"Projected climate changes during the present century and beyond have the potential to initiate future large-scale and possibly irreversible changes in various Earth systems, resulting in impacts at continental or global scales. Fred Pearce in the New Scientist (12 February 2005) aptly referred to these possibilities as 'waking the sleeping giants'.
They are suggested by some model simulations and by past historical and palaeo-records (see Chapter 2). Their likelihood within the next 100 years is in most cases considered to be low, although some scientists argue that more rapid changes are possible...with possibly huge impacts on natural and human systems."
These "sleeping giants" include large, abrupt changes such as:
The longer global warming continues, the greater the risk of "waking the sleeping giants"—major feedbacks such as ice sheet collapse, methane "burps," or ecosystem collapse—that could ignite abrupt or runaway warming beyond our control.