A long, long time ago, our home planet more resembled Hoth, the ice planet in the Star Wars universe. While Earth was not entirely blanketed in glaciers, large sheets of ice covered North America, Europe, and Asia. This was during the peak of the last ice age, about 20,000 years ago.
At that time, the average temperature of Earth was only about 5.5°C (10°F) lower than the middle 20th century. The atmospheric carbon dioxide level was 180 parts per million (ppm), less than half of the level today. More striking, the sea level was 400 feet (120 meters) lower than today.
For comparison… some present elevations above sea level:
- Raleigh, NC: 435 feet
- Richmond, VA: 166 feet
- Philadelphia, PA: 30 feet
But subtle changes in Earth’s orbit altered how the planet absorbed solar energy, and there was shuffling of ocean circulations. By themselves, these were not enough to drive Earth out of its glacial state. However, they did lead to an increase in atmospheric carbon dioxide to 280 ppm, warming Earth and helping make it the hospitable place we enjoy today, more along the lines of Endor, the forest moon where the Ewoks made their stand in Return of the Jedi.
Human emissions of greenhouse gases, like carbon dioxide, have increased dramatically over the last century, dwarfing the natural cycle. The concentration is at 400 ppm and climbing, which is the primary reason that the average global temperature has risen about 1°C (1.8°F) since pre-industrial times. This type of rise took several centuries to occur naturally, yet it has occurred in the last hundred years due to human activities.
While no one expects Earth to turn into the desert world of Tatooine (after all, that planet has two suns), further carbon dioxide emissions will create more planetary warming through the end of the century and beyond. The amount of warming will determine how much more ice is lost at the poles, and thus, how much further global sea levels will rise, with big differences for each degree of warming.
So. Have a nice day.