There is a global trend of a warming atmosphere. The main reason for this warming is that more heat is captured by the atmosphere than there is released. This heat has 2 sources: new heat through sunlight reaching the earth, and the release of old stored heat through burning of fossil fuels (coals, oil and natural gas, which are all products of fossilized plant material).  

Trees are beneficial for the climate thanks to the carbon they absorb. With up to 50% of a tree’s biomass consisting of carbon, trees are ideally suited to reduce carbon dioxide levels in the atmosphere. In order to curb climate change, just increasing the carbon storage capacity may not be enough.

Forests are critical to rainfall and inextricably connected to the hydrological cycle.  The degree to which forests, deforestation, and reforestation can drive, remove and restore the potential for rainfall are factors of critical importance for consideration in forest preservation and restoration program

Trees contribute to the forming of clouds in two ways:
First of all, through their roots, they absorb water from the ground water, which is subsequently evaporated through the leaves. The increased amount of water in the air directly can contribute to an increase of clouds. Secondly, with the evaporated water, small organic particles are released into the sky. These particles can play an important role in forming clouds in their role as condensation nuclei.