There are several hundred European Voluntary Service projects per year that offer volunteering opportunities in the field of the environment, climate change, and development cooperation; and you could be a part of it.
The best way to get involved is to register on the European Solidary Corps database as over 5600 European Voluntary Service organisations have full access, so they can choose volunteers for their projects from the pool of people registered.
If you are really motivated and want to be proactive, there is another possibility for you. You can choose the project yourself though the volunteering database on the European Youth Portal and apply that way. You can either search for a project by choosing a specific country, project topic and your available dates or chose from advertised projects in the map.