On climate and the physical science

1. Human activities have warmed the atmosphere, ocean and land, producing widespread

and rapid changes in the atmosphere, ocean, cryosphere and biosphere.

2. The scale of recent changes across the climate system are unprecedented over many

centuries to many thousands of years. Many changes are irreversible for centuries to

millennia, especially in terms of the ocean, ice sheets and global sea level.

3. Human-induced climate change affects every region. There is growing evidence of links

to extreme heatwaves, heavy precipitation, droughts and tropical cyclones.

4. Global surface temperature will continue to increase until at least the middle of

the century. Unless we make sharp reductions in greenhouse gas emissions in

coming decades, global warming will exceed 1.5 degrees Celsius, after which climate

consequences will be even more severe.

5. The more the world warms, the greater the changes in the climate system become. This

includes more frequent and intense hot extremes, marine heatwaves, heavy precipitation,

agricultural and ecological droughts in some regions, the proportion of intense tropical

cyclones, and reductions in Arctic sea ice, snow cover and permafrost.

6. Continued global warming will further intensify the global water cycle, making it more

variable, and changing monsoon precipitation and the severity of wet and dry events.

7. As carbon dioxide emissions rise, the ocean and land will be less effective at absorbing

and slowing the accumulation of carbon dioxide in the atmosphere.

8. With further global warming, every region will increasingly experience changes in

the drivers of climatic impacts. Drivers will be more widespread at 2 degrees Celsius

compared to 1.5 degrees Celsius, and even more so at higher levels of warming.

9. Ice sheet collapse, abrupt ocean circulation changes and warming beyond current

projections are less likely outcomes but cannot be ruled out.

10. Limiting human-induced global warming requires limiting cumulative carbon dioxide

emissions, reaching at least net zero. Strong reductions in other greenhouse gas

emissions such as methane would also be required.

11. Achieving low or very low greenhouse gas emissions would lead within years to

discernible effects on greenhouse gas and aerosol concentrations and air quality.

Discernible differences in global surface temperature would emerge in around 20 years.

Source: Based on findings and projections from the IPCC’s Climate Change 2021: The Physical Science.

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