October 31, 2006

New Northern Eurasian Snow Cover Data Not Cooperating

Filed under: Arctic, Polar

The cryosphere, or Earth’s frozen realm, is widely thought of as a wonderful monitor of climate change. The idea that warming reduces the area extent and/or persistence of frozen ground, snow cover, sea ice, and glaciers seems rather straightforward. Using the cryosphere as a natural barometer of global warming appears to be ideal considering the fact that the high latitude regions of the Northern Hemisphere are associated with some of the largest increase in surface air temperature both observed during the 20th century and predicted for the 21st century. Reduction of the cryosphere should be a train run amok, as frozen surfaces positively feed back to the overlying atmosphere such that without refrigeration from beneath, the overlying atmosphere should become even warmer.

Information about changes in the cryosphere has become widely available over the past two decades through satellite-derived data sets. However, in-situ observations of the cryosphere, or direct measurements from on the ground, are valuable because they can be used for validation of remote sensing products. But more importantly, in-situ observations provide a much longer record than satellite data sets, making them better monitors of the long-term climate. A newly assessed “state of the ground” data set for northern Eurasia has hit the streets, and the in-situ data offer an interesting caveat to the global warming debate.

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October 27, 2006

Reverse Spin on Tropical Cyclones

Filed under: Climate Extremes, Hurricanes

Look at any popular presentation on the threat of global warming, and it is highly likely you will be led to believe that the buildup of greenhouse gases and the accompanying rise in planetary temperature will surely increase hurricane activity in the years to come. Who could ever forget the drumbeat during and after Katrina from the global warming crowd; Al Gore was all over this concept in his movie. Somewhat surprisingly to most, the Intergovernmental Panel on Climate Change (IPCC) concluded in the Summary for Policymakers “Changes globally in tropical and extra-tropical storm intensity and frequency are dominated by inter-decadal and multi-decadal variations, with no significant trends evident over the 20th century.”

What you call hurricanes, the professional climatologists around the world call tropical cyclones to avoid confusion regarding different names for the same meteorological phenomenon (e.g., “hurricanes” in the western Pacific are called typhoons). Anyway, a team of scientists from various Chinese agencies examined trends in the number of tropical cyclones and the rainfall from these events over the period 1957 to 2004. The results are published in a recent issue of Geophysical Research Letters, and given what they found, they are absolutely certain to get zero press coverage.

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October 26, 2006

Relief for Africa

Droughts and/or floods – blame global warming, right? Time and Newsweek are all too quick to blame either one on global warming, Al Gore’s movie certainly gave us vivid images of both severe droughts and severe floods, and to this day, ongoing drought in the Southwest is blamed on global warming in some circles. The Summary for Policymakers in most recent (2001) Intergovernmental Panel on Climate Change (IPCC) Report claims “In the mid- and high latitudes of the Northern Hemisphere over the latter half of the 20th century, it is likely that there has been a 2 to 4% increase in the frequency of heavy precipitation events.” Also, IPCC notes “Over the 20th century (1900 to 1995), there were relatively small increases in global land areas experiencing severe drought or severe wetness.” However, IPCC claims “In some regions, such as parts of Asia and Africa, the frequency and intensity of droughts have been observed to increase in recent decades.” In the main body of the document, we find in Southern Africa “significant decreases in precipitation being observed since the late 1970s.”

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October 24, 2006

For Peat’s Sake: Warmer is Better

Imagine your dog digging a hole in the backyard, and somehow, you then have an intricate story to tell about the climate history of human civilization. This is somewhat the case from an article published recently in the journal (we doubt you read regularly) Palaeogeography, Palaeoclimatology, Palaeoecology. In the global change fraternity, it is referred to as “Palaeo.”

A team of scientists from China’s State Key Laboratory of Loess and Quaternary Geology and the State Key Laboratory of Environmental Geochemistry turned their attention to a peat bog at Hongyuan in central China; they extracted a 5 meter core from the peat that contained a climate signal of the past 6,000 years. The grasses that built the peat over the centuries preserved an oxygen 18 isotope (d18O) signal over the entire 6,000 year period. The team of Xu, Hong, Lin, Zhu, Hong, and Jiang note that “For plants using precipitation as source water, the isotopic signals of precipitation can be modulated and recorded into plant cellulose through series of plant physiological processes. Since both the relative humidity and the amount of precipitation vary mildly, the oxygen/hydrogen isotopic fractionations during the plant physiological processes should be relatively constant. Therefore, the variation of d18O in plant cellulose should mainly reflect that of the precipitation. Because source water of the grass in the studying peat land is predominantly meteoric water, the d18O of peat cellulose should be quantitatively correlated to that of the precipitation, and thereby to air temperature.” More simply, the peat can tell us about the temperature over the past 6,000 years.

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October 23, 2006

Tropical Seas Sink Hockey Stick

Defending the “Hockey Stick” depiction of hemispheric or global temperature for the past 1,000 years just got a lot tougher. The “Hockey Stick” curiously wipes out the “Medieval Warm Period” of 1,000 years ago and the “Little Ice Age” that began 450 years ago and ended around 1900. We are supposed to look at the blade of the stick and conclude that the warming of the past 100 years is completely unlike anything seen for at least 1,000 years. It comes as no surprise that the “Hockey Stick” is prominently presented in many of the documents of the Intergovernmental Panel on Climate Change (IPCC). Defenders of the “Hockey Stick” make claims that the Medieval Warm Period and Little Ice Age were confined to the mid-to-high latitudes of the Northern Hemisphere and not felt throughout the rest of the world. This always seemed odd to us at World Climate Report given that variations of solar output seem to explain the higher temperatures 1,000 years ago and the colder temperatures of the Little Ice Age.

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October 20, 2006

Diatom Diatribe

If you have followed World Climate Report over the past few years, you are aware that we have taken countless swings at the “Hockey Stick” depiction of planetary temperature. The “Stick” is popular with the global warming crowd for it wipes out the “Medieval Warm Period” of 1,000 years ago and the “Little Ice Age” that began 450 years ago and thankfully ended around 1900. The “Stick” makes the warming of the 20th century look incredible, disturbing, and completely unmatched over the past 1,000 years. The only explanation for the recent warming must be the dreaded buildup of greenhouse gases.

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October 19, 2006

Bogged Down in Soil Moisture

Filed under: Droughts, Precipitation

The Intergovernmental Panel of Climate Change (IPCC) provides itself a great deal of wiggle room in its predictions of future soil moisture levels. On one hand, IPCC predicts in the future that “The globally averaged mean water vapour, evaporation and precipitation increase.” That makes sense when one considers that warmer temperatures will cause an increase in evaporation, and the water that evaporates will ultimately fall from the sky. IPCC also predicts “Most tropical areas have increased mean precipitation, most of the sub-tropical areas have decreased mean precipitation, and in the high latitudes the mean precipitation increases.” Of course, IPCC predicts (and Gore et al. make the most of it) “Intensity of rainfall events increases.” But with respect to the United States, IPCC predicts “There is a general drying of the mid-continental areas during summer (decrease in soil moisture). This is ascribed to a combination of increased temperature and potential evapotranspiration that is not balanced by increases in precipitation.”

Yet another article has appeared in the literature that provides effectively zero empirical support for the prediction of decreased summer soil moisture levels. The latest article is entitled “Summer moisture availability across North America” and is published in the Journal of Geophysical Research by a team of scientists from the United States and United Kingdom. The van der Schrier et al. group reviewed the literature on drought studies in the United States and correctly identified that (a) many researchers use the very popular Palmer Drought Severity Index (PDSI) and (b) the PDSI has many substantial limitations. Among its many problems, they note “A significant drawback of the PDSI is that despite its intended value as a geographically comparable index, it can be poorly suited for investigation of moisture conditions across diverse climatological regions.”

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October 18, 2006

Tread Carefully on Snow Cover

Filed under: Climate Changes, Precipitation

The depth and extent of Earth’s snow cover have been championed as tools for measuring climate variability and change since the early 1970s when satellite-derived measurements of large-scale snow became reliable. The scientific literature of recent years is well stocked with research articles that document various trends toward decreasing snow cover across portions of the Northern Hemisphere. This corresponds nicely with the atmospheric warming that has occurred across the hemisphere, and intuition leads to the conclusion that snow cover reduction is a response to global warming. Armed with this idea, it’s off to the global warming debate we go…on the wings of a common mistake. A deeper intuition suggests that precipitation is also a necessary ingredient of snow cover, and therefore variability in snow cover is not solely dependent on temperature.

One can argue that across Earth’s cryosphere, or its frozen realm, precipitation can be more completely monitored with snow cover than can atmospheric temperature. Consider this: decreases in snow cover across regions with seasons that are persistently below freezing have nothing to do with air temperature and they have everything to do with precipitation. This fact is well demonstrated in a recent article appearing in the Journal of Climate: “Snow cover distribution, variability, and response to climate change in western China” authored by Qin Dahe of the Cold and Arid Regions Environmental and Engineering Research Institute in Lanzhou, China, and two of his colleagues. The impetus for their work is twofold: (1) snow cover is a vital water resource in western China, and (2) “The majority of the climatic community is convinced of a pronounced reduction in seasonal snow cover in response to CO2-induced global warming.” In partial response to the second issue, Dahe et al. point out that “Up to now global snow cover monitoring has not found any convincing evidence of the trend in snow cover variations on global scale.”

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October 17, 2006

Another Swipe at the Hockey Stick

We have covered the “Hockey Stick” controversy many times at World Climate Report, but an article appeared recently in the Proceedings of the National Academy of Sciences that further buries the “Hockey Stick” depiction of planetary temperature.

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October 13, 2006

Overturning Ocean Hype

Filed under: Climate Changes, Gulf Stream

You may remember a major study regarding the greenhouse debate that surfaced last Christmas season. Harry Bryden and two associates at the UK’s National Oceanography Centre had analyzed five decades of data regarding the ocean circulation of the North Atlantic. They concluded in Nature magazine that “The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 percent between 1957 and 2004.” The greenhouse crusade went wild, the media produced widespread coverage of Bryden’s findings, and the public was warned that the oceanic response to the build up of greenhouse gases could produce catastrophic results, particularly for European countries.

The story was straight out of “The Day After Tomorrow.” We were all told that the meridional circulation of the Atlantic carries warm upper waters into the mid-to-high latitudes and returns cold deep water southward across the Equator. We all learned about the “thermohaline circulation” that is a critical component in the energy balance of the earth-atmosphere system. The Bryden et al. findings could only heighten fears that human activities were having a profound impact on air-sea interactions, and if you recall, this could only lead to climate disasters – the entire story was straight out of a movie set.

We at World Climate Report were skeptical and questioned immediately why a 30 percent reduction in the thermohaline circulation had not produced noticeable cooling effects in Europe, after all, a complete shutdown of the circulation is expected to cause a cooling of 4°C in Europe, according to some computer models. We pointed out that the literature on ocean circulation contained evidence that the thermohaline circulation may be strengthening, exactly opposite what Bryden et al. claimed to have found.

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