Geographic coverage by these proxies is necessarily sparse, and various proxies are more sensitive to faster fluctuations. From these, proxy temperature reconstructions of the last 2000 years have been performed for the northern hemisphere, and over shorter time scales for the southern hemisphere and tropics. Quantities such as tree ring widths, coral growth, isotope variations in ice cores, ocean and lake sediments, cave deposits, fossils, ice cores, borehole temperatures, and glacier length records are correlated with climatic fluctuations. Proxy measurements can be used to reconstruct the temperature record before the historical period. Tree rings and ice cores (from 1,000-2,000 years before present) The Holocene Climatic Optimum was generally warmer than the 20th century, but numerous regional variations have been noted since the start of the Younger Dryas. The 10,000 years of the Holocene epoch covers most of this period, since the end of the Northern Hemisphere's Younger Dryas millennium-long cooling.
As the present article is oriented toward recent temperatures, there is a focus here on events since the retreat of the Pleistocene glaciers. The field of paleoclimatology includes ancient temperature records. Many estimates of past temperatures have been made over Earth's history. Also, the records from low-latitude regions helped scientists confirm that the 20th century was the warmest period in the last 1000 years. According to these records, scientists found the evidence which can prove the Last Glacial Maximum (LGM) was colder in the tropics and subtropics than previously believed. The Guliya record is the longest record from low-latitude, high altitude regions, which spans over 700,000 years. Ice cores in low-latitude regions usually locates in high altitude areas. The ice core records from low-latitude regions are not as common as records from polar regions, however, these records still provide much useful information for scientists. Ice core records from low-latitude regions Exploring more drilling stations is the primary goal for current research institutions. Although Antarctica is covered by the ice core records, the density is rather low considering the area of Antarctica.
īy comparing with current climate records, the ice core records in Antarctica further confirm that polar amplification. Due to the uniqueness of the Antarctic ice sheet, the Antarctic ice core not only records the global temperature changes, but also contains huge quantities of information about the global biogeochemical cycles, climate dynamics and abrupt changes in global climate. In recent years, more and more new studies have provided older but discrete records. The Antarctic ice sheet originated in the late Eocene, the drilling has restored a record of 800,000 years in Dome Concordia, and it is the longest available ice core in Antarctica. The variation of methane from Greenland records makes a unique contribution for global temperature records undoubtedly. As a component of greenhouse gases, methane plays an important role in global warming. Increase in methane concentration shown by Greenland ice core records implies that the global wetland area has changed greatly over past years.
When scientists explored the trapped gas in the ice core bubbles, they found that the methane concentration in Greenland ice core is significantly higher than that in Antarctic samples of similar age, the records of changes of concentration difference between Greenland and Antarctic reveal variation of latitudinal distribution of methane sources. Also, Greenland has the clearest record of abrupt climate changes in the ice core, and there are no other records that can show the same time interval with equally high time resolution. Warming phase only needs simple steps, however, the cooling process requires more prerequisites and bases. According to the records, changes in global climate are rapid and widespread. The World Paleoclimatology Data Center (WDC) maintains the ice core data files of glaciers and ice caps in polar and low latitude mountains all over the world.Īs a paleothermometry, the ice core in central Greenland showed consistent records on the surface-temperature changes.