We’re headed for 4 degrees of global warming
Looking at a future where we don’t stop climate change
In 2018, there was a call to limit warming under 1.5 degrees Celsius, or 2 degrees at the worst.
We’re already at 1.3 degrees, and we’re going to blow past both limits in the next few decades.
We had the Paris agreement. Politicians made some promises to do better. Despite all that, oil companies are drilling faster than ever. The UN publishes a production gap report, which compares what’s needed to stop climate change with the amount of fossil fuels countries actually plan to produce. Here’s what the report predicts, for the next 20 years:
To stay under 2 degrees, we need to start reducing fossil fuel use now and keep decreasing it every year.
In reality, we’re on track to burn more fossil fuels in 20 years than we are today. More oil, more natural gas, and almost as much coal:
Perhaps you’ve heard that we’re making progress towards green energy in the United States? We are building more solar power, but it’s not enough.
The US Energy Information Administration predicts that renewable energy will still make less than 20% of the energy used in 2050:
Despite the hype about electric cars, the EIA predicts that only 30% of vehicles will be electric in 2050:
They predict the US will be burning more oil and more natural gas in 30 years than today:
That’s a lot of oil, but we’re unlikely to run out. The Permian basin in Texas has at least 25 years of oil and gas to extract, at the rate we’re going. If it does run dry, drillers can just start fracking in other states.
CO2 emissions in the US will stay high. There might be some progress in Europe. Japan has restarted their nuclear energy program. China and India will keep on growing their economies with oil and coal, purchased cheap from Russia. Worldwide, we might hit 25% renewable energy by 2050.
We could do better, if we wanted. We could build solar more quickly. We could invest heavily in battery research. We could start a massive nuclear energy program. But most politicians don’t think that big, they think about getting re-elected in 4 years.
It looks like we’re headed for at least 30 more years of global warming.
Will things get better, after 2050?
Most government forecasts don’t go that far. Here’s a prediction from William Nordhaus, an economist who won the Nobel prize for his work on predicting climate change:
If we don’t do anything, we’ll emit a lot more CO2 in 2100 than we do today. To keep warming under 2.5 degrees, we have to cut back now and be done burning by 2040. Government forecasts don’t think that’s happening. Nordhaus says it would cost too much.
Nordhaus thinks there’s an economically optimal path, somewhere in between, where emissions peak around 2050 and are in decline by 2100.
It’s not certain that will happen. Countries will still have to work together to limit their emissions. If they don’t, emissions might not slow down at all.
For an even more pessimistic projection, here’s a prediction from fossil fuel enthusiast Bjorn Lomborg:
He thinks people will be burning more fossil fuels in 2100 than today.
This century’s going to be a hot one.
How much will the world warm up?
Before the industrial revolution, we were at 280 ppm of CO2.
Right now we’re at 420 ppm of CO2.
By sometime around 2050, we’ll be at 560 ppm, double the pre-industrial amount.
CO2 is a greenhouse gas. It lets sunlight into the atmosphere, but it keeps infrared radiation from the Earth from leaving back into space. The Earth ends up warmer:
As you put more and more CO2 in the atmosphere, there’s more warming. But the effect slows down as you add more. Each bit you add has slightly less effect.
The Earth has a climate sensitivity. Let’s pretend it’s 1 degree Celsius.
The equation says that if you double the CO2, the temperature goes up by 1 degree. If you increase it by 4 times, it doesn’t go up by 4 degrees, it only goes up by 2 degrees. If you increase CO2 8 times, it doesn’t go up 8 degrees, it only goes up 3 degrees. Each time you double it gets you another +1 degree.
In some sense, that’s good news. Global warming should slow down. We’re on track to double natural CO2 by 2050, we could maybe quadruple it someday. It would take a long time to get to 8 times the natural CO2 and even longer to get to 16 times.
The bad news is that the climate sensitivity is higher than 1 degree per doubling of CO2.
The climate sensitivity would be 1 degree for a theoretical atmosphere with nothing but CO2.
But the actual Earth is a complex system with feedback loops. If you increase CO2, temperature goes up. That increases water vapor, and water vapor is also a greenhouse gas, so the warming gets faster.
As the world warms, polar ice melts. Snow and ice are good at reflecting sunlight back into space. The water or land underneath is a darker color than the ice, so it doesn’t reflect as well. Less sunlight gets reflected back into space, the warming accelerates.
As polar regions heat up, the permafrost starts to melt. Roads in Alaska start to buckle:
Trees start to tilt as the ground shifts:
The permafrost releases methane. Methane is a potent greenhouse gas.
Those are all positive feedback loops. On the other hand, higher temperatures may create more clouds. Clouds reflect light better than the land or water underneath them. So that would be a negative feedback loop.
So we don’t know exactly how strong all the feedback loops are. So we don’t know what the climate sensitivity is. There are two ways to figure it out.
One is to just look at what’s happened so far.
We are 58% of the way to the first doubling of CO2. We’ve had 1.3 degrees of warming in that time.
That means the climate sensitivity is 2.25 degrees Celsius.
But that’s not a perfect approach, for a couple reasons.
First, we pollute with other gasses besides CO2. Methane makes the world warmer, Sulfur Dioxide makes it cooler. We’d have to look at all the other pollution to know the exact value. In another article, I estimated that if we cleaned up all the Sulfur Dioxide pollution, mostly from China, then the world would warm up another 0.7 degrees.
That means the climate sensitivity from CO2 might actually be higher, since the sulfur pollution is keeping some of it in check.
Second, it takes time for the feedback to happen. Even if we stopped burning fossil fuels tomorrow, the world would keep warming. It’s hot enough that glaciers are melting. The warming would still continue for decades, or even hundreds of years, after we stop, as ice in Greenland and other places slowly melts.
The other way to figure out the climate sensitivity is computer modelling of the climate. The computer models don’t all agree.
According to the most recent IPCC report, our climate sensitivity is “somewhere between 2 and 5 ℃”.
We’ve already measured the sensitivity around 2.25 degrees, so it’s at least that high. But the feedbacks will take time to kick in and then we’re in for more warming than that. We don’t know exactly how much more.
William Nordhaus made a forecast for temperatures for the next century. He thinks we’ll exceed 4 degrees of warming if we make no effort to stop climate change. In his economically optimal model where we make a big effort to reduce CO2, we’ll hit 3.5 degrees by the end of the century:
So, that’s 3.5 degrees in the best case, and we’re still not done with warming. We’d still be emitting some CO2 by 2100, and the climate feedbacks will keep the temperature rising after we stop.
I think we’re headed for at least 4 degrees total. If the feedbacks are large and slow, 4 degrees could turn into 6 degrees by 2200.
Warming will be uneven:
4 degrees still might not sound like a lot.
First off, this is Celsius. For the Americans that think in Fahrenheit, multiply all numbers by 1.8 (or just double them, if that makes the mental math easier).
Beyond that, the warming will be worse than that, in a lot of places.
We’ve had 1.3 degrees of warming, so far, since the pre-industrial era. But 1.3 degrees is just an average of every spot on the Earth.
The oceans warmed one degree and the land warmed two:
Even on land, the warming is uneven.
The warming has been especially pronounced at far northern latitudes:
When we talk about 4 degrees of warming in 2100, that could be closer to 6 degrees on land and 9 degrees in the Arctic.
In Fahrenheit, we’re talking 11 degrees on land and 16 degrees in the Arctic. That will be enough to melt a lot of ice.
Heat waves will get worse
Take the highest temperature your city has seen in summer. Add 6 degrees Celsius or 11 degrees Fahrenheit.
If you live in Seattle, a 77 degree F summer is now 88 degrees. That sounds kind of pleasant.
If your summer weather already hits 100 degrees, the increase might not be as desirable.
Phoenix averages 106 degrees F, in July. Could it go all the way up to 117?
Some places will get fatally hot
The human body can survive high heat, but only if it’s dry heat. If it’s hot and humid, there’s a fatal point where you can’t sweat to cool off.
That’s called the “Wet bulb temperature” limit. It’s 35 degrees Celsius or 95 Fahrenheit with high humidity.
Right now, there are parts of the United States that see wet bulb temperatures around 29 degrees. Add 6 degrees and you’re pushing near the limit on the east coast and the south. Parts of Arizona and Mexico would go over the limit:
Big parts of India and the Middle East would go over the limit:
Some other parts of the world will be in trouble — West Africa, Brazil, most of Australia:
Sea level will rise
Sea level will rise, but not quickly. Most scientists predict less than 3 feet of sea level rise by 2100.
The amount of warming is enough to melt the entire Greenland ice sheet, which would cause 20 feet of sea level rise. But the ice sheet is incredibly thick and only a part will melt, each year. It will take hundreds of years, maybe even over a thousand, to melt entirely, and the ocean will keep rising the whole time.
If things get hot enough that Antarctica starts melting, the process could speed up a bit and the long term rise could be up to 200 feet.
For more details, see this article:
Sea ice in the arctic will melt
Unlike the thick ice sheets in greenland, sea ice is very thin.
Summer ice extent is already much lower than it was in 1980.
We’ll start having ice free summers in the Arctic ocean. The open water will absorb more sunlight that the ice currently reflects into space. That’s one of the unknown feedbacks that will make the warming keep happening.
The oceans will get more acidic
One forecast predicts that Coral reefs will stop growing around 2030, as CO2 reaches 450 ppm. When it reaches 550 ppm, maybe around 2050, coral reefs in many areas will start to dissolve.
Some changes will be irreversible
A small amount of warming is reversible by pulling the CO2 back out of the atmosphere. A large amount is not.
If we melt a thousand year old glacier, then cooling the planet again won’t bring the glacier back. We’d need to lower the temperature even more than normal, get it to snow for a thousand years, and wait for the glacier to refreeze.
The ice in Antarctica is a few million years old.
Any species that go extinct will stay extinct.
Humans can adapt well to many different climates. Plants and animals may not adapt to rapid changes. It’s hard to predict the effects on ecosystems, but there will likely be a large scale loss of bio-diversity.
The world won’t end
Life could get miserable in some countries.
Food production is not forecast to decline until we get above 3 degrees. But in tropical countries, crops will start to be affected at 1–2 degrees.
There will be climate refugees. A lot of animals will go extinct.
Many wealthy people’s lives won’t be affected enough that they stop to care about it. They’ll buy air conditioning and keep driving cars, while things keep getting worse.
Will we do anything about it?
I hope so, but I doubt it.
We’re not very good at solving problems until they become serious. In America, Covid was “a liberal hoax” or “just the flu” until New York hospitals got overwhelmed. Then we took it kind of seriously for a while, then we ignored it again while a million people died.
Rather than working together, countries shut their borders.
Current green energy technology isn’t good enough to solve global warming, mostly because we need better batteries. Nuclear could help, but most people are too afraid of it, and we’d still need to research new types of reactors.
A few groups are working on this. There’s a Bill Gates funded company working on Uranium breeder reactors. There’s a small company working on Thorium reactors. There are many groups working on improving green energy and batteries.
Let’s hope that technology will save us, because the politicians are still making empty promises.
