Climate Study Project
Paleoclimate is the circumstance of much earlier mean meteorological conditions, for times prior to instrumental weather measurements. Most discussions of paleoclimate relate to prehistoric times, where written records of meteorology are n,ot extant. Paleo-climatologists use information from natural climate proxies, such as tree rings, ice cores, stalagmites, corals, and ocean (Seas of the world) and lake sediments, that record variations in past climate.
Records of past climate from these proxy records are important for several reasons. Instrumental records of climate are limited in many parts of the world to the past 100 years or less, and are too short to assess whether climate variability, events, and trends of the 20th and 21st centuries are representative of the long-term natural variability of past centuries and millennia. For example, was the 1930s Dust Bowl drought, a widespread and severe event in the United States, a rare occurrence or have similar events occurred in past centuries?
Knowledge of the long-term natural variability of the Earth Climate system, and its causes, will also allow an understanding of the roles of natural climate variability and human-induced climate change in the current and future climate. In particular, reconstructed temperatures (Groups Article) from proxy data for the past 1000 years have allowed an assessment of the warming over recent decades and indicate that at least part of this warming is due to the impact of human activities on climate, according to the Intergovernmental Panel on Climate Change.
Entrance to Danger Cave, Utah, where stalagmite evidence shows greatest megadroughts in this region occurred in the early Holocene from totally natural cycles.
There are numerous examples of ancient Holocene drought conditions; some of these, such as the Danger Cave Native American site in Utah, are based upon stalagmite studies do document time history of droughts. The Great Basin Desert Culture peoples of Danger Cave prospered over a period dating to at least as early as 7000 BC. Their ability to adapt to megadroughts is evident from their cultural remains in this important site. Stalagmite data shows that the most prolonged drought in the Great Basin since the start of the Holocene lasted for thousands of years, surpassing the minor droughts of current time and even the last five centuries. (Snow, 2011)
Ancient lakebed in the Kalahari Desert, Botswana, where megadrought began 150,000 years ago as a major river changed course. Source: C. Michael Hogan
Similar findings of megadroughts are observed in Europe, Africa
and West Asia. Tree ring studies show that the most severe modern droughts are associated with the time periods circa 1315 AD (chiefly West Asia and northeast Mediterranean); 1540 AD (central Europe); 1616 AD (central Europe); 1741 AD (northern Europe, Scandinavia
, British Isles
); 1893 AD (northern and western Europe); 1921 AD (western Europe). In summary, there is no correlation in Europe and West Asia between anthropogenic forcing, industrial activity, greenhouse gases
Typhoon and Hurricane Frequency
Typhoon at Daimotsu Bay in Settsu Province in 1188 AD by artist Utagawa Yoshitora. Collection of Austrian Gallery of Applied Arts.
It is more difficult to find proxy records for hurricane type events; moreover, the New World does not have as long a historical record as Asia. In China, there is copious historical documentary records in the form of Fang Zhi (semiofficial local gazettes), providing an excellent way for providing a high-resolution historical data for the frequency of typhoon landfalls. Examining the millennium long time series of typhoon landfalls in the Guangdong Province of south China since 975 AD from Fang Zhi data. Although the 571 typhoon landfalls from historical documents may underrepresent the total number of typhoon landfalls in Guangdong, calibration of the historical data against the observations during the instrument period 1884-1909 suggests that the trends of the two datasets are significantly correlated (r = 0.71), confirming that the time series reconstructed from historical documentary evidence contains a reliable record of variability in typhoon landfalls.
On a decadal average, the twenty-year interval from 1660 to 1680 AD is the most intense typhoon period of record, with 28 to 37 typhoon landfalls per decade. The variability in typhoon landfalls in Guangdong parallels observations in other Asian paleoclimatic proxies (such as tree rings, ice cores). Notably, the two periods of highest typhoon landfalls in Guangdong (AD 1660-1680, 1850-1880) coincide with two of the coldest periods in China during the Little Ice Age. Thus, as in the case of hurricanes, there is no correlation of typhoon activity with industrialization, combustion of fossil fuels, global warming or greenhouse gases. In fact, highest typhoon frequency occurred in the coldest century of the last millennium.(Liu et al, 2003)
In North America, distinct sand layers survive in the nearshore sediments of Alabama's Lake Shelby as a result of storm-tide overwash of beaches and dunes. Sediment cores from the lake center hold multiple sand layers, suggesting that major hurricanes of category 4 or 5 intensity directly struck the coast at circa 3.2-3.0, 2.6, 2.2, 1.4, and 0.8 ka (14C year), with an average recurrence interval of approximately 600 years. There is no evidence to suggest prehistoric or historic hurricane frequencies have altered during the Holocene. (Liu & Mirriam, 1993)
Polar sea mean temperature vs time (millions of years before present). Note: Only leftmost x-axis numbers in millions. Source: Robert A. Rohde
Geological evidence demonstrates that the Earth's climate is dynamic, and has varied widely from our everyday experience. Over the past two million years, numerous glacial periods have covered much of the northern hemisphere in glacial ice, dropped sea level as much as 125 meters, and significantly cooled even tropical regions. In the more distant past, the Cretaceous Period was significantly warmer than today, with less polar ice, raising sea levels and allowing warm weather organisms to thrive at higher latitudes than previous. In the past 150 years, instrumental weather records indicate that the Earth has warmed by approximately 0.6°C since 1870, after taking account of the overestimate of terrestrial warming due to the urban heat island effect.
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