The image above is a series of real photographs of Neptune, taken with the Hubble Space Telescope. Dr. Laurence Sromovsky et al. from University of Madison-Wisconsin has calculated that this is a 40% increase in brightness.

On Earth, weather is driven by energy from the sun as it heats the atmosphere

NEPTUNE: Neptune has become 40 percent brighter in infrared since 1996, and is fully 100-percent brighter in certain areas. Also, Neptune’s moon Triton has had a “very large percentage increase” in atmospheric pressure and temperature, comparable to a 22-degree Fahrenheit increase on Earth.

On Neptune, the Sun is 900 times dimmer and scientists have yet to understand how Neptune's weather-generating machinery can be so efficient. "It's an efficient weather machine compared to Earth," said Sromovsky. "It seems to run on almost no energy."…

PLUTO: As of September 2002, Pluto has experienced a 300-percent increase in its atmospheric pressure in the last 14 years, while also becoming noticeably darker in color.