| thranx said: And why dont they include sun activity, and the role the sun plays? I mean it is the source of our heat right? But lets forget about that and focus on a non harmful gas that feeds plants. If i'm not mistaken at one point the sarah desert was at one point not a desert, but it is now and that happened before the industrial revolution. who is to blame for that one? |
Solar UV radiation/the irradiation intensity has a ~20 year cycle, but it's variations are very minute and viewed within a period of a few thousend years this irradiation intensity is pretty much constant, yet the sun is slowly sending out more energy (getting hotter) > in 500million to 1 billion years carbon based life on the earth's surface (same orbit) might not be viable anymore. The sun's wildly changing magnetic activity however has no measureable impact on temperature/our climate, as long as it doesn't blast away our atmosphere (which is protected by earth's magnetic field).
A bigger influence on the earth's short scale climate (10k years - 100k years) is it's cyclical changes in orbit. When earth is sligthly closer to the sun it gets warmer and colder when it's further away - this cycles (100k years cycle) closest approach to the sun was 6k-8k years ago, during the so called holocene climate optimum and since then the earth's orbit has become slightly larger.
The desertification of the Sahara obviously is a very complex theme, but the gist of it is that it's being drained of humidity due to the "Hadley Cell", a tropical air circulation system, and it's normal state during our ice age is that of a desert. Yet due to a large number of factors (cyclical shifts in earth's rotational axis, melt water influx, displacement of the Hadley Cell system etc) the Sahara had 3 known short green phases within the last 200k years - latest one being from 8k years to 5.9k years before now (~2k years in duration).
Btw ofcourse scientists looked at a great great many factors that influence our climate before and still track them, but the only one actually changing dramatically and hence looking like the main trigger to the manifold of changes we observed in the last decades is atmospheric CO2/H2O/CH4/N2O concentration > human emissions.
