Earth ecosystem and climatic changes:


SENSITIVITY - refers to the degree to which a system will be affected (beneficially or adversely) by climate variability and change.

ADAPTIVE CAPACITY - refers to the ability of a system to adjust to climate variability, extremes, and change in order to (a) moderate potential damages, (b) take advantage of the opportunities, and/or (c) cope with the consequences of change. Human adaptive capacity and coping ability depend on factors such as wealth, technology, education, information, skills, infrastructure, access to resources, and management capabilities.

VULNERABILITY - refers to the degree to which a system is susceptible to, and unable to cope with, the adverse effects of climate change, including climate variability and extremes. Vulnerability varies with location, time, and social, economic and environmental conditions. Vulnerability is also a function of the character, magnitude, and rate of climatic variation to which a system is exposed as well as that system's sensitivity and adaptive capacity.

Recent regional climate changes, particularly temperature increases, have already affected many physical and biological systems. Examples of observed changes in response to 20th century warming include shrinking glaciers, thawing permafrost, earlier break-up of river and lake ice, lengthening of mid- to high-latitude growing seasons, poleward and altitudinal shifts of plant and animal ranges, declines of some animal and plant populations, and earlier tree flowering, insect emergence and egg-laying in birds. Many long-term studies from many types of environments have documented changes in physical and ecological systems that correlate with observed temperature changes. The probability that the observed changes in the expected direction could occur by chance alone is now negligible.

While other factors such as land use change and pollution also act on environmental systems and can make causal attribution difficult in individual cases, esro experts conclude with high confidence that the observed regional changes in temperature have had "discernible impacts on many physical and biological systems." The relative impacts of climate-related extreme events on human systems are difficult to disentangle from other factors such as land use changes and population shifts. This makes it challenging to quantify these climate-related impacts. There has been a recent increase in the frequency of floods and droughts in some regions, and they clearly have had significant social and economic impacts. If extreme events increase in frequency, vulnerable human systems could see increasing damages.

Natural systems are vulnerable to climate change, and some will be irreversibly damaged. Glaciers, coral reefs, atolls, mangroves, boreal and tropical forests, polar and alpine ecosystems, prairie wetlands, and remnant native grasslands can be especially vulnerable to climate change because of limited adaptive capacity. Some natural systems are at risk of significant and irreversible damage. While some species may increase in abundance or range, climate change will increase existing risks of extinction of already threatened or vulnerable species and biodiversity loss. The degree or extent of damage will increase with the magnitude and rate of climate change.

Human systems most sensitive to climate variability and change are water resources, agriculture, forestry, coastal zones and fisheries, human settlements, energy, industry, insurance and other financial services, and human health. Examples of projected adverse impacts include reductions in crop yields in most tropical and sub-tropical regions; decreased water availability in many regions that already experience water scarcity; an increase in certain diseases, heat stress mortality and risk of flooding; and increased energy demand for cooling during warmer summers.

The vulnerability of human societies to droughts, floods, heat waves, avalanches, and windstorms is demonstrated by the damage, hardship, and death caused by these extreme events. While changes in the frequency or intensity of these climatic extremes cannot yet be predicted with certainty, some extremes are projected to increase with global warming. Hence it can be expected that the severity of impacts will also increase.

The possibility of large-scale (continental or global), irreversible changes in Earth systems resulting in widespread and sustained impacts cannot be ruled out. These possibilities are scenario-dependent, and the range of possibilities is yet to be fully evaluated. Examples include a significant slowing of ocean circulation that transports warm water to the North Atlantic; large reductions in the Greenland and West Antarctic ice sheets; much faster warming than expected due to positive feedback effects; and releases of additional greenhouse gases from permafrost regions and coastal sediments. While these types of changes are currently thought to be low-probability/high-consequence events with widespread and lasting effects, their probability of occurring increases with the magnitude, rate, and duration of global warming.

The "adaptation has the potential to reduce adverse impacts of climate change and enhance beneficial impacts, but will incur costs and will not prevent all damages." Human and natural systems will adapt autonomously to some degree and in some instances, but can and should be supplemented with planned adaptation, especially where options for autonomous adaptation are limited. Adaptation to current climate variability and extremes can serve as a guide for future adaptation and can produce present-day benefits. There are constraints, however, on realizing the full range of potential adaptation options. Also, maladaptations (e.g., development in risk-prone areas) that increase present and future damage potentials can and already do occur.

There is potential to enhance the adaptive capacity in both developed and developing countries, but the least developed, poorest countries are typically least endowed with the attributes that facilitate adaptive capacity. The resulting vulnerability is therefore greatest in these least developed countries (or poorest communities within more developed countries).

To conclude, "policies that lessen pressures on resources, improve management of environmental risks, and increase the welfare of the poorest members of society can simultaneously advance sustainable development and equity, enhance adaptive capacity, and reduce vulnerability to climate and other stresses." Including climate risks in national and international development plans can help address multiple stresses and goals.