A number of “positive feedback” loops are operating on a planetary level, amplifying the effects of anthropogenic climate change. As you can surmise from the term, feedbacks are self-reinforcing and require intervention from an outside force to turn them around. As in the current scenario, a feedback loop may operate at a rate which obscures the ongoing going effects from humans. However, when a critical threshold is cross (a so called tipping point) is reached, then all hell may break loose very quickly.
Let’s look at the most common examples.
Melting sea ice / black water absorption
As sea ice shrinks, more black water is exposed to solar rays. White ice reflects these rays back into space, but black water absorbs them. Rather than bouncing back, the heat energy of the sun is absorbed into the ocean, which is warming faster than the atmosphere. There will be a point where it can no longer absorb heat, and it will begin radiating heat into the atmosphere. That will be very bad.
As the water warms, more ice melts. The overall area of Arctic sea ice is shrinking, while at the same time the volume of the ice (thickness) is decreasing.
This could turn out to be the most powerful of the carbon cycle feedbacks, but we are in the early stages of research. The “for sure” component is that the tundra is thawing as temperatures rise. The stability of the permafrost ground has begun to deteriorate. In the short term, this is putting major pressure on human infrastructure such as roads and buildings.
The more potentially dangerous effect, however, is the release into the atmosphere of methane (CH4), a greenhouse gas about more powerful than CO2.
As the soil thaws, microbes go to work, generating natural CO2 and methane. But potentially worse, there are quantities of CH4 trapped beneath the permafrost.
This process is just beginning and no one knows for sure how this will play out. This video seems to be pretty even handed on the topic.