Present climate and biological change - Climate Change: Biological and Human Aspects - page 232

circulation transports warm air from the tropics polewards to higher latitudes. What
Oliver Pauluis and colleagues showed was that when averaged on moist isentropes
(an entropy measure), as opposed to dry isentropes, the total mass transported by
the circulation is twice as large. This is of importance in climate models as it could
account for perhaps up to half of the air in the upper troposphere in high latitude,
polar regions. Such new understanding needs to be considered by climatologists
and incorporated into their climate models. Although the above is not a biological
dimension to climate change (the principal focus of this topic) it is worth mentioning
because climate models are not so good at reflecting high-latitude (polar) climate
change: the poles (especially the north pole) are warming faster than elsewhere
and computer models do not fully reflect this. This faster warming of the poles,
especially in the northern hemisphere, is sometimes called Arctic amplification or
polar amplification, and models in the past have had difficulty reflecting this; even
today they do not fully capture the effect even though they include elements such as
albedo feedback effects due to declining reflective surface ice (Figure 1.8b). Other
evidence that it is atmospheric energy transport from lower latitudes into the Arctic
that may explain (at least part of ) the Arctic amplification mystery came in 2008 from
Rune Graversen, Thorsten Mauritsen and colleagues from Stockholm University. This
phenomenon may be explained by heat transported by air above the lowest part of the
atmosphere (the middle troposphere).
As said, the climate system is made up of many dimensions and interacting factors
of various, and often changing, strength. And so, as our understanding of the cli-
mate system improves, changes are made to models so that the next generation is
improved. In addition to the new, purely climatological considerations there is con-
tinually improved understanding of Earth system biology and the latest computer
models include biological dimensions. One example of an area of biological con-
cern is how much carbon dioxide is drawn through photosynthesis each year and how
much is released through respiration. The amount of atmospheric carbon drawn down
through photosynthesis is clearly related to global gross primary production (the fix-
ation of inorganic carbon into organic forms by autotrophs). This is a key part of the
carbon cycle the understanding of which is continually improving through research
(see section 1.3 and Figure 1.3). Here the annual biological addition and removal
of carbon dioxide to the Earth's atmosphere is part of the biological components
included in recent climate models. In 2011 those developing models could not fail
to take notice in the work of Lisa Welp and Ralph Keeling who led an international
team that presented 30 years' worth of data on 18 O/ 16 O in carbon dioxide from the
Scripps Institution of Oceanography global flask network (Welp et al., 2011). They
used this isotopic ratio together with what happens in an El Nino year (part of the
El Ni no Southern Oscillation, or ENSO) in a simple model to infer global primary
production. Their analysis suggests that current estimates of global gross primary
production, of 120 petagrams (Pg; or Gt) of carbon per year, may be too low, and
that a better estimate might be of 150-175 Pg of carbon per year; that is, a 25-46%
increase. Of course, if there is greater carbon draw dawn by plant and algal photo-
synthesisers in a year then equally there must be greater respiration releasing carbon
(otherwise atmospheric carbon dioxide would decline), and this in turn means that
the fast carbon cycle (as opposed to the deep carbon cycle; see section 1.3) must be