These fascinating videos show how trees can mitigate climate change by reducing CO2 out of the climate.  During the winter in the Northern hemisphere where the majority of the forests are, the trees are sleeping.  Therefore carbon dioxide accumulates in the atmosphere.  In the Spring when the trees wake up, they draw out the CO2 from the atmosphere and convert it to oxygen.  This is the Earth alive and breathing.  Watch these amazing videos

Greenpeace UK has a nice video on Facebook

Anthropocene CO² Emissions

Every year humans emit 36 billion tons of CO² into the atmosphere, increasing the amount from pre-industrial era (c. 1780) of 270 parts per millions to 400 ppm today.  Although CO² makes up only a small percentage, it can have a very big impact in the change of the composition of the atmosphere.  The sources for human emmissions are (i) burning of fossil fuels (coal, petroleum, natural gas), and (ii) deforestation.

Calculations

In the video below, the author presents calculations of how many trees can offset the amount of CO² that humans have added to the mix.

1 tree = 20 kg CO² per year, so 50 trees can absorb 1 ton of CO².  Therefore in order to offset the 36 billion tons of CO² humans emit in the atmosphere each year, would require 1.4 trillion trees, which would require 140 million km².

The assumptions and calculations are certainly debatable, but the point is that trees alone are not the solution.