Around 50 million years ago, the Earth's polar regions used to be filled with lush forests and diverse creatures instead of miles-thick ice sheets. In a recent study, scientists investigated the role of invisible clouds in speeding up the warming of the poles.
Polar Warming Estimates
During the Eocene, the concentration of greenhouse gases was much higher than today, causing a natural period of global warming. One of these gases is methane, 80 times as potent a planet-warmer as carbon dioxide. Methane was especially high during the Eocene, increasing temperatures and allowing animals and plants to migrate towards the North and South Pole.
Today, the Arctic region is warming up to four times faster than the rest of the world due to gnarly feedback loops. As ice melts, it exposes darker water or land underneath, which heats up faster and leads to more warming and more melting. This phenomenon is referred to as polar amplification.
READ ALSO: Why Is the South Pole Warming Faster Than the Rest of the World? Details Explained in Study
Threat from Invisible Clouds
When methane is in the atmosphere, it oxidizes and produces water vapor. The water vapor travels upward into the stratosphere and helps form polar stratospheric clouds (PSCs).
Conventional predictive climate models usually underestimate polar warming since the observations tend to be more grim than the models suggest. This disagreement is even larger for past climates like the Eocene, and scientists believe that PSCs could be the missing piece that explains why this happened.
PSCs are currently less common in the Arctic compared to Antarctica. With the increase in greenhouse gas emissions, experts wonder whether these clouds could be more prevalent over both poles in the future.
In the study "Early Eocene low orography and high methane enhance Arctic warming via polar stratospheric clouds," researchers suggest that methane may have been heating the poles subtly by creating a blanket of invisible clouds that trap warmth against the surface. This could have boosted polar warming by 7 degrees Celsius during the coldest winter months.
Clouds have always been a major source of uncertainty in climate science, but they are not always included in simulations. Given the limits of computing power, existing climate models can only handle so much detail.
In the polar regions, PSCs appear between 9.3 and 15.5 miles (15 and 25 kilometers) in the sky during cold winter. They are usually invisible but can also be seen when the Sun is at the right angle. Like other high clouds, PSCs form an insulating layer over the poles, preventing rapid temperature decline.
Continental shift in the past 50 million years has changed the Earth's topography and atmospheric circulation, which thinned this blanket. PSCs still form and trap heat but are not as abundant as before. However, if man-made activities continue to release methane into the atmosphere, more stratospheric water vapor will be supplied to form more invisible clouds.
Understanding how the Eocene stratosphere affects modern climate can help scientists understand what to expect in the future. As described by climate scientist Deepashree Dutta from the University of Cambridge, these past climates can provide a testbed for checking current climate models. As a result, improved models can be a better tool for predicting the transformations of polar ecosystems.
RELATED ARTICLE: Marine Species are Moving Towards the Poles Six Times Faster than Terrestrials Amid Climate Change: Here's Why
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