Naciones Unidas, 10 mar (EFE).- El secretario general de la ONU, Ban Ki-moon, anunció hoy una revisión independiente de la labor del Grupo Intergubernamental contra el Cambio Climático (IPCC) tras los errores detectados por sus críticos en sus informes.
"Tenemos que saber con claridad qué es lo que sabemos y también las incertidumbres. Tenemos que comunicarnos con transparencia y debatir con inteligencia", dijo Ban, quien también aseguró que "no hay pruebas que refuten la principal conclusión del informe" del IPCC de que el hombre es responsable del calentamiento global.
El secretario general realizó el anuncio en una comparecencia ante la prensa, acompañado por el presidente del IPCC, el científico indio Rajendra Pachauri, quien se ha convertido en blanco de las críticas de quienes consideran que se ha exagerado la existencia de un cambio climático.
Naciones Unidas encargó la revisión de los procedimientos que emplea el IPCC a la organización científica internacional InterAcademy Council, señaló Ban, quien consideró un "imperativo" contar con la mejor información para elaborar una respuesta adecuada al calentamiento global.
"Quiero que quede claro: La amenaza del cambio climático es real. Nada de lo que se ha revelado o se ha dicho en los medios recientemente altera el consenso científico fundamental sobre cambio climático", agregó Ban.
Por su parte, Pachauri expresó su respaldo a la iniciativa del secretario general de la ONU, que dijo que "reforzará los procedimientos que empleamos para elaborar nuestros informes".
"Es muy importante que la información científica en nuestros informes, que divulgamos ampliamente, sea aceptada por comunidades de todo el mundo, gobiernos, el sector privado y la sociedad civil", agregó.
El científico indio también aseguró que el IPCC, que prepara un quinto informe sobre el cambio climático, es "receptivo y sensible" a las críticas que ha recibido en los últimos meses.
El IPCC tuvo que admitir recientemente errores en la conclusión contenida en su informe de 2007 de que los glaciares del Himalaya pueden desaparecer para 2035.
El organismo también recibió fuertes críticas a raíz de la divulgación el año pasado de correos electrónicos de la Unidad de Investigación Climatológica (CRU) de la Universidad británica de East Anglia, uno de los centros de más prestigio internacional en esta materia, que sugerían un intento de ocultar ciertos documentos a los responsables de la ONU.
En su comparecencia de hoy, en la que no aceptó preguntas de la prensa, el secretario general de la ONU insistió en que mantiene su confianza en la labor del IPCC.
"Lamentablemente se produjeron algunos pequeños errores, en el cuarto informe, pero hay que recordar que estamos hablando de una síntesis de 3.000 páginas de datos científicos complejos", advirtió Ban, que ha hecho del cambio climático uno de los estandartes de su gestión al frente de la ONU.
Asimismo, desestimó que la decisión de revisar los procedimientos de trabajo del IPCC pueda afectar a las negociaciones para alcanzar un tratado vinculante sobre el cambio climático en la conferencia internacional que se celebrará a finales de año en México. EFE
Aunque en buena parte del mundo, incluyendo España, se recuerde el pasado invierno como bastante frío, lo cierto es que mientras nevaba en lugares como Florida o Sevilla, los termómetros no sufrían los rigores invernales en zonas usualmente gélidas como Groenlandia o Alaska. Si a esto le sumamos que en otras vastas áreas del planeta, como el sur de Asia, todo el norte de África y buena parte de los trópicos han vivido unos meses anormalmente calurosos, el resultado es que en lo que llevamos de año la anomalía térmica es positiva y la temperatura media global —tanto en tierra como en los océanos— en estos cuatro primeros meses fue la más cálida desde 1880, cuando comenzaron a realizarse estos registros.
Son las cifras aportadas por el Centro Nacional de Datos Climáticos de la Agencia Atmosférica y Oceánica de Estados Unidos (NOAA) que analiza mensualmente la temperatura global en el planeta. En concreto, la temperatura media global para tierra y mar fue de 13,3 grados centígrados entre enero y abril, lo que supone un aumento de 0,69 grados sobre la media del siglo XX.
En España abril fue muy cálido
Los datos de la Agencia Atmosférica y Oceánica de Estados Unidos (NOAA) para abril revelan que en buena parte de Europa las temperaturas fueron superiores a la media. Es el caso de España. Según los datos de la Agencia Estatal de Meteorología (Aemet), el mes de abril ha resultado muy cálido, con una temperatura media en torno a 2 grados centígrados por encima de su valor medio, que le sitúa como el tercer mes de abril más caluroso de los últimos 40 años.
Desde finales de mayo una ola de calor ha tostado Pakistan y la India.
Las temperaturas en el norte de la India se han cobrado cientos de victimas en lo que se cree el verano más calido desde que se tienen registros a finales de 1800. En la última semana de mayo la temperatura alcanzó los 48,5ºC.
El 27 de mayo pasado en Lahore , el polvo levantó ráfagas de viento que siguió soplando durante todo el día bajando algo la temperatura máxima de 47 º C el miércoles 26 de mayo a 44,5 º C el día 27.
Multan registró 50 grados C , rompiendo un record de 54 años de la temperatura máxima más alta en el mes de mayo. Se fue de 47 grados C el miércoles 26 . La temperatura más alta registrada hasta la fecha en esta ciudad fue de 49 grados C que se registró el 29 de mayo de 1956.
Mohenjodaro seguía siendo el lugar más caluroso a pesar de que su temperatura máxima se redujo de 53,5 grados C del miércoles a 51,6 grados C. La temperatura de 53,5ºC el la más alta nunca registrada en Asia.
La temperatura máxima de Jacobabad fue de 51 grados C , 50,5 Sukkur , Rohri Larkana y 50 cada una, Dadu y Nawabshah 49,5 cada uno, Bahawalnagar , Bahawalpur y Bhakkar 49 cada uno, Dera Ghazi Khan 50,5 , Faisalabad 47, Jhang 47,2 , 46,5 Jhelum , Khanpur 49,2 , Rahim Yar Khan 50 y 49,5 grados C. Shorkot A 20 de junio la situación se mantenía aunque con temperaturas ligeramente más bajas. Larkana y Mohenjodaro fueron los lugares más calientes del país, con 51 grados C. En Punjab , Rahim Yar Khan registraron 50,2 grados C. La temperatura máxima en Bahawalnagar y Bhakkar fue de 49 grados C. Bahawalpur registraron 47,3 grados C , Dera Ghazi Khan (48) , Faisalabad (46), Jhang (46,2) , Jhelum (46), Khanpur (46,3) , Mandi Bahauddin (46), Mianwali y Multan (47,5) , Murree (32), Noorpur Thal (48), Okara (47), Sahiwal (46), Sargodha (46,5) , Sialkot (45,7) y Toba Tek Singh (46,2) y no se esparaba una bajada significativa hasta final de mes con la llegada de los monzones.
Abrupt climate changes, such as the collapse of the West Antarctic Ice Sheet, the rapid loss of the Greenland Ice Sheet or large-scale changes of ocean circulation systems, are not considered likely to occur in the 21st century, based on currently available model results. However, the occurrence of such changes becomes increasingly more likely as the perturbation of the climate system progresses.
Physical, chemical and biological analyses from Greenland ice cores, marine sediments from the North Atlantic and elsewhere and many other archives of past climate have demonstrated that local temperatures, wind regimes and water cycles can change rapidly within just a few years. The comparison of results from records in different locations of the world shows that in the past major changes of hemispheric to global extent occurred. This has led to the notion of an unstable past climate that underwent phases of abrupt change. Therefore, an important concern is that the continued growth of greenhouse gas concentrations in the atmosphere may constitute a perturbation sufficiently strong to trigger abrupt changes in the climate system. Such interference with the climate system could be considered dangerous, because it would have major global consequences.
Before discussing a few examples of such changes, it is useful to define the terms ‘abrupt’ and ‘major’. ‘Abrupt’ conveys the meaning that the changes occur much faster than the perturbation inducing the change; in other words, the response is nonlinear. A ‘major’ climate change is one that involves changes that exceed the range of current natural variability and have a spatial extent ranging from several thousand kilometres to global. At local to regional scales, abrupt changes are a common characteristic of natural climate variability. Here, isolated, short-lived events that are more appropriately referred to as ‘extreme events’ are not considered, but rather large-scale changes that evolve rapidly and persist for several years to decades. For instance, the mid-1970s shift in sea surface temperatures in the Eastern Pacific, or the salinity reduction in the upper 1,000 m of the Labrador Sea since the mid-1980s, are examples of abrupt events with local to regional consequences, as opposed to the larger-scale, longer-term events that are the focus here.
One example is the potential collapse, or shut-down of the Gulf Stream, which has received broad public attention. The Gulf Stream is a primarily horizontal current in the north-western Atlantic Ocean driven by winds. Although a stable feature of the general circulation of the ocean, its northern extension, which feeds deep-water formation in the Greenland-Norwegian-IcelandSeas and thereby delivers substantial amounts of heat to these seas and nearby land areas, is influenced strongly by changes in the density of the surface waters in these areas. This current constitutes the northern end of a basin-scale meridional overturning circulation (MOC) that is established along the western boundary of the Atlantic basin. A consistent result from climate model simulations is that if the density of the surface waters in the North Atlantic decreases due to warming or a reduction in salinity, the strength of the MOC is decreased, and with it, the delivery of heat into these areas. Strong sustained reductions in salinity could induce even more substantial reduction, or complete shut-down of the MOC in all climate model projections. Such changes have indeed happened in the distant past.
The issue now is whether the increasing human influence on the atmosphere constitutes a strong enough perturbation to the MOC that such a change might be induced. The increase in greenhouse gases in the atmosphere leads to warming and an intensification of the hydrological cycle, with the latter making the surface waters in the North Atlantic less salty as increased rain leads to more freshwater runoff to the ocean from the region’s rivers. Warming also causes land ice to melt, adding more freshwater and further reducing the salinity of ocean surface waters. Both effects would reduce the density of the surface waters (which must be dense and heavy enough to sink in order to drive the MOC), leading to a reduction in the MOC in the 21st century. This reduction is predicted to proceed in lockstep with the warming: none of the current models simulates an abrupt (nonlinear) reduction or a complete shut-down in this century. There is still a large spread among the models’ simulated reduction in the MOC, ranging from virtually no response to a reduction of over 50% by the end of the 21st century. This cross-model variation is due to differences in the strengths of atmosphere and ocean feedbacks simulated in these models.
Uncertainty also exists about the long-term fate of the MOC. Many models show a recovery of the MOC once climate is stabilised. But some models have thresholds for the MOC, and they are passed when the forcing is strong enough and lasts long enough. Such simulations then show a gradual reduction of the MOC that continues even after climate is stabilised. A quantification of the likelihood of this occurring is not possible at this stage. Nevertheless, even if this were to occur, Europe would still experience warming, since the radiative forcing caused by increasing greenhouse gases would overwhelm the cooling associated with the MOC reduction. Catastrophic scenarios suggesting the beginning of an ice age triggered by a shutdown of the MOC are thus mere speculations, and no climate model has produced such an outcome. In fact, the processes leading to an ice age are sufficiently well understood and so completely different from those discussed here, that we can confidently exclude this scenario.
Irrespective of the long-term evolution of the MOC, model simulations agree that the warming and resulting decline in salinity will significantly reduce deep and intermediate water formation in the Labrador Sea during the next few decades. This will alter the characteristics of the intermediate water masses in the North Atlantic and eventually affect the deep ocean. The long-term effects of such a change are unknown.
Other widely discussed examples of abrupt climate changes are the rapid disintegration of the Greenland Ice Sheet, or the sudden collapse of the West Antarctic Ice Sheet. Model simulations and observations indicate that warming in the high latitudes of the Northern Hemisphere is accelerating the melting of the Greenland Ice Sheet, and that increased snowfall due to the intensified hydrological cycle is unable to compensate for this melting. As a consequence, the Greenland Ice Sheet may shrink substantially in the coming centuries. Moreover, results suggest that there is a critical temperature threshold beyond which the Greenland Ice Sheet would be committed to disappearing completely, and that threshold could be crossed in this century. However, the total melting of the Greenland Ice Sheet, which would raise global sea level by about seven metres, is a slow process that would take many hundreds of years to complete.
Recent satellite and in situ observations of ice streams behind disintegrating ice shelves highlight some rapid reactions of ice sheet systems. This raises new concern about the overall stability of the West Antarctic Ice Sheet, the collapse of which would trigger another five to six metres of sea level rise. While these streams appear buttressed by the shelves in front of them, it is currently unknown whether a reduction or failure of this buttressing of relatively limited areas of the ice sheet could actually trigger a widespread discharge of many ice streams and hence a destabilisation of the entire West Antarctic Ice Sheet. Ice sheet models are only beginning to capture such small-scale dynamical processes that involve complicated interactions with the glacier bed and the ocean at the perimeter of the ice sheet. Therefore, no quantitative information is available from the current generation of ice sheet models as to the likelihood or timing of such an event.
La NASA ha podido registrar el desprendimiento de una sección del glaciar Jakobshavn Isbrae de Groenlandia. Un bloque inmenso del tamaño de 7 kilómetros cuadrados, equivalente a una octava parte de la isla de Manhattan en Nueva York, empezó a separarse el 6 y 7 de julio, como muestran las imágenes captadas por los monitores de la NASA.
Se trata de un suceso inusual porque se produce justo después de un caluroso invierno en el que no se formó nada de hielo en la bahía circundante
"Aunque se han producido desprendimientos de hielo de esta magnitud del Jakonbshavn y de otros glaciares en el pasado, este suceso es inusual porque se produce justo después de un caluroso invierno en el que no se formó nada de hielo en la bahía circundante", dijo Thomas Wagner, del 'cryospheric program scientist' de la NASA.
"Mientras se determina la relación exacta entre estos acontecimientos, cobra peso la teoría de que el calentamiento de los océanos es responsable del deshielo observado en Groenlandia y la Antártida"
Más del 10 % de todos los icebergs que se desprenden en Groenlandia proceden del glaciar Jakobshavn
Los investigadores cuentan con las imágenes de varios satélites, incluido el Landsat, Terra, y Aqua, para obtener una amplia visión de los cambios experimentados en las capas de hielo de ambos polos. Los días previos al desprendimiento el equipo recibió imágenes del satétite 'WorldView 2' de 'DigitalGlobe', que mostraban la formación de grandes fracturas y grietas.
El glaciar Jakobshavn Isbrae está situado en la costa oeste de Groenlandia y ha disminuido su tamaño más de 45 kilómetros a lo largo de los últimos 160 años, 10 kilómetros en la última década. A medida que el glaciar menguaba, se bifurcaba en dos partes, la norte y la sur. El desprendimiento se ha producido esta semana en la rama norte.
Los científicos estiman que más del 10 % de todos los icebergs que se desprenden en Groenlandia proceden del glaciar Jakobshavn. Es considerado el mayor contribuidor en el aumento del nivel del mar en el hemisferio norte.
For most of the 20th century, Chesapeake Beach, Maryland, was known for its boardwalk, amusement park and wide, sandy beaches, popular with daytrippers from Washington, D.C. “The bathing beach has a frontage of three miles,” boasted a tourist brochure from about 1900, “and is equal, if not superior, to any beach on the AtlanticCoast.”
Today, on a cloudless spring afternoon, the resort town’s sweeping view of Chesapeake Bay is no less stunning. But there’s no longer any beach in ChesapeakeBeach. Where there once was sand, water now laps against a seven-foot-high wall of boulders protecting a strip of pricey homes marked with “No Trespassing” signs.
Surveying the armored shoreline, Jim Titus explains how the natural sinking of the shoreline and slow but steady sea-level rise, mostly due to climate change, have driven the bay’s water more than a foot higher over the past century. Reinforcing the eroding shore with a sea wall held the water back, but it also choked off the natural supply of sand that had replenished the beach. What sand remained gradually sank beneath the rising water.
Titus, the Environmental Protection Agency’s resident expert on sea-level rise, first happened upon Maryland’s disappearing beaches 15 years ago while looking for a place to windsurf. “Having the name beach,” he discovered, “is not a very good predictor of having a beach.” Since then, he’s kept an eye out for other beach towns that have lost their namesakes—Maryland’s Masons Beach and Tolchester Beach, North Carolina’s Pamlico Beach, and many more. (See a map of Maryland’s phantom beach towns here.) A 54-year old with a thick shock of hair and sturdy build, Titus could pass for a vacationer in his Panama hat, khakis and polo shirt. But as he picks his way over the rocky shore, he’s anything but relaxed.
For nearly 30 years, Titus has been sounding the alarm about our rising oceans. Global warming is melting polar ice, adding to the volume of the oceans, as well as warming up seawater, causing it to expand. Most climatologists expect oceans around the world to rise between 1.5 and 5 feet this century. Some of the hardest-hit areas could be in our own backyard: Erosion and a shift in ocean currents could cause water to rise 4 feet or more along much of the East Coast. Titus, who contributed to the Intergovernmental Panel on Climate Change’s Nobel Prize-winning 2007 report, has done more than anyone to determine how those rising seas will affect us and what can be done about them.
Like his occasional collaborator, NASA climatologist James Hansen, Titus has decided to speak out. He’s crisscrossed the country to meet with state and local officials in coastal areas, urging them to start planning now for the slow-motion flood. Yet his warnings have mostly fallen on deaf ears. “We were often told by midlevel officials that their bosses did not want to plan for anything past the next election,” he says.
Neither, it seems, does the federal government. Over the past decade, Titus and a team of contractors combined reams of data to construct a remarkably detailed model of how sea-level rise will impact the eastern seaboard. It was the largest such study ever undertaken, and its findings were alarming: Over the next 90 years, 1,000 square miles of inhabited land on the east coast could be flooded, and most of the wetlands between Massachusetts and Florida could be lost. The favorably peer-reviewed study was scheduled for publication in early 2008 as part of a Bush Administration report on sea-level rise, but it never saw the light of day — an omission criticized by the EPA’s own scientific advisory committee. Titus has urged the more science-friendly Obama administration to publish his work, but so far, it hasn’t — and won’t say why.
So Titus recently launched a personal website, risingsea.net, to publish his work. “I decided to do my best to prevent the taxpayer investment from being wasted,” he says. The site includes “When the North Pole Melts,” a prescient holiday ditty recorded by his musical alter ego, Captain Sea Level, in the late ’80s.
Titus gazes at ChesapeakeBeach’s jagged shoreline, where two children scramble over the barrier of large gray boulders known as a revetment. “The children of 21st-century ChesapeakeBeach, what do they do?” he asks. “They play on revetments.” A generation ago, these kids might have been skipping through the waves. A generation from now, many of the rocks they’re playing on will almost certainly be underwater.
Living near the ocean has always come with the risk of getting wet. Yet coastal dwellers whose homes got swamped by the occasional storm surge could rely on the water to eventually recede. That certainty is gone. Titus has calculated that a 3-foot rise in sea level will push back East Coast shorelines an average of 300 to 600 feet in the next 90 years, threatening to submerge densely developed areas inhabited by some 3 million people, including large parts of New York City, Philadelphia, and Washington, D.C.As Margaret Davidson, director of the National Oceanic and Atmospheric Administration’s Coastal Services Center in Charleston, South Carolina, puts it, “Today’s flood is tomorrow’s high tide.”
The rising waters can be kept at bay by constructing dikes and bulkheads, pumping sand to fill out receding beaches, and elevating existing buildings and roads on embankments or pylons. But such efforts may prove prohibitively expensive: Titus says that in the lower 48 states alone, they could cost as much as $1 trillion over the next century. He estimates that in the process, 60 to 90 percent of the east coast’s wetlands could be destroyed as bulkheads and other defensive measures restrict the movement of estuaries and marshes, drowning them when the ocean rises.
So are developers getting ready for the water? The National Association of Home Builders, the housing industry’s largest trade group, has no policy on adapting coastal projects to account for rising sea levels. “While sea-level rise may be a real issue in some areas,” Susan Asmus, NAHB’s senior vice president of regulatory and environmental affairs, told me in an e-mail, “it is but one of many considerations that are likely already taken into account during the planning process.” Mother Jones contacted the nation’s 10 largest homebuilders, including D.R. Horton, Pulte Homes, and Lennar. None would say how they are responding to sea-level rise.
Nor is there any evidence that the issue has much traction with homeowners — and why should it? Property insurance is readily available in most coastal areas, if not through private insurers, then through state governments and FEMA’s National Flood Insurance Program. Though the NFIP requires policyholders to live above the 100-year high-water mark, it doesn’t account for how that line may creep inland in the future. Besides, most people would plan to resell their beach houses long before they expect them to be swallowed by encroaching waves.
What about government? Most coastal states have done little or nothing to regulate shoreline development, often from fear of litigation. In 1988, South Carolina’s Beachfront Management Act required new beach homes to be set back far enough from the water to be protected from at least 40 years of erosion. A property owner named David Lucas sued, and the U.S. Supreme Court eventually ruled that the construction ban had deprived him of any “economically viable use” of his coastal properties, a “taking” that required the state to compensate him. “After Lucas, fewer people spoke seriously about stopping development,” Titus says.
A few state and local governments have taken more constructive action. Several states limit development near tidal waters (Maine and Rhode Island have done this specifically in response to sea-level rise). Chatham, Massachusetts, cites sea-level rise as one reason why it prohibits new homes, even elevated ones, below 100-year flood lines. (State courts have upheld those limits in Chatham and Maine because they still allow property to be used for recreation, farming, and other profitable activities.) In California, where erosion and winter storms routinely knock multimillion-dollar homes off seaside cliffs, the state’s Coastal Commission has long required anyone who builds on coastal bluffs to submit a geotechnical report proving that their home won’t fall into the ocean. Three years ago, it began requiring the reports to account for sea-level rise. And in a groundbreaking 2008 executive order, Governor Arnold Schwarzenegger directed state agencies to plan for sea-level rise in their construction projects.
A handful of developers have also started to seriously grapple with sea-level rise. A residential high-rise project on Treasure Island, a former naval base in San FranciscoBay, is being built far from the shoreline and is reserving funds for a protective berm if the water rises even higher than the 3 feet that’s anticipated. And in the wake of Hurricane Katrina, the insurance industry drew up standards to fortify houses for stronger hurricanes and higher waves. So far, though, only 200 houses nationwide have been built to comply with the standards.
Most coastal dwellers are focused on riding out the next surge, not the next century. You can’t really blame them — nobody really wants to hear that their days on the beach are numbered.
Case in point: Beyoncé’s dad. Matthew Knowles has been locked in a bitter struggle to save his beach house in Galveston, Texas, which now sits on top of the high-tide line thanks to Hurricane Ike. In most states, Knowles would be allowed to shore up his home, but not in Texas, which is known for one of the most progressive laws in the country on beach access. The state’s Open Beaches Act provides that beach is a public resource that must be protected from “erosion or reduction caused by development.”
Last year, after Knowles started reinforcing his property with tons of cement, the Texas General Land Office informed him that paving over the beach is illegal. Even so, he continued and then surrounded his home with sod, planters, and sandbags. In March, the agency notified Knowles that it was preparing to fine him up to $2,000 a day for violating the Texas Open Beaches Act by interfering with “the right of the public to use the beach.” Knowles did not respond to a request for comment.
Historically, the 51-year-old law has been used to prevent property owners from walling off the beach in front of their homes. But officials say the law clearly applies even when the beach comes to the houses, rather than vice versa. “Even if you make $80 million a year, we don’t care,” says Jim Suydam, a spokesman for the Texas General Land Office. “The beach is the public’s.” Incorporated into the state constitution last year and vigorously supported by the state’s conservative, gun-packing land commissioner, the Open Beaches Act is remarkably popular, in part because it can guarantee beach access for ATVs.
Titus views the Texas Open Beaches Act as one of the more promising tools for preparing for higher water. It has unintended environmental benefits, ensuring that beaches can migrate inland instead of being walled off and at the same time, it sidesteps any debate over climate change. “Developers who deny that the sea will rise would view the policy as costing them nothing,” because it wouldn’t prevent them from building near the shore, he notes. Only the diehard beach dwellers would stand to get soaked.
Until the 1990s, the dominant view of climate change was that Earth’s climate system has changed gradually in response to both natural and human-induced processes. Evidence pieced together over the last few decades, however, shows that climate has changed much more rapidly—sometimes abruptly— in the past and therefore could do so again in the future.
Abrupt climate change generally refers to a large shift in climate that persists for years or longer—such as marked changes in average temperature, or altered patterns of storms, floods, or droughts—over a widespread area such as an entire country or continent, that takes place so rapidly and unexpectedly that human or natural systems have difficulty adapting to it. In the context of past abrupt climate change, “rapidly” typically means on the order of a decade.
Severe droughts and other past abrupt climate changes have had demonstrable, adverse effects on human societies. While it is important not to be fatalistic about the threats posed by abrupt climate change, denying the likelihood or downplaying the relevance of past abrupt events could be costly. Increased knowledge is the best way to improve the effectiveness of response; research into the causes, patterns, and likelihood of abrupt climate change can help reduce vulnerabilites and increase our ability to adapt.
Evidence of Abrupt Climate Change
Researchers first became intrigued by abrupt climate change when they discovered striking evidence of large, abrupt, and widespread changes preserved in paleoclimatic archives—the history of Earth's climate recorded in tree rings, ice cores, sediments, and other sources. For example, tree rings show the frequency of droughts, sediments reveal the number and type of organisms present, and gas bubbles trapped in ice cores indicate past atmospheric conditions. With such techniques, researchers have discovered repeated instances of large and abrupt climate changes over the last 100,000 years during the slide into and climb out of the most recent ice age—local warmings as great as 28°F (16°C) occurred repeatedly, sometimes in the mere span of a decade.
Some of the best known and most well studied widespread abrupt climate changes started and ended the Younger Dryas cold interval, a near global event that began abruptly about 12,800 years ago and ended even more suddenly about 11,600 years ago (see Figure 1).
Climate records show that much of the northern hemisphere was affected by extraordinary cold, dry, windy conditions; dust and other wind-blown materials were more abundant in Greenland by a factor of 3 to 7, and methane concentrations were lower indicating loss of wetland areas, among other evidence. The 110,000-yearlong ice-core records from central Greenland, and m any other climate records, indicate that the Younger Dryas was one in a long string of abrupt climate changes.
More recently, less dramatic though still rapid climate changes have continued to occur. For example, a multidecadal drought is implicated in the collapse of the classic Mayan civilization in the ninth century.
Paleoclimatic records from the last 10,000 years include apparent abrupt shifts in hurricane frequency, flood regimes, and droughts. Examples of abrupt change in the past century alone include the rapid warming of the North Atlantic from 1920 to 1930 and the Dust Bowl drought of the 1930s.
Triggers of Abrupt Climate Change
Abrupt climate change can occur when the Earth system gets pushed across a threshold, whether by some sudden event like a massive volcanic eruption or by the accumulation of more gradual forces, or “forcings” on the system.
Much as the slowly increasing pressure of a finger eventually flips a switch and abruptly turns on a light, or as a passenger’s leaning more and more over the side of a canoe will at some point cause the craft to suddenly capsize, the slow effects of drifting continents or wobbling orbits or changing atmospheric composition may “switch” the climate to a new state. The more rapid the forcing, the more likely it is that it will “flip a switch,” causing an abrupt change on the time scale of human economies or global ecosystems. Such forcings may occur through perturbations in key components of the Earth system such as:
Oceans. Because water has enormous heat capacity, oceans typically store 10-100 times more heat than equivalent land surfaces. Thus the oceans exert a profound influence on climate through their ability to transport heat from one location to another. Changes in ocean circulation, and especially the thermohaline circulation in the North Atlantic (see Figure 2) have been implicated in abrupt climate change of the past such as the Younger Dryas. Floods of glacial meltwaters that would have freshened the North Atlantic and reduced the ability of its waters to sink, immediately preceeded the coolings of the Younger Dryas and another short cold event 8,200 years ago, suggesting causation.
Cryosphere. The portion of the Earth covered in ice and snow, the cryosphere, greatly affects temperature. When sea ice forms, it increases the planetary reflective capacity, thereby enhancing cooling. Sea ice also insulates the atmosphere from the relatively warm ocean, allowing winter air temperatures to steeply decline and reduce the supply of moisture to the atmosphere.
Glaciers and snow cover on land can also provide abrupt-change mechanisms. The water frozen in a glacier can melt if warmed sufficiently, leading to possibly rapid discharge, with consequent effects on sea level and atmospheric flow patterns. Meanwhile, snow-covered lands of all types maintain cold conditions because of their high reflectivity and because surface temperatures cannot rise above freezing until the snow melts.
Atmosphere. The atmosphere is involved in virtually every physical process of potential importance to abrupt climate ch ange, providing a means of rapidly propagating the influence of any climate forcing from one part of the globe to another. Atmospheric temperature, composition, humidity, cloudiness, and wind determine the Earth’s energy fluxes. Wind fields help dictate the ocean's surface circulation and upwelling patterns. Atmospheric-moisture transport—most prominently, through precipitation— helps govern the freshwater balance, overall water circulation, and the dynamics of glaciers.
Land surface. The reflective capacity of the land can change greatly, with fresh snow or ice sheets reflecting more than 90% of the sunlight striking them while dense forests absorb more than 90%. Changes in surface characteristics can also affect solar heating,
cloud formation, rainfall, and surface-water flow to the oceans, thus feeding back strongly on climate.
External factors. Phenomena external to the climate system can also be agents of abrupt climate change.
For example, the orbital parameters of the Earth vary over time, affecting the planet's distribution of solar energy. Fluctuations in solar output—prompted by sunspot activity or the effects of solar wind—may cause major climate fluctuations. The drying of the Sahara in the Holocene is linked to variations in the Earth's orbit around the sun.
Global Warming as a Possible Trigger
Greenhouse gases such as carbon dioxide are accumulating in the Earth's atmosphere and causing surface air temperatures and subsurface ocean temperatures to rise. These gradual changes, along with other human alterations of the climate system (e.g., land-use changes), are producing conditions in the Earth’s climate that are outside the range of recent historical experience. Although it is not known whether these or future changes will trigger more abrupt climate changes, past abrupt climate changes have been especially common when the climate system itself was being altered.
A question of great societal relevance is whether the North Atlantic circulation, including the Gulf Stream, will remain stable under the global warming that is expected to continue for the next few centuries. A shutdown of the circulation would not induce a new ice age, but would cause major changes both in the ocean (major circulation regimes, upwelling and sinking regions, distribution of seasonal sea ice, ecological systems, and sea level) and the intensity, frequency, and paths of storms).
Other potential impacts of a global-warming induced abrupt climate change could be associated with increased frequency of extreme events related to land-surface hydrology. Great variability in precipitation patterns, ranging from heavy rainstorms and flooding to persistent drought, might become more common. In particular, some models suggest that greenhouse warming will cause El Niño manifestations to become stronger and more frequent. It is important to note that not all models agree on the potential impacts of global warming on abrupt climate change.
Improving our Understanding
Scientists don’t know enough about the details of abrupt climate change to accurately predict it. With better information, society could take more confident action to reduce the potential impact of abrupt changes on agriculture, water resources, and the built environment, among other impacts. A better understanding through research of such things as sea-ice and glacier stability, land-surface processes, and atmospheric and oceanic circulation patterns is needed. Moreover, to effectively use any additional knowledge of these and other physical processes behind abrupt climate change, more sophisticated ways of assessing their interactions must be developed, including:
Better models. At present, the models used to assess climate and its impacts cannot simulate the size, speed, and extent of past abrupt changes, let alone predict future abrupt changes. Efforts are needed to improve how the mechanisms driving abrupt climate change are represented in these models and to more rigorously test models against the climate record.
More paleoclimatic data. More climate information from the distant past would go a long way toward strengthening our understanding of abrupt climate changes and our models of past climate. In particular, an enhanced effort is needed to expand the geographic coverage, temporal resolution, and variety of paleoclimatic data.
Appropriate statistical tools. Because most statistical calculations at present are based on the assumption that climates are not changing but are stationary, they have limited value for nonstationary (changing) climates and for climate-related variables that are often highly skewed by rapid changes over time—such asfor abrupt-change regimes. Available statistical tools themselves need to be adapted or replaced with new approaches altogether to better reflect the properties of abrupt climate change.
Ecological and Economic Impacts
One way of understanding the potential impacts of abrupt climate change is to think about how it could disrupt the timely replacement, repair, or adaptation of “capital stocks,” whether of natural systems or nations' economies. For example, a rapid sea-level rise could inundate or threaten coastal populations; significant changes in patterns of droughts or frosts could destroy forests or agricultural systems; and sudden temperature shifts could render improperly insulated, heated, or cooled buildings uninhabitable.
To date, however, relatively little research has addressed the ecological and economic impacts of abrupt climate change; most studies focus on gradual climate change. Given the accumulating evidence of past abrupt changes and their capacity to affect human societies, some attention should be focused on potential future abrupt change scenarios. Concurrently, impact assessment models need to be made increasingly sophisticated so they can accommodate diverse variables and represent interactions and outcomes in ways that more closely approximate reality.
Adapting to Abrupt Climate Change
Although our understanding of the causes and consequences of relatively abrupt changes in climate is imperfect, it makes sense to develop practical strategies that could be used to reduce economic and ecological systems' vulnerabilities to change. In that spirit, it is worth investigating “no-regrets” policies that provide benefits whether an abrupt climate change ultimately occurs or not. By moving scientific and public-policy research in directions that enhance system adaptability, it might be possible to reduce vulnerability at little or no net cost.
For example, the phaseout of chloro-fluorocarbons over the past two decades, and their replacement with relatively benign gases having shorter atmospheric residence times, reduced nations' contributions to global warming while also diminishing the risks posed by ozone depletion.
No-regrets measures in anticipation of abrupt climate change could include low-cost steps to: slow climate change; improve climate forecasting; slow biodiversity loss; improve water, land, and air quality; render institutions more robust to major disruptions; and adopt technological innovations that increase the resiliency of market and ecological systems (see sidebar).
The potential value of such measures is not restricted to the United States. With growing globalization, adverse social and economic impacts are now more likely than ever to spill across national boundaries. It is especially important that the needs of poorer countries, which could be highly vulnerable to the effects of abrupt climate change, be given sufficient attention and support.
Potentional No-Regrets Strategies
The report highlights a few policy areas to explore in
developing no-regrets options:
Energy policies. Options to slow climate change, such as moving away from coal-burning toward other fuels, can also have benefit ts in reducing health or environmental effects of emissions. Ecological policies. In land-use and coastal planning, managers may be helped by information on the effects of nonlinear climate changes on ecosystems.
Scientists and government organizations at various levels could collaborate to develop and implement regulations and policies that reduce environmental degradation of water, air, and biota.
Forecasting of weather and weather-related events.
The frequency and intensity of hurricanes and other storms could increase as a result of an abrupt climate change, having large societal impacts. Efforts to improve forecasting and alert capabilities can reduce the loss of life by facilitating evacuations.
Institutions. Research should be conducted on improved institutions that will allow societies to withstand the greater risks associated with climate change, for example, water systems that better withstand drought, and insurance systems that hold up to increased demands for losses due to fires, floods, and storms.
Committee on Abrupt Climate Change:
Richard B. Alley (Chair), PennsylvaniaStateUniversity, University Park;
Jochem Marotzke, Southampton Oceanography Centre, United Kingdom; William Nordhaus, YaleUniversity, New
Haven, Connecticut; Jonathan Overpeck, University of Arizona, Tucson; Dorothy Peteet, National Aeronautics and
Space Administration, New York, New York; Roger Pielke, Jr., Center for Science and Technology Policy Research,
University of Colorado, Boulder; Raymond Pierrehumbert, University of Chicago, Illinois; Peter Rhines, University
of Washington, Seattle; Thomas Stocker, University of Bern, Switzerland; Lynne Talley, Scripps Institution of
Oceanography, La Jolla, California; J. Michael Wallace, University of Washington, Seattle.
This report brief was prepared by the National Research Council based on the committee’s report. Support for this publication was provided by the Presidents’ Circle Communications Initiative of the National Academies.
For more information, contact the Ocean Studies Board at 202-334-2714. Abrupt Climate Change: Inevitable Surprises is available from the National Academies Press, 500 Fifth Street, NW, Washington, DC 20001; 800-624-6242 or 202-334- 3313 (in the Washington area); www.nap.edu.
Permission granted to reproduce this brief in its entirety with no additions or alterations.
