NOAA's Earth System Research Laboratory
Mauna Loa, the Hawaiian Volcano from which researchers have been monitoring atmospheric carbon dioxide for decades.
April 19, 2012 --
Forty years ago this week, the crew of Apollo 16 captured this image of Earth rising above the lunar landscape. The Apollo missions enabled humanity to see for the first time our planet as it appears from space. As Apollo 13 commander Jim Lovell once said: “When I was orbiting the moon and could put my thumb up to the window and completely cover the Earth, I felt a real sense of my own insignificance. Everything I'd ever known could be hidden behind my thumb.” As we approach Earth Day on April 22, we look at the efforts of people throughout the ages to explore, understand and portray our world and its place in the Universe.
Trustees of the British Museum (image rotated
Babylonia Believed to be the earliest known representation of Earth, this stone tablet from Babylon shows the world as a disc, surrounded by a ring of water called the "Bitter River." The world is dominated by the area surrounding Babylon itself, and the Euphrates River bisects most of the inner circle. Unearthed in southern Iraq in the late 1800s, the tablet is housed in the British Museum.
Sixteenth-century interpretation of Ptolemy's
Celestial Spheres In his 2nd century treatise, the "Almagest," Claudius Ptolemy proposed an explanation for the apparent movement of stars and planets, in which Earth was central and immovable, and surrounded by, at progressively greater distances, the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn and a sphere of ‘fixed stars.’ This geocentric view of the cosmos did not meet its first real challenge until Copernicus proposed that the planets revolved around the Sun, and Galileo used his telescope to observe the phases of Venus.
Library of Congress, via the History Blog
Flat Earth The Greek philosopher Aristotle determined that Earth was spherical and not flat almost 2,500 years ago. The notion of a flat earth retained at least a few die-hard devotees for a surprisingly long time. For example, this 1893 map by Orlando Ferguson, recently acquired by the Library of Congress, cites “Scripture that condemns the globe theory” and promotes a book that “knocks the globe theory clean out.”
ANALYSIS: What if Earth Were a Cube?
De Costa, B.F. (September 1879). "The Lenox G
Lenox Globe It is popularly believed that ancient cartographers filled in unknown and unexplored areas of the world with the phrase ‘Here be dragons’. In fact, only one known ancient map – the so-called Lenox Globe, which is believed to date to around 1510 - displays the phrase ‘HC SVNT DRACONES’, from the Latin “hic sunt dracones.” (The phrase is written near the equator on the eastern cost of Asia.) Some nineteenth-century writers, however, believed that it referred, not to dragons, but to the ‘Dagroians’, a people who “feasted upon the dead and picked their bones.”
PHOTOS: Sea Monsters Real & Imagined
Image Database of the Kano Collection, Tohoku
Terra Australis Incognita In this copy of a 1602 map that was created on behalf of China’s Wanli emperor by Italian Matteo Ricci and collaborators, the familiar outlines of most of the world’s continents are coming into shape, although obviously many details remain unfinished. To the map’s makers, however, the likes of Australia, New Zealand and Antarctica are not even figments of the imagination, replaced instead by an enormous southern landmass. The notion of an unknown southern land – a terra australis incognita - was first mooted by Aristotle in 322 BCE; not until 1820 did Fabian von Bellingshausen become the first man to see the Antarctic continent.
South Pole For centuries, gaps in maps were filled by explorers who set out across land and sea, often at immense personal risk. The true nature of “Terra Australis” had long been established by the time Robert Falcon Scott and comrades stood at the South Pole on Jan. 17, 1912; but existing knowledge could not diminish the terrible toll the conditions exacted on the men. “Great God!” wrote Scott in his journal, “this is an awful place.” All five members of Scott’s polar team died before they could reach their base camp.
PHOTOS: Forgotten Discoveries of Scott's Antarctica
Moscow at night Time and technology have enabled us to explore, not just across the surface of the globe or even beneath its waves, but from on high. Here, Moscow is seen at night from the International Space Station, flying at an altitude of approximately 240 miles on March 28, 2012. A solar array panel for the space station is on the left side of the frame. The Aurora Borealis, airglow and daybreak frame the horizon.
Pale Blue Dot In contrast to earlier suppositions about our place in the firmaments, we know now that our globe is not at the center of the cosmos, and that other celestial bodies are not attached to interlaced spheres that rotate around us. We are but one world among many, in one solar system among many, in one galaxy among many. In this image, taken by the Voyager I spacecraft from a distance of 4 billion miles, Earth is but a speck – a pale blue dot – in the cosmic night.
NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring
Blue Marble If satellite images of Earth now seem almost routine, they never lose their ability to enthrall. This picture of the western hemisphere was captured on January 25 by NASA’s latest Earth observation satellite, Suomi NPP. By February 1, it had registered over 3 million views on Flickr – testament to the beauty and fascination of our Blue Marble.
PHOTOS: Earth's Blue Marble Beauty
The proportion of carbon dioxide in the atmosphere is set to break 400 parts per million this month, levels not seen in 3 million years, according to one of the best climate records available.
The Keeling Curve, a daily record of atmospheric carbon dioxide, has been running continuously since March 1958, when a carbon dioxide monitor was installed at Mauna Loa volcano in Hawaii. On its first day, the observatory measured a carbon dioxide concentration of 313 parts per million (ppm). That number means there were 313 molecules of carbon dioxide in the air for every 1 million air molecules.
The number continued to climb through May 1958 and then slowly started to drop, reaching a minimum in October that year. This maximum-minimum pattern, repeated seasonally, reveals how trees withdraw carbon dioxide from the air in summer to grow and then release it through dead, decaying leaves and wood in the winter.
But humans release carbon dioxide into the air, too, by burning fossil fuels. This activity has caused the Keeling Curve to creep ever upward since 1958: The lows get a little higher each year, as do the highs. (The Reality of Climate Change: 10 Myths Busted)
Because carbon dioxide typically peaks in May, researchers are expecting the Keeling Curve to break a milestone of 400 ppm this year. (If not, the number will almost certainly be reached in May 2014.) As of May 1 of this year, the last day data was available, the Mauna Loa observatory recorded 399.39 ppm of carbon dioxide in the air.
There will be no huge atmospheric or climatic shift once carbon dioxide hits 400 ppm, but the milestone has symbolic significance, said Michael Mann, a climate scientist at Pennsylvania State University.
"It is a reminder of just how uncontrolled this dangerous experiment we're playing with the planet really is," Mann told LiveScience.
What 400 ppm means
In the 1,000 years that occurred before the Industrial Revolution of the 18th century, atmospheric carbon dioxide held steady at around 270 to 280 parts per million.
Scientists believe that the most recent period to reach 400 ppm was the Pliocene Epoch, between 5 million and 3 million years ago, according to the Scripps Institution of Oceanography, which keeps track of the Keeling Curve.
Back then, it was a different world. Global average temperatures during the period were between 5.4 and 7.2 degrees Fahrenheit (3 to 4 degrees Celsius) higher than today, and sea level was as much as 131 feet (40 meters) higher in some places. Even the least-affected regions saw sea levels 16 feet (5 meters) higher than today's.
A major difference between then and now, though, is the speed at which carbon dioxide is rising today. Typically, in the last 40 to 50 years, the Keeling Curve shows increases of 2 to 2.5 ppm a year, Mann said. In the 1950s and 1960s, carbon dioxide increased by less than 1 ppm each year, according to Scripps.
"We're on course for more than 450 ppm in a matter of decades if we don't get our fossil fuel emissions under control quite soon," Mann said.
More from LiveScience:
Images of Melt: Earth's Vanishing Ice
Earth in the Balance: 7 Crucial Tipping Points
8 Ways Global Warming Is Already Changing the World
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