Nick Stokes' site,
http://moyhu.blogspot.com/2010/07/jaxa-arctic-ice-extent-melt-rate-and.html
|
|
|
SuperTopo on the Web
|
Let us know!