New IPCC Assessment Report Released

The Intergovernmental Panel on Climate Change has just released its sixth comprehensive assessment of the physical science of climate change. To create the report, hundreds of expert authors drew together over 14,000 papers from the peer-reviewed literature into a nearly 4000-page review and summary of the current state of climate science, in one of the largest scientific review efforts in history. The release of the report comes just months ahead of the 26^th United Nations Climate Change Conference of the Parties (COP26), to be held in Glasgow, Scotland, beginning on October 31^st of this year.

The report echoes and strengthens statements made in previous IPCC assessment reports, finding that “it is unequivocal that human influence has warmed the atmosphere, ocean and land,” and that the scale of recent changes to the climate are “unprecedented over many centuries to many thousands of years.” The report notes that evidence has grown stronger for observed changes in climate extreme events, such as heatwaves and heavy precipitation, and for the effect of human influence on extreme events.  

In terms of future projections, the report finds that, absent deep emissions reductions, temperatures will exceed the 1.5°C and 2°C Paris Climate Accord temperature limits by later this century. Future climate projections also show that further warming will increase the frequency and intensity of extreme events, such as heat waves, heavy precipitation and droughts, and intensify the global water cycle and its variability, affecting the rain that falls during monsoons, and the severity of wet and dry events—all while the land and ocean become less effective at slowing the buildup of carbon in the atmosphere. Climate impacts are found to be more widespread and severe with greater warming. Many of the projected changes, such as the reduction of ice sheets and increased global sea level will be irreversible for centuries to millennia. The report finds that natural drivers and internal variability will modulate the effects of climate change, especially regionally and over the short term, but have little effect over the timescale of the century. Further, the report notes that low-likelihood events such as ice-sheet collapse and abrupt changes to ocean circulation patterns cannot be ruled out.

To limit the effects of future climate change, the report finds that strong reductions in greenhouse gas emissions are necessary, and that low greenhouse-gas emissions scenarios “lead within years to discernable effects on greenhouse gas and aerosol concentrations, and air quality” and that, following such scenarios, discernable differences in global surface temperature would begin to emerge in the next 20 years.

This report will be followed by the contributions of Working Group II, focused on impacts, adaptation and vulnerability, and Working Group III, which will discuss climate mitigation.

Read the report, Climate Change 2021: The Physical Science Basis. Contribution of Working Group 1 to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
Read the Summary for Policy Makers.
Access these and other reports, along with errata, regional facts and an interactive atlas on the IPCC's website.