Changes in precipitation and evaporation patterns, plant growth processes, and incursions of sea water into coastal aquifers as sea levels rise will all affect the rate of groundwater recharge, the absolute volume of groundwater available, groundwater quality, and the physical connection between surface and groundwater bodies. Increased temperatures generally have a negative impact on water quality in lakes and rivers, typically by stimulating growth of nuisance algae. Changes in heavy precipitation, runoff, and stream flow can also be expected to have an impact on a diverse set of water quality variables.
Water quality will also be affected by saltwater intrusion into coastal aquifers as sea levels rise. In general, the water quality implications of climate change are even less understood than impacts on water supply. Effective management of water supplies requires fairly precise information about current and expected future water availability.http://gelatocottage.sg/includes/2020-05-18/3571.php
Review of the evidence base for ecosystem-based approaches for adaptation to climate change
However, the complex processes involved in the hydrologic cycle prevent simplistic conclusions about how to manage water supplies based on climate model projections. In many regions, the uncertainties associated with projections of rainfall and runoff coupled with uncertainties in other changes, such as changes in land use and land cover, leads to cascading uncertainties about changes in freshwater resources. These uncertainties are compounded by uncertainties in the technical capacity to store, manage, and conserve water resources, which in turn are shaped by socioeconomic, cultural, institutional, and behavioral issues that determine the use of water.
Two clear messages that emerge from research on water management is that water managers will need to make decisions while facing persistent and sometimes considerable uncertainty, and that improved decision-support tools would be helpful for planning purposes.
Changes in freshwater systems are expected to create significant challenges for flood management, drought preparedness, water supplies, and many other water resource issues. Responding to these challenges will require better data and improved model projections as well as a better understanding of both the impacts of climate change and the role of water governance on future water resources.
Significant gaps remain in the knowledge base that informs both projections of climate impacts on water resources and governance strategies that can build adaptive capacity of water systems to climate effects. Key research needs, which are explored in more detail in Chapter 8 , include the following:.
Improve projections of changes in precipitation and other water resources at regional and seasonal time scales. Develop long-term observational systems for measuring and predicting hydrologic changes and planning management responses. Improve tools and approaches for decision making under uncertainty and complexity.
Develop vulnerability assessments of the diverse range of water users and integrative management approaches to respond effectively to changes in water resources. Increase understanding of water institutions and governance, and design effective systems for the future. Evaluate effects, feedbacks, and mitigation options of water resource use on climate. Decades of research on terrestrial and marine ecosystems and their biodiversity have improved our understanding of their importance for society and their links to climate.
Ecosystems provide food, fuel, and freshwater. They regulate climate through the global carbon cycle and the hydrologic cycle. They buffer against storms, erosion, and extreme events and provide cultural, nonmaterial benefits such as space for recreation, education, and spiritual practices.
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For additional discussion and references, see Chapter 9 in Part II of the report. Shifts in climate are changing the geographical range of many plant and animal species.
A series of place-based observations and syntheses of existing data indicate that many plants and animals have experienced range shifts over the past 30 years that approach the magnitude of those inferred for the last 20, years the time of the last glacial maximum.
The phenology seasonal periodicity and timing of life-cycle events of species is also changing with the earlier onset of spring and longer growing seasons. The implications of these changes for biodiversity, the provision of ecosystems services, and feedbacks on climate are not well understood. Large and long-duration forest fires have increased fourfold over the past 30 years in the American West. Forest fires are influenced by many factors, including climate change, but warming has increased the length of the fire season by more than two months in some locations, and the increasing size of wildfires can be attributed in part to earlier snowmelt, temperature changes, and drought.
Decomposition and respiration of CO 2 back to the atmosphere also increase as temperatures warm. Finally, populations of forest pests such as the spruce beetle, pine beetle, spruce budworm, and wooly adelgid are increasing in the western United States as a result of climate change.
Both the amount and rate of warming will influence the ability of plants and animals to adapt. In addition, temperature changes will interact with changes in CO 2 , precipitation, pests, soil characteristics, and other factors. Tree species, for example, are expected to shift their ranges northward or upslope, with some current forest types such as oak-hickory expanding, others such as maple-beech contracting, and still others such as spruce-fir disappearing from the United States altogether Figure 2.
Experimental and modeling studies indicate that exposure to elevated CO 2 and temperatures can lead to increases in photosynthesis and growth rates in many plant species, although at higher temperatures this trend may reverse. Projections suggest that forest productivity will increase with elevated CO 2 and climate warming, especially in young forests on fertile soils where water is adequate.
Erik Beever, Ph.D.
Where water is scarce and drought is expected to increase, or where pests increase in response to warming, however, forest productivity is projected to decrease. Some analyses have indicated the possibility of major changes in ecosystems due to the combined effects of changes in temperature and precipitation, potentially affect-.
Many forest types shift their ranges northward or shrink in areas, while some expand their areas. For further details see Figure 9.
For example, drier conditions in the Amazon could potentially lead to increased susceptibility to fire, lower productivity, and shifts from forest to savanna systems in that region. The strong warming observed across the Arctic is already leading to poleward shifts of boreal forests into regions formerly covered in tundra, and these shifts are expected to continue. Just as on land, ranges of many marine animals have shifted poleward in recent decades Figure 2. The pace of these changes can be faster in the sea because of the high mobility of many marine species.
Changes have also been observed in ocean productivity, which measures the photosynthetic activity of organisms at the base of the marine food web. Model projections suggest that some habitats, such as polar seas and areas with coastal upwelling, may see increases in productivity as climate change progresses. The majority of ocean areas, however, are projected to experience declines in productivity as warm, nutrient-poor surface water is increasingly isolated from the colder, nutrient-rich water below.
Even in highly productive coastal upwelling systems, it is possible that even stronger upwelling could draw up deeper, low-oxygen hy-.
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The average shift among the species examined was approximately 19 miles north of its location red line. Such hypoxic dead zones have recently appeared off the coasts of Oregon and Washington. Continued losses of sea ice and stronger warming at higher latitudes are expected to drive major habitat alterations in Arctic ecosystems. Ice dynamics plays an important role in ocean productivity, and sea ice is a critical habitat for many species, including birds and mammals.
Although the details are uncertain, polar ecosystems are at the threshold of major ecosystem changes due to climate change. Without careful management, these changes may be exacerbated by expanding human uses in polar seas as sea ice continues to decline. In the tropics, warm temperatures pose a bleaching threat to corals.
Corals are animals, but they depend on algae growing in their tissues for much of their nutrition. Models suggest that the fate of corals under future warming scenarios depends critically on the pace of warming. Roughly one-quarter of the CO 2 currently released by human activities is absorbed in the sea. While some of the CO 2 is taken up by marine organisms, most if it combines with water to form carbonic acid. The result has been a roughly 30 percent increase in ocean acidity since preindustrial times.
If CO 2 emissions continue to increase at present rates, ocean acidification could intensify by three to four times this amount by the end of this century. In addition, ocean acidification may reduce the ability of the ocean to take up CO 2 ; this represents a positive feedback on global warming because it would lead to faster CO 2 accumulation in the atmosphere. Although the acidification of the sea is highly certain, the response of ocean ecosystems to changing ocean chemistry is highly uncertain.
Acidification can disrupt many biological processes, including the rates at which marine animals can form shells. Coral reefs are particularly sensitive. If atmospheric CO 2 levels reach twice their preindustrial values, the resulting increase in acidity could mean there will be few places in the. Polar seas could also experience major changes, since many of the species at the base of the food web may be disrupted. Hence, ocean acidification poses a major threat to ocean ecosystems, but the details are only beginning to be understood. Plants on land and in the ocean take up carbon during photosynthesis and release it through respiration.
Experimental research has shown that some land ecosystems respond to higher atmospheric concentrations of CO 2 by taking up and storing more carbon in plant tissues, soils, and sediments. Based on a combination of ecosystem models and observations, it has been estimated that for the period to , land ecosystems removed roughly one-third of the CO 2 emitted by human activities. However, roughly half of this carbon sink was offset by changes in land use that resulted in net CO 2 emissions back to the atmosphere mainly through tropical deforestation. If the balance between CO 2 absorption and emissions by ecosystems were to change in response to either future climate changes or changes in management, this could lead to a significant positive or negative feedback on atmospheric CO 2 levels.
For example, the warming of ocean surface waters across much of the world may represent a positive feedback on climate change, because warming of surface waters commonly reduces the uptake of CO 2 by phytoplankton, which could lead to less ocean uptake of CO 2 , faster CO 2 accumulation in the atmosphere, and accelerated greenhouse warming. However, a number of factors influence the storage of carbon in ocean- and land-based ecosystems. For instance, the availability of nutrients and water can limit uptake by land plants, and increases in temperature or large wildfires can increase GHG emissions from land-based ecosystems to the atmosphere.
Other important factors modulating the carbon sink provided by terrestrial ecosystems include species redistributions and changes in growing season lengths, drought, insects, pathogens, and land use.
Related Ecological Consequences of Climate Change: Mechanisms, Conservation, and Management
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