scalbers

And by the way in the paper they mention the energy of the gamma-rays runs up to the TeV range.

I can start on that by mentioning tau is the gamma-ray delay in seconds to the galaxy they're studying, in proportion to the gamma-ray energy in GeV. The refractive index is the fractional slowing in the speed of light relative to c. E is the gamma ray energy, though I wonder what M(qg) is - a quantum gravity mass they've somehow derived from the Planck mass? The PDF file (link in upper right) is a bit more readable for the abstract equations. In the body of the paper, equation (1) helps to spell out the relationships.

Apparently there is evidence from gamma-ray bursters that high energy gamma rays arrive after the low energy ones. One possible explanation is a dispersion effect in the vacuum, that I assume represents a slowing relative to the speed of light. More at this link that we touched upon offline: http://arxiv.org/abs/0708.2889 Steve

Hello all, Interesting discussion. Unsure if this is remotely related - here is an arXiv paper on measuring graviton spin resonance: http://arxiv.org/abs/hep-ph/0006114

I'd suggest the "natural" CO2 level is what it would have been at present without human influence, perhaps at 280ppm. I also think this is desirable. Recall that about 300ppm is the highest level there has been in the history of the human species, and it seems to me we should keep the upper limit from going noticeably above this in terms of climate forcing. Natural temperature levels go in a similar manner, in that we would want to keep our influence on them from going to higher levels than they've been in human history. The rate of warming at the end of the YD may have been comparable to today, though again we should consider the difference of having a high rate of warming starting from the warmer initial temperature of today. Good reminder by npts2020 that it is very difficult to remove CO2 once it is let into the atmosphere, so we'd be best to know what we are doing ahead of time. As for 12000 years ago, I personally would go with letting nature take its course. That is an interesting debate though, similar to whether we should try and intercept incoming asteroids. The present debate though about humans' influence on the Earth, now maybe in the Anthropocene Epoch, is whether we have the moral authority to make major changes in the planet's ecosystems, with the reduction in biodiversity. These changes would affect the Earth for geological time scales in the future.

Hot off the press, an impact explanation for the Younger Dryas... http://www.cnn.com/2009/TECH/science/01/02/comet.diamonds/index.html Was this the cause of the extinction of the mammoth? If so, it was apparently from the smoke from fires rather than the ongoing temperature changes. As for present climate, I agree we are in a warmer regime as the starting point than we were during the warming at the end (of recovery) from the Dryas period. This is a reason why the present human caused warming is of particular concern. Here's a good Wikipedia article on the overall picture of impacts on Earth: http://en.wikipedia.org/wiki/Impact_event

An impact large enough to disrupt ecosystems and climate on a global scale probably comes only on the time scale of millions of years. The percentage of Earth occupied by large cities is small enough to it would take a fair number of Tunguska level events to hit the "target". How often do Tunguska level events occur somewhere on Earth? I've asked this to Clark Chapman who is an expert on this and he said around 1000 years, though I personally do think it may be less than that. Regarding land vs ocean impacts, I think an ocean event might still produce a damaging tsunami in coastal areas. Here is an example of one possibility: http://www.nytimes.com/2008/12/30/nyregion/30tsunami.html There is a certain qualitative difference between a human caused event vs a non-human caused one, though admittedly a good subject of philosophy. By the way it seems the Greenland temperature change in the younger Dryas could have been greater than the overall global rates of change.

Hansen 2008 is both informed opinion and scientific study. He makes scientific assertions about short-term and long-term feedbacks that I was wondering about. I also applaud him for connecting the dots and explaining the relationships between the climate, environment, and society. I think that's fair game for climate and other scientists to be more interdisiplinary. Too many stovepipe specialists in society can be blinding. What if the alarmist things are largely true, are they still alarmist? Let's address the facts here, are the species at risk? CO2 values and temperatures now are heading towards values warmer than any time since when many of todays' species even evolved. Combined with habitat loss they may indeed be in danger. I define coping as the ability of various species to avoid major population loss or extinction. Having a CO2 goal is useful to come up with a rational strategy. If we're not exactly sure we can pick the best guess now and refine it later. It might be arbitrary whether it's 350 or 360, but 350 vs. 450 is a significant choice. If the CO2 doubling sensitivity is 3C, then 450ppm should be a top limit (or perhaps less). If the CO2 doubling sensitivity is 6C, then 350ppm should be a top limit (or again perhaps less). I would suggest ultimate warming should be kept at today's values (about 1C), so with the 6C sensitivity possibility I would arrive at a safe value of about 320ppm.

Yes, I'm also a Terra Preta fan so glad to see more of them on this forum. There is a thread on TP that you may have seen here: http://www.scienceforums.net/forum/showthread.php?t=23533

Yes, the fraction of the carbon that gets bound up in sediments and geologically sequestered would be important to consider. As a thought experiment lets assume it is reasonably large - about .33. I would submit that this might not be large enough to be beneficial since the remainder (.67) would still reside in the ocean/atmosphere system over a 1000 year time scale and would still be contributing to global warming and ocean acidification. It would be better to have not emitted it in the first place, or perhaps sequester it in soils instead. Or even mechanical sequestration in the ocean sediment if that can be trusted. In other words, ocean fertilization may have a short term atmospheric CO2 reduction over a few decades or centuries, but would likely be quite limited in terms of a reduction 1000 years out. The levels at the 1000 year time scale are longer than human lifetimes, though still worth considering in my view. In the short term this may also increase deep ocean acidification for those lifeforms that exist there. On a separate note, there could be unintended ecological disruptions caused by ocean fertilization.

SkepticLance, Off-hand I think this might be stated differently, since over the 1000 year time scale carbon that falls towards the deep ocean may decompose or dissolve, then mix back to the surface waters and atmosphere. It's unclear to me how much of the carbon would fall all the way to the sea floor and not be metabolized or dissolved or somehow end up back into the ocean waters. It would have to sit on the ocean floor for many thousands of years before geological "removal" would take place.

Yes, this sinking to the deep ocean is the biological pump I referred to in post 91. Ultimately all the carbon on a thousand year time scale ends up in the same place. The processes of mixing and decomposition ends up producing an equilibrium concentration (I think of carbonic acid) in the ocean and this in turn is in equilibrium with the atmosphere. One might hasten the oceanic uptake of carbon in the short term with fertilization, but the long term limit remains the same. So therefore we have no long term benefit of ocean fertilization. In fact we are simply hastening the day that we have set up a long term acidification of the ocean.

Yes inow, I take it you agree with me this wouldn't be a good idea overall, just some limited atmospheric CO2 benefit in the short-term and even that is outweighed by other problems that you are providing good details about. My main point is that the proposed fertilization would hasten the day that the deep ocean sinks weaken.

Actually the ocean fertilization might just be a temporary benefit in moving CO2 into the ocean sooner. Since the ocean systems ultimately have limited capacity to absorb carbon this might just hasten the day that oceans help slow the growth of atmospheric carbon? In other words if we use the "biological pump" to move carbon to the ocean bottom, this will in effect do the mixing that normally takes about 1000 years in a shorter period of time. Once the ocean is mixed then CO2 uptake slows down quite a bit.

So what would be best for the planet? Supposedly the 2C warming level would be set at 450ppm, though I personally would prefer a stronger limit of 1C warming and 350ppm. However if the recent Hansen study is correct (a reasonable debate at this point), and climate sensitivity to CO2 doubling (long term) is about 6C instead of 3C, then this means we'd need to halve the CO2 excess over pre-industrial values. What are the scientific arguments about the climate sensitivity estimates? In other words, would CO2 at 350ppm still yield 2C warming anyway? What should the warming limit be in terms of both CO2 levels and long-term temperature rise? There is also a "safe" limit for ocean acidification as per this article: http://features.csmonitor.com/environment/2008/12/18/world%E2%80%99s-oceans-turning-acidic-faster-than-expected/

To put things in a bit of context it might be an interesting challenge (thus strengthening one's paper) to address these skepticisms about whether an electron is a black hole: http://cow.physics.wisc.edu/~ogelman/guide/e/

As Skeptic Lance points out a model can just as easily underestimate global warming effects as overestimate it. On another note I just read Jim Hansen's paper from this year today where he lays out the rationale for 350ppm as CO2 concentration limit. He points out that models and other estimates only take into account short-term feedbacks and ignore longer term feedbacks that would increase the effect. It's also interesting to consider what time in history (and what CO2 levels) the Antarctic and Greenland icecaps formed, and this helps provide a guide to future potential climate impacts.

And thanks for the wiki link, inow. I would highly recommend reference 41 on that page for better understanding for all engaged in this debate: http://geosci.uchicago.edu/~archer/reprints/archer.2005.fate_co2.pdf It's interesting about the interplay of changes in atmospheric CO2, oceanic CO2, and the geological reservoir that we may eventually need to act, even though it takes thousands of years. In other words, some, but not all of the atmospheric CO2 is taken up by oceans in the shorter time spans. As I understand it water vapor is kind of a "slave" gas that changes in response to the CO2/methane buildup. So the main cause is the CO2/methane and the water vapor increase acts like a mild positive feedback, though that still roughly doubles the effect.

Greetings, This article supports what I've been saying for quite a while about the longetivity of CO2 in the atmosphere and oceans... http://www.independent.co.uk/environment/climate-change/greenhouse-gases-will-heat-up-planet-for-ever-1041642.html Some of the excess CO2 apparently will stay in the atmosphere for many thousands of years unless a way is found to remove it.

Most of the "after the fact" remedies have side effects. I think removing the cause (i.e. greenhouse gases) would be a cleaner solution. For example, solar shades would reduce solar energy that drives the water cycle, hence less rainfall. There would also be less photosynthesis to grow plants (feeding most life on earth). Seeding the oceans with iron would alter ecosystems and may cause species extinctions. Besides the CO2 would still be there with the ocean acidification stressing those shelled creatures. Better again to take care of the CO2 directly.

New documentary relating to Terra Preta on the National Geographic Channel: Superdirt Made Lost Amazon Cities Possible?

Skeptics do a good service by pointing out mistakes such as this. I think they also do a disservice by magnifying the doubt since the bottom line is that faster action should be taken based on the inertia considerations I've mentioned from time to time.

I see nothing there that underpins the notion that there has been a dramatic warming trend globally over the past couple of decades. I've also never seen much talk by skeptics about how to avoid the risk of irreversable changes in the Earth's climate if we fail to act in the near future, due to inertia in the system.

Even though we can very confidently say that humans are causing present global warming, an important related question is are we too late to prevent the possibility of significant warming in the future? Note the inertia of the atmosphere, oceans, geological carbon storage, and societal changes that must be considered to answer this. A third related question revolves around ocean acidification.

What are the similarities and differences in the two, just the enrichment level of the uranium?