Global climate has changed in the past due to 1._ and 2._ 1. earthquakes, air pollution, or plate tectonics
2. global warming, milankovitch cycles, or lunar phases

Theres several things, deforestation, air pollution. Humans are increasingly influencing the climate and the earth's temperature by burning fossil fuels, cutting down rainforests and farming livestock. This adds enormous amounts of greenhouse gases to those naturally occurring in the atmosphere, increasing the greenhouse effect and global warming.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.