Why is there a runaway greenhouse effect on planet Venus?

The runaway greenhouse effect on Venus can be blamed on carbon dioxide/CO2, which constitutes for about 96% of the planet’s atmosphere. The 250 kilometers thick and gaseous envelope of this peculiar planet has enough carbon dioxide to fill more than 1 billion fire extinguishers. Composed of molecules that have one atom of carbon and two atoms of oxygen, carbon dioxide is a relatively strong greenhouse gas, while nitrogen, which is the most abundant molecule in the Earth’s atmosphere, is not. However, the abundance of carbon dioxide on Venus does not mean that, as a whole, it is richer in CO2 than the planet Earth. The carbon dioxide found in the Earth’s atmosphere has largely been consumed or even removed by various plants or locked up in deposits of limestone. Since Venus is considered an inhabitable planet, it doesn’t have any plants that can consume carbon dioxide.

Moving around the Sun to perform a revolution at an average distance of 108.2 million kilometers, the planet Venus is a truly smoldering greenhouse, where no astronaut or any other living being would survive in its hellish environment. At 470 degrees Celsius, the surface temperature of Venus is usually more than enough to melt lead and even has 100 degrees left over to make any form of steel hot. At an altitude of about 49 kilometers, where the dense clouds on the planet begin to form, the temperature drops to only 70 degrees Celsius. However, at about 68 kilometers above Venus, the temperature drops drastically to nearly 0º Celsius, which is quite strange considering the entirety of the planet is considered hot.

It was during the 1960s when earthbound radars indicated and calculated the piping hot Venusian environment, although there were many scientists who were skeptical about the planet’s temperature at that time. The result, however, was verified with the help of the increasingly sophisticated Venus space probes launched a decade later. The planet Venus, it turns out, is a greenhouse planet that doesn’t have a keeper to maintain balance in its composition, and it could also be said that its thermostat has broken down long in its past. Because of how the planet is so close to the Sun, the sunlight it receives comes in as short-wave radiation that heats up Venus’ atmosphere as well as its surface, although the heat is usually trapped within the planet (see the diagram above). Very little of the heat that it gets from the Sun is reflected, and the heat that it reflects is turned in the form of long-wave infrared that escapes through the dense atmosphere of carbon dioxide.

The process where heat cannot escape the planet and forces its atmosphere to remain hot has been called the runaway greenhouse effect, which somehow continues to operate without being regulated by any balances or systems. It is a self-feeding machine that requires no further input of CO2 to keep going. In the present time, our own planet seems to be heading for a similar disaster wherein the temperature wouldn’t cool down. Unless we immediately put an end to excessive carbon dioxide emissions, the Earth will eventually go the way Venus went in the past.

Why is Venus hotter than Mercury?

Our science class would often tell you that Venus is the hottest planet on the solar system; however, Mercury is the nearest on to the Sun, so why is Venus still hotter? The answer to that particular question lies in the runaway greenhouse effect, as most of the heat that Venus gets from the Sun cannot escape. Mercury does not have a runaway greenhouse effect, mainly because its atmosphere doesn’t have carbon dioxide, which absorbs heat and infrared gases. The runaway greenhouse effect on Venus creates a sulfuric acid haze above its surface, and the haze is what traps the heat on the planet. However, scientists believed that Venus wasn’t the hottest planet millions of years ago, and it is theorized that the planet had the same temperature as today’s Earth. As the Sun became bigger and bigger, the sunlight and heat energy that it provides for the planets nearer to it is becoming too much for both Mercury and Venus to control, hence the reason why it has become an uninhabitable planet in the past.