Climate-related changes to Earth's ice and oceans are now 'irreversible for centuries to millennia,' a new report says

• Some of the climate crisis' effects on oceans and ice will last millennia, a new report says.
• That report, the Intergovernmental Panel on Climate Change's sixth assessment, was released Monday.
• It found glaciers would keep melting and seas would rise for hundreds or thousands of years.

Earth won't be the same again for thousands of years. Human activities have altered our planet's systems so dramatically that seas will continue to rise and glaciers continue to melt long after the 21st century.

That's according to a long-awaited report, released Monday, from the Intergovernmental Panel on Climate Change - a UN body that recruits hundreds of scientists from across the globe to summarize years of research on the climate crisis.

That aggregated research paints a dismaying portrait of both our planet's long-term future and the short-term impacts of climate change, including increasingly extreme weather. In burning fossil fuels, humans have pumped so much carbon dioxide into Earth's atmosphere that it would continue heating the planet even if the world's emissions dropped to net zero today.

That warming commits Earth to major upheavals in the coming decades - rising seas, disappearing glaciers, extreme heat, floods, drought, and tropical storms. Some of those changes, the IPCC report found, will be "irreversible for centuries to millennia."

Glaciers will melt and seas will rise for millennia to come

Already, the Arctic is losing its permafrost, a layer of soil that used to stay frozen year-round. That frozen layer has captured carbon from plants and animals that have died over past centuries - about twice as much carbon as currently exists in the atmosphere.

As rising temperatures thaw the permafrost, though, that carbon escapes into the atmosphere, where it traps heat and contributes to additional warming. This carbon release may last hundreds of years, according to the IPCC.

Changes to Earth's oceans, too, "are irreversible on centennial to millennial time scales," according to the report. The oceans have been absorbing about 31% of carbon-dioxide emissions, which makes them more acidic. They're also heating up along with the rest of the planet. Warmer water holds less oxygen, a resource that's crucial to marine life.

Warming will also keep glaciers melting at the poles and on mountaintops for decades, possibly centuries, the report says. If emissions rise further, some limited evidence suggests the melting of the Antarctic ice sheet could accelerate for centuries.

All that melting ice would contribute to even more sea-level rise. Over the next 2,000 years, oceans could rise as much as 72 feet. The IPCC report says with "high confidence" that sea levels "will remain elevated for thousands of years."

Other takeaways from the IPCC report

The UN created the IPCC in 1988 to inform policymakers about how the climate is changing. This is its sixth climate assessment.

For these reports, hundreds of scientists from across the globe comb through thousands of scientific papers. They describe how the climate is changing, the consequences of those changes, risks for the future, and what can be done.

Monday's report is the first part of the IPCC's new assessment, and it comes from a working group that hadn't released new findings since 2013. This portion comes three months before scheduled climate talks in Glasgow, Scotland. The next two parts of the report are expected in early 2022. Governments of 195 countries must approve each one before its release.

Here are other key takeaways from the new IPCC report:

• The global average temperature from 2001 to 2020 was about 1 degree Celsius higher than it was from 1850 to 1900.
• The average global sea level rose by about half a foot (0.2 meters) from 1901 to 2018. The rate of annual sea-level rise nearly tripled during that time.
• In 2019, the concentration of carbon in the atmosphere was higher than at any other time in at least 2 million years. Concentrations of methane and nitrous oxide - more-potent greenhouse gases than CO2 - were higher than at any time in at least 800,000 years.
• Annual average Arctic sea-ice levels from 2001 to 2020 were their lowest since 1850, and the Arctic is likely to have a sea-ice-free September at least once before 2050.
• Major tropical cyclones, heat waves, and heavy precipitation events have increased in frequency around the globe over the past four decades.
• Combinations of extreme events like heavy rainfall and hurricane-caused storm surge, paired with rising sea levels, will continue to make flooding more likely in coming decades.
• The Atlantic Meridional Overturning Circulation, an ocean current that carries warm water north and cold water south, is weakening. If the current slows enough, Europe and the US East Coast would be hit by freezing temperatures.