The American Meteorological Society has given its direst warning yet of the dangers of climate change.
The Society warns of widespread melting of snow and ice, fast rising sea levels of nearly one metre and rising temperatures bringing abnormal variations of weather in the decades to come.
In its latest Report the Society warns: “Warming of the climate system now is unequivocal, according to many different kinds of evidence. Observations show increases in globally averaged air and ocean temperatures, as well as widespread melting of snow and ice and rising globally averaged sea level.”
Experts says the earth’s surface temperature data for Earth as a whole, including readings over both land and ocean, show an increase of about 0.8°C (1.4°F) over the period 1901─2010 and about 0.5°C (0.9°F) over the period 1979–2010.
All of the 10 warmest years in the global temperature records up to 2011 have occurred since 1997, with 2005 and 2010 being the warmest two years in more than a century of global records.
The warming trend is greatest in northern high latitudes and over land. In the U.S., most of the observed warming has occurred in the West and in Alaska; for the nation as a whole, there have been twice as many record daily high temperatures as record daily low temperatures in the first decade of the 21st century.
The effects of this warming are especially evident in the planet’s polar regions. Arctic sea ice extent and volume have been decreasing for the past several decades. Both the Greenland and Antarctic ice sheets have lost significant amounts of ice. Most of the world’s glaciers are in retreat.
Globally averaged sea level has risen by about 17 cm (7 inches) in the 20th century, with the rise accelerating since the early 1990s. Close to half of the sea level rise observed since the 1970s has been caused by water expansion due to increases in ocean temperatures. Sea level is also rising due to melting from continental glaciers and from ice sheets on both Greenland and Antarctica.
Even small rises in sea level in coastal zones are expected to lead to potentially severe impacts, especially in small island nations and in other regions that experience storm surges associated with vigorous weather systems.
There are indications that large regions of the permafrost in parts of Alaska and other northern polar areas are already thawing, with the potential to release massive amounts of carbon into the atmosphere beyond those being directly added by human activity. The portion of the increased CO2 release that is absorbed by the world ocean is making the ocean more acidic, with negative implications for shell- and skeleton-forming organisms and more generally for ocean ecosystems
The Report says climate is always changing but adds: “However, many of the observed changes noted above are beyond what can be explained by the natural variability of the climate.
“It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide.
“The most important of these over the long term is CO2, whose concentration in the atmosphere is rising principally as a result of fossil-fuel combustion and deforestation.
“While large amounts of CO2 enter and leave the atmosphere through natural processes, these human activities are increasing the total amount in the air and the oceans.
“Approximately half of the CO2 put into the atmosphere through human activity in the past 250 years has been taken up by the ocean and terrestrial biosphere, with the other half remaining in the atmosphere.
“Since long-term measurements began in the 1950s, the atmospheric CO2 concentration has been increasing at a rate much faster than at any time in the last 800,000 years. Having been introduced into the atmosphere it will take a thousand years for the majority of the added atmospheric CO2 to be removed by natural processes, and some will remain for thousands of subsequent years.”
In the 21st century, global sea level also will continue to rise although the rise will not be uniform at all locations.
With its large mass and high capacity for heat storage, the ocean will continue to slowly warm and thus thermally expand for several centuries.
Model simulations project about 27 cm (10 inches) to 71 cm (28 inches) of global sea level rise due to thermal expansion and melting of ice in the 21st century. Moreover, paleoclimatic observations and ice-sheet modeling indicate that melting of the Greenland and the West Antarctic ice sheets will eventually cause global sea level to rise several additional meters by 2500 if warming continues at its present rate beyond the 21st century.
The increased water content in the atmosphere will cause violent and unpredictable storms punctuated by severe drought across Africa, Europe and North America.
The Report warns that future warming of the climate is inevitable for many years due to the greenhouse gases already added to the atmosphere and the heat that has been taken up by the oceans. Amelioration might be possible through devising and implementing environmentally responsible geoengineering approaches, such as capture and storage measures to remove CO2 from the atmosphere.
It concludes: “Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Science-based decisions are seldom made in a context of absolute certainty. National and international policy discussions should include consideration of the best ways to both adapt to and mitigate climate change. Mitigation will reduce the amount of future climate change and the risk of impacts that are potentially large and dangerous. At the same time, some continued climate change is inevitable, and policy responses should include adaptation to climate change. Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life.”