Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 238

It is time for another little digression. Sometime in the fourth century BCE, a geographer
called Pytheas from the Greek colony of Massilia (modern Marseilles) sailed through the
StraitsofGibraltarandturnednorth.Onlyfragmentsremainofhisrecords,buttheycontain
the first surviving written description of a frozen sea. It included the little poetic gem that
opens this chapter. Its visual imagery perfectly captures the nexus between North Atlantic
and Arctic Ocean waters. It is tempting to dream of “the lung of the sea” as a prescient al-
lusion to meridional overturning in the Nordic seas and Arctic shelves!
The fact that the carbon cycle has limitations to the rate at which it can remove carbon
from the atmosphere to the oceans and from the oceans to consolidated sediment leads to a
concept that climate scientists call “commitment”. The oceans have already removed about
half the anthropogenic carbon released to the atmosphere since the Industrial Revolution.
However, as the oceanic concentration of CO 2 rises, its ability to take up more CO 2 de-
creases partly because it is approaching saturation, the saturation concentration for CO 2 is
lower in a warm ocean than in a cold ocean, and it is related to certain characteristics of
carbonate chemistry. Climate models tell us that even in the impossible emission scenario
of global economies moving tonight to carbon neutrality, Earth's mean global temperature
will continue to rise well into the future because our past emissions have committed the
globe to this outcome. As every year goes by, the size of the commitment increases. It is
because of this concept of commitment that many climate scientists believe our politicians
should be aiming for achieving carbon-neutral economies within the next 50 years if we
are to maintain temperatures at manageable levels. IPCC AR5 summed it up with these
words: “Cumulative emissions of CO 2 largely determine global mean surface warming by
the late 21st century and beyond. Most aspects of climate change will persist for many cen-
turies even if emissions of CO 2 are stopped. This represents a substantial multi-century cli-
mate change commitment created by past, present and future emissions of CO 2 .” 6 In other
words, warming and rising sea levels would continue for centuries even if GHG emissions
were reduced and concentrations stabilized. 7
Why is the IPCC so confident in attributing the warming global temperature trend of
the last 50 years to the increase in anthropogenic GHG emissions? Of course, there is the