Venus has a climate that has varied over time due to the interplay between tectonic activity in its interior and atmospheric changes. It is closer to the Sun than Earth, resulting in much higher temperatures.
Earth and Venus were almost the same size and composition , yet their evolutionary paths diverged, resulting in two entirely different planets. Has Venus experienced climate change ? This question also prompts us to consider climate change on Earth.
Venus, the planet hell
The surface temperature of Venus is around 460°C, compared to our average of 15-17°C on Earth . This temperature is so high that it makes rocks glow to the naked eye. The planet is dominated by a lethal greenhouse effect, maintained by an atmosphere whose main component is carbon dioxide. There is also no liquid water on the planet; it would obviously evaporate since the boiling point of water is 100°C.
In addition to the above, the planet's conditions create an atmospheric pressure almost double that of Earth. Its clouds, instead of being composed of water vapor, are composed of sulfuric acid.
Until recently, little was known about the evolution of Venus because its sulfuric acid clouds obscured terrestrial processes such as volcanism and tectonics. However, over the past 56 years, thanks to 22 space probes that have photographed, explored, analyzed, and landed on Venus, we have learned much more about it. These probes have been crucial in understanding climate change on Venus.
The probe photographs reveal that Venus is a planet that has experienced enormous volcanic eruptions, and that these eruptions are almost certainly still active. These discoveries lead us to consider just how unique Earth's climate is, as we can ask ourselves why, if very similar forces were at play in the formation of both planets, Earth experienced entirely different effects and an evolutionary path completely diverging from the other.
Scientists attribute this disparate evolution to our privileged position in the solar system and our location relative to the Sun. What use can we get from knowing the climate evolution of other planets if we don't live on them? The answer is simple: with the increasing volume of waste, industrial society, and greenhouse gas emissions into the atmosphere, we are modifying our climate. If we can identify which factors influence climate on other planets, we can understand the natural and anthropogenic mechanisms that alter our own.
Climate and geology of Venus vs Earth
One of the causes of Earth's climate variability lies in the nature of its atmosphere, a product of the continuous exchange of gases between the crust, mantle, ocean, polar ice caps, and outer space. Geothermal energy, the driving force behind geological processes, also fuels the evolution of the atmosphere. This geothermal energy is released primarily through the decay of radioactive elements in the Earth's interior. However, explaining heat loss in solid planets is not so simple. The two main mechanisms involved are volcanism and plate tectonics.
As far as the Earth is concerned, its interior has a conveyor belt system associated with plate tectonics. Whose continuous recycling of gases has exerted a stabilizing force on the Earth's climate. Volcanoes pump gases into the atmosphere; the subduction of lithospheric plates return it to the interior. While most volcanoes are associated with plate tectonic activities, there are notable volcanic structures (such as the Hawaiian Islands formation) that have formed "hot spots" independent of the contours of the plates.
Craters and plate tectonics
What happened on Venus? Plate tectonics, if it plays a role, will be on a limited scale; at least in the recent past, heat was exchanged through the eruption of vast basaltic lava plains and, later, through the volcanoes that formed on top of them. Understanding the effects of volcanoes is a necessary starting point for any approach to the planet's climate.
The scarcity of impact craters on Venus, despite its atmosphere being sufficient to protect the planet from small impacts, highlights the lack of large craters. This is also evident on Earth. The action of wind and water has eroded older craters. However, the surface of Venus is so hot that it prevents the existence of liquid water; furthermore, surface winds are quite weak. Without eruptions, the processes that alter and, in the long run, erase impact craters will be volcanic and tectonic activity.
Most of the craters on Venus appear recent. Where did the ancient craters go, if most of the ones that remain have not been disturbed? If they have been covered by lava, why aren't more partially covered craters visible, how did they disappear without randomly losing their original placement?
The most widely accepted theory by the scientific community is that widespread volcanism erased most of the impact craters and created extensive volcanic plains 800 million years ago , followed by a moderate level of incessant volcanic activity to this day.
Forms of water on the surface of Venus
First, we can distinguish several curious linear structures, reminiscent of soils sculpted by water. They are the very image of our rivers and floodplains. Many of these structures end in outlet channels similar to deltas. The extreme aridity of the environment makes it unlikely that water carved out these features.
So what causes them? Perhaps calcium carbonate, calcium sulfate, and other salts are to blame. Lavas laden with these salts melted at temperatures ranging from a few tens to a few hundred degrees higher than current surface temperatures on Venus. In the past, a slightly higher surface temperature could have released fluid, salt-rich lava onto the surface, the stability of which would explain the sculpting action of the features we see today.
Evidence of the change in climate of Venus
Greenhouse effect and gas concentration
We must keep in mind that greenhouse gases allow sunlight to reach Venus's surface, but block the emitted infrared radiation . Carbon dioxide, water, and sulfur dioxide each absorb a particular band of wavelengths in the electromagnetic spectrum. Without these gases, solar and infrared radiation would balance, resulting in a surface temperature of around 20 degrees Celsius. This information is crucial for understanding how Venus interacts with other planets.
The water and sulfur dioxide that volcanoes release into the atmosphere are then removed. Sulfur dioxide reacts well with carbonates on the surface, while ultraviolet solar radiation dissociates water.
Cloud cover and temperature
Sulfuric acid clouds vary in thickness after a global series of volcanic eruptions. Initially, the clouds thicken as water and sulfuric acid are ejected into the air. They then thin as the concentration of these gases decreases. After about 400 million years from the start of volcanism, the acidic clouds are replaced by thin, high-altitude water clouds.
Climate variations on Venus
Cracks and folds crisscross the planet. Some of these configurations, at least the wrinkled mountain ranges, may be related to temporal variations in climate. Theory shows that these strange and hostile environmental conditions are maintained due to complementary properties of the atmosphere's constituents. Water vapor, even in trace amounts, absorbs infrared radiation at wavelengths that carbon dioxide does not.
At the same time, sulfur dioxide and other gases block certain wavelengths. Taken together, these greenhouse gases make Venus's atmosphere partially transparent to incoming solar radiation but almost completely opaque to emitted infrared radiation. Consequently, its surface temperature is three times higher than it would be without an atmosphere. By comparison, Earth's greenhouse effect raises its surface temperature today by only 15% . If it is true that volcanoes roamed the surface of Venus 800 million years ago, they must have also released a massive amount of greenhouse gases into the atmosphere in a relatively short period.
A climate model of the planet has been developed that includes the release of gases from volcanoes, cloud formation, the loss of hydrogen in the upper layers of the atmosphere, and the reaction of atmospheric gases with surface minerals. A subtle interaction occurs among these processes, cooling the planet. Given these opposing effects, it is impossible to determine the impact of the injection of the two gases on Venus's global climate.
That is why, in conclusion, we can say that there was a , but we do not know to what extent the gases could have acted on its changes.