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| | | Climate Change |
Maintained by WMO |
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| | Introduction | | | Human activities are increasing the atmospheric concentrations of greenhouse gases (which tend to warm the atmosphere) and, in some regions, aerosols (which tend to cool the atmosphere). These changes in greenhouse gases and aerosols, taken together, are projected to lead to regional and global changes in climate and climate-related parameters such as temperature, precipitation, soil moisture, sea level and ocean acidification.
Based on the range of sensitivities of climate to increases in greenhouse gas concentrations reported by the Intergovernmental Panel on Climate Change (IPCC) and plausible ranges of emissions and aerosol concentrations, climate models project an increase in global mean surface temperature. For the next two decades a warming of about 0.2°C per decade is projected and an associated increase in sea level of about 18-59 cm. The reliability of regional-scale predictions is still low and the degree to which climate variability may change is uncertain. However, potentially serious changes have been identified, including an increase in some regions in the incidence of extreme high-temperature events, floods and droughts, with resultant consequences for fires, pest outbreaks, and ecosystem composition, structure and functioning, including primary productivity.
Policymakers will have to decide to what degree they want to take precautionary measures by mitigating greenhouse gas emissions and enhancing the resilience of vulnerable systems by means of adaptation. Uncertainty does not mean that a nation or the world community cannot position itself better to cope with the broad range of possible climate changes or protect against potentially costly future outcomes. Delaying such measures may leave a nation or the world poorly prepared to deal with adverse changes and may increase the possibility of irreversible or very costly consequences. Options for adapting to change or mitigating change that can be justified for other reasons today (e.g., abatement of air and water pollution) and make society more flexible or resilient to anticipated adverse effects of climate change appear particularly desirable. |  | | Photo title: Concept of Climate Change | | Photo credit: 2007 IPCC Report: Intro Fig 1-1 | | | | Climate Change and the Oceans | | | | The oceans play a vital role in the global climate system, generating oxygen and absorbing carbon dioxide from the atmosphere, while also providing essential goods and services for sustaining life on Earth. Changes to the climate, brought about by increasing levels of greenhouse gases in the atmosphere, will thus lead to changes in the oceans, including sea-level rise and ocean acidification, which will put marine ecosystems and coastal communities at risk.
Recent observations indicate that the impacts of climate change on the oceans will exceed the projections of the Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report of 2007. Many key climate indicators, including sea-level rise, global ocean temperature, Arctic sea ice extent and ocean acidification, are already moving beyond the patterns of natural variability within which contemporary society and economy have developed and thrived. With unabated greenhouse gas emissions, many adverse trends in climate will likely accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts.According to recent studies, the past decade has been the warmest on record and the warmer climate has contributed to rising sea levels and sea-surface temperature. Ice cover in the Arctic Ocean has continued to decrease and 2009 marked the third smallest area of sea-ice extent. Arctic sea ice has become thinner and more prone to rapid melting, with growing proportions of one- and two-year old ice. Ocean acidification has also progressed at rates that far exceed models and projections, with impacts on shellfish and corals in the surface layer of the oceans.
| | | The oceans and coastal zones have been far warmer and colder than is projected in the present scenarios of climate change. Marine life has been in the oceans nearly since when they were formed. During the millennia they endured and responded to CO2 levels well beyond anything projected, and temperature changes that put tropical plants at the poles or had much of our land covered by ice more than a mile thick. The memory of these events is built into the genetic plasticity of the species on this planet. IPCC forecasts are for warming to occur faster than evolution is considered to occur, so impacts will be determined by this plasticity and the resiliency of affected organisms to find suitable habitats. In the oceans, major climate warming and cooling is a fact of life, whether it is over a few years as in an El Niño or over decades as in the Pacific Decadal Oscillation or the North Atlantic Oscillation. Currents, temperatures, salinity, and biology changes rapidly to the new state in months or a couple years. These changes far exceed the changes expected with global warming and occur much faster. The one degree F. rise since 1860 is virtually noise in this rapidly changing system. Sea level has been inexorably rising since the last glaciation lost its grip a mere 10,000 years ago. It is only some few thousand years since trees grew on Georges Bank and oysters flourished on its shores. Their remains still come up in dredges and trawls in now deep water, with the oysters looking like they were shucked yesterday. In the face of all these natural changes, and possible anthropogenic changes, some species flourish while others diminish. (Source: Statement of Dr. John Everett.)
Nevertheless, we must all be prudent in modifying our activities so that we are good stewards of our environment. | | | | |
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| CLIMATE CHANGE II: First US Assessment Shows Broad Impact
by UN Wire, UN Wire 01 June 2000 | |
| | UNWire, 12.6.2000 CLIMATE CHANGE II: First US Assessment Shows Broad Impact The first national assessment of the possible effects of global warming on the United States to be released today predicts a dramatic impact on the country's climate in the coming decades. The report, prepared by a panel of government officials, academics, industry representatives and nongovernmental organizations, predicts US temperatures will rise 5 to 10 degrees Fahrenheit over the next century. The predictions include an increase in droughts and floods; rising sea levels, which will shrink coastal wetlands and increase storm surges; disproportionately hotter cities; and more heat waves (CNN.com ). The report includes regional and national effects, including predictions that Pacific Northwest salmon are likely to be harmed by rising water temperatures; forests could replace deserts in the southwest; and Native Alaskans will have more difficulty hunting ice-dwelling seals, an effect they have already begun to experience. The report also includes some positive impacts of warming, such as increased agricultural yield and fewer ice-hindered shipping lanes in Alaska and the Great Lakes (Andrew Rifkin, New York Times ). Global warming skeptics pointed to discrepancies in the study's two computer models as evidence of inaccuracy. "Look at North Dakota. One [model] turns it into a desert, the other a swamp," said S. Fred Singer of the Science and Environmental Policy Project . "Neither will probably happen" (Curt Suplee, Washington Post ). Environmental groups applauded the draft report as a "balanced assessment" of the potential impacts of warming. "America's alarm bells should go off today," said World Wildlife Fund Climate Change Campaign Director Jennifer Morgan. "The national assessment shows that now more than ever the United States must act to protect its national treasures" (Union of Concerned Scientists release , 9 Jun). (All cites 12 June unless otherwise noted.) (Back to Contents) | |
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