You might have seen the phrase “climate sensitivity” come up in mainstream media articles, but what exactly is it, and how does it affect your environmental wellness?
Let’s start at the beginning: burning fossil fuels means that we have increased carbon emissions, which is known as the greenhouse effect. Because there is more carbon dioxide in the air, more heat has been trapped in the Earth’s atmosphere and this has caused a global energy imbalance. As it stands, there is more energy incoming than escaping, which will lead to the planet warming until it reaches equal levels of incoming and outgoing energy. This is known as equilibrium, or a new balanced energy state.
If you were to double the amount of carbon dioxide in the atmosphere, then the increased greenhouse effect that this would create would cause the planet’s average surface temperature to warm about 1.2°C (2.2°F) in response. This may sound like a small difference, but when you think that the difference between an ice age and the current warm period is only about 5°C (9°F), you begin to see the problem. When it comes to the earth’s climate, seemingly small temperature changes make a big impact.
On top of all this, there are feedbacks which can dampen or amplify the warming from the increased greenhouse effect. When ice melts, for example, it makes the Earth’s surface less reflective. This means that the planet will absorb more sunlight and warm further. If the atmosphere is warmer, it will also hold more water vapor, and water vapor is another greenhouse gas.
Once you have your head around this, you begin to understand what we mean by “equilibrium climate sensitivity”. This much-used phrase simply refers to the total amount of warming that will occur at the Earth’s surface once it reaches a new balanced energy state. This includes both the increased greenhouse effect from a doubling of atmospheric carbon dioxide, and the feedback effects. There is still a lot of uncertainty about the Earth’s exact climate sensitivity. However, while it’s an important question to resolve, from a policy standpoint, it really doesn’t matter; climate sensitivity will only be a relevant issue once we start to take serious steps to reduce carbon emissions from fossil fuels.