06/24/2014

Ask a Scientist: Can Earth Become a Second Venus?

MIPT’s press office would like to present a new section on the institute’s website: Ask a Scientist. In this section, MIPT-based researchers will answer non-specialists’ questions about science.

The first question, “Can the greenhouse effect cause temperatures on the Earth to reach those found on Venus?”, was prompted by a recent article about a new infrared spectrometer, a unique device developed to control greenhouse gases on the Earth. Alexander Rodin, a leading author working in this area, answered this question:

All terrestrial planets are subjected to the greenhouse effect one way or another. On the Earth, it’s about 38 degrees, which is a huge value. Without the greenhouse effect neither the biosphere nor modern civilization could exist. The danger lies not in the greenhouse effect itself, but in its changes could it outpace the adaptation of ecosystems and the socio-economic environment.

In the Arctic zone, for instance, an increase in average temperatures of a few degrees can have very far-reaching consequences – from the destruction of economic infrastructure built on permafrost to direct military threats to the vast territories of our country, which have remained too remote and unattractive to external aggressors for centuries.

Despite the fact that carbon dioxide and methane are commonly referred to as greenhouse gases, the largest contribution to the greenhouse effect is made by water vapor – a polar asymmetric water molecule absorbs infrared radiation very efficiently in the vibrational-rotational spectral bands.* However, because the amount of water vapor in the atmosphere cannot exceed the saturation limit (excess amounts condense in the clouds and fall onto the surface as rain), water itself cannot regulate climate.

It’s akin to a modern car with power steering: the driver turns the steering wheel to the desired position, and the power unit turns the wheels until they reach a position corresponding to that of the steering wheel. In climate, carbon dioxide and, to a lesser extent, methane plays the role of the driver, and water acts as power steering. With temperatures growing, the pressure of saturated vapor also grows, and quite quickly, but on the surface of the Earth saturation occurs faster. It should also be noted that the atmosphere’s capacity to hold water is strictly limited.

The fundamental difference between Venus and the Earth is that when the concentration of water vapor in Venus’ atmosphere increases, temperatures grow faster than the saturation curve. That’s mainly due to its closer distance to the Sun. This means that, hypothetically speaking, the greater the absolute humidity of Venus’ air, the lower its relative humidity. If there were an ocean on Venus, it would evaporate completely, and the atmosphere would be heated up to such an extent that no precipitation would be possible.

We believe that Venus suffered a climate catastrophe, which is sometimes called the runaway greenhouse effect. The result was the planet’s almost complete loss of water, which literally vanished through the exosphere.

More precisely, at high temperatures water molecules dissociated into hydrogen and oxygen, and hydrogen atoms, having acquired escape velocity, left the planet’s gravity field. Heavier isotopes of hydrogen, in particular, deuterium, were lost at a much slower rate, resulting in an anomalously high ratio of deuterium to hydrogen, from 100 to 250 times higher than it is on the Earth. This discovery, made by a team of MIPT researchers and the Russian Space Research Institute, led by Anna Fyodorova, in cooperation with international colleagues, was one of the most significant results of the international mission “Venus Express.”

Does such a scenario threaten the Earth? Probably not. For that, a greater inflow of solar energy would be needed. However, it is possible to launch a variety of other, weaker mechanisms of positive feedback that are quite capable of, if not destroying the biosphere as a whole, at least seriously undermining our wellbeing.

For example, these days there is a broad discussion about the exchange of carbon dioxide between the atmosphere and the world’s oceans. Even a small increase in the average temperatures of the sea surface and accelerating convection in the water can lead to the release of carbon dioxide in amounts comparable to or greater than the anthropogenic impact. The degradation of ice in the polar regions reduces the albedo (reflectance coefficient) of our planet and, ultimately, increases the proportion of absorbed energy of solar radiation.
Only a careful study of these and many other, more subtle mechanisms as well as continuous monitoring of the global climate system can allow both individual countries and mankind as a whole to come up with an optimal development strategy for ensuring the preservation of our planet’s natural paradise conditions, the perpetuity of which is by no means guaranteed.

You are welcome to send questions on any science-related topics to press@mipt.ru, the subject being “Ask a Scientist.”

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