Commitment is a fundamental feature of the climate system. It means that locked in (committed) future warming is several times today's warming even if all greenhouse gas (GHG) emissions were to be rapidly stopped.
Before we look at the commitments according to the climate science, we must address the very real policy sources that we are presently committed (or condemned) to.
The combined national formal UN pledges on emissions commits us to a warming of 4.4C by 2100.
All economy and energy plans are for continued fossil fuel business as usual,. There is no other plan. That, as the International Energy Agency has been warning since 2008, commits us to at least 6C by 2100.
Our actual commitment to future GHG emissions then is at least 6C by 2100.
Climate system science
There are a number of unavoidable sources of additional warming, onaccount of climate science, that make today's already locked warming several times today's warming (0.8C).
o Socio-economic-technological lag is the warming over the time taken for a rapid reduction of GHG emissions that stabilizes atmospheric GHG levels.
o 'Hidden' heat of the ocean heat lag that about doubles the (realized or transient) warming at the time of atmospheric GHG stabilization. This eventual equilibrium warming is about the realized warming.
o Deferred warming of air pollution aerosol cooling that will be unmasked when fossil fuel emissions are cut for atmospheric CO2 stabilization.
o Incurred warming of carbon feedbacks caused by the above unavoidable warming in total.
Carbon feedback from the terrestrial carbon cycle - vegetation and soil, is called terrestrial feedback and it has modeled for 15 years. It does not inldude the large carbonstors in wetland peat and the Arctic.
By far the largest carbon feedback source is the in the Arctic - peatlands permafrost and sub sea floor methane hydrate. As 1.5C or less is the tipping point for extensive permafrost thaw (Vaks , committed warming from the ocean heat lag alone is enought to add an extremely large degree of Arctic warming.
As the ocean heat lag alone doubles the warming today it is easy to see that the full committed unavoidable warming is several times today's warming even assuming a rapid planetary response.
Total commitment 3C by 2100
We have calculated from a simple summation of all the unavoidable sources of warming (minumum) that we are commiited to 3C- excluding the large Arctic feedbacks.
Even if Arctic warming stayed at 3X the global warming (it will be amplified even more) it is clear Arctic warming commitment alone is many times today's Arctic warming.
Climate commitment in an uncertain world K. C. Armour and G. H. Roe GRL 2011
Fundamental constraints preclude Earth returning to pre‐industrial temperatures for the indefinite future. These same constraints mean that observations are currently unable to eliminate the possibility that we are already beyond the point where the ultimate warming will exceed dangerous levels.
Climate response to zeroed emissions of greenhouse gases and aerosols H. D. Matthews and K. Zickfeld
Nature Climate change 2012
Atmospheric composition, irreversible climate change, and mitigation policy S. Solomon et al 2012