Childhood’s End
The Future of Humanity, Part 4
This is Part 4 of my 7-part series on the future of humanity. The series starts here.
“Elements of modern human civilization — our cities, agricultural practices, fossil fuel dependence — have not withstood the test of time, nor can they.” — Tom Murphy, Energy and Human Ambitions on a Finite Planet, p. 406.
Anticipating a 2–4°C warmer world
It’s time to look more closely at how an energy transition in a 2–4°C warmer world is likely to play out. It’s not a pretty picture. In fact, we end up learning rather quickly that all the dire warnings we have been hearing from the IPCC and others about possible catastrophic effects of climate change are probably underestimations because they are based on models that do not include many of the second-order “unknowns” that might emerge in a hotter world: potential interaction effects (effect A and effect B occur simultaneously and exacerbate each other), cascading effects (A triggers B, which triggers C, etc.), and tipping points (A reaches a level that produces an irreversible and extremely hazardous effect).
It is instructive and perhaps revealing that while governments and politicians continue to sing the tune of a 1.5°C warmer world, climate scientists are becoming more concerned about the need to better understand the potential impacts and consequences of more extreme temperature outcomes. As one team noted in a paper released this year:
“As noted by the Intergovernmental Panel on Climate Change (IPCC), there have been few quantitative estimates of global aggregate impacts from warming of 3 °C or above (source). Text mining of IPCC reports similarly found that coverage of temperature rises of 3°C or higher is underrepresented relative to their likelihood (source).”
The authors note a spate of recent research that appears to leave the 1.5° goal in the dust, including a recent “gold standard” study we reviewed in Part 2:
“Recent findings on equilibrium climate sensitivity (ECS) (source, source) underline that the magnitude of climate change is uncertain even if we knew future GHG [greenhouse gas] concentrations. According to the IPCC, our best estimate for ECS is a 3 °C temperature rise per doubling of CO2, with a “likely” range (66 to 100% likelihood) of 2.5 °C to 4°C. While an ECS below 1.5 °C was essentially ruled out, there remains an 18% probability that ECS could be greater than 4.5 °C (source, p. 13). The distribution of ECS is “heavy tailed,” with a higher probability of very high values of ECS than of very low values.”
Perhaps due to an academic culture that shuns drama and alarmist rhetoric, or more likely, perhaps due a quite reasonable desire to avoid frightening their audience into resignation and paralysis, climate scientists have been reticent to fully explore climate scenarios beyond the 1.5°C threshold (source). But that reticence is fading, as outcomes beyond that threshold are now becoming more probable than not.
Living in a 2–4°C warmer world
Around the periphery of the IPCC process, some climate scientists have begun looking more closely at the potential impacts of extreme global mean temperatures (GMT) on the planet and the species inhabiting it, including us.
Launched in 2012, the Inter-Sectoral Impact Model Intercomparison (ISI-MIP) project brought together 30 research teams from 12 countries to assess climate impacts within and between five key sectors: water, agriculture, ecosystems, human health, and coastal infrastructure. The project’s first major report, published in 2016 and titled “The Challenge of a 4°C World by 2100”, lays out multiple ways a significantly hotter world might impact each of these sectors, as well as several ways global warming beyond 2°C might produce interactive, cascading, or tipping point effects within and between them. Its findings, combined with results from more recent studies of extreme warming (e.g., source, source, source), provide a roadmap to where we’re heading, and what we might find when we get there.
First-order effects are direct impacts of a hotter world on the five sectors. Second-order effects are additional consequences arising from first-order effects. These may be interactions, cascades, or tipping points, as noted above. For example, “wet bulb” temperatures can kill humans directly (first-order effect), but they can also cause crop failures or droughts that can lead to starvation and kill humans indirectly (second-order effect).
First-order effects
In 2016, USA Today reported that the world was experiencing temperatures not seen in 125,000 years (source). Yet human civilization — defined by farming, domesticated animals and plants, and permanent settlements — began only about 12,000 years ago (source). From an evolutionary point of view, modern humans, the plants and animals we have bred to our needs over a few thousands years, and the towns and cities we have built, have never had to function in a world this hot.
To say we are out of our comfort zone is a gross understatement. As a civilization, we are now operating in a world that has already diverged significantly from the one we “grew up” in. And it will diverge much more. As we race toward the unknown, having squandered decades in which we knew what we were doing, but did nothing about it, we have no choice but to learn as we go.
The primary first-order effects of global warming are heatwaves and radically shifting precipitation patterns. Crucially, these effects are expected to vary dramatically across the globe.
Heatwaves. The first major direct effect of a hotter climate is, not surprisingly, heat. In a 4° hotter world, heatwaves of unprecedented magnitude — up to five standard deviations outside historical averages — are expected to occur over 60% of the planet’s land surface. Today’s extremes, like the devastating heatwaves in Europe and the Pacific Northwest in 2021, will be the “new normal”, occurring regularly across 80% of all land areas.
Rainfall and snowfall. The second major direct effect of a hotter climate is radically changing rainfall and snowfall patterns. Climate scientists expect rainfall to be significantly disrupted in a 2–4° hotter world. In Southeast Asia, for example, which is historically dependent on predictable monsoon rains, scientists expect precipitation to increase by up to 30% in wet seasons and decrease by up to 30% in dry seasons, producing more devastating floods and more severe droughts than the region is already experiencing today.
Geographic variations. As noted in Part 2, climate change impacts will not be evenly distributed across the planet. Poorer countries will of course be more vulnerable to climate disruptions, due to their already-fragile infrastructures and struggling populations. But the prosperous industrialized regions of the world will not escape devastating effects, which will also vary by region. For example, as warming reaches 3°C, drought conditions are expected to become critical in several regions: across North and South America (including the American Southwest), in large parts of tropical and southern Africa, the Mediterranean region, southeast China, and Australia. Decreased drought conditions are expected in only a few places: northern Canada, north-east Russia, the Horn of Africa and parts of Indonesia (source).
Socioeconomic variations. Although climate change will deliver its effects on rich and poor nations alike, without discrimination, humanity’s ability to respond to those effects will vary considerably, given differences in economic and technological capacities.
There is a very real chance that as climate crises accelerate in a hotter world, an attraction to Garrett Hardin’s “lifeboat ethics” will grow in the more wealthy nations, especially those ruled by rightwing authoritarian governments or weakened by rightwing authoritarian movements. Despite its deep connections to eugenics and racism, “the case against helping the poor” is likely to find sympathetic listeners among the wealthy as their lives become less and less comfortable. Indeed, it could be reasonably argued that modern rightwing movements like the American Republican Party are already espousing a “lite” version of Hardin’s lifeboat ethics in their attitudes toward immigrants and, more directly, in their reactions to the COVID-19 pandemic. Indeed, rightwing writers and journals are already laying the ideological groundwork for connecting possible climate change policies to lifeboat ethics.
But we’re getting ahead of ourselves. These political repercussions are probably better thought of as second-order effects of of heat and rain, to which we now turn.
Second-order effects
What happens when first-order effects collide? Often, more than just the sum of the parts (source). Interactions, cascades, and tipping points all generate new emergent properties and positive feedback loops above and beyond what their impacts would be individually. We know less about them than we should because they are very difficult to model and predict, due to the high levels of uncertainty that surround them.
Here are some of the most significant and consequential second-order effects scientists see as possibilities in a 2–4° warmer world.
Sea level rise. Predicting sea level rise with any precision is difficult because so many factors may or may not come into play over the coming years. The biggest “known unknown” in these projections is the rate of melting of the planet’s great ice sheets in Antarctica and Greenland. As the world gets hotter, sea levels rise because water, as the air gets warmer, expands. This is called thermal expansion. Over recent decades, thermal expansion has raised sea levels about 1.2 millimeters per year on average. On top of that, melting ice is the second major contributor to sea level rise. It has recently been adding about 2.4mm/yr, for a total annual rise of about 3.6mm (source). That’s about the thickness of two American quarters. Sounds tolerable.
Sadly, recent rates are not a good benchmark for sea level rise in a 2–4° warmer world, because that much more heat means that much more melting ice. How much more? Antarctica and Greenland cover about 2.7% and 0.3% of the planet’s surface, respectively. The Greenland ice sheet is on average 1.7 kilometers thick (about 1 mile) and the Antarctic ice cap is about 1.9km thick. If all that ice melts, simple math says Greenland will contribute about 7.4 meters to current sea levels and Antarctica will contribute a whopping 58 meters (source). Add those up and you’re looking at sea level rise equivalent to the height of a 20-story building. That kind of change would almost certainly be civilization ending.
This is the problem with predicting sea level rise. It’s somewhere between the thickness of two quarters and the height of a 20-story building. What we really need to know is the rate at which these ice sheets are melting. And we know that rate is not linear because the more ice melts, the less ice there is to reflect the sun’s heat, which raises temperatures and causes remaining ice to melt faster. A recent study suggests that sea level rise in a warmer world could reach somewhere between 30 and 49 cm by 2100, or about 1–1.6 feet (source). More recent studies suggest similar results under a variety of warming scenarios (source). At a minimum, these increases would double the amount of sea level rise we’ve already seen since 2000. The good news, I suppose, in that it is less than 200 feet.
The bad news, however, in that this amount of sea level rise will still result in significant damage to vulnerable coastal cities and infrastructure, due to more frequent storm surges and flooding. One recent study, using the IPCC RCP4.5 climate model (which assumes a global temperature rise of 2–3°C by 2100), estimates that 140–170 million people are now living on land that will be underwater at high tide by 2050, increasing to 160–260 million by 2100. Adding in the potential effects of a collapsing Antarctic ice sheet (see below), this number increases to 380–630 million by 2100 (source). As with other climate change effects, impacts will vary significantly across geographies. Countries where the most people are vulnerable to displacement due to rising sea levels include Bangladesh, China, Vietnam, Indonesia, and the Philippines. Without augmented or new coastal defenses, populations in these areas may face regular flooding or permanent inundation within 30 years (source, source).
Freshwater scarcity. In a 2–3°C warmer world, 10% of the world’s population will be impacted by absolute water scarcity (defined as less than 500 cubic meters of water available per person per year), compared to 2% today (source). Geographies most likely to experience water scarcity before 2100 include the Mediterranean region, the Middle East, the American South and southern China. Cities are expected to be particularly vulnerable to water scarcity. A 2021 report projects that 1.7–2.4 billion urban dwellers will face water scarcity by 2050, including residents of 10 to 20 of the world’s megacities (source).
In a 3–4°C warmer world, drought conditions are expected to increase in North and South America, large parts of tropical and southern Africa, the Mediterranean region, southeast China and Australia. Minor changes or decreased drought conditions are found only in northern Canada, northeast Russia, the Horn of Africa and parts of Indonesia.
Agricultural shortages. Globally, agriculture is the largest consumer of the world’s fresh water, accounting for about 70% of all water usage per year (source). The effects of temperature and water scarcity on agricultural production in a hotter world are likely to be severe. Recent studies have estimated that a 4°C increase in mean global temperature could result in a 50% reduction in yields for important crops such as wheat and maize in the hottest tropical regions. Such an outcome would be catastrophic in a world struggling to feed 8 billion mouths.
A key concern for the agriculture sector is “breadbasket failures”, steep declines in major food producing regions due to floods, droughts, wildfires and other environmental disruptions caused by rising temperatures. For example, one recent study found that in the four top maize-producing regions on the planet, which today produce 87% of the world’s maize, the likelihood of production losses greater than 10% increases from 7% annually in a 2°C warmer world to 86% in a 4°C warmer world (source).
Geographically, an OECD assessment of future food production risks concludes that without further action, northeast China, northwest India, and the southwest United States will be among the most severely affected regions, with both domestic and global repercussions.
The impacts of climate change on food production tend to be treated rather abstractly and indirectly in the scientific literature. For example, the above referenced study of breadbasket failures notes that such a failure could have “significant consequences in humanitarian, economic or political dimensions”. What that means is: a lot of people are going to starve to death, food supply chains are going to be massively disrupted, and political unrest is going to break out all over the world.
Anodyne phrases like “significant consequences” no longer suffice to describe the death and destruction likely to accompany the hotter world we are creating for ourselves.
We can no longer afford to be so fastidious in describing the cliff we are rapidly approaching.
Ecosystem disruption tipping points
Human-produced global warming is not just affecting the lives and deaths of humans. It is also fundamentally altering natural ecosystems that have evolved over millions of years, reaching states of equilibrium within a relatively narrow temperature range, long before humans started roaming the planet and then artificially heating it up.
Ecosystems provide services to the species that occupy them, such as plants taking CO2 out of the air, bacteria decomposing wastes, or bees pollinating flowers. We are now seeing many ecosystems come under stress due to global warming. Their potential to pass tipping points — thresholds beyond which they become unstable, shift to a new equilibrium, or collapse altogether — add huge elements of uncertainty to our future trajectory.
Here are three of the major ecosystem tipping points that scientists are monitoring today:
Transformation of the Amazon rain forest. The largest carbon sink on the planet is threatened by deforestation, wildfires, and an insane rightwing Brazilian government. Global warming could cause the rainforest to “die back” into a savannah, resulting in massive biodiversity collapse and 25% more CO2 being released into the atmosphere. About 20% of the Amazon has been destroyed over the past fifty years, and some scientists believe the tipping point for dieback is between 20–25% deforestation (source).
Retreat of the Northern Boreal forests. Extreme heat will put the vast coniferous forests covering the northern latitudes of Canada and Asia at risk. These forests are already threatened by heatwaves, droughts, and wildfires, all of which are releasing additional amounts of CO2 into the atmosphere. Contraction of the northern boreal forests due to global warming would significantly diminish the planet’s ability to absorb CO2 out of the atmosphere (source).
Destruction of coral reefs. Shallow-water reefs provide habitat for more than a million marine species, as well as food, income, and coastal surge protection for approximately 500 million humans (source). Coral is very sensitive to water temperature and reefs around the world are dying as ocean waters have become warmer and more acidified. Widespread loss of coral reefs will produce ecosystem collapse, failed fishing-based economies, and greater exposure to coastal storm surges and flooding.
Second-order effects of melting ice at the poles
Other potential tipping points involve cascading effects of melting ice sheets (discussed above in relation to sea level rise) and melting sea ice, including significant changes in atmospheric and oceanic circulation patterns.
Melting of the Arctic sea ice. As the world heats up, the Arctic sea ice, which floats on water, is breaking up. This has been identified as a potential tipping point because it impacts the Earth’s albedo — the extent to which the planet can reflect sunlight back into space rather than absorbing it as heat. Ice has a high albedo but ocean water does not. Scientists have warned that melting ice could trigger a feedback effect: less ice means lower albedo, lower albedo means more heat absorbed by the ocean, more heat means more ice melting, which lowers albedo further, etc. (source). More recent studies, however, have cast some doubt on this scenario, identifying other dynamics that appear to be enhancing Arctic ice formation in the cold winter months, thus delaying any albedo-driven feedback effects (source).
Collapse of the West Antarctic Ice Sheet (WAIS). A key source of uncertainty in projecting future sea level rise is the fate of this massive ice sheet which consists of about 10% of the Antarctic land mass. If fully melted, WAIS would raise sea levels by 3.3 meters (about 11 feet). Because this ice sheet rests on bedrock, it could detach due to warmer water circulating at its base. This, in turn, would destabilize other ice masses and greatly accelerate the rate of global sea level rise (source). Although 2°C is generally considered the warming level at which this process would become critical, the timing of collapse is highly uncertain, currently estimated at between 200 and 1,000 years, depending on future temperature ranges (source).
Loss of the Greenland ice sheet. This is the second largest ice mass on Earth. It holds enough water to raise sea levels by 7.2 meters (about 24 feet) if it all melts. It is currently experiencing accelerating rates of melting as the atmosphere warms. Researchers now believe 2°C warmer temperatures over time will trigger irreversible Greenland ice melt, a process estimated to take between 2,000 and 10,000 years to complete, depending on duration and magnitude of global warming (source).
Slowdown of the Atlantic Meridian Overturning Circulation (AMOC). The AMOC is a system of currents in the Atlantic Ocean, including the Gulf Stream, that bring warm water up to Europe from the tropics and beyond. The system depends on the saltiness of sea water, which can be diluted by rainfall and melting Greenland ice. Scientists believe the AMOC has weakened by about 15% over the last 70 years (source). According to the IPCC, it could shut down completely if temperatures increase above 2°C (source). This would result in significant cooling in the North Atlantic region, rising seas along the North American east coast, and severely disrupting marine ecosystems (source). Recent studies have determined that complete shutdown is unlikely to occur before 2100, but could reach a 50% probability by 2300 under a continued high emissions scenario (source).
Disruption of the South Pacific El Niño-La Niña oscillation pattern. The El Niño Southern Oscillation (ENSO) is a cycle of warm (El Niño) and cool (La Niña) weather patterns that happen every few years in the tropical Pacific Ocean. It produces one of the most dramatic year-to-year variations in the Earth’s climate system, affecting agriculture, public health, freshwater availability, power generation, and economic activity in the US and around the world. A recent analysis of changes in the ENSO due to global warming finds that climate change is already impacting these patterns. Scientists now expect extreme El Niño and La Niña events to double in frequency by 2100, assuming greenhouse gas concentrations continue to rise in the atmosphere. Expected impacts include extreme rainfall shifting further east during El Niño events and further west during La Niña events. Scientists are less certain about potential changes in rainfall patterns in the mid-latitudes, but believe extreme weather events may be more pronounced as global warming causes ENSO patterns to become more frequent and more extreme as the planet gets hotter (source).
Methane release tipping points
Methane is a greenhouse gas that breaks down much more quickly in the atmosphere than CO2, but also is up to 25 times more potent at trapping heat. Methane currently accounts for about 20% of annual emissions produced by human activity (source). Recently, scientists have identified two additional potential sources of methane release that could be triggered by global warming.
Melting of the Arctic permafrost. The Arctic permafrost, located across Siberia and North America, holds massive amounts of CO2 and methane in its frozen depths. As the atmosphere warms, the permafrost has begun to melt, potentially releasing those chemicals into the air and doubling the amount of CO2 in the atmosphere (source). Considerable uncertainty surrounds the questions of whether, when, and to what extent this release might occur. One influential study from 2015 argued that the release, even under high warming conditions, would be “gradual and prolonged” (source). More recent studies have raised additional concerns about “abrupt thawing” that could expose significant releases of permafrost carbon into the atmosphere “on the timescale of days to a few years” (source). Although uncertainties remain, most recent simulations indicate that permafrost melting is happening now and will be highly sensitive to different levels of warming, with emissions expected to be relatively manageable under 2°C warming, but much more severe under 3°C and 4°C scenarios (source).
Methane emissions from the ocean. Methane hydrates are solid compounds of methane trapped in frozen water stored in sediments on the ocean floor, mostly on continental shelves bordering northern land masses. The total amount of methane stored in these compounds is believed to be substantial, but has not been precisely measured. Methane hydrates decompose as ocean water warms, releasing methane into the sea and, eventually, into the atmosphere. Initially considered a potential “methane bomb” that could release gigatons of methane into the atmosphere as global warming accelerates, more recent studies have found that little or none of this methane is likely to reach the ocean surface, because it is oxidized by bacteria before it gets there (source). Scientists now believe that widespread decomposition of methane hydrates will not be a significant multiplier of global warming, at least not for the next few hundred years (source, source).
Effects of a hotter world on human health and mortality
Saving the worst for last, we need to consider the potential effects of a 2–4° hotter world on human health. The CDC has noted a number of direct effects of greater heat on human health, including increased respiratory and cardiovascular diseases, injuries and premature deaths caused by extreme weather events like hurricanes and tornadoes, and greater spread of water-borne and food-borne illnesses and other infectious diseases due to damaged or overwhelmed sanitation systems. Particularly concerning in the wake of COVID-19 is the fear that global warming will significantly increase viral transmissions across species, potentially triggering new and highly-transmissible infections and pandemics (source).
Many additional health risks have been identified. But for the most part, scientists are estimating first-order effects only. For example, a recent study reported that the “mortality cost of carbon” would be 83 million excess deaths due to climate change by 2100 (source). Although news reports treated this number as unspeakably large and a cause for panic (source), it is in fact unspeakably small and falsely reassuring. As the author notes, it includes only deaths directly attributable to heat, not deaths caused by flooding, mega-storms, droughts or second-order effects like crop failures, starvation, ecosystem collapse, vector-borne diseases, mass migrations, civil unrest, or any of the other tipping-point scenarios described above.
The total mortality cost of humanity’s short and dangerous flirtation with fossil fuels is likely to be much, much higher than scientists are currently projecting.
The world we are heading toward is not one of independent crises happening in isolation from one another. It is a world of complex interacting systems and feedback loops now being forced into new configurations thanks to the introduction by humans of environmental perturbations not seen in millions of years. I’ve listed 17 well-researched first- and second-order impacts of climate change, but I have not tried to describe the many ways they may interact with each other to produce even more dire outcomes.
Climate scientists have begun to look more closely at these interactions and potential tipping points. A recent study by Kemp et al. makes the case that the climate research community needs to focus more on “catastrophic climate change scenarios” in order better understand the full range of risks humanity is facing from global warming. They present a useful causal loop diagram, reproduced below, that captures many of the potential interactions, cascades and tipping points that will determine if and how humanity will survive the climate crisis we’ve created for ourselves.
Although incomplete and subject to many caveats, this diagram still does a nice job of visualizing some of the more important interactions at play in the climate crisis we have unleashed on ourselves. Yellow ovals represent relatively direct effects of global warming, many of which we have covered. Red ovals represent potential flashpoints for political conflict, including the thorny problem of massive migration due to climate displacement (source). Orange ovals represent ecosystem impacts. And purple ovals represent impacts on humans and their institutions.
Those last elements are what ultimately matters — food, water, and fuel shortages, institutional capacity, and mortality. As this cascade of climate-induced challenges rains down upon us, how bad will these shortages be, how resilient will our institutions be, and how many of us will live through the coming decades?
