8.5 Long-Term Climate Change
The impacts of actual CO 2 emissions will last for centuries even if the anthropogenic emissions of greenhouse gases are stopped. Global warming will remain
after 2100, except for the RCP2.6 scenario of the AR5 Report. The forecasts of
AR5 are that global temperature will be stationary, remaining high long after an
eventual termination of anthropogenic CO 2 emissions. To revert the current forecasts of climate change until 2100, there must be continuous extraction of atmospheric CO 2 during a significant period. Also, the direct impacts of climate change,
for example, soil carbon and ecosystems re-equilibrium, ice sheets, and sea-level
rise, have long-term dynamics of their own, so that their effects will be felt even
after the global temperatures stabilize. Mitigation may, however, strongly reduce
the number of heat extremes by the second half of the twenty-first century (Coumou
and Robinson 2013).
The global mean sea level will go on rising for centuries beyond 2100, and the
same can be said about ocean acidification if CO 2 emissions go unchecked. The
RCP2.6 projections for the sea-level increase until 2300, indicate that sea rise can
be lower than the 1 m above the pre-industrial era, if the GHG concentrations are
kept below the 500 ppm CO 2 -eq. The rise could be higher than 3 m if the GHG
concentrations range from 700 ppm CO 2 -eq. to 1500 ppm CO 2 -eq., under scenario
RCP8.5.
It should be noted that the Antarctica solid ice discharge contribution is underestimated, so that the sea-level rise in 2100 could be higher. In this context, sustained
ice mass loss could cause a larger sea-level rise, under an irreversible scenario. For
Greenland, continued global warming ranging from 1 °C to about 4 °C would deliver
a drastic mass of ice during a millennium time scale, which would eventually cause a
sea-level rise as high as 7 m.
A scenario of a sudden drastic instability in response to climate forcing is
possible, although the evidence available is not enough to carry out an accurate
quantitative assessment. The RCP4.5, RCP6.0, and RCP8.5 profiles, corresponding
to medium to high GHG emissions scenarios, could abruptly disrupt regional scale
terrestrial, marine, and freshwater systems, both in terms of composition and
structure.
An example of an impact condition with global consequences is the reduction in
permafrost areas which will occur if the global temperatures rise further. Under the
RCP8.5 climate profile, net carbon emissions in the twenty-first century from
permafrost could range from 180 Gt CO 2 to 920 Gt CO 2 adding to the 2040 Gt CO 2
already accumulated carbon emissions, and almost reaching the 2900 Gt CO 2
threshold critical to attaining a likely dangerous climate change.
8.4 Occurrence of Extreme Events
291
The impacts of actual CO 2 emissions will last for centuries even if the anthropogenic emissions of greenhouse gases are stopped. Global warming will remain
after 2100, except for the RCP2.6 scenario of the AR5 Report. The forecasts of
AR5 are that global temperature will be stationary, remaining high long after an
eventual termination of anthropogenic CO 2 emissions. To revert the current forecasts of climate change until 2100, there must be continuous extraction of atmospheric CO 2 during a significant period. Also, the direct impacts of climate change,
for example, soil carbon and ecosystems re-equilibrium, ice sheets, and sea-level
rise, have long-term dynamics of their own, so that their effects will be felt even
after the global temperatures stabilize. Mitigation may, however, strongly reduce
the number of heat extremes by the second half of the twenty-first century (Coumou
and Robinson 2013).
The global mean sea level will go on rising for centuries beyond 2100, and the
same can be said about ocean acidification if CO 2 emissions go unchecked. The
RCP2.6 projections for the sea-level increase until 2300, indicate that sea rise can
be lower than the 1 m above the pre-industrial era, if the GHG concentrations are
kept below the 500 ppm CO 2 -eq. The rise could be higher than 3 m if the GHG
concentrations range from 700 ppm CO 2 -eq. to 1500 ppm CO 2 -eq., under scenario
RCP8.5.
It should be noted that the Antarctica solid ice discharge contribution is underestimated, so that the sea-level rise in 2100 could be higher. In this context, sustained
ice mass loss could cause a larger sea-level rise, under an irreversible scenario. For
Greenland, continued global warming ranging from 1 °C to about 4 °C would deliver
a drastic mass of ice during a millennium time scale, which would eventually cause a
sea-level rise as high as 7 m.
A scenario of a sudden drastic instability in response to climate forcing is
possible, although the evidence available is not enough to carry out an accurate
quantitative assessment. The RCP4.5, RCP6.0, and RCP8.5 profiles, corresponding
to medium to high GHG emissions scenarios, could abruptly disrupt regional scale
terrestrial, marine, and freshwater systems, both in terms of composition and
structure.
An example of an impact condition with global consequences is the reduction in
permafrost areas which will occur if the global temperatures rise further. Under the
RCP8.5 climate profile, net carbon emissions in the twenty-first century from
permafrost could range from 180 Gt CO 2 to 920 Gt CO 2 adding to the 2040 Gt CO 2
already accumulated carbon emissions, and almost reaching the 2900 Gt CO 2
threshold critical to attaining a likely dangerous climate change.
8.4 Occurrence of Extreme Events
291