Interested in how scientists attempt to predict the amount of temperature increase caused by increases in the amount of CO2 in the atmosphere? then you may be interested in this article about climate sensitivity.

Climate scientists are certain that human-caused emissions have increased carbon dioxide in the atmosphere by 44 per cent since the Industrial Revolution. Very few of them dispute that this has already caused average global temperatures to rise roughly 1 degree. Accompanying the warming is disruption to weather patterns, rising sea levels and increased ocean acidity. There is no doubt that further emissions will only make matters worse, possibly much worse. In a nutshell, that is the settled science on human-caused climate change.

What scientists cannot yet pin down is exactly how much warming we will get in the future. They do not know with precision how much a given quantity of emissions will lead to increased concentrations of greenhouse gases in the atmosphere. For climate impact it is the concentrations that matter, not the emissions. Up until now, 29 per cent of human emissions of carbon dioxide has been taken up by the oceans, 28 per cent has been absorbed by plant growth on land, and the remaining 43 per cent has accumulated in the atmosphere. Humans have increased carbon dioxide concentrations in the atmosphere from a pre-industrial level of 280 parts per million to over 400 today, a level not seen for millions of years.

There’s a possibility that the 43 per cent atmospheric fraction may increase as ocean and terrestrial carbon sinks start to become saturated. This means that a given amount of emissions will lead to a bigger increase in concentrations than we saw before. In addition, the warming climate may well provoke increased emissions from non-fossil fuel sources. For example, as permafrost thaws, the long-frozen organic matter contained within it rots and oxidizes, giving off greenhouse gases. Nature has given us a major helping hand, so far, by the oceans and plants taking up more than half of our added fossil carbon, but there’s no guarantee that it will continue to be so supportive forever. These so-called carbon-cycle feedbacks will play a big role in determining how our climate future will unfold, but they are not the largest unknown.