Recent content by Graeme M

Thanks BillTre. That seems more what I am wondering about. What tells us that Melanesian folk, for example, are modern humans with Denisovan ancestry rather than Denisovans with modern human ancestry? Perhaps russ_watters is explaining that: I think this is where I am being confused. What does...

The book is "The World Before Us: How Science is Revealing a New Story of Our Human Origins" by Tom Higham, an English archaeological scientist. I found it very informative. Just to clarify, I'm not suggesting anything about humans and Denisovans being the same "species". Denisovans branched...

That isn't really addressing what I asked. What I am getting at is that modern humans and Denisovans must have very similar DNA. I read that in most African and European populations there is next to zero Denisovan DNA, but it is much higher (4-6%) in Melanesians which presumably is a result of...

This question probably shows my ignorance about how genetics work. I have just finished a great book outlining the current state of play regarding our understanding of human evolution and how modern humans gradually spread around the world, displacing other human lineages such as Neanderthals...

I am aware that it is claimed that ruminant farming and animal agriculture more generally are significant contributors to anthropogenic emissions. Here in Australia, for example, about 80% of emissions from the ag sector are from methane and nitrous oxide. Various groups propose finding ways to...

I think I shall leave it here. My main aim was to derive a simple explanation for others I talk to who are sceptical about CO2 warming the atmosphere. It's still not clear to me why back radiation is seen as a dominant factor. I guess I am misunderstanding something about the process, however I...

Genava, yes I agree that the notion of "surface" is not clear and may not explicitly mean "the ground". But I suspect most people reading about the GHE would indeed draw that inference - that the warmed atmosphere directly warms the ground leading to yet more thermal radiation from the ground...

I admit to not really following your comments, in particular this one. My understanding is that the atmosphere is matter. Some of that matter is warmed by the surface of the earth. Of concern in that regard is CO2, a well mixed gas, which is being emitted by human activity. If we measure the...

OK... that all got very complicated very quickly. Thanks for the many clarifications, however I was trying to keep it to a very simple explanation. My main divergence from the general explanation is not to mention back radiation, but commenters seem certain it must be included. I'm still not...

Tom, I am not sure that is how a greenhouse really works. When I think about it, it would appear that the main reason it works is down to containing the air rather than allowing it to disperse upwards to be replaced by cooler air. That is, it seems to me that a greenhouse works more by blocking...

Yes, though in my explanation I mean to observe that because the air is made of matter, it is warmed by the sun and the earth, just as any matter is warmed by a heat source. The main contribution in this case is the warmed earth; so as I see it, it isn't so much that the IR is blocked but that...

This is a very simple question. I've read a fair bit about the greenhouse effect and how GHGs affect the Earth's surface temperature and I know it can get very complex. But if I boil it down, it seems to be a very simple thing. Am I right to think of it this way? Radiation from the sun reaches...

I guess that the bottom line is that trying to assign values to arbitrary non-physical models is somewhat of an approximation. The bottom line just is that a blackbody stand-in for Earth with the same emissivity/albedo would be -18C. The real Earth with a complete atmosphere and variable land...

Hi Genava, yes, I know we can derive the temperature for a given set of parameters. I am more trying to get my head around the model being proposed. I get that this is a gross simplification and completely unphysical, but as I say, those numbers (-18C, 15C, 33C) are everywhere so they must refer...

Hmmm... unless I am misunderstanding what's been said, Genava and Bandersnatch are at odds with each other. Bandersnatch says that an Earth with an atmosphere transparent to IR and with an albedo of about 30% would have a surface temperature about the same as if it were a blackbody with the...