The climate change assessments give model projections for changes in crop yields at temperature increase surrogates for a few climate change effects. But that is a terribly misleading presentation for food security.
For food security we need crop changes from committed global temperature increases and climate change, which is a very different matter.
It has been known since the very first IPCC assessment in 1990 and that the global temperature increase at any particular time is only about half of the long term eventual temperature increase commitment. And this magnitude of the slams is confirmed in the latest climate change assessment by the national research council climate stabilization targets 2010.
This committed doubling of today's temperature increase is due to the ocean heat lag. Much of the increase in heat from the increasing atmospheric greenhouse gases is hung up in the vast oceans that release this heat to the surface as a recorded temperature increases very slowly.
This illustration opposite shows a commitment of 2.4°C with a large risk of 4°C due to the global cooling aerosol effect added to the ocean heat lag (Ramanathan Feng PNAS 2008).
As is well known the combustion of fossil fuels produces air pollution. Acid aerosols are part of this pollution and they are cooling because they reflect some of the incoming solar energy back out to space.
This cooling effect is quite large and it makes for a committed additional heating which we are presently deferring to all future generations.
The reason it's a definitely added commitment is we have two stop burning fossil fuels because of the definite science of zero carbon emissions. This science of atmospheric carbon dioxide is well recognized by the scientists and means that only zero carbon emissions can possibly ever stop the global temperature, climate change (and also ocean acidification) from continuing to increase.
When the combustion of fossil fuel stops the aerosol cooling effect will rapidly disappear and an extra amount of warming will be 'unmasked' rapidly increasing the global average temperature some more.
The commitment of the global temperature increase includes the additional warming to come from the 'hidden' ocean heat lag and the additional warming to come when the acid aerosols 'hidden heat' is unmasked.