Computer model explains warm Arctic of 70 million years ago

Scientists in Japan have used a computer model^*1 to study the climate^*2 of the Earth about 70 million years ago. At that time, the Arctic, the area around the North Pole, was very warm. The new study shows that the model can explain this warm Arctic better when it includes changes in the tilt^*3 of the Earth and in its path around the Sun.

The team was Ayako Abe and Wing Le Chan of the University of Tokyo, and Taro Higuchi and Ryota Oishi of the Institute of Science Tokyo. Both are universities in Tokyo, the capital of Japan.

Scientists know about the warm Arctic from fossils^*4. The fossils show that the Arctic 70 million years ago was more than 10 degrees Celsius warmer than in pre-industrial times^*5.

The team used a computer model called MIROC. They ran it on a supercomputer^*6. They used a map of the continents^*7 from 70 million years ago. Then they changed two things in the model: the amount of carbon dioxide^*8 in the air, and the tilt and orbit^*9 of the Earth.

The results showed that the tilt of the Earth mattered much more 70 million years ago than it does today. When the tilt of the Earth grew, the far north became several times warmer than it would today. The scientists think there are two reasons for this. At that time, there were no large ice sheets^*10 on the land, like the ones we have today. Also, there was more land in the far north than there is now.

With these changes, the model matched the fossil evidence better than earlier results did.

The study was published on July 22 in Geophysical Research Letters, a science journal^*11.

1. *1 computer model: a computer program that copies how something in the real world works
2. *2 climate: the usual weather of a place over many years
3. *3 tilt: how much something leans to one side instead of standing straight
4. *4 fossils: the remains of plants or animals from a very long time ago, kept in rock
5. *5 pre-industrial times: the time before people built many factories, about 250 years ago
6. *6 supercomputer: a very big and very fast computer
7. *7 continents: the biggest pieces of land on Earth, like Asia or Africa
8. *8 carbon dioxide: a gas in the air that holds heat and makes the Earth warmer
9. *9 orbit: the path that a planet takes around the Sun
10. *10 ice sheets: very thick ice that covers a very large area of land
11. *11 journal: a magazine where scientists print their studies