Dendrochronology is the scientific method of dating tree rings to the exact year they were formed. As well as dating them this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from wood. Dendrochronology is useful for determining the precise age of samples those that are too recent for radiocarbon dating, which always produces a range rather than an exact date, to be accurate. However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide, it gives data on the timing of events and rates of change in the environment and in wood found in archaeology or works of art and architecture, such as old panel paintings. It is used as a check in radiocarbon dating to calibrate radiocarbon ages. New growth in trees occurs in a layer of cells near the bark. A tree's growth rate changes in a predictable pattern throughout the year in response to seasonal climate changes, resulting in visible growth rings.

Each ring marks a complete cycle of one year, in the tree's life. As of 2013, the oldest tree-ring measurements in the Northern Hemisphere are a floating sequence extending from about 12,580 to 13,900 years. Dendrochronology derives from Ancient Greek: δένδρον, meaning "tree", χρόνος, meaning "time", -λογία, "the study of"; the Greek botanist Theophrastus first mentioned. In his Trattato della Pittura, Leonardo da Vinci was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew. In 1737, French investigators Henri-Louis Duhamel du Monceau and Georges-Louis Leclerc de Buffon examined the effect of growing conditions on the shape of tree rings, they found that in 1709, a severe winter produced a distinctly dark tree ring, which served as a reference for subsequent European naturalists. In the U. S. Alexander Catlin Twining suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronologies of various trees and thereby to reconstruct past climates across entire regions.

The English polymath Charles Babbage proposed using dendrochronology to date the remains of trees in peat bogs or in geological strata. During the latter half of the nineteenth century, the scientific study of tree rings and the application of dendrochronology began. In 1859, the German-American Jacob Kuechler used crossdating to examine oaks in order to study the record of climate in western Texas. In 1866, the German botanist and forester Julius Ratzeburg observed the effects on tree rings of defoliation caused by insect infestations. By 1882, this observation was appearing in forestry textbooks. In the 1870s, the Dutch astronomer Jacobus C. Kapteyn was using crossdating to reconstruct the climates of the Germany. In 1881, the Swiss-Austrian forester Arthur von Seckendorff-Gudent was using crossdating. From 1869 to 1901, Robert Hartig, a German professor of forest pathology, wrote a series of papers on the anatomy and ecology of tree rings. In 1892, the Russian physicist Fedor Nikiforovich Shvedov wrote that he had used patterns found in tree rings to predict droughts in 1882 and 1891.

During the first half of the twentieth century, the astronomer A. E. Douglass founded the Laboratory of Tree-Ring Research at the University of Arizona. Douglass sought to better understand cycles of sunspot activity and reasoned that changes in solar activity would affect climate patterns on earth, which would subsequently be recorded by tree-ring growth patterns. Horizontal cross sections cut through the trunk of a tree can reveal growth rings referred to as tree rings or annual rings. Growth rings result from new growth in the vascular cambium, a layer of cells near the bark that botanists classify as a lateral meristem. Visible rings result from the change in growth speed through the seasons of the year. Removal of the bark of the tree in a particular area may cause deformation of the rings as the plant overgrows the scar; the rings are more visible in trees which have grown in temperate zones, where the seasons differ more markedly. The inner portion of a growth ring forms early in the growing season, when growth is comparatively rapid and is known as "early wood".

Many trees in temperate zones produce one growth-ring each year, with the newest adjacent to the bark. Hence, for the entire period of a tree's life, a year-by-year record or ring pattern builds up that reflects the age of the tree and the climatic conditions in which the tree grew. Adequate moisture and a long growing season result in a wide ring, while a drought year may result in a narrow one. Direct reading of tree ring chronologies is a complex science, for several reasons. First, contrary to the single-ring-per-year paradigm, alternating poor and favorable conditions, such as mid-summer droughts, can result in several rings forming in a given year. In addition, particular tree-species may present "missing rings", this influences the selection of trees for study of long time

Aída Fernández Ríos

Aída Fernández Ríos was a climate scientist, marine biologist, a professor at the Instituto de Investigaciones Marinas in Spain, specializing in the study of the Atlantic Ocean. She was the director of the Spanish National Research Council, a member of the Royal Galician Academy of Sciences. Fernández's research work in marine biology began in 1972 when she began working with the Instituto de Investigaciones Pesqueras in Uruguay, she received her doctoral degree in biology in 1992 from the University of Santiago. From 2006 to 2011, Ríos was the director of the Spanish National Research Council, she led an International Geosphere-Biosphere Programme committee focused on studying climate change from 2005 to 2011, she was initiated into the Royal Galician Academy of Sciences on 6 June 2015, where she gave an inaugural speech on the increasing acidity of the Atlantic Ocean due to carbon dioxide titled, "Acidificación do Mar: Unha consecuencia das emisións de CO2."Fernández died in a car accident in Moaña on 22 December 2015.

Fernández was considered "one of Europe's leading experts" on the relationship between carbon dioxide emissions and ocean acidity. Through her work, Ríos argued that observations of increased acidity in the Atlantic Ocean is best explained by changes in the accumulation of carbon dioxide produced by human activity rather than from natural sources

Door County Maritime Museum

The Door County Maritime Museum is an American maritime museum located in Sturgeon Bay, with additional sites in Gills Rock and the Cana Island Light. The museum was founded in Gills Rock, Wisconsin, in 1969 and began operating at the Cana Island Light in 1971; the Gills Rock location was opened in 1975. In 1993, the museum began a capital campaign to build a year-round facility in Sturgeon Bay, accomplished in 1997. In 2015, the museum began another capital campaign to expand their Sturgeon Bay museum with the construction of an 11-story lighthouse tower, which will contain exhibit space and an observation deck; the main Door County Maritime Museum site was opened in 1997. It contains; the site hosts the tugboat John Purves, built in 1919, served the U. S. Army in World War II, sailed on the Great Lakes; the site hosts CG-41410, the last 41-foot Utility Boat, Large in active service with the U. S. Coast Guard. In 2019, the museum began an effort to add an addition onto the museum, including a lighthouse tower.

Work is anticipated to be complete by 2021-2022. The Gills Rock site opened in 1975, it contains exhibits that focus on pirates on the Great Lakes. The site hosts a 45-foot wooden fishing boat, built in 1930; the site is open seasonally from May to October. Prior to 2018, it is still referenced today; the Cana Island Lighthouse was constructed in 1869 and opened as a museum site in 1971. It is located near Wisconsin. Access to the island is via a causeway. After the winter of 2015-16, heavy snow and decreased evaporation caused Lakes Michigan and Huron to rise 30+ inches. Summers of 2017 and 2018, the causeway was always covered. Volunteers drive the tractor; the lighthouse keeper's residence has been restored and is a museum depicting life for a lighthouse family. Restoration as of summer 2018:Phase 1 has been completed and included new restroom facilities and a maintenance building. Phase 2 was completed in 2017 and included restoring the out buildings including the oil house and barn. Phase 3 is scheduled for late 2018/early 2019 and includes construction of a visitor's center to replace the temporary building.

Phase 4 is scheduled to start after construction are complete. Phase 4 will restore the interior of the keeper’s house; the 89-foot light tower is open for tours. Wisconsin Maritime Museum, another Maritime Museum, located south in Manitowoc, Wisconsin