The Danger is Not the Gamma Rays directly (Score 2, Informative)

The real problem is ozone depletion and the formation of odd Nitrogen compounds, such as NO2. NO2 absorbs visible light (i.e. it gets dark and cold) and also steals ozone, O3, which is what saves our DNA from getting destroyed by UV light. Its not the gamma rays themselves that will kill us, they'll only last for 10 seconds and plenty of people will survive by simply being on the other side of the planet at the time. the radiation isnt going to cover the entire planet, but the argument they are trying to make is that it will make a hole in the ozone layer and might lower global temperatures. Here are some quotes from a preprint paper of theirs that I dug up at http://www.arxiv.org/ftp/astro-ph/papers/0503/0503 625.pdf "For some time, it has been known that high energy radiation may, through dissociation of N2 , create a variety of "odd nitrogen" compounds which lead to ozone depletion, making the atmosphere more transparent to solar UVB (290-315 nm) radiation. UVB is strongly absorbed by the DNA molecule and hazardous to life [e.g. Cockell 1999]." "Reid et al. [1978] noted two other potentially important effects, which have been acknowledged [Thorsett 1995] but not yet treated quantitatively in subsequent discussions of GRB atmospheric ionization effects. NO2 is one of the primary compounds formed. It has a major role in O3 depletion, but also absorbs strongly in the visible, giving it a brown cast. Such absorption may easily lower global temperatures, if sufficient NO2 is formed. Also, rainout of dilute nitric acid (HNO3) is one of the principal mechanisms of removal for the so-called "odd nitrogen" or "NOy" compounds formed. This can potentially contribute large amounts of biologically active nitrogen to the biosphere. The results are unpredictable but may be major, since biota are typically nitrate-starved and highly responsive to supplementation [Schlesinger 1997]"