Environmental Engineering Reference
In-Depth Information
(1)
climate change (CO
2
concentration in the atmosphere \350 ppm and/or a
maximum change of +1 W m
-2
in radiative forcing);
(2)
ocean acidification (mean surface seawater saturation state with respect to
aragonite C80 % of pre-industrial levels);
(3)
stratospheric ozone (\5 % reduction in O
3
concentration from pre-industrial
level of 290 Dobson Units);
(4)
biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation
of N
2
to 35 Tg N yr
-1
) and phosphorus (P) cycle (annual P inflow to oceans
not to exceed 10 times the natural background weathering of P);
(\4,000 km
3
yr
-1
(5)
global
freshwater
use
of
consumptive
use
of
runoff
resources);
(6)
land system change (\15 % of the ice-free land surface under cropland);
(7)
the rate at which biological diversity is lost (annual rate of \10 extinctions
per million species).
Two additional planetary boundaries for which a boundary level was not yet
determined are chemical pollution and atmospheric aerosol loading.
According to Rockström et al. (
2009
) ''transgressing one or more planetary
boundaries may be deleterious or even catastrophic due to the risk of crossing
thresholds that will trigger nonlinear, abrupt environmental change within conti-
nental- to planetary-scale systems''. These authors estimated that humanity has
already transgressed three planetary boundaries for climate change, rate of bio-
diversity loss, and changes to the global nitrogen cycle. And a recent study (Garcia
et al.
2014
) confirms the devastating impacts of climate change on biodiversity
loss. As a consequence of this worrying status, it remains crucial to act in order to
address those problems in a context in which urban human population will almost
double, increasing from approximately 3.4 billion in 2009 to 6.4 billion in 2050
(WHO
2014
). Other authors also agree that this is the most vital challenge of the
twenty-first century (Griggs et al.
2013
; Gerst et al.
2014
). As Spence et al. (
2009
)
have showed this increase in urban population is economically motivated. The
higher the urbanization rate of a country, the higher its GDP. Countries high a
GDP per person over $10.000 have a urbanization rate over 60 % while countries
with a GDP per person over $30.000 have a urbanization rate around 80 %.
Internally the economic importance of working in cities can be assessed by the
urban-rural income gap. In China the urban-rural residents' income ratio surged
from 2.57:1 in 1978 to 3.13:1 in 2011 (Li et al.
2014a
,
b
).
Climate change is one of the most important environmental problem faced by
the Planet Earth (IPCC
2007
; Schellnhuber
2008
) being due to the increase of
carbon dioxide (CO
2eq
) in the atmosphere, for which the built environment is a
significant contributor, with around one-third of global carbon dioxide emissions.
In the early eighteenth century, the concentration level of atmospheric CO
2eq
was
280 parts per million (ppm) at present it is already 450 ppm (Vijayavenkataraman
et al.
2012
).
Keeping the current level of emissions (which is unlikely given the high economic
growth of less developed countries with consequent increases in emission rates) will
Search WWH ::
Custom Search