We all like trees don’t we? Never hear a bad word said against them. They’re just there, solid and dependable and green. Soaking up evil carbon-dioxide, spitting out copious amounts of life-giving oxygen. Even the British Tory part got in on the act in 2006 when they adopted a tree as their new party logo.
Unfortunately, even though the idea that planting trees will save the planet from global warming has firmly–erm–planted itself in the public’s imagination, the notion is not backed up by the science.
Did he just say something bad about trees? Not really. To understand why planting trees won’t solve global warming, let’s unpack some of the basic science.
First of all, the amount of carbon in the Earth’s biosphere is constant (give or take satellite launches etc). It cannot be created or destroyed, only change form. This movement of carbon through its various forms is called the carbon-cycle, and it can be divided into two main parts: active and inert.
Trees absorbing carbon-dioxide and converting it into glucose and oxygen through the process of photosynthesis is one part of the active cycle, as carbon constantly moves through plants, organisms, water, and the atmosphere. In contrast, reserves of fossil fuels–underground lakes of natural gas and oil, and seams of coal–are inert; their carbon is locked away and plays no part in the active cycle unless we burn them. Note that movement between the inert pool and the active cycle is one-way on human timescales–no carbon will return to the inert pool unless it undergoes the millenial-long geological processes that brought it about in the first place.
From a global warming perspective, when carbon is in the guise of carbon-dioxide it adds to the greenhouse effect, which causes solar energy to be trapped within the Earth’s atmosphere leading to rises in global temperature.
So won’t planting trees cause carbon-dioxide to be taken out of the air? Yes. But what’s conveniently forgotten is that trees don’t only photosynthesize. Like all living organisms they respire too. And die. Two processes that produce carbon-dioxide. No carbon gets “locked-up” in the same way that fossil fuels sequester the element, only temporarily held in the structure of the tree. Even if planted trees are sustained for perpetuity, the amount of carbon coming out of the inert part of the cycle through the burning of fossil fuels dwarfs this small sink. And that gap is only going to get bigger.
Carbon offsetting schemes are so enticing because they offer us a quick monetary fix to preserve the lifestyle we’ve become accustomed to. Sadly, the only incontrovertible way to stop climate change is to drastically limit the quantity of fossil fuels being extracted.
The Carbon Neutral Myth provides much excellent in-depth reading if you’re interested in finding out more.
Image Credit: Wiki Commons