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Climate Change: Polar Regions
Published in Yeqiao Wang, Atmosphere and Climate, 2020
The start of the post-glacial Holocene period is dated from 11,500 years ago when conditions approached those of today. In the Arctic region, the warmest conditions appear to have occurred in the early Holocene, coincident with the precessional timing of the boreal summer solstice, occurring when the Earth was nearest to the Sun (perihelion), making northern summers relatively warmer. The precession of the equinoxes has a period of approximately 23,000 years; currently, summer solstice occurs at aphelion, when the Earth is most distant from the Sun, making summers relatively cooler. In the early Holocene the distribution of bowhead whale bones indicates at least periodically ice-free summers along the length of the Northwest Passage and the same pattern is repeated much later from approximately A.D. 500-1250.
Hydrogen Economy, Geothermal and Ocean Power, and Climate Change
Published in Roy L. Nersesian, Energy Economics, 2016
Another group of cooling adherents are pointing in another direction, taking a paleoclimate view covering hundreds of thousands of years. During these long stretches of time, in rough numbers, ice ages last about 100,000 years with interglacial periods of about 12,000 years. This rhythm of climate stems from three Milankovitch cycles of variation in the shape of the Earth’s orbit that has a period of 100,000 years, variation in the tilt of the Earth that has a period of 41,000 years, and the precession of the equinoxes, the Earth’s wobble, that has a period of 26,000 years. These three periods, working together, are responsible for variation in the degree of solar radiation falling on the northern hemisphere, resulting in 100,000-year cycles of ice ages interspersed with 12,000-year periods of interglacial warming. Paleoclimate advocates criticize the anthropogenic global warming view of focusing on a timeline measured in decades, not tens of thousands of years. To a lesser extent, this same criticism can be applied to those who believe in solar cycles having a strong effect on climate. The real risk is that we may be at the end of the Holocene period of interglacial warming and about to plunge into the next ice age (a view, by the way, that was as popular in the 1970s as global warming is today). In fact a few of the leading alarmists of climate change/global warming had their teeth cut as ice age alarmists 40 years ago.76 If paleoclimate or solar cycle advocates are correct and cool weather is about to descend on us, then pumping carbon dioxide into the atmosphere may turn out to be a virtue rather than a vice.
Looking at the Sky
Published in José Guillermo Sánchez León, ® Beyond Mathematics, 2017
However, over very long periods we can notice discrepancies that at first sight may seem insignificant during a person’s lifetime but become quite obvious after several generations. Hipparchus of Nice (c. 190 BC – c. 120 BC) compared the stellar maps available at the time (celestial cartography is over 2,500 years old!) and realized that there was a relative movement of the stars with respect to the ecliptic. This movement is nowadays known as the precession of the equinoxes. This is probably his most famous discovery. The displacement happens when the Earth’s axis, moving along a circumference with respect to the ecliptic, rotates with a period of 25,771 years.
Monteiro da Rocha and the international debate in the 1760s on astronomical methods to find the longitude at sea: his proposals and criticisms to Lacaille’s lunar-distance method
Published in Annals of Science, 2022
Fernando B. Figueiredo, Guy Boistel
The MS BNP 511 manuscript ends with a stellar catalog providing right ascension, declination, and annual variation of about 70 stars. Monteiro da Rocha says that this catalog is just an example of catalogs he intends to publish in the future: «At the end of each Ephemeride Nautica, we will provide a similar star catalog with the star's longitude and latitude, calculated every four months with all equations of the precession of the equinoxes and nutation. However, the one we present here only gives the right ascension and declination (for the year 1770). According to the method we follow, these coordinates do not need to be calculated for each year because they do not require the ultimate accuracy such as longitude and latitude.» (MS BNP 511, fl. 40)