Recent experimental evidence suggests that accumulation of collective impacts of human activity upon our environment across centuries, mostly occurring in recent decades, is pushing a number of natural feedback systems past their 'tipping points' for maintaining a dynamic equilibrium. For each system, match the observable responses to our 'anthropogenic forcing' that suggest a shift from negative feedback to positive feedback in recent years. a. ocean heat saturation
b. melting permafrost
c. melting glaciers in Greenland
d. deforestation of Amazon