According to you guys, the Sahara at least - and presumably other deserts - will green up naturally given a shift in natural weather patterns. In fact, you believe that the Sahara has undergone 200+ GSPs (lol) over the past umpteen million years. Okey dokey. My question is ...Are there any deserts presently greening naturally?Or is this "deserts will green up naturally" just another piece of wild speculation dressed up in sciency language?
the Sahara has undergone 200+ GSPs (lol) over the past umpteen million years.
re there any deserts presently greening naturally?Or is this "deserts will green up naturally" just another piece of wild speculation dressed up in sciency language?
Yes, there "any deserts presently greening naturally".I posted lots of links to Ethiopian deserts that greened naturally when grazing was stopped.However, in general, global warming means that deserts are currently getting dryer, not wetter. You'd expect deserts to green when humidity increases not when it is reducing.
Quote from: Pingu on June 12, 2016, 04:23:04 AMYes, there "any deserts presently greening naturally".I posted lots of links to Ethiopian deserts that greened naturally when grazing was stopped.However, in general, global warming means that deserts are currently getting dryer, not wetter. You'd expect deserts to green when humidity increases not when it is reducing.Let me ask it this way ... You've seen the current Google Earth world maps showing deserts all over the world.What do you think that Google Earth map would look like 4000 years ago? I think there would be hardly any desert areas at all ... Maybe none. How about you? What's your guess? How would you go about making an educated guess?
Too bad the TR archives are lost.There were countless examples there that support my analysis. Kalksjon would be a perfect example.But let's look at this thread.Have you recognized any "valid objections" to your "idea" that the Sahara desert was man-made?
I am not interested - in this thread - in what happened more than 4000 years ago. My question pertains to the last 4000 years. I have given you evidence that a pastoral society existed in SE Algeria up until about 1000 BC.So 4000 years ago, the area that is now the Sahara was probably pretty dang green. Why wouldn't other (present day) deserts be green back then too?
Probably no point at all for you because you don't seem interested in the topic
As for the Sahara, what objections were raised that the (most recent) drying of the Sahara was not caused by man?
During the warm early to mid-Holocene (8 000- 5 000 yBP), the global climate that resulted from glacial retreat brought an increase in the intensity of the monsoon throughout the sub-tropical arid lands. Lake Chad became a freshwater inland lake bigger than today's Caspian Sea, in an area that has again become a complete desert. Tropical forests and dry woodlands around the equator expanded north and south, while deserts moved into the mid-latitudes. During that period, the southern Sahara and the Sahel were much wetter than today, with extensive vegetation cover, thriving animal communities, and numerous human settlements.Sometime between 6 000 and 5 000 yBP, there was again a transition to more arid conditions. Mesic vegetation communities disappeared rapidly, lake levels declined dramatically, and highly mobile pastoralist cultures started to dominate and replace sedentary lacustrine and riparian traditions. The Liwa region of the United Arab Emirates, for example, experienced phases of sand deposition that lead to the formation of a large (up to 160 m high) mega-dune. A similar transition towards more arid conditions occurred in North America, where the Holocene brought the arrival of Mojave, Chihuahuan and Sonoran desert scrub elements from the south, such as the agaves, cacti, ocotillos (Fouquieria), and creosote bushes that characterize the area today.
I am not interested - in this thread - in what happened more than 4000 years ago. My question pertains to the last 4000 years. I have given you evidence that a pastoral society existed in SE Algeria up until about 1000 BC.So 4000 years ago, the area that is now the Sahara was probably pretty dang green.
Why wouldn't other (present day) deserts be green back then too?
6,500-5,000 14C y.a. Conditions across northern, central and east Africa became somewhat drier than before, but were still moister than today. For example, on the basis of pollen and charcoal, Neumann et al. (1995) suggest a mixture of semi-desert and denser scrub and grassland for the western Sahara, in areas that are now extremely arid. A similar picture is obtained by Ritchie (1994) on the basis of pollen evidence, and by Lario et al. (1997) for the Blue Nile on the basis of sedimentological and zoological indicators.Conditions across the Sahara region and the Arabian Peninsula at 6,00014C y.a. have been summarized in a 1-degree database and set of biome maps presented by Hoelzmann et al. (1998), using pollen and charcoal data. Their map suggests a picture that is in essence similar to that given in the maps below; note however that from their useage of categories for the present-actual map, their category of 'steppe' appears to correspond to 'semi-desert' in the QEN vegetation scheme, and their 'savanna' corresponds more closely to the QEN 'grasslands' and 'scrub'. Hoezelmann et al. also suggest a very extensive area of wetlands south-east of Lake Mega-Chad, rivalling the lake itself in scale; they suggest that at 6,000 14C y.a., rainfall in the catchment area was around 300-350mm higher than today in order to sustain this high water level. Other extensive wetland areas are suggested for the interior of the eastern Arabian Peninsula. The map reconstructions of Hoelzmann et al for 6,000 14C y.a. are downloadable from this linkEast Africa may also have been moister than at present, though drier than it had been during earlier stages of the Holocene (Hamilton 1982, Maitima 1991).There may also have been a temporary return of moisture conditions and lake levels to early-Holocene conditions at around 5,500 - 5,000 14C y.a. (Petit-Maire & Gua 1996), for which period the map given here may not give enough moist-climate vegetation (maps for 8,000-7,000 14C y.a. could be more representative for this phase). Throughout the period 6,500-5,000 14C y.a., the Sahara was mainly vegetated (Lezine 1989, Ritchie 1994), and rainforest extent was greater than today (Hamilton 1988, and see main QEN review for 5,000 14C y.a. timeslice).After about 5,000 14C y.a., lake levels suggest that aridity in north Africa became more severe, culminating in an arid phase about 3,800 14C y.a., a part-way return to moist conditions 4,000-3,000 14C y.a., and a decline to aridity thereafter (Petit-Maire & Gua 1996).-------------Since 5,50014C y.a., the climate across Africa seems to have been relatively similar to the present. An arid phase with some forest retreat is observed for around 2,600 14C y.a. in pollen records from Cameroon and some places in central Africa (Elenga et al. 1994, van Geel et al. 1996).