by OK, a couple of quick points. This is just the surface temperature of the earth. Since the sun’s light only hits the surface and the earth radiates from the surface, this ignores any interactions with the very hot molten core.
Also note that this is a bit colder than that actually Average temperature of the earth (13.9 C) – a difference of 27.1 degrees C. This is because the earth is not actually bare rock. Instead, we have a great atmosphere that protects us from what life would be like if the world were actually that cold.
What would the earth look like at this temperature? Well, there are already places on Earth that are much colder, many of them in Antarctica where it can get below -90C. And while few scientists live on bases in Antarctica, there are other places in the Yukon, Alaska, and Siberia that are permanently settled and where temperatures can drop below -60C. So we shouldn’t assume that a colder Earth would be uninhabitable for humans or other life forms based on temperature alone, but most of them would likely cluster towards the warmer parts of the Earth. (Remember that -13.2 degrees Celsius is an average, so just like on Earth today, the poles would be colder than the equator. Antarctica and the Arctic would both be much much colder than they are now.)
And because an average of -13.2C means more of the planet would be below freezing (0C), much more of the water would be ice. However, locations slightly above average could have liquid water depending on atmospheric pressure.
Surprisingly, you would still need a fridge for your food and drinks. However, this fridge wouldn’t keep things cold, it would insulate them from the outside temperature to prevent stuff from freezing.
Earth would still be warmer than Mars, which has an average of about −63°C. But Mars has some other issues that make it not so pleasant for humans. The atmosphere is super thin and contains very little oxygen. And without an atmosphere, Earth would have this problem too. Life forms here would have evolved without oxygen – and humanlike visitors would need some sort of spacesuit for protection and breathing.
Luckily for us earthlings, we actually have an atmosphere. It consists mainly of nitrogen, but also contains a lot of oxygen and contains 0.04 percent by volume of carbon dioxide. The carbon dioxide, along with water vapor, absorbs infrared radiation emitted by the Earth’s surface, keeping things at a temperature we can handle – for now.
But carbon dioxide is a growing problem. Too much means the atmosphere will reach even higher temperatures, leading to all the potential problems of climate change, including catastrophic glacier melt, sea level rise and extreme weather. That’s why the Paris Climate Agreement is an international target to keep the warming line at 1.5 degrees Celsius above pre-industrial levels – and the bad news is that the past nine years have been the hottest on record. If temperatures continue to rise, the earth will no longer be perfect for humans – or for many of the other creatures on it.
