Why does climate change get described as a stock-flow problem?
Economists often describe climate change as a ‘stock-flow’ problem. This refers to the fact that the greenhouse effect, and in turn climate change, depends on the concentration of greenhouse gases in the atmosphere – the ‘stock’ – while the thing humans can control as a response is the rate at which additional greenhouse gases are emitted – the ‘flow’.The total stock of atmospheric greenhouse gases depends on the difference between man-made emissions and the natural removal of greenhouse gases from the air, particularly by oceans and plant life.
Imagine a bathtub. The tub itself represents the atmosphere and the water it contains represents the stock of greenhouse gases. The taps represent manmade emissions, whilst a slow-draining plug represents the natural removal of greenhouse gases. If the taps are left running and the plug can only drain the liquid away slowly, the volume of water in the tub will increase. That’s what’s happening at present: humans are adding greenhouse gases to the air faster than natural processes can remove them. The result is an increasing stock of greenhouse gases and, in turn, rising temperatures.
To arrest man-made global warming, the world needs to stop the atmospheric stock of greenhouse gases from increasing. This requires emissions to be reduced until they balance with the rate of natural removal from the atmosphere. At this point the atmospheric stock is stabilised, which is why many economists and scientists talk about targets for ‘stabilisation’.
The lower the level at which the atmospheric stock of greenhouse gases is stabilised, the greater the chance the world will have of meeting its agreed target to limit global temperature rise to 2ºC.
For a 50% chance of success, scientists recommend that annual emissions should peak and fall to 40–48 billion tonnes of CO2 equivalent by 2020, before eventually falling to 14–17 billion tonnes in 2050.Annual global emissions were around 50 billion tonnes in 2010 and are continuing to rise, so fast action will be needed if these targets are to be met.
This article was written by Naomi Hicks and Simon Dietz and is a reproduction of the following article “Why does climate change get described as a stock-flow problem?“ © 2012, The Guardian, used under a Creative Commons No Derivative Works licence.
