Previously, we covered the basic science of greenhouse gas theory, the focus on CO2, and the trends we’ve observed so far.
In this article, we’ll examine the predictions for the future. This is a hefty article so I’ve included a TL;DR after the intro.
All predictions are wrong. That’s ok.
Much has been written about the coming catastrophe. I (like many of you) have spent a fair amount of time doom-scrolling climate disaster scenarios stating that unless we dramatically reduce emissions immediately we’ll be living in a hellscape by 2050.
However, this isn’t a fair representation of the science. Rather, there are many potential futures, some worse than others, with consequences unequally distributed. Instead of boiling the ocean (🥁), let’s focus on a “likely” warming scenario.
I put “likely” in quotes because accurate projections require:
Correctly projecting greenhouse gas emissions
Correctly projecting the warming from those emissions
Correctly predicting the effects of that warming on our ecosystems
This is hard for many reasons. There is no climate prediction as it depends heavily on the interpretation of these 3 variables. The IPCC has acknowledged this predicament with comforting words like:
“The climate system is a coupled non-linear chaotic system, and therefore the long-term prediction of future climate states is not possible. Rather the focus must be upon the prediction of the probability distribution of the system’s future possible states by the generation of ensembles of model solutions.” (source)
Just because we don’t know exactly what will happen does not mean we should ignore every prediction. Instead, we can make assumptions for each variable to project a middle-ground future. The models will be wrong, and that’s ok! But so long as it’s directionally correct, it’s still useful to make decisions for the future. Now that we got that major disclaimer out of the way, let’s dig in.
How much warmer will the future be?
First, we need to estimate future emissions. The International Energy Agency (IEA) recently released a report outlining what it takes to get to net-zero by 2050. It covers 2 extremes: ‘business as usual’ and ‘fulfilled commitments’. Since we’re trying to figure out what’s at stake if we don’t do anything, let’s be pessimistic and assume no herculean efforts are taken and global energy emissions approximately flatline from here on out.
If this sounds unlikely, emissions for the largest historic emitters (i.e. US, UK, Japan, etc) have already flatlined for the last 20 years. CO2 accounts for 75% of GHG emissions, so we need to apply to a multiplier to account for other GHGs to get to ~45 GtCO2 equivalents . Under this emissions scenario, we’d expect CO2e concentrations in 2100 to reach ~850ppm1.
Next, we need to translate this concentration into temperature change. The IPCC has consolidated many many models (>30) to transform potential CO2e concentrations into real-world outcomes based on the projected radiative forcing. These projected pathways are known as RCPs & 850ppm lands us right around RCP 6.0, or 6W / m^2.
Side note: If this sounds like gibberish, dig into my past posts for a refresher on how this science works!
Based on our assumptions that (1) the world doesn’t fulfill its commitments, (2) the IEA emissions projections are correct and (3) the IPCC warming estimates are close (which is hard), we can expect ~2.8℃ of warming by 2100.
What happens as the world warms?
Short on time? The ultimate TL;DR:
Many of our reefs will die, directly harming 25% of all fish and food for 500M people
The arctic will continue to melt, raising sea level on ~800M people {4.3.2.2} & dramatically change the arctic biosphere.
Earth will be hotter & precipitation more extreme. Already wet regions will experience deluges. Already dry regions will be more susceptible to drought. Everyone will experience this to some extent.
The people who will suffer most live in coastal, low elevation, and drought prone regions. Weather extremes will decrease regional staple food output by at least 20% {3.5.5.9} & expose 350M to deadly heat stress {3.5.5.8}.
All this wild weather will hurt economic output, ~$38T by 2100 {3.5.2.4}
In the landmark 2018 1.5° report, the IPCC outlined the 5 major ‘Reasons for Concern’ (RFC) from warming to 1.5°C above pre-industrial levels. For context, the Earth has warmed ~1.0°C since 1850, but our CO2 emissions have increased precipitously in recent years suggesting we need to strap in for more. The high end serves as a great proxy for our estimate of ~2.8℃.
By analyzing each RFC, we can project what Earth will look like under different scenarios. All confidence & likelihood levels are copy/pasted from IPCC. If you want the full picture, look here.
Unique & Threatened Systems
Rising temperatures are having an outsized impact on specific vulnerable systems. Most notably reefs & the arctic.
Reefs
TL;DR: Very sure coral reefs (and the fish they support) will decline significantly, there is high confidence this is from human-induced ocean warming & acidification.
Since 1800, the ocean has absorbed ~90% of the heat and 25% of the CO2, causing ocean acidification. Coral reefs are particularly sensitive to changes in ocean temperature and shelled creatures are particularly sensitive to acidification.
Rising ocean temperatures & acidification are virtually certain to occur at 1.5C and pose very high risk {5.3} to reefs which support 25% of Earth’s fish & feed 500M people. The second order effect of these ecosystems collapsing is unknown.
Arctic
TL;DR: Very sure the Arctic is warming & high confidence it caused current sea ice loss & sea level rise. High confidence it will continue to warm, but medium confidence future sea ice loss will be from humans. High confidence that a warming Arctic increases the risk of permafrost loss, but medium-low confidence it will actually happen.
While the Earth has warmed by 1C on average, the Arctic has warmed at double that rate (likely) with Arctic winters now 6C warmer than 20th century averages (medium evidence, high agreement). There is a strong link between Arctic warming and human emissions, leading to high confidence {3.1} for future warming.
A warming Arctic has 2 major global effects: sea ice loss, permafrost exposure. Arctic sea ice has declined ~12% per decade (very high confidence) which is unprecedented in a 1000 year window (medium confidence), causing sea level rise of ~1.2mm / year, up 700% from 1992 {3.3.3}.
Perpetually frozen soil (permafrost) is at risk of melting as temperatures rise (very high confidence), but there is medium evidence and low agreement that projected warming is currently causing northern permafrost regions to release additional methane and carbon dioxide {3.4.1; 3.4.3}. The risk of significant permafrost meltdown is possible at RCP 8.5, but that scenario is unlikely.
But what about the rainforests and other endangered species? - Reasonable Person
Hot Take 🔥 :Our human footprint on this planet extends far beyond the gas we put into the atmosphere. Deforestation, pollution, and other land-use impacts have had a dramatic impact on ecosystems around the world. If our goal is to preserve the Amazon rainforest or protect collapsing fisheries, there are separate problems we’d need to solve first (like overfishing).
Extreme Weather Events
TL;DR: Rising temperatures increase surface and ocean temperatures, an important ingredient for extreme weather. We experience this as more frequent extreme droughts, heat, and storms. (pg 254)
Temperature changes will not be equally distributed & it’s likely that land-temperatures will increase >2.5C (4.5F). Similarly, precipitation changes will also be unevenly distributed. Subtropics will trend towards drying while northern latitudes will trend towards wetting.
Increased risk of regional agricultural drought is likely in presently dry regions and are projected with medium confidence by the end of the 21st century under the RCP8.5 scenario (which is hotter than likely). The Mediterranean and southern Africa are most at risk from regional precipitation reductions and droughts {12.4.5}
Globally, a shift to more intense individual storms and fewer weak storms is likely as temperatures increase. Over most of the mid-latitude land-masses (e.g. North America) and over wet tropical regions (S.E. Asia), extreme precipitation events will very likely be more intense and more frequent in a warmer world, increasing flood risk in flood prone regions.
Storms are harder to predict. While there is a trend in storm frequency, there is medium confidence that we will face high risk from increasing storm intensity at 2C, but again, it’s very hard to predict.
Distribution of Impacts
TL;DR: There is high confidence that equatorial, low elevation communities that are already vulnerable to flood / drought will be increasingly susceptible to weather extremes {3.5}.
Risks are generally greater near the equator and for disadvantaged people in developing communities. Higher temperatures & more intense precipitation (floods / droughts) put these communities at a higher risk of regional crop interruption and water scarcity at > 2C.
Specifically, there is medium confidence that the African Sahel, the Mediterranean, central Europe, the Amazon, and western and southern Africa will experience even higher risks of food shortages. {3.5.2.3}
At 2C, more than 90% of the world’s coastlines will experience sea level rise greater than 8 inches. An estimated 630M people currently live below projected high-tide levels by 2100. You can experiment with this NOAA tool to see how it plays out for the US.
What’s worse, already hot regions will only get hotter. Rising surface temperatures are predicted to expose 350M to deadly heat stress {3.5.5.8}. The record heatwaves this summer are an ominous warning that we are just beginning to understand.
Global Aggregate Impacts
TL;DR: All of the damage mentioned above will cost us ~3.5% gross world product (GWP) by 2100 and a non-trivial ~13% of species will go extinct. However, since these are 3rd order effects, they have wide error bands.
Economic impacts are hard to predict, but there is a consensus that the impact will be negative at 1C, and will continue to get worse the warmer it gets {3.5.2.4}. As we observed with COVID, supply chain disruptions on the other side of the planet affect everyone. The world’s factory is now in Asia & will increasingly be in the future. Meaning, even if North America is less affected by rising seas, we will still pay for it in a higher cost of goods.
An estimated 3.5% of GWP is at risk with our status quo approach ($10T by 2050, $38.5T by 2100) (pg 256). Money managers & insurers have taken note & are increasingly applying their leverage to mitigate this risk.
More importantly, we will save lives by transitioning to clean energy & stoves. While clean electricity is more cost-effective in some markets, we gain much more as a society by saving the 7M people who die annually from fossil-fuel induced air pollution, adding 0.5% of GWP {3.5.2.4}.
13% of Earth’s land area is projected to undergo a biome destabilization at 2C (warmer air, precipitation changes, etc). Insects are particularly vulnerable with 18% projected to lose at least half of their natural biome. Since temperature change is not uniform, the impact on a specific species in a specific region is hard to pin down precisely.
Large-scale Singular Events
TL;DR: there is limited evidence that we’ll cross a point of no return in the 21st century. However, if our status quo continues past 2100, future generations will have to grapple with irreversible climate shocks.
These ‘tipping-points’ are run-away events that cause dramatic changes to our climate. There are 3 major areas of concern: permanent ice loss, shut-down of Atlantic current, and permanent El Niño instability.
Ice: There is little evidence {12.4.6} in global climate models of an imminent tipping point (or critical threshold) in the transition from a perennially ice-covered to a seasonally ice-free Arctic Ocean beyond which further sea ice loss is unstoppable and irreversible. However, a maintained temperature increase of 1.5-2C may initiate an irreversible loss of the West Antarctic ice sheet over millennia {3.5.2.5}.
Currents: It’s more likely than not that the Atlantic Meridional Overturning Circulation (AMOC), which moves heat along the Atlantic Basin, has weakened in recent decades, but there is limited evidence linking this to anthropogenic warming {3.5.2.5}. It’s very likely that it will weaken over the 21st century by ~11%, but there is no evidence that the AMOC will undergo an abrupt transition or collapse in the 21st century.
El Niño: Extreme El Niño events that bring heavy rain to the Americas & drought to southeast Asia appear to increase in frequency as surface temperatures rise. With 2C of warming, the frequency of these events may double (~10 years), but then stabilize. This is the most serious risk as more frequent extreme drought in Asia places billions at risk.
So what do we do about it?
The climate system is incredibly complex. We cannot yet explain everything we observe, but the consequences of our actions are already clear. Every year, once-in-a-decade weather is now normal. In order to avoid future warming, we need to limit the quantity of GHGs in the atmosphere.
The obvious way to do this seems to be to cut all GHG emissions ASAP. However, it’s not that simple. Fossil fuels play an integral role in nearly everything we associate with ‘modern life’ which extends far beyond dirty energy generation.
We need to think beyond the greenification of our grid and consider how we got into this mess in the first place: exploding energy demand. Why do we need so much energy? What is it used for? How can we minimize our demand for energy?
Next time, I’ll explain the root causes of climate change & how we can build a more sustainable future.
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Until next time,
Logan
Want more?
Dig into the core science of climate change here & the IPCC assessments on long-term effects , warming at 1.5C, and models. Page 264 also has a great summary of the risks.
Chomping at the bit for more climate change content? Here are some of my favorites:
The Carbon Curve: Learning about the frontiers of carbon dioxide removal and carbon tech - and how to scale it up
Going Green: What problems need to be solved on the path to a carbon-free economy (digital and physical)?
🤷🏽♂️ Not My Problem: Startups across the world that are working towards improving the health of the planet
Evergreen: The main climate challenges and opportunities in front of us. Breaking down the particular causes of emissions within our economy and what solutions will get us to net zero.
Climate Money: How climate and money (finance, currencies, market opportunities) intersect
Climatic Thoughts: Solutions towards keeping the world under 2 degrees of warming
Climate Pioneers: Exploring low- and high-tech climate solutions.
Extra disclaimer: Science is never done and we’re always learning more. What’s presented here is the current global understanding from an ensemble of climate scientists across leading government organizations pulling from a range of peer-reviewed research (i.e. NASA, IPCC). This will change.
Usual disclaimers: I’m not an expert and will never claim to be. I’ll probably be lacking context, too vague, or flat-out wrong frequently & I hope folks will hold me accountable. After all, the fastest way to find the right answer is to post the wrong answer visibly on the Internet. Lastly, there is a ton of great information online already (e.g. Drawdown, Breakthrough Energy playbooks). I will synthesize and cite as I go.
Doing the math:
1 GtC = 44 gCO2/12 gC = 7.8 GtCO2e / ppm
Annual CO2 = 45 GtCO2e / year
Years to 2100 = 80
CO2 added = 2800 GtCO2e
Added ppm: ~460ppm > total ppm 860ppm