Cryosphere
From ClimateWiki
The effects of climate change are visible in the cryosphere (places on Earth so cold that water is usually in solid form as snow or ice), in sea level change and other ocean dynamics, in patterns of precipitation, and in rivers and streamflow. Computer models have been used to project trends in each of these areas, while observations and data are available to test those projections.
According to the Intergovernmental Panel on Climate Change (IPCC), “recent decreases in ice mass are correlated with rising surface air temperatures. This is especially true in the region north of 65°N, where temperatures have increased by about twice the global average from 1965 to 2005” (IPCC 2007, p. 339). The IPCC goes on to report decreased snow cover “in most regions, especially in spring and summer,” freeze-up dates in the Northern Hemisphere occurring later, breakup dates occurring earlier, declines in sea ice extent, and similar findings (ibid.).
In their 2009 Nongovernmental International Panel on Climate Change (NIPCC) report, Idso and Singer (2009) contended that many of the IPCC’s findings on this subject were incorrect, the result of cherry-picking data or misrepresenting available research. The authors found,
Glaciers around the world are continuously advancing and retreating, with a general pattern of retreat since the end of the Little Ice Age. There is no evidence of an increased rate of melting overall since CO2 levels rose above their pre-industrial levels, suggesting CO2 is not responsible for glaciers melting.
Sea ice area and extent have continued to increase around Antarctica over the past few decades. Evidence shows that much of the reported thinning of Arctic sea ice that occurred in the 1990s was a natural consequences of changes in ice dynamics caused by an atmospheric regime shift, of which there have been several in decades past and will likely be several in the decades to come, totally irrespective of past or future changes in the air’s CO2 content. The Arctic appears to have recovered from its 2007 decline (Idso and Singer 2009, p. 4).
Similar disagreement between IPCC and NIPCC was found on ocean dynamics, with IPCC claiming “there is high confidence that the rate of sea level rise has increased between the mid-19th and the mid-20th centuries” (IPCC AR4, p. 387, emphasis in the original) while NIPCC found “the mean rate of global sea level rise has not accelerated over the recent past” (Idso and Singer 2009, p. 4). While the IPCC claimed “it is likely that … heavy precipitation events will continue to become more frequent” (IPCC AR4, p. 15), NIPCC said “global studies of precipitation trends show no net increase and no consistent trend with CO2, contradicting climate model predictions that warming should cause increased precipitation” (Idso and Singer 2009, p. 4).
This chapter reinforces NIPCC’s findings of 2009, with new research finding less melting of ice in the Arctic, Antarctic, and mountaintops than previously feared, no sign of acceleration of sea-level rise in recent decades, no trend over the past 50 years in changes to the Atlantic meridional overturning circulation (MOC), and no changes in precipitation patterns or river flows that could be attributed to rising CO2 levels.
Antartica
The study of Antarctica’s past, present, and expected future climate has provided valuable insights and spurred contentious debate over issues pertaining to global climate change. Although many individuals concerned about global warming expect Earth’s polar regions to manifest the earliest and most severe responses to CO2-induced climate change, real-world data from Antarctica do not support such expectations. In the 2009 NIPCC report, Idso and Singer (2009) discussed the results of several scientific analyses that demonstrated there is nothing unusual, unprecedented, or unnatural about the climate on this vast continent of ice. In this interim report we highlight the results of several more papers in support of their findings.
Starting with the Antarctic Peninsula, Hall (2009) offered “a summary of existing data concerning Holocene glacial extent and fluctuations within Antarctica and the sub-Antarctic islands.” She begins by noting, “in several areas, ice extent was less than at present in mid-Holocene time,” which suggests, in her words, “the magnitude of present ice recession and ice-shelf collapse is not unprecedented.” She also reports “the first Neoglacial ice advances occurred at ~5.0 ka” and “glaciers in all areas underwent renewed growth in the past millennium.” More specifically, Hall states, “the Antarctic Peninsula, along with the adjacent sub-Antarctic islands, yields one of the most complete Holocene glacial records from the southern high latitudes,” and most of these locations “show an advance in the past few centuries, broadly coincident with what is known elsewhere as the Little Ice Age.” Likewise, she reports “glaciers on most if not all” of the Indian/Pacific sector sub-Antarctic Islands “underwent advance in the last millennium, broadly synchronous with the Little Ice Age.” And she notes “glaciers in all areas” have “subsequently undergone recession,” but only in “the past 50 years.”
In another study, Tedesco and Monaghan (2010) reviewed what has been learned about the melting of snow and ice over all of Antarctica since 1979, when routine measurement of the phenomenon via space-borne passive microwave radiometers first began. Their results revealed that over the course of the past three decades the continent-wide snow and ice melting trend was “negligible.” They also observe that during the 2008–2009 austral summer, scientists from the City University of New York and the U.S. National Center for Atmospheric Research observed that snow and ice melt was “a record low for the 30-year period between 1979 and 2009,” or as they alternatively describe it, “a new historical minimum.” In addition, they note, “December 2008 temperature anomalies were cooler than normal around most of the Antarctic margin, and the overall sea ice extent for the same month was more extensive than usual.”
Turning our attention to the West Antarctic Ice Sheet (WAIS), often described as the world’s most unstable large ice sheet, it has been postulated that future global warming may cause the WAIS to disappear, resulting in a sea-level rise of several millimeters per year. Yet three groups of researchers have shown in recent papers that the WAIS is likely much more stable than the models predict.
Gomez et al. (2010) state that several studies (Oppenheimer, 1998; Meehl et al., 2007; Vaughan, 2008; Smith et al., 2009) have suggested “climate change could potentially destabilize marine ice sheets, which would affect projections of future sea-level rise.” The studies specifically highlight “an instability mechanism (Weertman, 1974; Thomas and Bentley, 1978; Schoof, 2007; Katz and Worster, 2010)” which they say “has been predicted for marine ice sheets such as the West Antarctic ice sheet that rest on reversed bed slopes, whereby ice-sheet thinning or rising sea levels leads to irreversible retreat of the grounding line.”
Noting existing analyses of this particular instability mechanism “have not accounted for deformational and gravitational effects that lead to a sea-level fall at the margin of a rapidly shrinking ice sheet,” Gomez et al. go on to present “a suite of predictions of gravitationally self-consistent sea-level change following grounding-line migration,” in which they “vary the initial ice-sheet size and also consider the contribution to sea-level change from various sub-regions of the simulated ice sheet.”
The four researchers report their new results “demonstrate that gravity and deformation-induced sea-level changes local to the grounding line contribute a stabilizing influence on ice sheets grounded on reversed bed slopes,” contrary to previously prevailing assumptions based on earlier analyses of the subject. In fact, they conclude, “local sea-level change following rapid grounding-line migration will contribute a stabilizing influence on marine ice sheets, even when grounded on beds of non-negligible reversed slopes.”
In a terse statement describing the implications of their work, Gomez et al. write their new and more “accurate” treatment of sea-level change “should be incorporated into analyses of past and future marine-ice-sheet dynamics.”
Introducing their study of the WAIS, Naish et al. (2009) write, “an understanding of the behavior of the marine-based West Antarctic ice sheet during the ‘warmer-than-present’ early-Pliocene epoch (~5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behavior in the context of future global warming,” and they thus undertook a project to provide such understanding. Specifically, as they describe it, they derived “a marine glacial record from the upper 600 meters of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL program,” which demonstrated the “well-dated ~40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the earth’s axial tilt (obliquity) during the Pliocene.” They state their data “provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ~3°C warmer than today and atmospheric CO2 concentration was as high as ~400 ppm,” the latter number being about 3 percent greater than what it is today.
An important implication of this last observation is that the much greater periodic warmth of the early-Pliocene was clearly not the primary result of periodic changes in the air’s CO2 concentration. The 56 researchers tacitly acknowledge that fact by attributing the variable warmth to periodic changes in the planet’s axial tilt that produced 40,000-year cycles of insolation.
How long did it take for such warmth to bring about a total collapse of the WAIS? An answer to this question can be found in the companion paper of Pollard and DeConto (2009), who state projections of future WAIS behavior “have been hampered by limited understanding of past variations and their underlying mechanisms.” With the findings of Naish et al. (2009), however, Pollard and DeConto gained important new knowledge that helped them frame a greatly improved “ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years.”
The two researchers report they modeled WAIS variations ranging “from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands.” And they say their work suggests “the WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C.” In a “News & Views” story on Pollard and DeConto’s findings, Huybrechts (2009) states, “the amount of nearby ocean warming required to generate enough sub-ice-shelf melting to initiate a significant retreat of the West Antarctic ice sheet ... may well take several centuries to develop.” Once started, he concludes, the transition time for a total collapse of the West Antarctic ice sheet would range from “one thousand to several thousand years.” This time period, he notes, “is nowhere near the century timescales for West Antarctic ice-sheet decay based on simple marine ice-sheet models,” such as have been employed in the past.
The specter of sea-level rise being measured in meters can be seen to be receding ever further into the distance of unreality.
I love the way Richard Black cannot bring siehmlf to actually quote the letter.RB: But scientists from the Scott Polar Research Institute say the figures are wrong; the ice has not shrunk so much.RB: As such, they back the contention that rising temperatures are cutting ice cover across the region, including along the fringes of Greenland; but not anything like as fast as the Times Atlas claimed.SPRI: We do not disagree with the statement that climate is changing and that the Greenland Ice Sheet is affected by this. It is, however, crucial to report climate change and its impact accurately and to back bold statements with concrete and correct evidence.The volume of ice contained in the Greenland Ice Sheet is approximately 2.9 million cubic kilometers and the current rate whereby ice is lost is roughly 200 cubic kilometers per year. This is on the order of 0.1% by volume over 12 years.
doDDqa <a href="http://jxwcoggjmqiu.com/">jxwcoggjmqiu</a>
Sea and Lake Ice
Though semi-permanent sea ice exists around the North Pole, fringing sea ice in both the Arctic and Antarctic is an annual, seasonal feature. Fringing sea ice is therefore particularly susceptible to fast advance or retreat depending upon local oceanographic and atmospheric changes. Even quite major sea-ice changes are not necessarily due to climatic change.
This dynamic, rather than climatic, aspect of sea-ice change is well documented in a recent study by Scott and Marshall (2010), two scientists with the British Antarctic Survey. They found “over the last four decades there has been a trend to earlier summer breakup of the sea ice in western Hudson Bay, Canada” and “the trend to earlier sea-ice breakup has been linked to the long-term effect of warming in the region (Stirling et al., 1999; Gagnon and Gough, 2005).” Subsequently, however, they report “the existence of a sufficiently long-term regional warming trend was disputed by Dyck et al. (2007),” and, therefore, they decided to explore the subject in more detail, to see if they could resolve the controversy.
Working with passive microwave data obtained from the Scanning Multichannel Microwave Radiometer onboard the Nimbus 7 satellite, plus three Special Sensor Microwave/Imager instruments onboard Defense Meteorological Satellite Program satellites, as well as Canadian Ice Service sea-ice charts considered to be “more accurate than passive microwave data for estimates of ice concentration, particularly in the presence of surface melt,” as described by Agnew and Howell (2002) and Fetterer et al. (2008), Scott and Marshall performed several new analyses on both datasets, “bringing the time series up to date” (to 2007, from a starting date of 1971) while looking at “temperature trends in the area around the time of breakup in more detail than was [done] in previous studies.”
With respect to the chief point of controversy, the researchers found “there has clearly not been a continuous trend in the [time of sea-ice breakup] data, and the change is best described by a step to 12 days earlier breakup occurring between 1988 and 1989, with no significant trend before or after this date.” In addition, they remark, “an increase in regional southwesterly winds during the first three weeks of June and a corresponding increase in surface temperature are shown to be likely contributing factors to this earlier breakup.”
Proponents of the theory of CO2-induced global warming have long publicized what they characterize as the gradual development, over the past four decades, of an earlier occurrence of the date of yearly sea-ice breakup in Canada’s Hudson Bay, claiming it was a manifestation of anthropogenic climate change that was negatively affecting the region’s polar bears. The newer findings of Scott and Marshall argue against that conclusion. Nevertheless—and correctly—the two researchers conclude their analysis by stating “it remains to be seen whether these changes in atmospheric circulation [which appear to be the proximate cause of the significant step-change in the date of sea-ice breakup] might be ascribed to human actions or simply to natural climate variability.”
Clearly, the science pertaining to this matter is not settled.
Floating ice pack that is responsive to climatic fluctuations forms on large, intra-continental lakes as well as on the ocean, and Wang et al. (2010) provide an analysis of 70 years of such floating ice for the Great Lakes of North America. Their study covers the winters of 1972–73 to 2008–09 and comprises an analysis of time series of annual average ice area and basin winter average surface air temperature (SAT) and floating ice cover (FIC) for the Great Lakes, which they remind us “contain about 95% of the fresh surface water supply for the United States and 20% of the world.”
The primary data of interest are depicted in Figure 4.1.1 below, where after an initial four years of relative warmth and lower annual average ice area, SATs declined and FIC area rose. Then, there began a long period of somewhat jagged SAT rise and FIC decline, which both level out from about 1998 to 2006, after which SAT once again slowly declines and FIC slowly rises. Both parameters terminate at about the same value they exhibited initially. Wang et al. conclude from their study that “natural variability dominates Great Lakes ice cover,” and that any trend in the data—of which there are some of a few years and one that is lengthier—“is only useful for the period studied.” Given this finding, there is no reason to attribute any change in the annual average ice area of the North American Great Lakes to anthropogenic global warming.
that Global Warming started with the Industrial Revolution, which began in the 18th erctuny. And what do you know, the glacier was out to the ocean in 1760-1780 and started receding in the decades that followed.Amazing.And then there is the guy above who said that the IPCC claims Global Warming started in the 70 s. Really? If we look at the Hockey Stick graph that you all hate so much we see that temperatures start to increase in the 1700, and continue to increase all the way through the 1800 s, 1900 s and all the way to today.Sure I know you guys deny the hockey stick, but you just posted evidence that supports it! That glacier seems to start receding and keep pace with the temperature rises shown in the Hockey Stick.Great job! You've helped prove Global Warming is not a myth. Bahahahaha!
