The Time of Winds

NAOC

Human-driven climate change is a serious threat to humanity. While climatologists continue to improve our understanding of its impact and consequences, they also look at nature-driven climate change going back millions of years. Whereas for human climate change, we only have a case study of one planet, for natural climate change we have a case study of two planets. Like Earth, Mars has undergone significant climate change in the past. We know, for example, that young Mars was both warm and wet. Its climate changed over a billion years to become the cold and dry world we know today. Even more recently, there have been shifts in the Martian weather, as noted in a recent study in Nature.¹

The data comes from the Tianwen-1 mission of the China National Space Administration (CNSA). This mission included an orbiting satellite, a lander, and a rover named Zhurong. Using both orbital imaging and on-site observations, the mission looked at the orientation and structure of dunes on Mars. As presented in this new paper, dunes at the site of the rover landing show a shift in winds over time. About 400,000 years ago the winds in the area shifted by about 70 degrees.

This wasn’t just a casual shift, such as an unusual breeze from a different direction, but a sustained shift. On Earth in the northern hemisphere, winds generally blow from west to east. Imagine if that changed in a short amount of time to start blowing from north to south. You can see how that would dramatically change the weather in your area. Thus, this research shows that the climate of Mars changed dramatically about 400,000 years ago.

Of course, the real question is what might have caused it. The team thinks it was likely due to changes in the axial tilt of Mars. Just like Earth, the seasons of Mars are caused by the fact that Mars has an axial tilt. On geological scales, that tilt can change by tens of degrees, which would change the Martian seasons. A similar thing has happened on Earth throughout history, where small shifts in Earth’s orbit and axial tilt have shifted the amount of sunlight the Earth gets in a year. This pattern of shift is known as the Milankovitch cycle.

The weather of Earth and Mars are fairly similar. Although Earth is warm and wet, and Mars cold and dry, they both have weather driven by wind and sunlight, and both seasons and climate cycles. By better understanding how the climate of Mars has changed over time, we can better understand Earth’s long-term climate cycles. This not only helps climate scientists separate nature-driven changes from human-driven human ones, but it could also help them find better ways to address our climate challenges.