Earth Day, celebrated Friday, April 22, across the globe, reminds us of the fragile state of our planet.

From land contaminated with toxic chemicals to bad air spewed into the atmosphere, most of us have been affected by pollution in some way.

To bring all of this closer to home, we’re listing the 10 most critical environmental problems in Southern California. Some are very recent; some have been going on for decades. But all are still relevant today. Especially today, when we turn our attention to the air, land, water and inhabitants of planet Earth.

1. Global Climate Change: While some parts of the country have experienced extreme weather, such as colder winters and massive flooding, the West has experienced hotter temperatures and unusually warmer winters these past several years. An overwhelming majority of scientists say man-made emissions, including carbon dioxide — produced from the burning of fossil fuels — become trapped in the atmosphere causing a heat or greenhouse effect.

Last year was the hottest year on Earth since record keeping began in 1880, according to scientists with the National Oceanic and Atmospheric Administration. February and March were even hotter than that mark.

The temperature rise in March was the 11th month in a row of record-breaking heat.

“It is a steady warming, with no evidence of change in the long term,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies in New York, told our sister newspaper, The Mercury News in January.

Overall, the planet’s temperature has risen about 1.8 degrees Fahrenheit since the late 19th Century. While California’s four-year drought was not caused by climate change, researchers from NASA and Columbia University said it aggravated the situation by causing more water evaporation and thereby making the state’s drought about 20 percent worse.

On Friday, nearly 160 nations are expected to sign an accord agreeing to cut greenhouse gases. The goal is to keep the global temperature from rising more than 3.6 degrees Fahrenheit, measured since before industrialization.

2. Porter Ranch gas leak: What many may not know that the Aliso Canyon gas fields are not just a place where methane is pulled from the ground. It is a place where natural gas is stored after being injected into the ground. With 115 wells, it is one of four underground natural gas storage facilities operated by Southern California Gas Co.

About 100,000 tons of methane leaked out of the underground storage field, the largest natural gas leak disaster in the United States, according to researchers with University of California, Irvine. Enough gas leaked every day for nearly four months starting in October 2015 to fill a balloon the size of the Rose Bowl, experts said. About 6,000 residents were relocated after many complained of headaches, nosebleeds and vomiting. SoCalGas said experts agree there are no long-term health effects.

The next question is: Can Aliso Canyon be reopened as a gas-storage facility? A new report says without that capacity, there may be a shortage of natural gas to power generators that produce electricity, potentially causing scattered blackouts this summer. Meanwhile, an old gas field in Montebello had six new leaks found at the same time Aliso Canyon was leaking; all were repaired. SoCalGas pulls 1 million cubic feet of natural gas from residual supplies and 100 barrels of oil every day from Montebello, despite a closure order issued 15 years ago.

3. Air pollution and SCAQMD: The South Coast Air Quality Management District is working on an update to the region’s Air Quality Management Plan. Hearings will take place in June and July, while adoption of the plan would be later this year, according to SCAQMD officials.

The agency will be forming its clean air plan under new leadership after longtime Executive Officer Barry Wallerstein was dismissed in March. All seven members of the 13-member governing board represent a new, Republican majority voted for his dismissal; five Democrats and one independent voted no. He was replaced in April with former EPA administrator Wayne Nastri, who was named acting chief. Protesters, environmental groups and members of the state Legislature criticized the moves as pandering to businesses, especially oil interests, who want softer regulations at the expense of public health.

While stratospheric ozone protects people from harmful ultraviolet rays, ground-level ozone is a health concern.

The Los Angeles air basin has the worst air quality of any area of the nation. The area does not meet the Clean Air Act health-based standards for ozone and fine particulate matter (PM2.5), two critical components of smog. The particulates violation stems from the unhealthful levels found at the SCAQMD’s monitoring station in the Mira Loma area of Jurupa Valley.

Ozone is formed in the lower atmosphere when sunlight causes a chemical reaction on emissions from cars, trucks and locomotives, namely nitrogen oxides (NOx) and other airborne chemicals. The single-largest stationery source of NOx are ships and other vehicles operating in the twin ports of Los Angeles and Long Beach, according to SCAQMD records. When NOx mixes with Volatile Organic Compounds (VOCs) from paints, coatings, refineries and mobile sources as well, the reaction with sunlight forms ozone (O3).

The greatest sources of PM2.5, tiny particles that slip into the lungs, are diesel trucks, off-road diesel tractors and bulldozers and diesel-powered locomotives, ships and cargo movers. In order to reach compliance, the four-county air basin would have to reduce oxides of nitrogen (NOx) by 60 percent, said Philip Fine, SCAQMD deputy executive officer.

Ozone pollution, which affects 107 million Americans, can cause shortness of breath, coughing and wheezing. Longer exposures have been linked with asthma and reduction in lung function, what the American Lung Association calls “a sunburn on the lung” that can lead to premature death.

4. Refinery fire in Torrance: The explosion at the ExxonMobil refinery in Torrance greatly reduced output of gasoline. Experts say the loss of supply drove up pump prices in Southern California. The explosion took place on Feb. 18, 2015, sending flames and ash into the sky. Four workers suffered minor injuries. Since then, the company has been working to install the necessary air pollution equipment to reopen the plant. The SCAQMD in early April gave approval to restart the plant for gasoline manufacturing. State regulators fined ExxonMobil $566,600 for 19 workplace health and safety violations in the aftermath of the explosion and investigation.

It is estimated ExxonMobil will pay $5 million in penalties for air pollution violations that could occur after the start-up during a brief period of excess pollution emissions. ExxonMobil caused the explosion by failing to fix equipment, despite knowing it could cause a life-threatening blast, state and federal regulators concluded in separate investigations. ExxonMobil has not said when the restart would occur. ExxonMobil plans to sell the refinery to PBF Energy.

5. Exide closure and cleanup: Exide Technologies, a battery recycling plant in Vernon, was ordered to close in March 2015 and ordered to pay $50 million for clean-up of the site and surrounding neighborhoods by the U.S. Department of Justice. The California Department of Toxic Substances Control informed Exide on Feb. 26 of that year that its permit to reopen was denied. Instead, the order called for the facility to be shuttered, demolished and cleaned up.

Lead-acid batteries, when melted down, produce a host of toxic emissions, including lead, cadmium and arsenic. The plant was releasing “high levels of lead emissions” for 18 consecutive days in March 2014, according to air pollution officials. Unacceptably high levels of lead were detected in the air monitor at the northeast corner of the Exide property at 2700 S. Indiana St., according to the SCAQMD.

Studies say residents of low-income areas are more likely to breathe in toxic air emissions. Closure of the Exide battery-recycling plant in Vernon, after state agencies found toxic compounds in nearby neighborhoods and numerous violations, is an example of environmental justice, said Los Angeles County Supervisor Hilda Solis.

Testing has begun at 500 homes near the closed Exide plant but only a handful had lead levels requiring cleanup so far, Reuters reported last week. About 10,000 properties will be tested in the communities around the shuttered plant.

Recently, the governor signed a bill that will set aside $176.6 million for more testing and cleanup within a 1.7-mile radius of the plant.

Lead exposure can interfere with a host of organs, including the heart and the nervous system. In children, who are more susceptible, inhalation or ingestion can lead to cognitive disorders, cause immune problems, and prevent the proper development of bones and teeth.

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6. Water shortages and conservation: The four driest years in California history, from 2011 to 2015, reduced the state’s snowpack to zero, dropped ground water basins and state reservoirs to historic lows. The winter’s El Niño storms helped build the snowpack to near 100 percent and brought back reservoir levels in Northern California to above their historical averages.

The State Water Resources Control Board enforced Gov. Jerry Brown’s emergency mandatory water conservation from June 2015 through February 2016. In that time, Californians saved close to 24 percent or about 1.19 million acre-feet of water, enough to supply more than 5.9 million residents for one year, or about the combined population of San Diego, Riverside and Tulare counties. The result was just short of the mandated 25 percent goal set by Brown.

7. Solar energy: Solar’s biggest year was 2015, when 7,260 megawatts of solar power was installed in the United States for a gain of 16 percent over 2014, according to the Solar Energy Industries Association. The SEIA, a leading trade group, predicts that number will double this year.

Residential solar is leading that growth, increasing 66 percent from 2014.

At the same time, larger solar farms and utility photovoltaic plants are also adding to the country’s renewable energy portfolio. But not without controversy.

The Ivanpah solar plant built in northeast San Bernardino County came on line in 2014. But because the plant burns natural gas as part of its process, it is not 100 percent green and is being labeled by some as a “hybrid.” The plant produced 46,000 metric tons of carbon dioxide in its first year of operation.

It also came under fire during construction for displacing more than 100 desert tortoises, a species threatened with extinction, and for its towers that burn birds in mid flight.

8. Hinkley: In this small town devastated by cancer-causing chromium-6 in its drinking water, news of recovery began to surface this past year.

The Lahontan Regional Water Control Board in November approved a comprehensive cleanup plan for the world’s largest known plume of the cancer-causing chemical. The order requires Pacific Gas & Electric to further define the plume, monitor it and reduce chromium-6 concentrations, especially in the core area near its Hinkley natural gas compression station.

In January, the community learned the toxic plume had shrunk by half over the previous four years. The community had hope that it could begin to rebuild, to attract more residents and to re-open Hinkley School, which closed in June 2013.

From 1952 until 1964, San Francisco-based PG&E discharged untreated chromium-6 from cooling towers in its Hinkley station into unlined ponds, a common practice during that era, before the cancer-causing properties of chromium-6 were fully understood. From the ponds, chromium-6 percolated into the ground.

Hinkley’s water contamination problems were thrust globally into public view in the 2000 film “Erin Brockovich” starring Julia Roberts.

9. Salton Sea: Various fixes to the Salton Sea, a dying lake occupying about 378 square miles in Imperial and Riverside counties, include a geothermal operation and algae harvesting.

Brown’s 2016-17 budget includes $80.5 million for the giant lake, labeled as a start but nowhere near the full amount needed to restore the sea.

Some have suggested that economic activity would pay back the cost of restoration, which at one point was tagged at $9 billion.

In February, Bruce Wilcox, whom Brown appointed as secretary for the Salton Sea Policy within the California Department of Natural Resources, spoke publicly about what can be done to save the lake.

If nothing is done, the giant sea will have shrunk by about 100 square miles by 2050, resulting in dust storms and hydrogen sulfide “bumps” that affect air quality throughout Southern California, documents show.

10. Plastic bags: The back-and-forth over the problem of plastic bags and the environment continues.

Brown in 2014 signed into law Senate Bill 270, which mandated a statewide ban on single-use plastic carry-out bags. Before the law could go into effect in July 2015, opponents of the bill gathered enough signatures to add a referendum to the upcoming November election.

A “yes” vote on the ballot measure upholds the ban. A “no” vote would overturn SB 270.

Environmental groups point out that plastic bags are litter. They are a danger to wildlife. Bags have been found in the stomachs of whales, snare and strangle fish and shorebirds.

Estimates say 25 percent of litter found in the Los Angeles river comes from plastic bag waste.

The ban on single-use plastic bags was supported by the grocery industry, who wanted a uniform policy statewide. To date, many cities and counties have enacted bans, making shoppers more comfortable bringing re-usable thick plastic or cloth bags to the checkout stand.

A total of 147 cities and counties in California already have bans on plastic bags.

Los Angeles County banned single-use plastic bags in 2011 as did cities of Pasadena, South Pasadena, Monrovia and Glendale. Arcadia is considering a city-wide ban on plastic bags at grocery stores, liquor stores and convenience stores.

Staff writers James Steinberg, David Danelski, Courtney Tompkins and Jessica Calefati contributed to this report.