Many people look at biodiesel as an environmentally friendly alternative to standard diesel fuel. Generally speaking using biodiesel instead of standard diesel means lower carbon dioxide emissions though this doesn't have to be always the case because the final amount of carbon dioxide emissions depends on several different factors.
Burning biodiesel produces carbon dioxide emissions just like burning standard diesel fuel. Increased carbon dioxide emissions are the main factor contributing to climate change.
When comparing the carbon emissions of biodiesel and standard diesel it is always important to have in mind that the plant feedstock used in the production of biodiesel absorbs carbon dioxide from the atmosphere when it grows in the process of photosynthesis. This is the main reason why some energy experts refer to biodiesel as being carbon neutral (the carbon emissions absorbed during the plant growth is released again while biodiesel is burnt) though this isn't always the case.
The several different studies have confirmed that biodiesel accounts for fewer emissions compared to standard diesel fuel (for instance biodiesel from rapeseed and sunflower oil produce 45%-65% lower greenhouse gas emissions than standard diesel). These studies however didn’t include land use change in the equation. Land use change can significantly contribute to the total amount of emissions, particularly in case of deforestation.
Many environmentalists fear that that the increased feedstock production directly affects the rate of deforestation which would make the benefits from lower biodiesel emissions negligible because deforestation is connected with huge carbon dioxide emissions.
So in order to keep biodiesel environmentally friendly the feedstock needs to be grown on existing cropland without clearing the forests. This could however disrupt the global food production because less land could be used to produce food crops. The key to solving this issue is to secure a sustainable biodiesel production.