Tropische Stürme und Hurrikane
IPCC 2013, AR5, WGI, Kapitel 2, Seite 216: “No
robust trends in annual numbers of tropical storms, hurricanes and major
hurricanes counts have been identified over the past 100 years in the
North Atlantic basin.”
Übersetzung: “Keine robusten Trends bei den jährlichen Zahlen von
tropischen Stürmen, Hurrikans und Stark-Hurrikans konnten in den
letzten 100 Jahren im Nordatlantischen Becken ausgemacht werden.
Tropische Zyklone
IPCC 2013, AR5, WGI, Kapitel 2, Seite 216: “Current
datasets indicate no significant observed trends in global tropical
cyclone frequency over the past century and it remains uncertain whether
any reported long-term increases in tropical cyclone frequency are
robust, after accounting for past changes in observing capabilities.”
Übersetzung: “Aktuelle Datensätze zeigen keine signifikanten
beobachteten Trends bei der weltweiten tropischen Wirbelsturmfrequenz
während des letzten Jahrhunderts und es ist ungewiss, ob ein berichteter
langfristiger Anstieg der tropischen Wirbelsturm-Frequenz robust ist,
nach Berücksichtigung der letzten Änderungen in den
Beobachtungs-Möglichkeiten.“
Außertropische Zyklonen
IPCC 2013, AR5, WGI, Kapitel 2, Seite 220: “In summary,
confidence in large scale changes in the intensity of extreme
extratropical cyclones since 1900 is low. There is also low confidence
for a clear trend in storminess proxies over the last century due to
inconsistencies between studies or lack of long-term data in some parts
of the world (particularly in the SH). Likewise, confidence in trends in
extreme winds is low, owing to quality and consistency issues with
analysed data.”
Übersetzung: “Zusammenfassend ist das Vertrauen in große
Änderungen in der Intensität extremer aussertropischer Zyklone seit 1900
gering. Es gibt auch [nur] ein geringes Vertrauen für einen klaren
Trend bei Sturm-Proxies wegen Inkonsistenzen zwischen den Studien oder
wegen dem Fehlen von Langzeitdaten des letzten Jahrhunderts in einigen
Teilen der Welt (vor allem auf der Südhemisphäre). Ebenso ist das
Vertrauen in Trends in extreme Winde niedrig, wegen der Qualität und
wegen Konsistenz-Problemen mit den analysierten Daten.“
Dürren
IPCC 2013, AR5, WGI, Technical Summery, Seite 50: ”There
is low confidence in a global-scale observed trend in drought or
dryness (lack of rainfall), owing to lack of direct observations,
dependencies of inferred trends on the index choice and geographical
inconsistencies in the trends.”
Übersetzung: “Es besteht ein geringes Vertrauen im globalen
Maßstab beobachteten Trend an Dürre oder Trockenheit (Mangel an
Niederschlag), aus Mangel an direkten Beobachtungen, Abhängigkeiten von
abgeleiteten Trends auf der Indexauswahl und wegen geographischer
Unstimmigkeiten in den Trends.“
sowie IPCC 2013, AR5, WGI, Kapitel 2, Seite 215: “In summary, the
current assessment concludes that there is not enough evidence at
present to suggest more than low confidence in a global scale observed
trend in drought ordryness (lack of rainfall) since the middle of the
20th century, owing to lack of direct observations, geographical
inconsistencies in the trends, and dependencies of inferred trends on
the index choice. Based on updated studies, AR4 conclusions regarding
global increasing trends in drought since the 1970s were probably
overstated. However, it is likely that the frequency and intensity of
drought has increased in the Mediterranean and West Africa and decreased
in central North America and north-west Australia since 1950.”
Übersetzung: „Zusammenfassend kommt die aktuelle Bewertung zu dem
Schluss, dass es zur Zeit nicht genug Hinweise und [nur] ein geringes
Vertrauen in einen beobachteten globalen Trend an Dürre oder Trockenheit
(Mangel an Niederschlägen) gibt, aus Mangel an direkten Beobachtungen
in der Mitte des 20. Jahrhunderts, geographischen Inkonsistenzen in den
Trends und Abhängigkeiten der abgeleiteten Trends auf der Indexauswahl.
Auf Basis aktualisierter Studien waren die AR4-Schlußfolgerungen
bezüglich global zunehmender Trends an Dürre seit den 1970er Jahren
wahrscheinlich übertrieben. Es ist jedoch wahrscheinlich, dass die
Häufigkeit und Intensität von Dürre im Mittelmeerraum und Westafrika
sich erhöhen könnte und im Zentrum von Nordamerika und
Nordwest-Australien seit 1950 abnehmen könnte.“
Nachtrag
Es ist bemerkenswert, dass alle diese Zitate und Aussagen in der 28-seitigen deutschen Fassung des Summary for policymakers (hier) fehlen!
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A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.
The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.
According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.
“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”
Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks.
But it might only take a few decades for Antarctica’s growth to reverse, according to Zwally. “If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses.”
The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two European Space Agency European Remote Sensing (ERS) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) from 2003 to 2008.
Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time.
“At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.
The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 0.7 inches (1.7 centimeters) per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.
Zwally’s team calculated that the mass gain from the thickening of East Antarctica remained steady from 1992 to 2008 at 200 billion tons per year, while the ice losses from the coastal regions of West Antarctica and the Antarctic Peninsula increased by 65 billion tons per year.
“The good news is that Antarctica is not currently contributing to sea level rise, but is taking 0.23 millimeters per year away,” Zwally said. “But this is also bad news. If the 0.27 millimeters per year of sea level rise attributed to Antarctica in the IPCC report is not really coming from Antarctica, there must be some other contribution to sea level rise that is not accounted for.”
“The new study highlights the difficulties of measuring the small changes in ice height happening in East Antarctica,” said Ben Smith, a glaciologist with the University of Washington in Seattle who was not involved in Zwally’s study.
"Doing altimetry accurately for very large areas is extraordinarily difficult, and there are measurements of snow accumulation that need to be done independently to understand what’s happening in these places,” Smith said.
To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. “ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil,” said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. “It will contribute to solving the problem of Antarctica’s mass balance by providing a long-term record of elevation changes.”