The activity that is NOT the most likely human activity causing global climate change is:
Increased ocean clean-up to improve carbon dioxide absorption.
While ocean clean-up may have positive environmental effects, it is not a major contributor to climate change and is not associated with the primary factors leading to global warming. The other activities listed (deforestation, burning fossil fuels, and increased nitrous oxide and methane emissions) are directly linked to increased greenhouse gas emissions and climate change.