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Even so far, the carbon emissions of all mankind, the carbon dioxide in the earth’s atmosphere is much less than that of Venus, and the earth is farther from the sun. However, if carbon emissions continue to grow at the current rate, is it possible to reach the tipping point of causing the greenhouse effect to run out of control, making the earth unable to live in any form of life?
When sunlight enters the Earth’s atmosphere, some will be reflected back to space by clouds, some will be reflected by bright surfaces such as ice and snow, and some will be absorbed by land and oceans.
In order to maintain balance, the earth releases energy back into space in the form of infrared or long-wave radiation. Certain long-wave radiation is absorbed into the atmosphere by heat-trapping gases such as carbon dioxide.
This is the well-known greenhouse effect.
Read more: Climate explanation: what the earth will look like if we don’t emit greenhouse gases into the atmosphere
As we all know, in the past 250 years, the concentration of carbon dioxide has increased, causing the average surface temperature to rise.
One result of the increase in the concentration of carbon dioxide in the atmosphere is that as the atmosphere warms, it may contain more water vapor. Since water vapor itself is a greenhouse gas, it can have an amplifying effect.
Generally, as the surface temperature increases, the earth emits more long-wave radiation into space to maintain energy balance. But there is a limit to how much long-wave radiation can be emitted.
If the atmosphere is fully saturated with water vapor, the earth’s surface and lower atmosphere will warm up, but the emission of long-wave radiation cannot be increased further.
This is called a runaway greenhouse, which means that the earth will become fatally hot and cannot cool itself by radiating heat into space.
In the end, this is the fate of the earth. Billions of years from now, the sun will become brighter and grow into a red dwarf star. As the luminosity of the sun increases, the earth will become hotter and the ocean will evaporate.
The hot and steaming atmosphere will ensure that the Earth is as uninhabitable in its current life forms as Venus is today.
However, can we solve this situation in a shorter period of time through continuous carbon dioxide emissions? The good news may not be.
We are safe now
Previous studies have found that due to the different properties of water vapor and carbon dioxide as greenhouse gases, adding carbon dioxide to the atmosphere may not be enough to trigger a runaway greenhouse gas.
Since the first industrial revolution about 250 years ago, carbon dioxide in the atmosphere is currently about 416 parts per million (ppm), and now it is about 280 ppm.
In terms of geology, this is a very large increase that has occurred in a short period of time. However, given the available fossil fuel reserves, human carbon dioxide emissions are considered insufficient to trigger a runaway greenhouse.
The earth should stay away from runaway greenhouses that have developed at least another 1.5 billion years.
All the warnings above indicate that the models that scientists use to study the future climate are based on known conditions in the past. Therefore, it is difficult to predict how certain parts of the climate system will operate under extremely high greenhouse gas emission scenarios.
For example, clouds can reflect sunlight back into space, or they can capture the heat emitted by the earth. In a warming world, scientists still don’t know what role the cloud will play.
Read more: Looking forward to New Zealand temperatures returning to normal temperatures
As we know, although an out-of-control greenhouse will make the earth completely unsuitable for human habitation, the losses caused by only a few degrees Celsius of global warming are serious, so discounts should not be allowed.
Rising sea levels, increasing frequency and intensity of extreme weather events, threats to endangered species and unique ecosystems are just a few of the many reasons we must pay attention to.
The silver lining is that we (probably) don’t have to worry about becoming our neighbor Venus anytime soon.