Complex sentence: An increase of more than five degrees Celsius (nine degrees Fahrenheit) is "likely to lead to major disruption and large-scale movement of population", and its effects would be "catastrophic" and "far outside human experience".
Split into simpler sentences: An increase of more than 5C is "likely to lead to major disruption and large-scale movement of population". It said the effects would be "catastrophic" and "far outside human experience".