Geoscience Reference
In-Depth Information
is a rare rock and has been on Earth for less than twenty per cent of its history. For most of
time, planet Earth has been warmer and wetter.
In the past, ecosystems thrived when there was a high atmospheric carbon dioxide
content—especially if it was warm. This is known by horticulturalists. They pump warm
CO
2
into glass houses. The optimum CO
2
content is more than 1,600 ppm (as compared
with the current atmospheric content of 400 ppm).
History shows that communities thrived when it was warm and there was massive
depopulation during cooler times. It is only recently—when Westerners have been very
affluent—thatpeoplehavefearedthewarmth.Informertimes,communitiesfearedthecold
because Jack Frost brought death, disease, famine, and war.
iii. There will be tipping points, sea level rise, extinctions and ocean
acidification Sea level changes
Point (iii) is not reflected by evidence. In the past, when atmospheric CO
2
was up to
one thousand times higher than at present, there were no tipping points, no carbon
dioxide-driven climate change, and no runaway global warming. In fact, the planet was
its normal wet-warm self, with the occasional ice age. Sea level rise is caused by water
covering the land or the land sinking. Water can rise over the land because the oceans fill
withsediment,largesubmarineigneousprovincesdisplacewater,theoceanfloorrises,and
continental glaciers and ice sheets melt.
The most common reason for water covering the land is ice melting. However, in each
of the six major ice ages there were hundreds of glaciations and warm interglacials. Ice
retreats and expands for many reasons and temperature is only one of the reasons.
When glaciation locks up more water as snow and ice, sea level falls and the land
covered by ice sinks, creating a land rise elsewhere. During an interglacial, sea level rises,
the land that was covered with ice rises and other land areas sink. Within the current
interglacial, sea level has risen about 130 metres over the last 12,000 years, the rate of sea
level rise has decreased (as would be expected towards the end of an interglacial), some
land areas that were covered by ice (e.g. Scandinavia) have risen, and near shore ice sheets
have been destabilised by sea level rise. Sea level changes are natural. Since the zenith of
thelastglaciation20,000yearsago,sealevelhasrisen.Whatisexpectedafteraglaciation?
A sea level fall or a sea level rise? What is important is that the post-glacial rate of sea
level rise is declining, exactly what would be expected at the end of an interglacial period.
Nature Geoscience
recently reported that since 2002, the rate of sea level rise has declined
by 31 per cent.
