Carbon Dioxide, Climate Change and The Role of Plants

How plants change the climate...
13 March 2005

Interview with 

Howard Griffiths, Plant Sciences, Cambridge University


Howard - I'm interested in photosynthesis and the driving force for life on earth, which is how plants acquire carbon and potentially sequester carbon. This may be part of the system that might help maintain the balance of carbon going into the atmosphere.

Chris - Why is carbon so important?

Howard - We are changing the atmosphere. In the last 200 years, carbon dioxide (CO2) in the atmosphere has gone up by one third, and it's quite possible that plants have absorbed the remaining two thirds of the remaining carbon that we have emitted into the atmosphere.

Chris - A 30% increase is a huge amount.

Howard - It certainly is, and this is why we know there is the so-called greenhouse effect. These gases help to trap the heat within the earth's atmosphere and that's led to a 0.6 degree warming in the last 50 years. This is at a global level rather than just a regional level.

Chris - What else do you work on?

Howard - I also work on what I think is the most important enzyme in the world: rubisco. It's the basis for life on earth and has been around for 3800 million years. It's products through photosynthesis ultimately led to the products that drove the industrial revolution. I'm interested in how the enzyme is regulated under a whole host of modern conditions. I look at how plants might respond to climate change in the future and whether trees will continue to sequester carbon and bury it below ground.

Chris - If you are growing tomatoes on your greenhouse, you can make them grow better if you pump in extra carbon dioxide. Don't our activities here on earth translate into better growth for plants?

Howard - That's the theory, but in fact for natural vegetation, they are nutrient limited. Although we are seeing plants responding and they are continuing to sequester carbon, we won't see this rampant growth that you might expect from your greenhouse plants.

Chris - You said at the start that CO2 concentrations have gone up by 30%. What does this actually add up to, because if there isn't much out there to start with, you don't have to add much to get a 30% increase.

Howard - It's now going up at an exponential rate. At the moment, we have 0.038% of CO2 in the atmosphere. Back in 1800, it was somewhere in the region of 0.028%. It's projected to go on increasing to 0.05 or even 0.08% by the end of this century.

Chris - How much CO2 does the average person put out? How much do I account for as an average British citizen on an annual basis?

Howard - If you were to fly to the United States, each person on the flight would emit about half a tonne of carbon. Just heating your house every year, you're probably producing about 6 tonnes of carbon, and if you drive around in your car for about 12 000 miles per year, you're probably emitting about 3.5 tonnes of carbon.

Chris - So when people say 'let's plant a tree', that's not going to solve the problem.

Howard - Funnily enough, it could in principle. There's been lots of publicity about celebrity forests recently, including Joe Strummer having one on the Isle of Skye. About a hectare of oak woodland can sequester about 3.5 tonnes of carbon per year, which is what everyone on earth uses on average. However, there are 6 billion people on earth, so it's quite a tall order to sequester all that carbon. It is impracticable. We need to think about other ways of reducing carbon. The worse thing that could happen is the northern boreal region or peat lands start to release their carbon, making them sources instead of sinks. The World Bank has now set up a system of carbon credits so that countries such as Mozambique and Uganda can set aside areas of forest. Richer countries can then pay for them to retain those resources.


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