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Impact of Climate Change
The next step is then to evaluate the impact of the rates of change
now occurring and expected over the next 60 years. Terrestrial and aquatic
ecosystems, human health, and socioeconomic systems such as agriculture,
forestry, fisheries and water resources, are key elements of human
development and well being that are all sensitive to climate change. The
impact of climate change on these areas is not uniform; in fact, some will
experience beneficial consequences while others will suffer irreversible
detrimental change.
The listed areas impacted by climate change already are subjected to natural and other human-induced stress. Climate change adds an important new stress for each of these areas, the impact of which may be exacerbated by already existing stresses. The impact of climate change when added to existing stresses is difficult and in some cases impossible to evaluate. If the impact of climate change is judged (whether it be by standards of economics, aesthetics, ethics, or survival) to be unacceptable we have two choices: mitigation or adaptation.
Mitigation and Adaptation
Mitigation assumes that some change of human behavior (e.g., less
use of fossil fuel) can be successfully implemented in time to sufficiently
reduce the stress due to climate change and prevent irreversible loss. The
tools and methods presented in our discussion over the last several
units then can be used to determine the level of behavioral change that
will be required to reduce the impact to a desired level. Of course all
such calculations carry a degree of uncertainty.
Adaptation suggests that humans are either unwilling or unable to collectively change their behavior to a sufficient level to mitigate stress due to human-induced climate change, and that resources should be focused on "hardening" the impacted systems so that they might better be able to withstand the increased stress due to climate change. Successful adaptation requires:
Some systems and geographic locations have better adaptive capacity than others. The vulnerability to change increases as the adaptive capacity decreases. The level of economic and institutional resources in a community or region influences the capability for adaptation. Less developed countries, more likely to be lacking such resources, are more vulnerable to negative impacts of climate change.
Detection of Climate Change
Clear and unambiguous detection of climate change and its impacts
on various systems are difficult. Climate change itself is difficult to
detect, so evaluating the effect of small changes of climate on natural
systems is doubly difficult. The complexity of influences, the presence of
both positive and negative feedbacks, and the possible synergistic effects
of multiple influences permit outcomes that may be much less or much
greater than can be estimated by evaluating impacts of isolated influences.
Surprises and unanticipated rapid changes cannot be ruled out. However,
neither should they be used as sole justification for demanding change in
human behavior. Continuing research and openness to new evidence are keys
to progress.
Impacts on Terrestrial
Ecosystems
Forests play a particularly unique role because of their long time
scale for change, their role as repository of 80% of all above-ground
vegetative carbon and 40% of below ground carbon, and their role as hosts
to two thirds of the planet's biodiversity. Global warming at a rate of
1.5 to 3.5 degrees over the next 100 years is equivalent to a poleward
shift of isotherms of 150 to 550 km or 150 to 550 m altitude shift in
mountainous areas over the same period. Typical forest migration rates, by
contrast, are estimated to be 4 to 200 km per century.
Rangelands are sometimes defined as unimproved grasslands,
shrublands, savannas, deserts, and tundra. They occupy 51% of the earth's
land surface and contain about 36% of the total living and dead plant
carbon. Small changes in extreme temperatures and precipitation have
disproportionately large effects in these regions because of the
vulnerability to water availability and water balance.
Deserts are characterized by extremely high temperatures and
extremely low rainfall. These extremes are likely to increase under
climate change. Desertification is defined as land degradation in
naturally dry areas resulting from various factors including climate
variations and human activities. Desertification is more likely to be
irreversible if the environment becomes drier.
Regions of snow, ice, and permafrost comprise the cryosphere.
These regions have provided some of the most notable indications of global
warming over the last century. Changes in the cryosphere produce changes in
water availability from melt water for cities, agriculture and
hydroelectric power generation. Reduction in high-latitude ice fields
change global albedo and allow thawing permafrost to release methane
hydrates.
Warming in mountain regions changes snow cover and may impact water
supplies, tourism, logging, and hydropower production. Ecosystems unique
to specific mid-slope locations may migrate upslope in a warmer climate,
but ecosystems indigenous to mountain-top locations have nowhere to
migrate under such changes.
The IPCC report points out that ecosystems contain the earth's
entire reservoir of genetic material and species diversity. They can be
thought of as providing both goods and services that are essential to human
individuals and societies. The report lists the following services
rendered by ecosystems:
Biome dependence upon temperature and precipitation.
The accompanying diagram shows the dependence of various biomes (vegetation
types) on temperature and precipitation. Temperature changes of 2 to 4
degrees C or precipitation changes of 200 mm per year can cause significant
changes in the boundary regions between these biomes.
Aquatic Ecosystems
Climate change will alter temperatures, flow conditions, and water levels which, in turn, affect species survival, reproduction and growth. Changes in mean and variability of precipitation patterns affect ecosystem productivity and biological diversity. Not all impacts are negative, however: high latitude lakes that might experience longer ice-free conditions and enhanced biological productivity.
Coastal ecosystems are highly active in production of plant carbon from atmospheric carbon dioxide. Coastal wetlands also are rich and diverse ecosystems. Human-induced changes in these regions, together with impacts of climate change such as sea-level rise and warming, create enhanced stresses on fragile natural systems.
Oceans occupy 71% of the surface of the planet. Evaporation and CO2 balance at the ocean surface is very temperature dependent. Climate change may alter sea level and ocean circulation, vertical mixing, and sea-ice cover. These, in turn, will affect nutrient availability, biological productivity, structure and functioning of marine ecosystems, and heat and carbon storage capacity. Such changes have implications for coastal human settlements, fisheries, tourism, recreation, transport, and off-shore structures.
Water
Water is a critical element of national welfare and productivity
because of the role it plays in many forms of consumptive use, ranging from
drinking, to sanitation, recreation, irrigation, power production,
transportation, and many other uses. It is vulnerable to degradation of
both quantity and quality. The benchmark minimum water availability is
1,000 cubic meters of water per year per person; nations having less than
this amount are considered to have a water scarcity. Currently the
following countries fall below this benchmark:
Kuwait
Jordan
Israel
Rwanda
Somalia
Algeria
Kenya
Libya
Egypt
South Africa
Iran
Ethiopia
Increased uncertainty in future supply and demand for water raises the urgency of developing sound water management strategies even in regions now not experiencing water resource difficulties.
Food and Fiber
Food and fiber production may be influenced by (a) direct effects
of changes in temperature, water balance, atmospheric composition, and
extreme events, and (b) indirect effects through changes in distribution
frequency and severity of pest and disease outbreaks, incidence of fire and
weed infestations or through changes in soil properties. Fisheries are
vulnerable to changes in water temperature, water levels, precipitation
patterns, and ocean circulation patterns.
Global agricultural production is relatively insensitive to global
climate change of the magnitude previously determined to be expected in the
next 60 years. However, marginal lands, much of which lies in developing
countries, will be more prone to reduced yields due to increased frequency
of crop failure and land degradation and desertification. Some regions,
such as Canada and Russia can expect increased yields.
Adaptation of
farming practices through new crops, improved water management, better
strategies on crop selection and planting will buffer adverse effects.
Tropical forests seem more vulnerable to land-use changes than
climate change (recall that climate in tropical areas is not projected to
change markedly under global warming). Boreal forests are more vulnerable
to reduction due to climate change. Increased demand for wood for various
human uses will create increased pressure on global forest
supplies.
Current levels of overfishing have more negative impact than
projected climate changes. High latitude production of fish in open waters
and through aquaculture likely will increase. Smaller lakes and streams
will be more negatively impacted by climate change than large rivers and
larger bodies of water. Loss of coastal wetlands as essential breeding
grounds may have significant impact.
Human Infrastructure
Most human infrastructure elements are insensitive to climate change, except some such as agriculture, hydropower production, and transportation in marginally navigable rivers. Demand for air conditioning will increase, but demand for space heating will diminish.
Sea-level rise will be particularly troublesome for some coastal zones and small islands. Studies indicate a 1-m rise in sea level, with no change in coastal protection, will result in land losses of 0.005% in Uruguay, 1% for Egypt, 6% for the Netherlands, 17.5% for Bangladesh, and up to 80% for the Majuro Atoll in the Marshall Islands. China and Bangladesh each have about 70 million people that would be affected by a 1-m rise in sea level.
Increased frequency of extreme events and disproportionate increase of population in regions vulnerable to natural disasters (e.g., coastal regions, suburban sprawl into forested and mountainous regions) are already increasing insurance payouts due to climatic events. Rates for coverage will have to be adjusted to account for changed frequency of such natural disasters.
Human Health
Impact of climate change on human health may come through direct or
indirect pathways.
Increased frequency of extreme warm events (heatwaves) will cause a large impact on human health. Extreme cold events cause fewer deaths on average, so reduction in these events will not balance increased mortality due to heatwaves.
Altered frequency and intensity of tornadoes, hurricanes, storm
surge, and lightning will impact human health and welfare.
Ecological - Changed populations, patterns and movement of pests and infective parasites due to climate change will put different human populations at risk. Increased temperatures generally promote increased pathogen populations thereby increasing chances of contamination of food and water supplies. Changed use of agricultural and horticultural pesticides due to changing patterns of pest populations will cause changes in contamination of food supplies.
Other - Sea-level rise and more extreme events causes more frequent displacements of populations and damage to infrastructure such as water supplies and sanitation systems. Rising temperatures leads to more civil disruption.