144
will be slowly released, meaning that the oceans would become a “very weak heat
source” and dampen the decline of surface atmospheric temperatures (Schewe et al.
2011). Hence, the effects of current increases in CO 2 concentrations will manifest
themselves in the future, much in the same way that present climate change is being
caused by past CO 2 emissions. Also, the process of CO 2 removal from the atmosphere is quite complex, and although more than half of the CO 2 emitted is removed
within a century, a fraction remains in the atmosphere for millennia. Another mechanism that slows down global cooling is the change in oceanic convection, which
enhances ocean heat loss in high latitudes and reduces the surface cooling rate by
almost 50% (Schewe et al. 2011). In this sense, greenhouse gases released at present
“commit” us to certain future effects, as yet unfelt.
Simulations by Schewe et al. (2011) suggest that if a maximum warming of
1.5 °C is reached by middle of the twenty-first century (for CO 2 concentrations of
just over 550 ppm), then temperatures will likely decline slowly afterwards and
reach present-day levels by 2500. This would be achieved by GHG concentrations
peaking in 2040 and declining subsequently to become negative after 2070. If this
is achieved, the rate of sea level rise caused by thermal expansion (where the volume of the seawater would increase due to the change in temperature) would continue for over 200 years after the peak in air temperatures and stabilize around 2250.
The rate of temperature decrease is significantly slower than the current rates of
temperature rise, and are on average around −0.16 °C per century. This slow rate of
cooling is quite significant, and highlights the need to rapidly reduce emissions of
greenhouse gases and the importance of current climate negotiations between different countries. Not achieving these objectives could result in global warming continuing for much more prolonged periods of time. Another scenario by Schewe et al.
(2011) shows how CO 2 concentrations of almost 1500 ppm by 2100 can see warming of up to 8.5 °C and result in 1.3 m of sea level rise due to thermal expansion
alone by 2250 and a 2 m rise by 2500 (though some of the ranges given in the IPCC
5AR are much higher, as noted earlier).
Past geological records of sea level rise indicate that sea levels could very well
have been much higher than current levels. For example, during a period known as
the marine isotope stage 11 (MIS 11, 401 to 411 ka), global temperatures may have
been 1.5–2.0 °C higher than those on the planet today, with sea levels possibly also
being 6–15 m higher (IPCC 5AR). Also, during the last interglacial period, temperatures might have been 1–2 °C higher than pre-industrial levels, with sea levels several metres (around 4–8 m, see IPCC 5AR) higher than at present. Since then, in the
late Holocene (some 12,000 years ago) it is likely that global sea levels rose 2 to
3 m to near present-day levels. All this indicates the necessity to factor time scales
into the framing of the problems that coastal areas face because of sea level rise.
Finally, it is worth pointing out that these projections have only been made at the
global level and on general, average terms. Although islands are expected to be most
vulnerable to sea level rise, precise information about how much sea level rise a
particular island or island state will experience are yet unavailable. Due to this, it is
important to further discuss the particular impacts of sea-level rise on coral islands
and the communities that inhabit them.
M. Esteban et al.
will be slowly released, meaning that the oceans would become a “very weak heat
source” and dampen the decline of surface atmospheric temperatures (Schewe et al.
2011). Hence, the effects of current increases in CO 2 concentrations will manifest
themselves in the future, much in the same way that present climate change is being
caused by past CO 2 emissions. Also, the process of CO 2 removal from the atmosphere is quite complex, and although more than half of the CO 2 emitted is removed
within a century, a fraction remains in the atmosphere for millennia. Another mechanism that slows down global cooling is the change in oceanic convection, which
enhances ocean heat loss in high latitudes and reduces the surface cooling rate by
almost 50% (Schewe et al. 2011). In this sense, greenhouse gases released at present
“commit” us to certain future effects, as yet unfelt.
Simulations by Schewe et al. (2011) suggest that if a maximum warming of
1.5 °C is reached by middle of the twenty-first century (for CO 2 concentrations of
just over 550 ppm), then temperatures will likely decline slowly afterwards and
reach present-day levels by 2500. This would be achieved by GHG concentrations
peaking in 2040 and declining subsequently to become negative after 2070. If this
is achieved, the rate of sea level rise caused by thermal expansion (where the volume of the seawater would increase due to the change in temperature) would continue for over 200 years after the peak in air temperatures and stabilize around 2250.
The rate of temperature decrease is significantly slower than the current rates of
temperature rise, and are on average around −0.16 °C per century. This slow rate of
cooling is quite significant, and highlights the need to rapidly reduce emissions of
greenhouse gases and the importance of current climate negotiations between different countries. Not achieving these objectives could result in global warming continuing for much more prolonged periods of time. Another scenario by Schewe et al.
(2011) shows how CO 2 concentrations of almost 1500 ppm by 2100 can see warming of up to 8.5 °C and result in 1.3 m of sea level rise due to thermal expansion
alone by 2250 and a 2 m rise by 2500 (though some of the ranges given in the IPCC
5AR are much higher, as noted earlier).
Past geological records of sea level rise indicate that sea levels could very well
have been much higher than current levels. For example, during a period known as
the marine isotope stage 11 (MIS 11, 401 to 411 ka), global temperatures may have
been 1.5–2.0 °C higher than those on the planet today, with sea levels possibly also
being 6–15 m higher (IPCC 5AR). Also, during the last interglacial period, temperatures might have been 1–2 °C higher than pre-industrial levels, with sea levels several metres (around 4–8 m, see IPCC 5AR) higher than at present. Since then, in the
late Holocene (some 12,000 years ago) it is likely that global sea levels rose 2 to
3 m to near present-day levels. All this indicates the necessity to factor time scales
into the framing of the problems that coastal areas face because of sea level rise.
Finally, it is worth pointing out that these projections have only been made at the
global level and on general, average terms. Although islands are expected to be most
vulnerable to sea level rise, precise information about how much sea level rise a
particular island or island state will experience are yet unavailable. Due to this, it is
important to further discuss the particular impacts of sea-level rise on coral islands
and the communities that inhabit them.
M. Esteban et al.