IPCC AR6

What is the IPCC?

The IPCC (International Panel on Climate Change) is a United Nations organization that provides scientific information on climate change for governments and the public. It does not conduct original research. Over a thousand scientists and experts review existing scientific literature and compile key information into “Assessment Reports” and additional “Special Reports”. These reports are internationally accepted and widely agreed upon by leading scientists; however, they tend to be conservative due to the IPCC’s approval process.

In simpler words, the IPCC is a bunch of top scientists who compile the latest climate science into reliable and publicly accessible documents that governments refer to when creating their climate policies.

The Sixth Assessment Report (AR6)

It takes around six to seven years to prepare and release each assessment report. The most recent report, the “Sixth Assessment Report” was released in three parts:

The Physical Science Basis (WGI)
Impacts, Adaptation and Vulnerability (WGII)
Mitigation of Climate Change (WGIII)

WG refers to Working Group, the group of scientists and organizers focusing on each part.

The full report is too long to read—thousands of pages long—so we just refer to the shortened summary reports and slightly longer technical reports.

Current Status of the Climate

Here is the current status of the climate relating to greenhouse gas emissions.

The global surface temperature is currently 1.1°C higher than the average between 1850 to 1900.

In addition, every major group of greenhouse gases has continued to increase in the past three decades, as you can see in the figure below.

In order to group all greenhouse gases together, non-CO2 gases such as methane and nitrous oxide, which have stronger warming effects, are converted to the equivalent of CO2 using a value called the global warming potential.

Future Scenarios

The IPCC report breaks down future emissions into five scenarios called SSPs (Shared Socioeconomic Pathways):

These scenarios show us how the world could evolve depending on the level of climate change mitigation.

The big questions become: which scenario are we headed towards, and what are its projected impacts?

In order to model the scenario the world is headed towards, researchers use the projected future total greenhouse gas emissions. This estimate is derived from Nationally Determined Contributions (NDCs), which are climate action plans that include specific targets for reducing emissions. Each country in the Paris Agreement is required to establish an NDC and update it every five years. They are non-binding.

For example, here is the United States’ most recent NDC from the official document submitted to the UN:

Combining all the countries’ NDCs, climate scientists can model the extent of future warming. The results are shown below in the UNEP’s (UN Environment Programme) Emissions Gap Report 2021.

The UN Emissions Gap Report 2021 states:

“Global warming at the end of the century is estimated at 2.7°C if all unconditional 2030 pledges are fully implemented and 2.6°C if all conditional pledges are also implemented. If the net-zero emissions pledges are additionally fully implemented, this estimate is lowered to around 2.2°C.”

This 2.7°C equates to SSP2-4.5, the middle-of-the-road scenario. This is far above the 1.5°C goal countries agreed to in the 2015 Paris Agreement.

Outcome of SSP2-4.5

What is the outcome of SSP2-4.5 according to the AR6?

Here are some of the figures provided in the report. I highlighted the impacts at the SSP2-4.5 level in yellow.

This is by no means a comprehensive look at the report. Refer to the summary and technical reports for further details, including topics not covered here such as adaptation and mitigation.

Some Thoughts

The projected scenario, and consequent outcome, hinges on the extent of greenhouse gas reduction achieved by individual countries, which we can estimate from NDCs. However, there is no guarantee countries will meet their NDC goals as they are non-binding. To further improve our assessment, we must take a closer look at each individual country’s progress toward meeting their NDCs—a task that is more difficult due to the lack of detailed reporting.

Looking back at the US’ NDC, a 50% reduction over the next eight years is about 6.25% per year. However, one has to ask: what policies do we have in place that will guarantee a decline of 6.25% in GHG emissions per year, or roughly a COVID-19 pandemic sized reduction, for this coming year, let alone the next seven years?

While the charts and figures provide a systematic assessment of the potential impacts, it is easy to overlook the true real world impact of what the data represents. For example, in panel (d) of the risks of global warming, the figure shows a transition from high to very high risk/impact at around 1.5°C for warm water corals. This seemingly inconspicuous detail represents the near complete loss of coral reefs that is likely to occur as the global temperature surpasses 1.5°C within the next few decades.