COMMITMENT We need to think in terms of today's total global warming commitment (the warming and climate change that is locked in) rather than only today's global warming.
Today's global warming temperature increase is 1,0C, but for all humanity and life it is much more than that, because of the ocean heat lag.
Here is why today's committed warming is far more than today's warming.
The climate system is characterized by its great inertia and momentum. This is largely due to the vast World Ocean, but also the amplifying carbon feedbacks and ice sheet feedbacks.
There is always a lot more heat 'in the pipe' than shows as the global average surface temperature increase.
The ocean heat lag commits us to as much as double today's warming in the distant future (IPCC 1990, NRC 2011). It was established at the first IPCC assessment in 1990 that the realized/transient warming (at atmospheric GHG stabilization) is only about half the eventual equilibrium warming. That puts us at 2C today.
CO2 is highly persistent and cumulative in the atmosphere. 20% of CO2 emissions last in the atmosphere for 1000 years. As a result all industrial carbon emissions must stop for atmospheric CO2 increase to slow enough to get near stabilization.
Figure 3: Time lag to reach equilibrium