Ten grim climate scenarios when global temperatures rise above 1.5 degrees Celsius

By Lorraine Chow

The summer of 2023 was intense: deadly wildfires, massive storms, and record-breaking heat. Although scientists exercise great care before linking individual weather events to climate change, the rise in global temperatures caused by human activities has increased the severity, likelihood, and duration of such conditions.

Globally, 2024 is on pace to be the hottest year on record. The Paris Agreement aims to limit the rise of the average global temperature to below 1.5 to 2 degrees Celsius above pre-industrial levels. However, if humankind continues its business-as-usual approach to climate change, there’s a 93 percent chance we’ll be barreling toward a world that is 4 degrees Celsius warmer by the end of the century, which is a potentially catastrophic level of warming.

A Warning and a Reckoning

In 1992, 1,700 scientists around the world issued a chilling “warning to humanity.” The infamous letter declared that humanity would be on a “collision course” with the natural world if we did not rein in their environmentally damaging activities.

Such apocalyptic thinking might be easy to mock and only partially helpful in inspiring political action if the end times are nigh. In 2019, however, more than 11,000 scientists from 153 countries co-signed their names to an updated—and even bleaker statement on the issue.

The most recent version, from 2020, is titled “World Scientists’ Warning of a Climate Emergency.” It asserts that most of the environmental challenges raised in the original letter remain unsolved and require “bold and drastic transformations regarding economic and population policies.”

Similarly, a 2017 paper states, “Especially troubling is the current trajectory of potentially catastrophic climate change due to rising [greenhouse gases] from burning fossil fuels, deforestation, and agricultural production—particularly from farming ruminants for meat consumption.”

“Moreover,” the authors wrote, “We have unleashed a mass extinction event, the sixth in roughly 540 million years, wherein many current life forms could be annihilated or at least committed to extinction by the end of this century.”

But they stressed, “Soon it will be too late to shift course away from our failing trajectory, and time is running out.”

In 2023, President Biden released the lengthy Fifth National Climate Assessment, a quadrennial report compiled by over a dozen federal agencies. Beneath optimistic talk about mitigation and adaptation, this report paints a grim picture, including “heat-related illnesses and death, costlier storm damages, longer droughts that reduce agricultural productivity and strain water systems, and larger, more severe wildfires.”

So what we saw in the summer of 2023? Unless humanity gets its act together, we can expect much worse. Here’s a peek into our climate-addled future.

1. Species Extinction

The Amazon, one of the most biodiverse places on Earth, could lose about 70 percent of its plant and amphibian species and more than 60 percent of its birds, mammals and reptile species from unchecked climate change, according to a 2018 study by the University of East Anglia, the James Cook University and World Wildlife Fund (WWF), which analyzed the impact of climate change on nearly 80,000 species of plants, birds, mammals, reptiles and amphibians inhabiting the WWF’s 35 “Priority Places” for conservation.

The study’s most alarming projection was for the Miombo Woodlands in Central and Southern Africa, one of the priority places most vulnerable to climate change. If global temperatures rose 4.5 degrees Celsius, the researchers projected the loss of 90 percent of amphibians and 80 percent or more of plants, birds, mammals, and reptiles.

Over 10,000 species of plants and animals are likely to become extinct in all, according to a 2021 report by 200 scientists and researchers. This incredible loss of biodiversity affects humans, too. Droughts, fires, and other “cascading effects would have tremendous impacts on climate and, in turn, agriculture, hydropower generation, and human health and well-being.”

2. Food Insecurity and Nutritional Deficiencies

While climate change could actually benefit colder parts of the world with longer growing seasons, tropical and subtropical regions in Africa, South America, India, and Europe could lose vast chunks of arable land.

“About 80 [percent] of the global population most at risk from crop failures and hunger from climate change are in [sub-Saharan] Africa, South Asia, and Southeast Asia, where farming families are [disproportionately] poor and vulnerable,” said the World Bank. For coastal countries, rising seas could inundate farming land and drinking water with salt.

Staple crops such as wheat, rice, maize, and soybeans, which provide two-thirds of the world’s caloric intake, are sensitive to temperature and precipitation and to rising atmospheric concentrations of carbon dioxide. A sweeping 2017 study showed that every degree Celsius of warming will reduce average global wheat yields by 6 percent, rice by 3.2 percent, maize by 7.4 percent, and soybeans by 3.1 percent.

According to a 2018 paper, carbon dioxide levels expected by 2050 will make staple crops such as rice and wheat less nutritious. This could result in 175 million people becoming zinc deficient (which can cause a wide array of health impacts, including impaired growth and immune function and impotence) and 122 million people becoming protein deficient (which can cause edema, fat accumulation in liver cells, loss of muscle mass and in children, stunted growth). Additionally, the researchers found that more than 1 billion women and children could lose a large portion of their dietary iron intake, putting them at increased risk of anemia and other diseases.

3. Farewell to Coastal Cities and Island Nations

According to the International Panel on Climate Change (IPCC) Sixth Assessment report, sea levels could rise by three feet by 2100 if we don’t cut heat-trapping greenhouse gases. This could bring high tides and surges from intense storms, devastating the millions of people living in coastal areas. The National Oceanic and Atmospheric Administration (NOAA) published a report in 2018 that predicted parts of Miami, New York City, and San Francisco could flood every day by 2100, under a three-foot sea-level rise scenario.

Due to global warming, entire countries could be swallowed by the sea. Kiribati, a nation of 33 atolls and reef islands in the South Pacific, is expected to be among the first.

Kiribati won’t be alone. Since 2016, at least eight islands have disappeared into the Pacific Ocean due to rising sea levels, and an April 2018 study said that most coral atolls will be uninhabitable by the mid-21st century.

Even those nations that do survive will be dramatically affected. “By mid-century, [about] 5 times more people will be flooded compared with present-day for the lowest emissions scenario… and nearly 7 times as many under the very high-emissions scenario,” said the authors of a 2023 study.

4. Social Conflict and Mass Migration

In 2017, New York Magazine Deputy Editor David Wallace-Wells wrote an alarming and widely read essay, “The Uninhabitable Earth,” that focused almost entirely on worst-case climate scenarios. He discussed that, with diminished resources and increased migration caused by flooding, “social conflict could more than double this century.”

The article’s scientific merit has been fiercely debated, but the World Bank did conclude in March 2018 that water scarcity, crop failure, and rising sea levels could displace 143 million people by 2050. The report focused on Sub-Saharan Africa, South Asia, and Latin America, which represent more than half of the developing world’s population. Unsurprisingly, the poorest and most climate-vulnerable areas will be the hardest hit.

We can see those effects already, said Lawrence Huang for the non-profit organization Migration Policy Institute; “more than 1 million Somalis were displaced by drought in 2022, primarily within Somalia… [i]n rural Honduras and Guatemala, [indirect effects of climate change] have combined and amplified other drivers to prompt people to move to cities, the United States, and other destinations.”

5. Lethal Heat

A 2017 analysis showed that around 30 percent of the global population suffers deadly heat and humidity levels for at least 20 days a year. If emissions continue increasing at current rates, the researchers suggest that 74 percent of the global population—nearly three in four people—will experience more than 20 days of lethal heat waves.

“Our attitude towards the environment has been so reckless that we are running out of good choices for the future,” Camilo Mora of the University of Hawaii at Manoa, the study’s lead author, told National Geographic.

“For heatwaves, our options are now between bad or terrible,” he added. “Many people around the world are already paying the ultimate price of heatwaves.”

“Extremely high temperatures of over 110 degrees Fahrenheit likely killed hundreds or thousands of people across multiple countries” in West Africa in March and April 2024, said Emmanuel Akinwotu for National Public Radio. Akinwotu further noted that a network of scientists had found that the disaster would not have been possible without “human-induced climate change.”

6. Surging Wildfires

The Camp Fire, which burned more than 150,000 acres in Butte County in November, was the deadliest and most destructive fire in California’s history, killing 86 people. The August Complex Fire, which started in August 2020 and torched roughly 1 million acres in Northern California, was the largest fire in the state’s modern history. The second-largest was 2018’s Mendocino Complex Fire, which burned about 300,000 acres in Mendocino and three other Northern California counties.

However, according to California’s Fourth Climate Change Assessment released by the governor’s office in August 201, the Golden State’s fires will only worsen. If greenhouse gases continue rising, large fires that burn more than 25,000 acres will increase by 50 percent by the end of the century, and the volume of acres that wildfires will burn in an average year will increase by 77 percent, the report said.

“Higher spring and summer temperatures and earlier spring snowmelt typically cause soils to be drier for longer, increasing the likelihood of drought and a longer wildfire season, particularly in the western United States,” The Union of Concerned Scientists explained in a blog post.

“These hot, dry conditions also increase the likelihood that wildfires will be more intense and long-burning once they are started by lightning strikes or human error.”

7. Hurricanes: More Frequent, More Intense

It’s not currently clear if climate changes directly lead to each major hurricane in a given summer. However, we know this: Moist air over warm ocean water is hurricane fuel.

“Everything in the atmosphere now is impacted by the fact that it’s warmer than it’s ever been,” CNN Senior Meteorologist Brandon Miller said. “There’s more water vapor in the atmosphere. The ocean is warmer. And all of that really only pushes the impact in one direction, and that is worse: higher surge in storms, higher rainfall in storms.”

NOAA concluded in June 2018, “It is likely that greenhouse warming will cause hurricanes in the coming century to be more intense globally and have higher rainfall rates than present-day hurricanes.”

8. Melted Polar Ice and Permafrost

The Arctic is warming at a rate twice as fast as the rest of the planet, and continued loss of ice and snow cover “will cause big changes to ocean currents, to the circulation of the atmosphere, to fisheries and especially to the air temperature, which will warm up because there isn’t any ice cooling the surface anymore,” Peter Wadhams, head of the Polar Ocean Physics Group at the University of Cambridge, told Public Radio International. “That will have an effect, for instance, on air currents over Greenland, which will increase the melt rate of the Greenland ice sheet.”

Also, frozen Arctic soil—or permafrost—is starting to melt, releasing methane, a far more potent greenhouse gas than carbon dioxide. The Arctic permafrost holds 1.8 trillion tons of carbon—more than twice as much as is currently suspended in the Earth’s atmosphere.

Wadhams explained that the fear is that the permafrost will melt in “one rapid go.” If that happens, “The amount of methane that comes out will be a huge pulse, and that would have a detectable climate change, maybe 0.6 of a degree… So, it would be just a big jerk to the global climate.”

9. The Spread of Pathogens

Disturbingly, permafrost is full of pathogens, and its melting could unleash once-frozen bacteria and viruses, The Atlantic reported. In 2016, dozens of people were hospitalized, and a 12-year-old boy died after an outbreak of anthrax in Siberia. More than 2,000 reindeer were also infected. Anthrax hadn’t been seen in the region for 75 years. The cause? According to NPR, scientists suggested that a heat wave thawed a reindeer carcass that was infected with the disease decades ago.

While we shouldn’t get too frightened about Earth’s once-frozen pathogens wiping us out (yet), the warming planet has also widened the geographic ranges of ticks, mosquitoes, and other organisms that carry disease.

“We now have dengue in southern parts of Texas,” George C. Stewart, McKee Professor of Microbial Pathogenesis and chair of the department of veterinary pathobiology at the University of Missouri, told Scientific American. “Malaria is seen at higher elevations and latitudes as temperatures climb. And the cholera agent, Vibrio cholerae, replicates better at higher temperatures.”

10. Dead Corals

As the world’s largest carbon sink, our oceans bear the brunt of climate change. But the more carbon it absorbs (about 22 million tons a day), the more acidic the waters become. This could put a whole host of marine life at risk, including coral reef ecosystems, the thousands of species that depend on them, and the estimated 1 billion people around the globe who rely on healthy reefs for sustenance and income. According to Science, “Researchers predict that with increasing levels of acidification, most coral reefs will be gradually dissolving away by the end of the century.”

These climate predictions are worst-case scenarios, but there are many more dangers to consider in our warming world. A report published in 2018 in the journal Nature Climate Change found “evidence for 467 pathways by which human health, water, food, economy, infrastructure, and security have been recently impacted by climate hazards such as warming, heatwaves, precipitation, drought, floods, fires, storms, sea-level rise and changes in natural land cover and ocean chemistry.”

“Even if humanity moves swiftly to rein in global warming, 70 to 90 percent of today’s reef-building corals could die in the coming decades. If we don’t, the toll could be 99 percent or more. A reef can look healthy right up until its corals start bleaching and dying. Eventually, it is a graveyard,” write Raymond Zhong and Mira Rojanasakul in an August 2024 New York Times report.

Half a Degree Matters

Since the 19th century, the Earth has warmed by over 1 degree Celsius. A major IPCC special report released in October 2018 warned that even a half-degree more warming could be disastrous. “Every extra bit of warming matters, especially since warming of 1.5 degrees Celsius or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems,” said Hans-Otto Pörtner, co-chair of IPCC Working Group II.

The panel said that “limiting global warming to 1.5 degrees Celsius compared to 2 degrees Celsius could go hand in hand with ensuring a more sustainable and equitable society.”

However, “[p]rojected CO2 emissions from existing fossil fuel infrastructure without additional abatement would exceed the remaining carbon budget for 1.5 degrees Celsius,” the IPCC said in 2023. In other words, staying under 2 degrees Celsius is increasingly unlikely, and because of that, a sustainable and equitable society stubbornly remains a distant dream.

Lorraine Chow is the stewardship and outreach coordinator at the Santa Fe Watershed Association. She is also an environmental journalist and a contributor to the Observatory. Her work has appeared in Truthout, EcoWatch, Nation of Change, Salon, AlterNet, and Common Dreams. She is based in Santa Fe, New Mexico. This article first appeared on Truthout and was produced in partnership with Earth | Food | Life, a project of the Independent Media Institute, which is the source of this article.