Attributed and expected effects
Global warming may be detected in natural, ecological or social systems as a change having statistical significance.Attribution of these changes e.g., to natural or human activities, is the next step following detection.
Global warming has been detected in a number of systems. Some of these changes, e.g., based on the instrumental temperature record, have been described in the section on temperature changes. Rising sea levels and observed decreases in snow and ice extent are consistent with warming. Most of the increase in global average temperature since the mid-20th century is, with high probability, attributable to human-induced changes in greenhouse gas concentrations.
Even with current policies to reduce emissions, global emissions are still expected to continue to grow over the coming decades. Over the course of the 21st century, increases in emissions at or above their current rate would very likely induce changes in the climate system larger than those observed in the 20th century.
In the IPCC Fourth Assessment Report, across a range of future emission scenarios, model-based estimates of sea level rise for the end of the 21st century (the year 2090-2099, relative to 1980-1999) range from 0.18 to 0.59 m. These estimates, however, were not given a likelihood due to a lack of scientific understanding, nor was an upper bound given for sea level rise. Over the course of centuries to millennia, the melting of ice sheets could result in sea level rise of 4–6 m or more.
Changes in regional climate are expected to include greater warming over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean. Snow cover area and sea ice extent are expected to decrease, with the Arctic expected to be largely ice-free in September by 2037.The frequency of hot extremes, heat waves, and heavy precipitation will very likely increase.
In terrestrial ecosystems, the earlier timing of spring events, and poleward and upward shifts in plant and animal ranges, have been linked with high confidence to recent warming.Future climate change is expected to particularly affect certain ecosystems, including tundra, mangroves, and coral reefs. It is expected that most ecosystems will be affected by higher atmospheric CO2 levels, combined with higher global temperatures. Overall, it is expected that climate change will result in the extinction of many species and reduced diversity of ecosystems.
Vulnerability of human societies to climate change mainly lies in the effects of extreme weather events rather than gradual climate change. Impacts of climate change so far include adverse effects on small islands, adverse effects on indigenous populations in high-latitude areas,] and small but discernable effects on human health. Over the 21st century, climate change is likely to adversely affect hundreds of millions of people through increased coastal flooding, reductions in water supplies, increased malnutrition and increased health impacts.
Future warming of around 3 °C (by 2100, relative to 1990-2000) could result in increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing the risk of malnutrition. A similar regional pattern of net benefits and costs could occur for economic (market-sector) effects. Warming above 3 °C could result in crop yields falling in temperate regions, leading to a reduction in global food production. Most economic studies suggest losses of world gross domestic product (GDP) for this magnitude of warming.
Some areas of the world would start to surpass the wet-bulb temperature limit of human survivability with global warming of about 6.7°C (12°F) while a warming of 11.7°C (21°F) would put half of the world's population in an uninhabitable environment. In practice the survivable limit of global warming in these areas is probably lower and in practice some areas may experience lethal wet bulb tempatures even earlier, because this study conservatively projected the survival limit for persons who are out of the sun, in gale-force winds, doused with water, wearing no clothing, and not working. (http://en.wikipedia.org/wiki/Global_warming)
JL. NASIONAL NO. 9 GAMPONG PADANG, KECAMATAN SEUNAGAN,KABUPATEN NAGAN RAYA, PROVINSI ACEH, INDONESIA 23671
SAMSUIR HUSAINI, SP
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