Every September, Arctic sea ice hits its minimum extent. Since the 1980s, that minimum has decreased by about 13% per decade.
In 1979, Arctic sea ice spanned about 2.7 million square miles (7 million square kilometers). By last month, the extent had dropped to 1.7 million square miles (4.3 million square kilometers). According to NASA data, this year has tied 2007 for the second-lowest sea ice extent on record. The worst year was 2012, when the ice shrank to under 1 million square miles (2.6 million square kilometers).
The decline is accelerating. Researchers at the European Space Agency have warned that the current rate of carbon emissions means we could see an ice-free Arctic in just decades.
The Northwest Passage, a sea route that connects the North Atlantic and Pacific Oceans, is often choked with sea ice, but in August 2016, it was nearly ice-free.
The Arctic is warming twice as fast as the rest of the planet, so a section of Northwest Passage has been open nearly every year since 2007.
Greenland's ice sheet is melting six times faster than it was in the 1980s.
An April study estimated that the Greenland ice sheet is sloughing off an average of 286 billion tons of ice per year. In 2012 alone, Greenland lost more than 400 billion tons of ice.
Two decades ago, the annual average was just 50 billion.
Antarctica's melting is also speeding up. In the 1980s, Antarctica lost 40 billion tons of ice annually. In the last decade, that number jumped to an average of 252 billion tons per year.
Together with Greenland's ice sheet, Antarctica contains more than 99% of the world's fresh water, according to the National Snow and Ice Data Center.
If both Antarctica and Greenland's ice sheets were to melt, that would lead sea levels to rise more than 200 feet.
Melting glaciers, coupled with warming oceans (because water, like most things, expands when heated), present a grave threat to coastal communities in the form of rising seas.
In the last 150 years, global sea levels have risen about 6 inches (15 centimeters). According to a recent report from the United Nations, sea levels are expected to rise by more than 3 feet by the end of the century.
The report found that by the end of the century, higher seas and flooding could displace or affect 680 million people who live in low-lying coastal zones, along with 65 million citizens of small island states.
Sea-level rise also increases the risk of flooding during high tides and storm surges.
During hurricanes and tropical storms, strong winds cause deadly and destructive storm surges — an abnormal rise in sea-level above the normal tide height.
As sea levels rise worldwide, that increases the amount of flooding storm surges can cause.
In September, Hurricane Dorian hit the Bahamas a Category 5 storm. With sustained wind speeds of 185 mph, Dorian brought up to 23 feet of storm surge in some areas.
Climate change also appears to be making hurricanes wetter and more sluggish.
Warming overall causes hurricanes to grow stronger and cause more devastation than they otherwise would because warmer air holds more water vapor, which enables tropical storms to unleash more precipitation.
Climate change is also causing hurricanes to move more slowly: Over the past 70 years or so, the speed of hurricanes and tropical storms has slowed about 10% on average, according to a 2018 study.
Hurricane Dorian was a prime example of this trend: After it made landfall, the storm stalled over the Bahamas for 24 hours, dumping 30 inches of rain and causing devastating flooding.
Dorian wasn't the only hurricane to stall in recent years. In 2018, Hurricane Florence hovered over a small region of North Carolina for more than 50 hours. The year before, Hurricane Harvey lingered over the Houston area for two days, plummeting the city with more than 60 inches of rain and causing an estimated $125 billion in damages.
Rising temperatures may also be linked to more frequent cold-weather snaps like the one that hit the US in January.
In general, a polar vortex is the term for the mass of low-pressure cold air that circulates in the stratosphere above the Arctic and Antarctic.
When the circulation of the polar vortex weakens, surges of frigid air splinter off and drift south. The freezing air is carried by the jet stream, a current of wind that extends around the northern hemisphere and divides the air masses in the polar region from those farther south.
But climate change may be altering the jet stream. Because temperatures are rising in the Arctic at double the rate of the rest of the planet, the difference between temperatures at the North Pole and continents at lower latitudes is decreasing. Less disparity in temperatures means less difference between air pressure levels, which weakens the jet stream. That can lead the jet stream to take longer, less direct paths.
If the jet stream wanders enough, that can disrupt the natural flow of the polar vortex.
The frequency of winter polar-vortex events has increased by up to 140% over the past four decades, a 2017 study found.
The January polar vortex forced 84 million Americans in the US Midwest and East Coast to contend with subzero temperatures. Some parts of Minnesota and Wisconsin saw windchill temperatures are as cold as minus 50 degrees Fahrenheit.
Temperature spikes are also linked to higher wildfire risk. This year, plumes of smoke that engulfed parts of Russia and Greenland were big enough to see from space.
More than 13.5 million acres of Siberia burned between June and August. All told, the European Union's Copernicus Atmosphere Monitoring Service said its team observed more than 100 intense and long-lasting fires in the Arctic Circle this summer.
Fires also spread through parts of British Columbia, Canada and Alaska.This year, 2.4 million acres of Alaskan forest burned. In June and July, plumes from the Swan Lake fire engulfed Anchorage.
Individual wildfires can't be directly linked to climate change, but accelerated warming increases their likelihood, size, and frequency.
"Climate change, with rising temperatures and shifts in precipitation patterns, is amplifying the risk of wildfires and prolonging the season," the World Meteorological Organization wrote.
That's because warming leads winter snow cover to melt earlier, and hotter air sucks away the moisture from trees and soil, leading to dryer land. Decreased rainfall also makes for parched forests that are prone to burning.
That warming trend is becoming more and more apparent. This year is on pace to be the third hottest on record globally, according to Climate Central.
July was the hottest month ever recorded, period. The month prior, meanwhile, was the hottest June ever in Earth's history, with temperatures nearly 20 degrees Fahrenheit above average.
The three hottest years ever were 2016, 2015, and 2017.
In the US, large wildfires now burn more than twice the area they did in 1970, likely due to climate change.
The Kincade Fire, pictured above, burned more than 77,000 acres between October 23 and November 6.
"No matter how hard we try, the fires are going to keep getting bigger, and the reason is really clear," climatologist Park Williams told Columbia University's Center for Climate and Life. "Climate is really running the show in terms of what burns."
In the western US, the average wildfire season is 78 days longer than it was 50 years ago, according to the Center for Climate and Energy Solutions.
"We're really seeing that window expanding, not only earlier into the spring but also later into the fall as things stay drier, longer," Leah Quinn-Davidson, a fire adviser for Humboldt County, California, previously told Business Insider. "We are at the point where we are in a crisis."
In California specifically, the portion of the state that burns from wildfires every year has increased more than five-fold since 1972, a recent study found.
Nine of the 10 biggest fires in the state's history have occurred since the year 2003.
In addition to wildfires, rising temperatures make extreme heat waves more frequent. Europe was hit by back-to-back deadly heat waves over the summer.
In France alone, 1,435 deaths were linked to the pair of heat waves that struck Europe in June and July. According to France's national weather agency, the number of heat waves in the country has doubled in the past 34 years and is expected to double again by 2050.
A study by researchers at the World Weather Attribution organization concluded that climate change has made such heat waves at least five times more likely.
"Every heat wave occurring in Europe today is made more likely and more intense by human-induced climate change," the scientists wrote in July.
The frequency and severity of droughts are increasing, too.
Last summer, parts of England, France, and Germany faced one of the worst droughts in decades.
NASA models predict that droughts will become more common and extreme as temperatures rise. That could lead to food and water shortages and, consequently, conflicts between people competing for limited resources.
Droughts also exacerbate wildfire risk, since parched soils and dry vegetation burn more easily.
Lakes and reservoirs around the globe are also drying up, since evaporation rates skyrocket when temperatures climb.
The water level in the US' Lake Mead dropped 135 feet between 1984 and 2016. Many US farmers, as well as some cities in Arizona, Nevada, California, and Mexico, all rely on water from the lake (which comes from snow melt in the Rocky Mountains).
A 24-month projection released in 2018 by the US Bureau of Reclamation revealed that the reservoir water levels are barely skirting the 1,075-feet threshold. A drop below that levl would trigger a federal shortage declaration and mandatory usage cuts. Currently, Lake Mead is 1,082 feet high.
Other lakes around the world are also shrinking. Iran's Lake Urmia is currently at 10% of its maximum size, and Lake Poopó in Bolivia has completely disappeared.
