figure 9. If global emissions
were to suddenly stop, it would
take a long time for surface air
temperatures and the ocean to
begin to cool, because the excess
CO2 in the atmosphere would
remain there for a long time and
would continue to exert a warming
effect. Model projections show how
atmospheric CO2 concentration
(a), surface air temperature (b),
and ocean thermal expansion (c)
would respond following a scenario
of business-as-usual emissions
ceasing in 2300 (red), a scenario
of aggressive emission reductions,
falling close to zero 50 years from
now (orange), and two intermediate
emissions scenarios (green and
blue). The small downward tick
in temperature at 2300 is caused
by the elimination of emissions
of short-lived greenhouse gases,
including methane. Source: Zickfeld
et al., 2013 | No. Even if emissions of greenhouse gases were to suddenly stop, Earth’s surface temperature
would not cool and return to the level in the pre-industrial era for thousands of years. If emissions of CO2 stopped altogether, it would take many thousands of years for atmospheric CO2 to
return to ‘pre-industrial’ levels due to its very slow transfer to the deep ocean and ultimate burial in ocean
sediments. Surface temperatures would stay elevated for at least a thousand years, implying extremely
long-term commitment to a warmer planet due to past and current emissions, and sea level would likely
continue to rise for many centuries even after temperature stopped increasing [Figure 9]. Significant
cooling would be required to reverse melting of glaciers and the Greenland ice sheet, which formed
during past cold climates. The current CO2-induced warming of Earth is therefore essentially irreversible
on human timescales. The amount and rate of further warming will depend almost entirely on how much
more CO2 humankind emits. |