As 2015 comes to a close, Mongabay is looking back at the year that was. This year saw President Obama reject the Keystone pipeline as historic droughts and a vicious wildfire season wracked the western US and Canada. The world committed to climate action in Paris as Southeast Asia was choking on the worst Indonesian haze in years, Shell aborted its plans to drill in the Arctic for the “foreseeable” future, and ExxonMobil is being investigated for lying to the public about climate risks. Here, in no certain order, are the top 15 environmental stories of 2015.

The current strong El Niño brewing in the Pacific Ocean shows no signs of waning, as seen in the latest satellite image from the U.S./European Ocean Surface Topography Mission (OSTM)/Jason-2 mission. 

El Niño 2015 has already created weather chaos around the world. Over the next few months, forecasters expect the United States to feel its impacts as well. 

The latest Jason-2 image bears a striking resemblance to one from December 1997, by Jason-2's predecessor, the NASA/Centre National d'Etudes Spatiales (CNES) Topex/Poseidon mission, during the last large El Niño event. Both reflect the classic pattern of a fully developed El Niño.

LSU paleoclimatologist Kristine DeLong contributed to an international research breakthrough that sheds new light on how the tilt of the Earth affects the world's heaviest rainbelt. DeLong analyzed data from the past 282,000 years that shows, for the first time, a connection between the Earth's tilt called obliquity that shifts every 41,000 years, and the movement of a low pressure band of clouds that is the Earth's largest source of heat and moisture -- the Intertropical Convergence Zone, or ITCZ.

"I took the data and put it through a mathematical prism so I could look at the patterns and that's where we see the obliquity cycle, that 41,000-year cycle. From that, we can go in and look at how it compares to other records," said DeLong, who is an associate professor in the LSU Department Geography & Anthropology.

The solar system might be a lot hairier than we thought.

A new study publishing this week in the Astrophysical Journal by Gary Prézeau of NASA's Jet Propulsion Laboratory, Pasadena, California, proposes the existence of long filaments of dark matter, or "hairs."

Dark matter is an invisible, mysterious substance that makes up about 27 percent of all matter and energy in the universe. The regular matter, which makes up everything we can see around us, is only 5 percent of the universe. The rest is dark energy, a strange phenomenon associated with the acceleration of our expanding universe.

Asteroid 2003 SD220 will safely fly past Earth on Dec. 24 at a distance of 6.8 million miles (11 million kilometers). Scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, have generated the highest-resolution images to date of this asteroid using the Deep Space Network's 230-foot (70-meter) antenna at Goldstone, California. The radar images were acquired between Dec. 17 and Dec. 22, when the distance to this near-Earth object (NEO) was narrowing from 7.3 million miles (12 million kilometers) to almost the flyby distance. 

"The radar images data suggest that asteroid 2003 SD220 is highly elongated and at least 3,600 feet [1,100 meters] in length," said Lance Benner of JPL, who leads NASA's asteroid radar research program. "The data acquired during this pass of the asteroid will help us plan for radar imaging during its upcoming closer approach in 2018."

Asteroid 2003 SD220 will safely fly past Earth on Dec. 24 at a distance of 6.8 million miles (11 million kilometers). Scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, have generated the highest-resolution images to date of this asteroid using the Deep Space Network's 230-foot (70-meter) antenna at Goldstone, California. The radar images were acquired between Dec. 17 and Dec. 22, when the distance to this near-Earth object (NEO) was narrowing from 7.3 million miles (12 million kilometers) to almost the flyby distance.

Fuel economy is at record highs and carmakers have surpassed strict greenhouse gas emissions standards for the third straight year, according to the Environmental Protection Agency, which released a pair of annual reports about the U.S. fleet of cars and trucks Wednesday.

Overall, fuel economy for vehicles in the U.S. did not budge from last year's record high of 24.3 miles per gallon, the EPA says. The figure includes a new high of 20.4 mpg for trucks, vans and SUVs from model year 2014.

A survey of 10 hot, Jupiter-sized exoplanets conducted with NASA's Hubble and Spitzer space telescopes has led a team to solve a long-standing mystery -- why some of these worlds seem to have less water than expected. The findings offer new insights into the wide range of planetary atmospheres in our galaxy and how planets are assembled.

Of the nearly 2,000 planets confirmed to be orbiting other stars, a subset of them are gaseous planets with characteristics similar to those of Jupiter. However, they orbit very close to their stars, making them blistering hot.

Their close proximity to the star makes them difficult to observe in the glare of starlight. Due to this difficulty, Hubble has only explored a handful of hot Jupiters in the past. These initial studies have found several planets to hold less water than predicted by atmospheric models.

Astronomers harnessing the combined power of NASA's Hubble and Spitzer space telescopes have found the faintest object ever seen in the early universe. It existed about 400 million years after the big bang, 13.8 billion years ago.

The team has nicknamed the object Tayna, which means "first-born" in Aymara, a language spoken in the Andes and Altiplano regions of South America.

Though Hubble and Spitzer have detected other galaxies that are record-breakers for distance, this object represents a smaller, fainter class of newly forming galaxies that until now had largely evaded detection. These very dim objects may be more representative of the early universe, and offer new insight on the formation and evolution of the first galaxies.

Industrial-scale batteries, known as flow batteries, could one day usher in widespread use of renewable energy—but only if the devices can store large amounts of energy cheaply and feed it to the grid when the sun isn’t shining and the winds are calm. That’s something conventional flow batteries can’t do. Now, researchers report that they’ve created a novel type of flow battery that uses lithium ion technology—the sort used to power laptops—to store about 10 times as much energy as the most common flow batteries on the market. With a few improvements, the new batteries could make a major impact on the way we store and deliver energy.