It is argued that climate change will be the most pressing environmental issue in the coming years because

The climate change affects many spectrum of human life. In fact, it affects subjects we might not even be aware of, as it is a new situation with unpredictable results.
Nowadays, it is known that the climate change affects on food production, as it changes the natural water cycle - It doesn't always rain when it is expected, and crops and harvesting is affected.  
This is just one example. Climate changes affects a whole system that was in harmony. The increase in the planet heat causes the melting of the icebergs, increases sea levels, might be responsible for many natural catastrophes. 
For all of these, and much more, it is one of the themes that everyone should care to know more about.
Hope this helps.