Here, equity is treated as allowed fair level of CO2 to be emitted (by any country).
"Above global equity" = Above fair level
"Below global equity" = Below fair level
Global Carbon Project (G.C.P) or any respective international organization might have agreed upon on some fair level of CO2 emission i.e. allowed level of CO2 emission.
So, the countries in the red are emitting CO2 than above fair level. Whereas, the countries in the blue are emitting CO2 than below fair level.
Equity according to Oxford Dictionary is
Meaning (Entry 1): The quality of being fair and impartial.
Usage: The focus here has rarely been on equity or on a fair deal for the poor