Ok so here Humans never migrated to the Americas. Because of that the tens of millions of people that never inhabited the Americas never affected it. This means the crops there were never domesticated and the trees never harmed. In fact there are many more trees then OTL. Because of this the world is cooler and the air is cleaner. It also means that Europe (not Med), Northern China, Siberia, Canada, Russia, and the Northern USA are all colder. Scandinavia, Canada, Britannia, Siberia, and Northern Russia in partictular are much colder. It also means that in contrast Mediterraen/Northern Africa/Middle East is wetter and so is South USA/Northern Mexico and South China. The affects of wetter and still warm Northern Africa is that the Med is though somewhat cooler for the most part retains its OTL climate. Meanwhile the Chihuahuan Desert is much smaller and in the areas where it isn't, is lush forest. South China and the South Pacific got the bad end of the stick and though more wet is also more stormy.
Glaciation will become quite extensive in a number of regions: Tibet, the Alps and the Andes in particular. The nascent Tibetan empire may collapse earlier than OTL in this timeline, while the development of Swiss culture is unlikely. In the Andes the glaciers as well as increased dessication caused by altered Pacific winds are going to retard the development of the civilizations there. Desertification will become a problem in a number of places. Central Asia and North-east India will become quite dessicated, with the Thar desert spreading further across the Aravallis toward the Ganges Valley. This will likely reduced the populations of these regions, perhaps even slowing the progress of Islam into both Central Asia and India. It may mean that the migrations of the Turkic peoples become more directly focused on a weaker China, and less likely to migrate into the Middle East (though Khazaria may remain fair game).
Monsoon effects are interesting. Reduced sea temperatures will result in a lessened monsoon effect on India. However, it is likely to become wetter and stormier in southern China and eastern Africa is likely to go through a long wet period (broken by occasional periods of dryness). Typhoons along the southern Chinese coast are going to make the development of maritime culture there more difficult, but not impossible. The North Pacific is going to be warmer than OTL. In Russia, the expanding ice pack will cause the Ob and the Yenisey to form large lakes.