imminent ice age?

From the environmental pages of The Observer comes this

The next Ice Age could take only weeks to engulf Britain. Scientists say the last great disruption to the Gulf Stream 12,800 years ago took only a couple of months to trigger a massive plunge in temperatures across Europe.

The Gulf Stream carries tropical heat from the Caribbean to northern Europe but is already being disrupted by meltwater pouring from the Arctic as global warming intensifies. One day it may switch off completely, say scientists.

Such an event occurred 12,800 years ago when a vast lake – created from melting glaciers at the end of last Ice Age – overflowed and poured into the north Atlantic, blocking the Gulf Stream. Europe froze – almost instantly, said Patterson.

So the last post-warming ice age was not caused by driving the kids to school in a 4x4 then but was part of a natural cycle but the next ice age is, relatively speaking and for all intents and purposes, going to be caused by human activity? Why?