Actionable Climate Science forPolicymakers

The burning of fossil fuels – oil, coal, and natural gas – is the primary source of man-made atmospheric carbon dioxide. Since the start of the industrial revolution, humans have contributed more than 2,000 billion metric tons of carbon dioxide to the atmosphere.

After it is released into the atmosphere, the carbon dioxide is naturally redistributed between the atmosphere, the oceans, and the biosphere.  However, none of the emitted carbon will return to the Earth by natural processes for many tens of thousands of years.  As a result, the carbon that humans release by burning fossil fuels will lead to increased levels of carbon in the atmosphere, ocean, and biosphere for many thousands of years.

If carbon dioxide is allowed to continue to accumulate in the atmosphere, it will be impossible for the world to stay below 2.0°C, let alone 1.5°C. The easiest way to avoid future warming is to rapidly decrease our use of fossil fuels, replacing them with low carbon alternatives such as wind, solar, hydro, and nuclear wherever possible.

A recent study found that 60% of remaining oil and methane (natural gas), and 90% of coal must stay in the ground if the world is to meet 1.5°C warming targets. For this to happen, oil and gas production would need to decline 3% annually through 2050. 

The 2015 Paris Climate Agreement mandated that signatories set ambitious targets for their “nationally determined contributions” to reduce carbon emissions.  Existing climate pledges, however, fall far short of the decarbonization necessary to meet warming targets: the NDC synthesis report published by UN Climate Change in February of 2021 found that national pledges would only reduce global emissions 12% by 2030, far short of the 45% required to meet 1.5°C, or 25% required to meet 2.0°C warming targets. 

Which brings us to COP26.

Since 2010 policy actions and transformations of energy systems have greatly reduced coal use, putting the world on a much lower greenhouse gas emissions trajectory. The more severe warming scenarios projecting 4°-5°C of average warming now seem increasingly unlikely. However, despite this progress, current policies are insufficient for meeting the goals of the Paris Agreement. 

As of October 2021 all but five eligible countries (Eritrea, Iran, Iraq, Yemen, and Libya) have ratified the Paris Agreement on Climate Change, thereby committing to set ambitious targets to reduce carbon emissions with the goal of limiting global warming well below 2.0°C.  

According to the September 2021 UN Climate Change NDC Synthesis Report, taking into account the nationally determined contributions (NDCs) of all 191 Paris Agreement signatories, global emissions in 2030 are still projected to rise by 16% above the 2010 baseline, despite a lower average rate of increase in emissions. Under these updated commitments, average warming of 2.7°C is projected by 2100. 

The more recent UNEP 2021 Emissions Gap Report, reflecting the updated Paris Agreement NDCs of 121 participating countries submitted as of October 2021, projects a temperature rise of 2.8°C. This report also suggests that despite the 5.4% reduction in global emissions in 2020 relative to 2019 due to COVID-19 shutdowns, 2021 emissions remain only 1% lower than 2019 numbers, with 2022 projected to surpass 2019 levels as “green recovery” efforts stall. China, Russia, and Brazil are on track to exceed their pre-pandemic emissions levels by the end of 2021. 

The window is rapidly narrowing to meet the 1.5°C warming target set by the Paris Agreement; the world would need a 55% reduction in global emissions by 2030 compared to the 7.5% reduction represented by current commitments. Limiting warming to 1.5°C by 2100 would require a 14% annual reduction in emissions beginning this year and continuing through 2040. 

There is nonetheless still reason for cautious optimism that the world could come close to meeting the stated goals of the Paris Agreement; the UNEP Gap Report suggests that should committed countries achieve their stated net-zero goals by mid-century, average estimated warming would be limited to approximately 2.2°C by 2100. 

Limiting warming from 2.2°C to the stated goal of 2.0°C would require immediate implementation of the more aggressive emissions cuts promised by net-zero pledges, rather than the more gradual roll-out over the next decade suggested by currently announced policies.  

A significant gap still exists between current policies and pledged reductions: Very few of the announced policies are currently backed by legislation or committed funding. Closing this gap will require significant legislative action and investment in the very near term.