| |
Figure 5-3: Stabilizing CO2 emissions
at current levels will result in a continously rising atmospheric CO2
concentration and temperature. Stabilization of atmospheric CO2
and temperature change will eventually require the emissions to drop well
below current levels. In all three panels the red curves illustrate the
result of emissions held constant at the level prescribed by the WRE 550
profile for the year 2000 (which is slightly higher than the actual emissions
for the year 2000), while the blue curves are the result of emissions following
the WRE 550 stabilization profile. Both cases are illustrative only: Constant
global emissions are unrealistic in the short term, and no preference is
expressed for the WRE 550 profile over others. Other stabilization profiles
are illustrated in Figure 6-1. Figure 5-3
was constructed using the models described in WGI
TAR Chapters 3 & 9.
|
WGI TAR Sections 3.7 &
9.3 |
| 5.7 |
Although warming reduces the uptake of CO2
by the ocean, the oceanic net carbon uptake is projected to persist under
rising atmospheric CO2 , at least for the 21st century. Movement
of carbon from the surface to the deep ocean takes centuries, and its
equilibration there with ocean sediments takes millennia.
|
WGI TAR Sections 3.2.3 &
3.7.2, & WGI
TAR Figures 3.10c,d |
| 5.8 |
When subjected to rapid climate
change, ecological systems are likely to be disrupted as a consequence of
the differences in response times within the system. The resulting
loss of capacity by the ecosystem to supply services such as food, timber,
and biodiversity maintenance on a sustainable basis may not be immediately
apparent. Climate change may lead to conditions unsuitable for the establishment
of key species, but the slow and delayed response of long-lived plants hides
the importance of the change until the already established individuals die
or are killed in a disturbance. For example, for climate change of the degree
possible within the 21st century, it is likely, in some forests, that when
a stand is disturbed by fire, wind, pests, or harvesting, instead of the
community regenerating as in the past, species may be lost or replaced by
different species.
|
WGII
TAR Section 5.2 |
| 5.9 |
Humans have shown a capacity
to adapt to long-term mean climate conditions, but there is less success
in adapting to extremes and to year-to-year variations in climatic conditions.
Climatic changes in the next 100 years are expected to exceed any experienced
by human societies over at least the past 5 millennia. The magnitude and
rate of these changes will pose a major challenge for humanity. The time
needed for socio-economic adaptation varies from years to decades, depending
on the sector and the resources available to assist the transition. There
is inertia in decision making in the area of adaptation and mitigation,
and in implementing those decisions, on the order of decades. The fact
that
adaptation and mitigation decisions are generally not made by the same
entities compounds the difficulties inherent in the identification and
implementation
of the best possible combination of strategies, and hence contributes to
the delays of climate change response.
|
WGII TAR SPM 2.7, WGII
TAR Sections 4.6.4, 18.2-4,
& 18.8, & WGIII
TAR Section 10.4.2 |
| |
Figure 5-4: The range of time
scales of major processes within the global carbon cycle leads
to a range of response times for perturbations of CO2 in the
atmosphere, and contributes to the development of transient sinks, as when
the atmospheric CO2 concentration rose above its pre-1750 equilibrium
level. |
|
| 5.10 |
There is typically a delay
of years to decades between perceiving a need to respond to a major challenge,
planning,researching and developing a solution, and implementing it.Thisdelaycan
be shortened by anticipating need sthrough the application of foresight,
and thus developing technologies in advance. The response of technological
development to energy price changes has historically been relatively rapid
(typically, less than 5 years elapses between a price shock and the response
in terms of patenting activity and introduction of new model offerings)
but its diffusion takes much longer. The diffusion rate often depends on
the rate of retirement of previously installed equipment. Early deployment
of rapidly improving technologies allows learning-curve cost reductions
(learning by doing), without premature lock-in to existing, low-efficiency
technology. The rate of technology diffusion is strongly dependent not only
on economic feasibility but also on socio-economic pressures. For some technologies,
such as the adoption of new crop varieties, the availability of, and information
on, pre-existing adaptation options allows for rapid adaptation. In many
regions, however, population pressures on limited land and water resources,
government policies impeding change, or limited access to information or
financial resources make adaptation difficult and slow. Optimal adaptation
to climate change trends, such as more frequent droughts, may be delayed
if they are perceived to be due to natural variability, while they might
actually be related to climate change. Conversely, maladaptation can occur
if climate variability is mistaken for a trend. |
WGII TAR Sections 1.4.1,
12.8.4, & 18.3.5,
& WGIII TAR Sections 3.2,
5.3.1, & 10.4 |
