Ireland can support such a range of plant species due to its unique position in the path of the Gulf Stream. While countries at similar latitudes freeze over regularly e.g. Newfoundland, Moscow, the warm air/water flowing up from the Gulf of Mexico largely keeps Ireland from dropping below 0oC. Changes in global temperatures can affect the flow of fluids (think of a bird riding a column of thermal air), and too much disruption will cause global currents to shift. As the climate continues to change and temperatures rise in certain areas, temperate Ireland will likely begin to see more storms, regular flooding events, drier summers, and the range of biodiversity that the island can support will continue to shrink.
Fun fact: There are a few species known as “resurrection plants” that can survive extreme dehydration for months to years, completely drying out before coming back to life again when they come in contact with water.