Last week the UN's Intergovernmental Panel on Climate Change (IPCC) released the first part of its Sixth Assessment Report, which secretary-general António Guterres described as a "code red for humanity." This report provides a high-level summary of the scientific community's understanding of the current state of the climate, including how it is changing and the role of human influence as well as the state of knowledge about possible climate futures.

This morning's report makes clear that "it is unequivocal that human influence has warmed the atmosphere, ocean, and land." When scientists speak with such confidence, the world ought to take notice.

"Human influence has warmed the climate at a rate that is unprecedented in at least the last 2000 years" the report states.

Key findings include:

• Each of the last four decades has been successively warmer than any decade that preceded it since 1850.
• Global surface temperatures are reaching levels not seen in 100,000 years.
• In 2019, atmospheric CO2 concentrations were higher than at any time in at least 2 million years.
• It is "virtually certain" that human-induced climate change is making hot extremes (heatwaves) more frequent and intense.
• Human-induced climate change is driving the frequency and intensity of heavy precipitation events across most land areas.

It's likely that climate change is increasing the incidence of tropical cyclones and scientists can say with high confidence that a warmer planet is causing these storms to bring heavier precipitation.

Why This Matters

In 2013, the IPCC authors concluded that humans were the "dominant cause" of the global warming seen since the 1950s. That assessment served as the basis for the Paris Climate Agreement signed in 2015, yet six years later there is an even more urgent need for the world to strengthen its commitments to rapid decarbonization. This year, IPCC authors stated without question that there is a near-linear relationship between cumulative CO2 emissions and the increase in global surface temperature. It's a more dire warning that the outcome of the upcoming COP26 in Glasgow will very much determine the future for human beings in coming decades and even millennia.

Time has run out for debate and slow walking, anything less than comprehensive action will set us on a course for drastic climate consequences.

More On the Report

This latest report uses five new illustrative emissions scenarios that all begin in 2015 and consider a range of greenhouse gas (GHG) emissions, land use, and air pollutant futures the nations of the world may experience.

• Scenarios with high GHG emissions and CO2 emissions roughly double by 2100 and 2050.
• Scenarios with intermediate GHG emissions and CO2 emissions, show levels would remain similar to current levels until the middle of the century.
• Scenarios that start off with low GHG emissions and CO2 emissions decline to net zero around or after 2050, followed by varying levels of net negative CO2 emissions.
• Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.

Also worth noting is that scientists haven’t previously had a full accounting of just how much human activity has contributed to warming as aerosols (in large part from pollution) have helped mask their effect through a cooling effect.

Inevitable Loss

The report makes clear that warming caused by humans has already reached irreversible thresholds especially as it pertains to the loss of sea ice. According to the report:

Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence). Loss of permafrost carbon following permafrost thaw is irreversible at centennial timescales (high confidence). Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and likely for the Antarctic Ice Sheet.

In addition, it’s virtually certain that global mean sea level will continue to rise over the 21st century. Yet by how much will depend on how rapidly the world can halt global greenhouse gas emissions.

Moving Forward

In the US, Congress must act swiftly to pass legislation that slashes emissions and sets the nation on a low-carbon path. As Congresswoman Kathy Castor (D-FL), Chair of the House Select Committee on the Climate Crisis, stated:

This report confirms what Americans are experiencing firsthand -- the devastating impacts of the climate crisis are here, and they are getting worse … The stakes of this crisis demand nothing less than the most ambitious plan for clean energy and resilient infrastructure in American history. We cannot afford to squander this once-in-a-generation opportunity to invest in affordable clean energy, deliver good-paying union jobs, and finally secure environmental justice for our communities.

Americans understand this, and it’s why they elected President Joe Biden. With his Build Back Better Agenda and our Climate Crisis Action Plan, we know what it will take to solve this crisis.

Congress must act with the urgency this moment demands, and get President Biden’s climate plan across the finish line.

At a global scale, Guterres points out that the world knows what it must do to ward off climate change’s worst effects:

The solutions are clear. Inclusive and green economies, prosperity, cleaner air and better health are possible for all if we respond to this crisis with solidarity and courage. All nations, especially the G20 and other major emitters, need to join the net-zero emissions coalition and reinforce their commitments with credible, concrete and enhanced nationally determined contributions and policies before COP26 in Glasgow.

TED: Johan Rockström, October 15, 2020.