Answer:
False
Step-by-step explanation:
The greenhouse effect is caused by greenhouse gases like CO2 and CH4 (known as methane).
Greenhouse gases are not necessarily caused by humans. The decomposition of dead animals, for example, generates CO2. Also, animals breathing generate CO2.
Also, cows digesting grass is a big contributor to CH4 increases in the atmosphere.
So no, the greenhouse effect is NOT solely caused by human activity.