Researchers found that in Europe, trees grown since 1750 have actually increased global warming.
The scientists believe that replacing broad leaved species with conifers is a key reason for the negative climate impact.
Conifers like pines and spruce are generally darker and absorb more heat than species such as oak and birch.
The authors believe the work has implications for current efforts to limit rising temperatures through mass tree planting.
Anything that plants more trees is a good thing.