Global Ethics


NASA:古気象史は2度温度上昇は海面25m上昇を示す by limitlesslife

Secrets from the past point to rapid climate change in the future

At the Earth’s current rate of carbon dioxide increases in the atmosphere, the planet is likely to experience several degrees increase in average temperatures and large-scale changes such as ice sheet loss that could lead to several meters of sea level rise this century, NASA’s James Hansen said in a recent paper. Credit: NASA’s Scientific Visualization Studio.
At the Earth’s current rate of carbon dioxide increases in the atmosphere, the planet is likely to experience several degrees increase in average temperatures and large-scale changes such as ice sheet loss that could lead to several meters of sea level rise this century, NASA’s James Hansen said in a recent paper. Credit: NASA’s Scientific Visualization Studio.
12.15.11
By Patrick Lynch,
NASA’s Earth Science News TeamNew research into the Earth’s paleoclimate history by NASA’s Goddard Institute for Space Studies director James Hansen suggests the potential for rapid climate changes this century, including multiple meters of sea level rise, if global warming is not abated.By looking at how the Earth’s climate responded to past natural changes, Hansen sought insight into a fundamental question raised by ongoing human-caused climate change: “What is the dangerous level of global warming?” Some international leaders have suggested a goal of limiting warming to two degrees Celsius (3.6 degrees Fahrenheit) from pre-industrial times in order to avert catastrophic change. But Hansen said at a press briefing at a meeting of the American Geophysical Union in San Francisco recently that a warming of two degrees Celsius (3.6 degrees Fahrenheit) would lead to drastic changes, such as significant ice sheet loss in Greenland and Antarctica.Based on Hansen’s temperature analysis work at the Goddard Institute for Space Studies, the Earth’s average global surface temperature has already risen 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1880, and is now warming at a rate of more than 0.1 degrees Celsius (0.2 degrees Fahrenheit) every decade. This warming is largely driven by increased greenhouse gases in the atmosphere, particularly carbon dioxide, emitted by the burning of fossil fuels at power plants, by cars and by industry. At the current rate of fossil fuel burning, the concentration of carbon dioxide in the atmosphere will have doubled from pre-industrial times by the middle of this century. A doubling of carbon dioxide would cause an eventual warming of several degrees, Hansen said.

In recent research, Hansen and co-author Makiko Sato, also of Goddard Institute for Space Studies, compared the climate of today, the “Holocene”, with previous similar “interglacial” epochs — periods when polar ice caps existed but the world was not dominated by glaciers. In studying cores drilled from both ice sheets and deep ocean sediments, Hansen found that global mean temperatures during the “Eemian” period, which began about 130,000 years ago and lasted about 15,000 years, were less than 1 degree Celsius (1.8 degrees Fahrenheit) warmer than today. If temperatures were to rise two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial times, global mean temperature would far exceed that of the Eemian, when sea level was four to six meters higher than today, Hansen said.

The average global surface temperature of Earth has risen by 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1880, and is now increasing at a rate of about 0.1 degrees Celsius (0.2 degrees Fahrenheit) per decade. This image shows how 2010 temperatures compare to average temperatures from a baseline period of 1951-1980, as analyzed by scientists at NASA’s Goddard Institute for Space Studies. Credit: NASA GISS.

The average global surface temperature of Earth has risen by 0.8 degrees Celsius (1.4 degrees Fahrenheit) since 1880, and is now increasing at a rate of about 0.1 degrees Celsius (0.2 degrees Fahrenheit) per decade. This image shows how 2010 temperatures compare to average temperatures from a baseline period of 1951-1980, as analyzed by scientists at NASA’s Goddard Institute for Space Studies. Credit: NASA GISS.

“The paleoclimate record reveals a more sensitive climate than thought, even as of a few years ago. Limiting human-caused warming to two degrees [Celsius] is not sufficient,” Hansen said. “It would be a prescription for disaster.”

Hansen focused much of his new work on how the polar regions and in particular the ice sheets of Antarctica and Greenland will react to a warming world.

Two degrees Celsius (3.6 degrees Fahrenheit) of warming would make Earth much warmer than during the Eemian, and would move Earth closer to “Pliocene”-like conditions, when sea level was in the range of 25 meters (82 feet) higher than today, Hansen said. In using Earth’s climate history to learn more about the level of sensitivity that governs our planet’s response to warming today, Hansen said the paleoclimate record suggests that every degree Celsius of global temperature rise will ultimately equate to 20 meters (66 feet) of sea level rise. However, that sea level increase due to ice sheet loss would be expected to occur over centuries, and large uncertainties remain in predicting how that ice loss would unfold.

Hansen notes that ice sheet disintegration will not be a linear process. This non-linear deterioration has already been seen in vulnerable places such as Pine Island Glacier in West Antarctica, where the rate of ice mass loss has continued accelerating over the past decade. Data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite is already consistent with a rate of ice sheet mass loss in Greenland and West Antarctica that doubles every ten years. The GRACE record is too short to confirm this with great certainty; however, the trend in the past few years does not rule it out, Hansen said. This continued rate of ice loss could cause multiple meters of sea level rise by 2100, Hansen said.

Ice and ocean sediment cores from the polar regions indicate that temperatures at the poles during previous epochs — when sea level was tens of meters higher — is not too far removed from the temperatures Earth could reach this century on a “business as usual” trajectory.

“We don’t have a substantial cushion between today’s climate and dangerous warming,” Hansen said. “Earth is poised to experience strong amplifying feedbacks in response to moderate additional global warming.”

Detailed considerations of a new warming target and how to get there are beyond the scope of this research, Hansen said. But this research is consistent with Hansen’s earlier findings that carbon dioxide in the atmosphere would need to be rolled back from about 390 parts per million in the atmosphere today to 350 parts per million in order to stabilize the climate in the long term. While leaders continue to discuss a framework for reducing emissions, global carbon dioxide emissions have remained stable or increased in recent years.

Hansen and others noted that while the paleoclimate evidence paints a clear picture of what Earth’s earlier climate looked like, but that using it to predict precisely how the climate might change on much smaller timescales in response to human-induced rather than natural climate change remains difficult. But, Hansen noted, the Earth system is already showing signs of responding, even in the cases of “slow feedbacks” such as ice sheet changes.

The human-caused release of increased carbon dioxide into the atmosphere also presents climate scientists with something they’ve never seen in the 65 million year record of carbon dioxide levels — a drastic rate of increase that makes it difficult to predict how rapidly the Earth will respond. In periods when carbon dioxide has increased due to natural causes, the rate of increase averaged about 0.0001 parts per million per year — in other words, one hundred parts per million every million years. Fossil fuel burning is now causing carbon dioxide concentrations to increase at two parts per million per year.

“Humans have overwhelmed the natural, slow changes that occur on geologic timescales,” Hansen said.

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NASA:気候変動は大生態系変動をもたらす by limitlesslife

Climate Change May Bring Big Ecosystem Shifts, NASA Says

Predicted percentage of ecological landscape being driven toward changes in plant species as a result of projected human-induced climate change by 2100. (Credit: NASA/JPL-Caltech)

ScienceDaily (Dec. 18, 2011) — By 2100, global climate change will modify plant communities covering almost half of Earth’s land surface and will drive the conversion of nearly 40 percent of land-based ecosystems from one major ecological community type — such as forest, grassland or tundra — toward another, according to a new NASA and university computer modeling study.

Researchers from NASA’s Jet Propulsion Laboratory and the California Institute of Technology in Pasadena, Calif., investigated how Earth’s plant life is likely to react over the next three centuries as Earth’s climate changes in response to rising levels of human-produced greenhouse gases. Study results are published in the journal Climatic Change.

The model projections paint a portrait of increasing ecological change and stress in Earth’s biosphere, with many plant and animal species facing increasing competition for survival, as well as significant species turnover, as some species invade areas occupied by other species. Most of Earth’s land that is not covered by ice or desert is projected to undergo at least a 30 percent change in plant cover — changes that will require humans and animals to adapt and often relocate.

In addition to altering plant communities, the study predicts climate change will disrupt the ecological balance between interdependent and often endangered plant and animal species, reduce biodiversity and adversely affect Earth’s water, energy, carbon and other element cycles.

“For more than 25 years, scientists have warned of the dangers of human-induced climate change,” said Jon Bergengren, a scientist who led the study while a postdoctoral scholar at Caltech. “Our study introduces a new view of climate change, exploring the ecological implications of a few degrees of global warming. While warnings of melting glaciers, rising sea levels and other environmental changes are illustrative and important, ultimately, it’s the ecological consequences that matter most.”

When faced with climate change, plant species often must “migrate” over multiple generations, as they can only survive, compete and reproduce within the range of climates to which they are evolutionarily and physiologically adapted. While Earth’s plants and animals have evolved to migrate in response to seasonal environmental changes and to even larger transitions, such as the end of the last ice age, they often are not equipped to keep up with the rapidity of modern climate changes that are currently taking place. Human activities, such as agriculture and urbanization, are increasingly destroying Earth’s natural habitats, and frequently block plants and animals from successfully migrating.

To study the sensitivity of Earth’s ecological systems to climate change, the scientists used a computer model that predicts the type of plant community that is uniquely adapted to any climate on Earth. This model was used to simulate the future state of Earth’s natural vegetation in harmony with climate projections from 10 different global climate simulations. These simulations are based on the intermediate greenhouse gas scenario in the United Nations’ Intergovernmental Panel on Climate Change Fourth Assessment Report. That scenario assumes greenhouse gas levels will double by 2100 and then level off. The U.N. report’s climate simulations predict a warmer and wetter Earth, with global temperature increases of 3.6 to 7.2 degrees Fahrenheit (2 to 4 degrees Celsius) by 2100, about the same warming that occurred following the Last Glacial Maximum almost 20,000 years ago, except about 100 times faster. Under the scenario, some regions become wetter because of enhanced evaporation, while others become drier due to changes in atmospheric circulation.

The researchers found a shift of biomes, or major ecological community types, toward Earth’s poles — most dramatically in temperate grasslands and boreal forests — and toward higher elevations. Ecologically sensitive “hotspots” — areas projected to undergo the greatest degree of species turnover — that were identified by the study include regions in the Himalayas and the Tibetan Plateau, eastern equatorial Africa, Madagascar, the Mediterranean region, southern South America, and North America’s Great Lakes and Great Plains areas. The largest areas of ecological sensitivity and biome changes predicted for this century are, not surprisingly, found in areas with the most dramatic climate change: in the Northern Hemisphere high latitudes, particularly along the northern and southern boundaries of boreal forests.

“Our study developed a simple, consistent and quantitative way to characterize the impacts of climate change on ecosystems, while assessing and comparing the implications of climate model projections,” said JPL co-author Duane Waliser. “This new tool enables scientists to explore and understand interrelationships between Earth’s ecosystems and climate and to identify regions projected to have the greatest degree of ecological sensitivity.”

“In this study, we have developed and applied two new ecological sensitivity metrics — analogs of climate sensitivity — to investigate the potential degree of plant community changes over the next three centuries,” said Bergengren. “The surprising degree of ecological sensitivity of Earth’s ecosystems predicted by our research highlights the global imperative to accelerate progress toward preserving biodiversity by stabilizing Earth’s climate.”

JPL is managed for NASA by the California Institute of Technology in Pasadena.