If the world stopped all unnecessary manufacture, production, power generation, transportation and building immediately, we could probably hold the fraction of Carbon Dioxide in the Atmosphere pretty much constant.
Tom Wigley calculates that this “constant composition” or “CC” could lead to an eventual rise in temperatures, averaged, globally to over 1 degree Celsius.
Why is this so ? We have only seen a rise of 0.7 degrees C to date. Why should it climb from there ? Because there is a “time lag” in the Earth System in responding to the extra warming from the extra Carbon Dioxide up there :-
“The Climate Change Commitment : T. M. L. Wigley : …Even if atmospheric composition were fixed today, global-mean temperature and sea level rise would continue due to oceanic thermal inertia. These constant-composition (CC) commitments and their uncertainties are quantified… The CC warming commitment could exceed 1 degree C…”
In the diagram above, I draw some simple lines and make some simple approximations of the integration of the area under the curve which represents the “added Carbon Dioxide burden” in the Atmosphere, and I arrive at a figure of 1.19 degrees Celsius.
Why do I conclude that only emissions up until 1980 have contributed to the warming experienced up until 2010 ? James Hansen and his colleagues have calculated a likely time lag :-
“…Evidence from Earth’s history and climate models suggests that climate sensitivity is 3/4 +/- 1/4 degrees C per Watt per metre squared, implying that 25-50 years are needed for Earth’s surface temperature to reach 60 percent of its equilibrium response…”
Here’s what Tamino concludes :-
“Our planet has already felt about half the global warming due to the CO2 [Carbon Dioxide] we’ve already added to the atmosphere; the rest is “in the pipeline,” and the impact of that extra warming on the availability of food and water is likely to be unpleasant. We’ll be very lucky indeed if we don’t pay a heavy price for the changes we’ve already wrought…”
The question you should ask yourself is – what temperature rise are we going to see by 2070, given that Carbon Dioxide emissions are continuing at such a rate that Atmospheric Carbon Dioxide is still rising sharply ?