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.