Environmental Engineering Reference
In-Depth Information
Warmer winter temperatures favor many populations of tree pest and pathogen spe-
cies normally kept at low levels by cold winter temperatures (Tubby and Webber, 2010).
Although climate change may reduce populations of some species, many others are better
able than their arboreal host to adapt to changing environments due to their short lifecycles
and rapid evolutionary capacity (Cullington and Gye, 2010; Tubby and Webber, 2010).
The consequences of these population changes are compounded by the fact that hot, dry
environments enrich carbohydrate concentrations in tree foliage, making urban trees more
attractive to pests and pathogens (Tubby and Webber, 2010).
Climate change alters water cycles in ways that impact urban forests. Increased winter
precipitation puts urban forests at greater risk from physical damage due to increased snow
and ice loading (Johnston, 2004). Increased summer evaporation and transpiration create
water shortages often exacerbated by urban soil compaction and impermeable surfaces.
More frequent and intense extreme weather events increase the likelihood of severe flood-
ing, which may uproot trees and cause injury or death to tree root systems if waterlogged
soils persist for prolonged periods (Johnston, 2004).
Especially cold regions may benefit from increased tourism, agricultural productivity,
and ease of transport as a result of climate change (Romero-Lankao, 2008). The potential
positive implications of climate change, however, are far eclipsed by the negative (Parry
et al., 2007). Rising temperatures, increased pest and pathogen activity, and water-cycle
changes impose physiological stresses on urban forests that compromise forest ability to
deliver ecosystems services that protect against climate change. Climate change will also
continue to alter species ranges and regeneration rates, further affecting the health and
composition of urban forests (Nowak, 2010; Ordonez et al., 2010). Proactive management
is necessary to protect urban forests against climate-related threats and to sustain desired
urban forest structures for future generations.
GEOLOGIC CARBON SEQUESTRATION
Geologic sequestration begins with capturing carbon dioxide from the exhaust of
fossil fuel power plants and other major sources. The captured carbon dioxide is
piped 1 to 4 kilometers below the land surface and injected into porous rock forma-
tions. Compared to the rates of terrestrial carbon uptake shown in
Figures 9.1
and
per year. Much larger rates of sequestration are envisioned to take advantage of the
potential permanence and capacity of geologic storage.
The permanence of geologic sequestration depends on the effectiveness of sev-
eral carbon dioxide trapping mechanisms. After carbon dioxide is injected under-
ground, it will rise buoyantly until it is trapped beneath an impermeable barrier,
or seal. In principle, this physical trapping mechanism, which is identical to the
natural geologic trapping of oil and gas, can retain carbon dioxide for thousands to
millions of years. Some of the injected carbon dioxide will eventually dissolve in
groundwater, and some may be trapped in the form of carbonate minerals formed
by chemical reactions with the surrounding rock. All of these processes are sus-
ceptible to change over time following carbon dioxide injection. Scientists are
studying the permanence of these trapping mechanisms and developing methods
to determine the potential for geologically sequestered carbon dioxide to leak back
to the atmosphere.
