Reading the AR6 Synthesis Report

Header photo: Antarctic Sea ice reaches another record low (February 2023). NASA Earth Observatory, public domain.

So, do you love your children? Your grandchildren? Your neighbor? Contemplating sacrificial love this Lent? 

Hold that thought.

You may have missed it amid wall-to-wall coverage of a tawdry conman possibly having to face justice (alas), but the Intergovernmental Panel on Climate Change (IPCC) released its scheduled 6^th Assessment Report (AR6) on March 20 (https://www.ipcc.ch/report/ar6/syr/). I read the full report on Sunday (85 pages) and you should too. Without hyperbole, it is the most important thing to have happened in the past two weeks. 

The full AR6 report has 56 authors and 28 contributing authors and was reviewed by 14 editors with oversight from IPCC’s Scientific Steering committee (30 people). The team represents countries and governments from around the world and assesses the looming climate justice crisis through the lenses of physical, chemical, and biological sciences, yes – but also social sciences, political science, and economics. I am aware of no scientific enterprise, even medicine, where assertions are more carefully vetted, tested, and scrutinized.

Concern for justice, particularly for the world’s poor and vulnerable, bleeds from nearly every paragraph. 

The report is a careful assessment of the Crisis’s current status and trends, long-term climate and development futures, and humanity’s near-term responses in a changing climate. It is a synthesis of current and emergent science (peer-reviewed journal publications) that adopts an explicit parenthetical classification of scientific-consensus-based confidence on assertions it makes. To illustrate, I might glance at the weather report for Madison and write, “The sun will rise at 6:45 am CST on 3/29 (very high confidence) and daytime temperatures in the high 30°s F probably will prevent the remnant snow from melting completely (high confidence) however net snow accumulation will decline despite flurries predicted for the afternoon (moderate confidence).”

This is important. Scientists are trained to quantify their uncertainty about observation patterns and predictions using rigorous statistical theory and experimental design principles; these are not subjective opinions. The authors are trying to capture and translate this for the reader. 

With that in mind, here’s the summary of current status and trends: 

Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850-1900 in 2011-2020. Global greenhouse gas emissions have continued to increase over 2010-2019, with unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change, lifestyles and patterns of consumption and production across regions, between and within countries, and between individuals (high confidence). Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. This has led to widespread adverse impacts on food and water security, human health and on economies and society and related losses and damages to nature and people (high confidence). Vulnerable communities who have historically contributed the least to current climate change are disproportionately affected (high confidence). (p.6)

Note that 1°C (Celsius) is about 2° Fahrenheit. Critically, climate warming is a function of cumulative emissions of greenhouse gas emissions (GHG) and global surface temperatures have risen faster since 1970 than during any 50-year period in the last 2000 years (high confidence, p.6). North America is the largest contributor to cumulative GHG emissions (23%, 1850-2019) and our recent (2019) per-person contribution is 19 tons per year, most (about 15 tons) coming from fossil fuels. Our nearest competitors in the dubious distinction are in Europe, Japan, New Zeeland and the Middle East (each about 13 tons total). East Asians contribute 11 tons while South Asians and Africans contribute 3-4 tons (p.9).   

Regarding long-term trends:

Future warming will be driven by future emissions and will affect all major climate system components, with every region experiencing multiple and co-occurring changes. Many climate-related risks are assessed to be higher than in previous assessments, and projected long-term impacts are up to multiple times higher than currently observed. Multiple climatic and non-climatic risks will interact, resulting in compounding and cascading risks across sectors and regions. Sea level rise, as well as other irreversible changes, will continue for thousands of years, at rates depending on future emissions. (high confidence) (p.33)

AR6 is notable because for the first time in an IPCC cycle, model predictions of global surface temperature, ocean warming, and sea level have become more certain because actual observations since AR5 (2014) confirm earlier predictions and inform and enhance model predictions for the future. 

Given policies in place at the end of 2020, model predictions are that global warming will increase to 3.2C° (range: 2.2 – 3.5) by 2100. What does that mean (remember, we’re at about 1.1C now)?

Climate-related risks to health, livelihoods, food security, water supply, human security, and economic growth are projected to increase with global warming of 1.5°C. In terrestrial ecosystems, 3–14% of the tens of thousands of species assessed will likely face a very high risk of extinction at a GWL of 1.5°C. Coral reefs are projected to decline by a further 70–90% at 1.5°C of global warming (high confidence). 

With about 2°C warming, climate-related changes in food availability and diet quality are estimated to increase nutrition-related diseases and the number of undernourished people, affecting tens (under low vulnerability and low warming) to hundreds of millions of people (under high vulnerability and high warming), particularly among low-income households in low- and middle-income countries in sub-Saharan Africa, South Asia and Central America (high confidence)

The need to address climate injustice is the most urgent thing facing humanity:

Deep, rapid and sustained mitigation and accelerated implementation of adaptation reduces the risks of climate change for humans and ecosystems. In modeled pathways that limit warming to 1.5°C (>50%) with no or limited overshoot and in those that limit warming to 2°C (>67%) and assume immediate action, global GHG emissions are projected to peak in the early 2020s followed by rapid and deep reductions. As adaptation options often have long implementation times, accelerated implementation of adaptation, particularly in this decade, is important to close adaptation gaps. (high confidence) (p.56)

Many changes in the climate system, including extreme events, will become larger in the near term with increasing global warming (high confidence). Multiple climatic and non-climatic risks will interact, resulting in increased compounding and cascading impacts becoming more difficult to manage (high confidence). Losses and damages will increase with increasing global warming (very high confidence), while strongly concentrated among the poorest vulnerable populations (high confidence). Continuing with current unsustainable development patterns would increase exposure and vulnerability of ecosystems and people to climate hazards (high confidence). (p. 62)

Achieving that 1.5°C increase (above) with minimal overshoot is the absolute best thing we can hope for but it requires radical transformation of economies, policies, and thinking. There are helpful and hopeful assessments – particularly on the cost-effectiveness of renewable energy sources (becoming cheaper than fossil fuel alternatives, p.20), countries making progress to net zero emissions, and increased adaptation financing but these positive trends are not yet meeting the magnitude or urgency of the need. 

That need is both maddeningly simple in principle and maddeningly complex in implementation. Humanity needs to stop using fossil fuels for the most part, stop investing in fossil fuel infra-structure (because it “locks-in” emissions and accelerating negative impacts, p. 43) and mobilize every technology, from reforestation to emerging carbon-capture chemistries, to remove GHGs from the atmosphere. The report explicitly describes needing to wrestle with known fossil fuel reserves becoming “stranded assets” (pp. 24, 59-60; i.e., “keep it in the ground”). 

The adaptation and long-term projection assessments are steeped in concern for the well-being of the world’s poor. If transition to a sustainable emissions future globally requires that near-term development and human flourishing for the world’s poor be fueled by fossil fuels, there are essentially two pools from which to draw: 1) the world’s known and unexploited fossil fuel reserves and 2) the waste, inefficiency, and fossil fuel gluttony of the developed countries – mostly in the global North. Drawing from pool 1 creates negative synergies that feedback to more damage and human suffering (the cumulative problem of GHGs and climate forcing). Drawing from pool 2 creates positive synergies that feedback to sustainability for nature and humans that depend on it (p.63-66).

The intersection of justice, love for neighbor, and western Christianity’s culpability in blessing cultural movements of colonialism, wealth accumulation, consumption, and separation of humanity from the rest of creation puts the issue of climate warming squarely in the laps of modern Christianity. Instead of giving up chocolate as a Lenten discipline to focus your contemplation, I suggest reading and contemplating the AR6.