Political reasons - They may have been exiled from their previous country by their government. War means they are not safe in their previous country.
Social reasons - Their life may be at risk of being taken by people from their previous country. Poverty and famine could also be a factor.
The greatest gas is nitrogen
Global climate change is when a change in weather appears in an area where it normally wouldn't. This is normally a change in the temperature, precipitation and/or wind. An example would be the ice caps melting in Antarctica because heat is making its way in where it should not be.
