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6th IPCC Physical Science Basis Report Shows Narrow Window for 1.5C Future

The 2021 Intergovernmental Panel on Climate Change (IPCC) Physical Science Basis report released Monday, August 9th emphasizes the extremely narrow path currently available to limit warming global temperatures to 1.5 degrees Celsius. Government officials from 195 countries have approved the contents of the report.

As compared to the fifth edition of the report released in 2013, which stated warming was “extremely likely” a result of human activities, the new sixth edition said, “it is unequivocal that human influence has warmed the atmosphere, oceans, and land.”

The science attributing climate change to human activity is clear. The report states that since the release of the 2013 report: “human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened.”

This report details the work of thousands of scientists and represents a review of the body of scientific literature on the topics it covers. It includes modeling of possible future climates and interactive maps demonstrating how climate will vary based on geographic region, specifically showing increasing rainfall in the Eastern United States and continued increasing drought conditions in the Western United States.

In response to these findings, BCSE President Lisa Jacobson said “Congress and President Biden must enact federal policy to drive this transition on the timeline called for by the scientific community in this report – starting with the bipartisan infrastructure framework.”

“Since the last IPCC Physical Science Basis report was released in 2013, scientists have made significant progress on measuring and projecting the impacts of climate change,” Jacobson said. “The sixth edition released today shows that we have a very small window of opportunity to stop global climate change at 1.5C of warming. It reinforces that 2C or more of warming would be exponentially worse for our planet and civilization.”

Jacobson also commented on the availability of technologies to address climate change, saying, “U.S. energy efficiency, natural gas and renewable energy businesses are dedicated to enabling the necessary energy transition with clean energy and energy efficiency technologies that support an affordable, reliable and sustainable energy system.”

The IPCC will release further reports in February and March of 2022 with information on expected impacts, vulnerabilities, adaptation strategies, and mitigation approaches due to, or in response to, climate change. The IPCC will also release a final report synthesizing all findings following the release of the February and March 2022 reports.

The New York Times and Bloomberg News published summaries of the report’s findings. Key results from the report include:

  • Each of the last four decades has been successively warmer than any decade that preceded it since 1850. Global surface temperature in the first two decades of the 21st century (2001-2020) was 0.99 [0.84- 1.10] °C higher than 1850-19009.
  • With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers would be more widespread at 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.
  • Human influence is attributed to several climatic impacts:
    • Human influence is very likely the main driver of the global retreat of glaciers since the 1990s and the decrease in Arctic sea ice area between 1979–1988 and 2010–2019.
    • Human influence has likely increased the chance of compound extreme events since the 1950s. This includes increases in the frequency of concurrent heatwaves and droughts on the global scale; fire weather in some regions of all inhabited continents; and compound flooding in some locations.
    • It is virtually certain that the global upper ocean (0–700 m) has warmed since the 1970s and extremely likely that human influence is the main driver.
    • It is virtually certain that human-caused CO2 emissions are the main driver of current global acidification of the surface open ocean.
  • In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH4 and N2O were higher than at any time in at least 800,000 years.
  • From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in methane (CH4) emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.


The full IPCC report, as well as the summary for policymakers and the technical summary can be found at Sixth Assessment Report (