Earth’s polar caps quickly losing ice. Coral reefs bleaching to a chalky white. Stronger storms devastating islands and cities, claiming lives and destroying homes. Those aren’t claims of what our world faces in a warmer future. Those climate change impacts are already happening — and due to worsen. That’s the finding of a new report from the United Nations Intergovernmental Panel on Climate Change, or IPCC.
The United Nations issued a summary of the new assessment on September 25. It’s the panel’s first comprehensive update on how human-driven climate change is upsetting not only Earth’s oceans, but also its frozen regions, or cryosphere. Just how severe things get will depend on whether most countries lower their releases of climate-warming greenhouse gases — or just continue pumping large quantities of them into the air.
The report focuses on two potential scenarios. One involves cutting greenhouse gases enough to limit global warming to around 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels. By the way, the world is already more than halfway there; global temps have warmed by 1.1 degrees C (2 degrees F) since 1900, according to a second new report. Prepared by the World Meteorological Organization, it was released September 22. In a second scenario, pollution continues at its current pace to where Earth eventually warms some 4 degrees C (7.2 degrees F).
Science News for Students took a look at the report’s predictions. They offer a scary view of potential changes that would impact societies and our natural world. They’re based on the latest available science.
Glaciers and ice sheets
Already, glaciers and ice sheets are shrinking. Some are disappearing super fast. The Greenland ice sheet lost an average 278 billion tons of ice per year from 2006 to 2015. That amount of water alone is enough to cause average global sea levels to rise about 7.7 millimeters (0.3 inch) a decade.
More dramatically, on July 31 a record-breaking 57 percent of that ice sheet showed signs of melting. Meanwhile, the Antarctic ice sheet has been losing an average 155 billion tons per year.
Glaciers from the Himalayas to Chile and Canada have seen big melts. Together, they’re losing another 220 billion tons of ice per year. Melt water from these glaciers today slakes the thirst of millions of people and their crops. If those glaciers disappear — and many are starting to — their downstream communities could become very thirsty.
Patches of thick ice has for millennia blanketed the Arctic Sea. Each winter the extent of that blanket expands and thickens. In summer, it shrinks and thins. The large expanse of white ice, here, plays an important role in reflecting sunlight away from Earth. This has kept the Arctic from getting too hot.
But that ice is shrinking. Its overall mass has been steadily falling for the last 40 years, the IPCC says. All that melting means that little ice now survives in place for at least five years. And that’s important. Such hardened ice tends to be sturdier than single-season ice. In fact, the fraction of sea ice older than five years is only about 10 percent of what it was 40 years ago, the report says.
Satellite records show that the lid of sea ice covering the Arctic Ocean is not just thinning. It’s also covering less water in summer. The 2019 summer minimum, reached September 18, is tied with two other years for the second lowest amount: 4.15 million square kilometers (1.6 million square miles).
The IPCC analysis predicts that if global warming can be limited to 1.5 degrees C (2.7 degrees F), the probability of September being ice free after the summertime melt is a mere 1 percent. But at 2 degree C (3.6 degrees F) warming, that risk jumps to between 10 and 35 percent. Arctic mammals, including polar bears, and birds depend on that ice.
And less ice also means more exposed water, which is dark. That dark water will absorb more sunlight and heat, intensifying feverish temperatures in polar regions.
Permafrost no more?
Permanently frozen soil, also known as permafrost, is undergoing a surprising warming across the globe. This carbon-rich soil has been warming an average of 0.29 degree C (0.52 degree F) from 2007 to 2016, the IPCC notes. This ground is estimated to contain almost twice as much carbon dioxide as is in the atmosphere. It also contains methane, another greenhouse gas. So if permafrost thaws, it could spew extra climate-warming gases into the air. To date, it’s not clear if much of that is happening yet.
But thaw it will, the IPCC report says. By 2100, the expanse of Earth’s permafrost could decrease by one quarter if greenhouse-gas emissions are lowered. And if things don’t change, more than two-thirds of that permafrost could thaw. It would exhale tens to hundreds of billions of tons of carbon, in the form of CO2 and methane, into the atmosphere by 2100. Thawed regions might see more plant growth. If that happens, those plants would pull some of that carbon back into the soil — but not nearly enough to make up for all the carbon being released by the thawing.
So far, oceans have swallowed up more than 90 percent of the climate’s excess heat. This has warmed them. Marine heat waves are getting more severe and lasting longer than they did decades ago. Such events can scorch coral reefs and help boost the frequency of toxic algal blooms. And human-caused climate change may have been responsible for nearly 90 percent of these events between 2006 and 2015, the IPCC says.
Those hot waters will get even hotter under any emissions scenario. Such an oceanic warming is already driving many ocean-dwelling animals to move toward cooler digs near the poles. But in new environments, migrant animals can interfere with local food webs. Climate-driven shifts in ocean species may have already begun shrinking the populations of food fish.
If greenhouse-gas emissions don’t drop dramatically, by 2100 ocean surfaces may be absorbing five to seven times more heat than they did in 1970. And heat waves would be 50 times more common than in 1900. But even in a low-emissions scenario, heat waves be more frequent by the end of the century — 20 times more frequent in 1900.
It’s not just heat that oceans absorb. Since the 1980s, the world’s biggest water bodies also have been taking in an estimated 20 to 30 percent of the excess carbon dioxide in the atmosphere. One result: The seas are becoming more acidic.
That’s going to continue, the IPCC report says. In a high-emissions scenario, the pH of the ocean surface is expected to drop by around 0.3 pH points (on a scale of 14) by the end of the century. That acidity may make it more difficult for creatures like snails, crabs and shrimps to build their shells. It also will harm the function of tiny algae that ferry carbon to the deep ocean. Acidity also depletes seawater of the minerals that corals use to build their exoskeletons.
Sea level rise
Sea levels are rising faster with time. And that swell is going to continue under any emissions scenario, the IPCC says. From 2006 to 2015, sea level rose some 2.5 times as fast as it did between 1901 to 1990. Melting ice sheets and glaciers are primarily to blame.
With higher sea levels come greater flooding and coastal erosion. Encroaching seawater can also shrink habitats and force species along coastlines to relocate — if they can. Nearly half of coastal wetlands already have disappeared over the last century, due partly to higher seawater.
Extreme events related to high seas that were once rare — happening once a century. In many places by 2050, especially in the tropics, such extreme flooding could happen at least once a year. That puts coastal areas and small islands in even greater danger.
Human-driven climate change has likely increased the amount of wind and rain associated with some hurricanes already. These storms will probably get more intense. They may bring bigger storm surges and record rains, even if emissions fall.
What could become more frequent, and possibly less predictable, are extreme El Niño and La Niña events. These are planet-wide swings in weather driven by water-temperature patterns in the Pacific Ocean. Extreme El Niños may hit twice as often in this century than in the last, the report says. These weather disturbances are also expected to become more hazardous, causing dryer droughts and more torrential downpours around the world.
acidic An adjective for materials that contain acid. These materials often are capable of eating away at some minerals such as carbonate, or preventing their formation in the first place.
acidification A process that lowers the pH of a solution. When carbon dioxide dissolves in water, it triggers chemical reactions that create carbonic acid.
algae Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.
Antarctica A continent mostly covered in ice, which sits in the southernmost part of the world.
Arctic A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice. The high Arctic is that most northerly third of this region. It’s a region dominated by snow cover much of the year.
atmosphere The envelope of gases surrounding Earth or another planet.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
bloom (in microbiology) The rapid and largely uncontrolled growth of a species, such as algae in waterways enriched with nutrients.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
climate The weather conditions that typically exist in one area, in general, or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
coral Marine animals that often produce a hard and stony exoskeleton and tend to live on reefs (the exoskeletons of dead ancestor corals).
cryosphere (adj. cryospheric) A term for those parts of Earth’s surface that are so cold that surface water will exist almost entirely in frozen form.
drought An extended period of abnormally low rainfall; a shortage of water resulting from this.
El Niño Extended periods when the surface water around the equator in the eastern and central Pacific warms. Scientists declare the arrival of an El Niño when that water warms by at least 0.4 degree Celsius (0.72 degree Fahrenheit) above average for five or more months in a row. El Niños can bring heavy rainfall and flooding to the West Coast of South America. Meanwhile, Australia and Southeast Asia may face a drought and high risk of wildfires. In North America, scientists have linked the arrival of El Niños to unusual weather events — including ice storms, droughts and mudslides.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
erosion (v. erode) The process that removes rock and soil from one spot on Earth’s surface, depositing it elsewhere. Erosion can be exceptionally fast or exceedingly slow. Causes of erosion include wind, water (including rainfall and floods), the scouring action of glaciers and the repeated cycles of freezing and thawing that occur in many areas of the world.
exoskeleton A hard, protective outer body covering of many animals that lack a true skeleton, such as an insect, crustacean or mollusk. The exoskeletons of insects and crustaceans are largely made of chitin.
food web (also known as a food chain) The network of relationships among organisms sharing an ecosystem. Member organisms depend on others within this network as a source of food.
frequency The number of times some periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.
glacier A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.
global warming The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.
greenhouse gases Gases that contribute to the greenhouse effect by absorbing heat. Carbon dioxide and methane are two examples of such gases.
Greenland The world’s largest island, Greenland sits between the Arctic Ocean and North Atlantic. Although it is technically part of North America (sitting just east of Northern Canada), Greenland has been linked more politically to Europe. Ice covers roughly 80 percent of Greenland. Indeed, the Greenland ice sheet is the world’s largest. If its frozen water were to melt, it could raise sea levels around the world by 6 meters (about 20 feet).
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
Himalayas A mountain system in Asia that divides the Tibetan Plateau to its north from the plains of India to the south. Containing some of the highest mountains in the world, the Himalayas include more than 100 that rise at least 7,300 meters (24,000 feet) above sea level. The tallest is known as Mount Everest.
hurricane A tropical cyclone that occurs in the Atlantic Ocean and has winds of 119 kilometers (74 miles) per hour or greater. When such a storm occurs in the Pacific Ocean, people refer to it as a typhoon.
ice sheet A broad blanket of ice, often kilometers deep. Ice sheets currently cover most of Antarctica. An ice sheet also blankets most of Greenland. During the last glaciation, ice sheets also covered much of North America and Europe.
Intergovernmental Panel on Climate Change, or IPCC. This international group keeps tabs on the newest published research on climate and on how ecosystems are responding to it. The United Nations Environment Programme and the World Meteorological Organization jointly created the IPCC in 1988. Their aim was to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and social impacts.
La Niña Extended periods when the surface water around the equator in the eastern Pacific cools for long stretches of time. Scientists will announce the arrival of a La Niña (lah NEEN yah) when the average temperature there drops by at least 0.4° C (0.72° degree F). Impacts on global weather during a La Niña tend to be the reverse of those triggered by an El Niño: Now, Central and South America may face severe droughts while Australia floods.
marine Having to do with the ocean world or environment.
methane A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.
millennia (singular: millennium) Thousands of years.
Pacific The largest of the world’s five oceans. It separates Asia and Australia to the west from North and South America to the east.
permafrost Soil that remains frozen for at least two consecutive years. Such conditions typically occur in polar climates, where average annual temperatures remain close to or below freezing.
pH A measure of a solution’s acidity or alkalinity. A pH of 7 is perfectly neutral. Acids have a pH lower than 7; the farther from 7, the stronger the acid. Alkaline solutions, called bases, have a pH higher than 7; again, the farther above 7, the stronger the base.
poles (in Earth science and astronomy) The cold regions of the planet that exist farthest from the equator; the upper and lower ends of the virtual axis around which a celestial object rotates.
population (in biology) A group of individuals from the same species that lives in the same area.
preindustrial An adjective that refers to the period before societies had begun to industrialize, using machines and fossil fuels to build products, often with assembly lines or big teams of workers. In the United States, that period began in the mid- to late-1700s.
probability A mathematical calculation or assessment (essentially the chance) of how likely something is to occur.
reef A ridge of rock, coral or sand. It rises up from the seafloor and may come to just above or just under the water’s surface.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)
scenario A possible (or likely) sequence of events and how they might play out.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
sea level The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.
seawater The salty water found in oceans.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
storm surge A storm-generated rise in water above normal tidal level. In most cases, the largest cause of storm surge is strong onshore winds in a hurricane or tropical storm.
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
tropics The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.
wetland As the name implies, this is a low-lying area of land either soaked or covered with water much of the year. It hosts plants and animals adapted to live in, on or near water.
World Meteorological Organization Created in 1950, this is a special agency of the United Nations. More than 190 nations and territories belong to WMO, which serves as the official “voice” on the status of the planet’s atmosphere and how it is behaving. WMO is based in Geneva, Switzerland.
Report: Intergovernmental Panel on Climate Change. IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC). 51st Session of the IPCC, Principality of Monaco, Monaco, published online September 25, 2019.