Climate Change

I was worried recently when I discovered that human activity is only responsible for a small percentage of the CO2 produced on our planet. 

It seems we produce around 29 gigatons every year, whereas natural processes produce around 750 gigatons. How can you say we are the main reason for global warming, I thought, if we contribute so little CO2 to the total amount produced.

Fortunately, I accidentally hit on an explanation, on the Skeptical Science website, which seems to me quite reasonable. It's easy to understand when you look at the following chart published by the Intergovernmental Panel on Climate Change:

Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).

So what happens is that vegetation and land produce 439 gigatons, but also absorb a bit more than that amount, whereas the ocean produces 332 gigatons but absorbs a bit more too. This relative balance between production and absorption has been relatively stable for millions of years.

But of course, adding 29 gigagtons without a corresponding absorption, puts the whole thing out of kilter, so CO2 levels in the atmosphere are now increasing every year. (The natural cycle does absorb around 40% of what we send up, but this is not enough to prevent a steady increase.)

We are now at 400 parts per million of CO2 in the atmosphere, whereas pre-industrial levels were fairly constant at around 280 ppm. Such a change has happened in the last century or so, whereas naturally it would take millions of years.

Also just read a great post by Andy Skuce debunking climate change deniers' claims.