The climate change science of zero carbon is definite, because of the definite basic science of carbon dioxide in the atmosphere. Carbon dioxide lasts in the atmosphere after it has been emitted for an extremely long time.
The mean atmospheric life time of CO2 is 50 to 100 years, but 33% lasts 100 years and 20% lasts 1000 years. This makes CO2 emissions extremely persistent and so cumulative in the atmosphere.
Therefore global climate total planetary catastrophe is inevitable unless carbon emissions is dropped to zero. This means converting off fossil fuel energy and onto clean zero carbon everlasting energy sources which are abundant.
The science was established 20 years ago by the the Intergovernmental Panel on Climate Change (IPCC) that an elevated level of atmospheric carbon dioxide would not drop unless carbon dioxide emissions dropped to zero. This is why 350.org is demanding an emergency climate change and zero, and response from all nations. The last 2007 assessment of the IPCC stated that the atmospheric carbon dioxide concentration could not be stabilized without dropping emissions to zero. Further research since the IPCC 2007 assessment has confirmed that only zero carbon dioxide emissions can stop the global temperature from continuing to rise. The latest assessment confirming zero carbon is the 2010 National Research Council's Climate Stabilization Targets.
The same science applies to ocean acidification, which cannot stop increasing unless the atmospheric carbon dioxide concentration stops increasing anmd that means no more CO2 added to the atmosphere. Ocean acidification cannot stop increasing without zero carbon emissions.
There are two imperatives from the climate science for zero carbon emissions. There is global warming and climate change- and there is also ocean acidification
Understanding global warming and climate change means understanding why it is a fact that global warmingn and ocean acidification cannot stabilize, unless carbon dioxide emissions are dropped to zero.
This means converting all fossil fuel energy to clean zero carbon and everlasting energies- that can provice many times the energy the world needs.
Stopping burning fossil fuels does not reduce only CO2 emissions, because fossil fuel emissions increase black carbon (soot) ground level ozone and methane.
Today's atmospheric carbon dioxide concentration is 395 ppm and is rising steadily. To avoid planetary catastrophe, it has to be dropped below 350 ppm. The science has been definite for many years the atmospheric carbon dioxide cannot start to drop unless carbon dioxide emissions are stopped- that's zero carbon.
Even virtual zero carbon emissions (like 90%) would not quite stabilize global warming, nor ocean acidifcation.
But zero carbon emissions would actually bring us below 1.5C.
We can achieve zero carbon e,issions by adding some so called 'negative emissions' to virtual zero. That means taking some CO2 out of the air and securing it out of the carbon cycle and to some extent that is possible.