Is Climate Change Due to the Use Of Fossil Fuels Irreversible?

Firstly, when addressing this questions it is important to realize that this is a highly debated question.  Due to the complexity of climate and many variables involved it is hard to know exactly how accurate model's predictions will be.  Moving away from this disclaimer Susan Solomon's opinion on this irreversibility will be examined in an article published on PNAS.org.  This paper focuses on irreversible climate changes in which three criteria are met.  Observed changes are already existing and there is evidence for anthropogenic contributions.  The change is based upon principals that are assumed to be understood.  Finally, projections must be broadly robust across models.  Carbon concentrations in the atmosphere are the first irreversible change.  Solomon states that the carbon cycle across long time spans was able to keep concentrations balanced, but since the industrial revolution human activity has dumped so much CO2 into the atmosphere to create an irreversible change.  According to her models if CO2 emissions were to completely cease the atmosphere still wouldn't return to pre-industrial concentrations.  The next irreversible climate change is atmospheric warming. This has a lot to do with the CO2 concentrations being high.  Precipitation changes are next.  These changes come about because of the warming of the atmosphere.  The final change is sea level rise.  This is expected to come about due to the warming and expanding of the oceans.  Also, melting of glaciers will produce this change.  By examining Solomon's model it is concluded that there is some degree of irreversibility in climate change due to carbon dioxide emissions.  Looking at this model it is seen how intricately all of these changes are connected.  However, describing how complicated the climate system is it is likely that there are errors in these models.

Could the CO2 increase be attributed to other phenomenon?
While it is important to focus on reducing fossil fuel use no argument is fair if only one side of the story is told.  For this reason it is important to consider other possibilities.  One of these is land use change.  It is hard to quantify how much CO2 increases due to deforestation every year; however, it is likely that it does.  Another possible phenomenon is altered efficiencies of CO2 sinks such as the oceans.

Source:
http://www.pnas.org/content/early/2009/01/28/0812721106.full.pdf+html
http://www.globalcarbonproject.org/carbonbudget/09/hl-full.htm#naturalsinks