(ORDO NEWS) — The Earth is said to be in an ideal “Goldilocks Zone” away from the Sun (not too cold and not too hot), allowing life to thrive on the planet’s surface.
But Earth’s mild temperatures would not be possible without the greenhouse effect, which traps solar energy on the Earth’s surface and keeps the planet warm.
The greenhouse effect is caused by the Earth’s atmosphere. Visible sunlight as well as invisible ultraviolet and infrared waves can penetrate the gaseous layer that covers our world.
Approximately 70% of these energy beams are absorbed by Earth’s oceans, land and atmosphere, while the remaining 30% are immediately reflected back into space.
As the planet’s surface heats up, it releases some of this infrared energy that it has absorbed. But this energy does not return back from the Earth’s gaseous atmosphere.
Instead of escaping back into space, the infrared energy is distributed across our planet and therefore raises the overall temperature of the Earth.
This is similar to how man-made glass greenhouses work, trapping heat from the sun and keeping plants warm in winter.
Without an atmosphere, our world would be as cold as the lifeless moon, which has an average temperature of -153 degrees Celsius. Due to the greenhouse effect, the Earth maintains an average temperature of about 15°C.
Greenhouse gases and climate change
Greenhouse gases include several naturally occurring molecules – such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone – as well as several industrial ones, such as chlorofluorocarbons.
Over the past century, human activities such as the burning of fossil fuels, intensive agriculture, animal husbandry and land clearing have dramatically increased the concentrations of greenhouse gases in the Earth’s atmosphere to the point that they are changing our planet’s climate.
Since the mid-20th century, human-produced greenhouse gases have become the most significant driver of climate change, according to the US Environmental Protection Agency.
Atmospheric carbon dioxide levels have increased by more than 40% since the start of the industrial revolution, from about 280 parts per million (ppm) to over 400 ppm today.
According to the Institute of Oceanography. Scripps in San Diego, the Earth’s atmosphere last had similar concentrations of carbon dioxide during the Pliocene epoch, 3 to 5 million years ago.
This is at least 2.8 million years before modern humans began to roam the planet. Fossils show that forests grew in the Canadian Arctic during the Pliocene, and savannahs and woodlands spread across the Sahara Desert.
While some people still doubt the reality of anthropogenic climate change, the evidence is overwhelming. Since the 1850s, global mean surface air temperatures have risen by about 0.8°C, and ocean temperatures are at their highest levels on record.
Increases in greenhouse gas emissions over the coming decades are expected to harm human health, exacerbate droughts, raise sea levels, and reduce national security and economic well-being around the world.
Greenhouse effect on other planets
Since the greenhouse effect is a natural process, it also affects other bodies in the solar system. In some cases, this gives a warning about how things can go wrong.
A perfect example of this is Venus, which is about the same size as the Earth and not much closer to the Sun.
Billions of years ago, when the sun was cooler and dimmer, Venus might have had a temperate climate that could have allowed liquid oceans to exist on its surface.
Simulations show that average temperatures on the planet have ranged from 20°C to 50°C for about 3 billion years, potentially even allowing Venus to support life.
But as the sun ages and becomes brighter, excess water vapor enters Venus’s atmosphere. This powerful greenhouse gas traps heat and raises the temperature of the planet’s surface, leading to a vicious cycle in which rising temperatures lead to more water vapor in the atmosphere, warming the world even more – a process known as the runaway greenhouse effect.
As Venus’ oceans evaporated, its planetary plate tectonics ground to a halt as there was no water left to help “lubricate” the shifting geological plates.
The atmosphere, which was getting thicker and thicker, could have slowed down Venus’s rotation period, leading to its strangely slow rotation, in which a day passes in two years.
The dense cloud cover has also led to hellish surface temperatures on present-day Venus, averaging 370°C – hot enough to melt lead.
“I think Venus is an important warning to us: the greenhouse atmosphere is not just a theory,” Ellen Stofan, director of the Smithsonian National Air and Space Museum and former NASA chief scientist, said earlier.
On Mars, greenhouse gases such as water and carbon dioxide may have been released during ancient collisions.
Some scientists suggest that this could raise the overall temperature of Mars, enough for the planet to have liquid water on its surface for significant periods of time.
However, because Mars is smaller than Earth, its gravitational pull is weaker. Consequently, these gases escaped into space and eventually the Red Planet returned to the cold and dry world that it is today.
Saturn’s distant moon Titan, which has a dense nitrogen atmosphere with about a thousand times more methane than Earth, is also experiencing a greenhouse effect.
Thanks to data from the European Space Agency’s Huygens probe, which landed on Titan in 2005, researchers are gaining a better understanding of how methane absorbs shortwave infrared radiation and are using that information to develop models of our planet’s climate change.
The greenhouse effect is also expected to warm the worlds of other star systems. Many astronomers talk about a narrow habitable zone around stars – a region where a planet would be at the perfect distance to support liquid water on its surface. For our star, this region extends from about 0.95 to 1.4 AU.
However, other scholars argue that such models need to be extended. For example, a thick atmosphere of molecular hydrogen, which is a powerful greenhouse gas, could potentially give the planet an acceptable temperature even if it is 15 times farther from the Sun than the Earth.
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