please see his post at the link above to see the charts and access hyperlinks in the article
There’s a big dispute in climatology, in regards to equilibrium climate sensitivity: How much does the Earth warm up, when you double CO2 in the air?
The IPCC maintains an estimate of 3 degree Celsius per doubling. Some, like James Hansen, think the number is much higher. He thinks it’s 4.8 per doubling, but many of the climate models the IPCC uses sit even higher, above 5 degree. The general idea is that these models “must be wrong”, so they’re not given the same weight when it comes to making predictions for how much warming we will get in the future as models that predict less dramatic warming get.
The main argument given to dispute the credibility of these models, is that they don’t properly reproduce the warming we have seen so far.
The dispute between models mostly comes down to differences in how the clouds are expected to respond. The “hot models” predict that the warming we experience from more CO2 results in a reduction in clouds that reflect sunlight. Thus these models are said to have “positive cloud feedback”.
But not everyone believes these models get it right of course, that’s why there is a scientific dispute. If these “apocalypse predicting” hot models were right, the Earth should be warmer than it actually is right now, that’s the idea upheld by those who are not convinced the hot models get it right.
The counter-argument to this idea, is that the hot models predict greater warming than we have seen so far, because there is other stuff we’re doing that is still keeping temperatures down.
So what are those things? One of them is the temperature reducing effect of air pollution, an effect known as global dimming.
This is the same effect that led some scientists to predict “global cooling” in the past, but as we succeeded at cleaning up a lot of this pollution, it became obvious we would find ourselves faced with rapid global warming in the future instead.
Estimates of how much global dimming we’re causing right now still vary quite a lot from one study to another.
How much it keeps temperatures down matters a lot, because this air pollution is something we will eventually stop dumping into the air: It kills millions of people by damaging our lungs and it acidifies the soil.
So far so good, anyone who has looked into climate change is probably familiar with what I have explained so far.
There is however another important thing we’re doing that helps keep our temperatures down, especially during summer. When you realise what it is, it feels pretty obvious, but it also confronts you with a massive looming problem.
As the author of one study puts it:
“In summary, we showed that irrigation expansion has regionally masked the historical warming of hot extremes from anthropogenic greenhouse gas emissions and all other climate drivers combined,”And as the authors of a different study put it:
Given our results for California and the global importance of irrigated agriculture, past expansion of irrigated land has likely affected observations of surface temperature, potentially masking the full warming signal caused by greenhouse gas increases.We irrigate about 17% of the world’s land, to produce 40% of the world’s food. This land has its surface temperature reduced by about 5 to 7 degree Celsius, because the land cools as the water evaporates. This is not all positive, as the resulting higher humidity makes it harder for humans and other animals to sweat, but it does bring temperatures down.
More importantly however, when the water evaporates, it increases the formation of clouds. With satellites you can see that irrigated land has an average cloud cover of 40% during the day, versus 25% for non-irrigated land. These clouds peak between 2 and 4 PM, which is also when the heat influx into the environment from the sun is most intense. These clouds reduce temperature stress for the crops and reduce their water demand. In addition, photosynthesis tends to benefit from how these clouds turn direct sunlight into diffuse sunlight.
In large parts of the world, the water that is evaporated from irrigation, leads to an increase in rainfall, often up to hundreds of kilometers downwind. As a good example, the irrigation in the central valley of California increases water availability by 28% in the Colorado river basin.
Irrigation causes significant cooling of global average surface temperatures, primarily over land. The authors estimate 0.07 degree Celsius reduction in global temperature for the Earth as a whole, or 0.17 degree specifically on land.
A lot of people have been wondering, why India is lagging behind in global warming, compared to the rest of the world. Over the past 40 years, India has only warmed by 0.09 degree Celsius per decade, versus the global average of 0.30C per decade, and below the 0.23C recorded for regions at similar latitudes.
How did that happen? Well we know the answer. They began ramping up their irrigation:
Right now, it’s estimated that around 1 degree of global warming is suppressed over India, thanks to irrigation, both from the direct effect and the indirect effect (enhanced cloud formation):
The effect is strongest, in India’s agricultural powerhouse, the Northwest:
In Northern Italy, studies find that irrigation reduces the peak of a heatwave, by 6.6 degree Celsius. Humidity in the air does increase, but the wind blows that humid air away, so you’re still much better off, thanks to the irrigation.
But here’s the thing. Around the world, a lot of the water we use to irrigate our crops is groundwater, 43%. That groundwater, is generally being depleted faster than natural processes can refill the aquifer. In other parts of the world, we’re getting the water for irrigation from rivers that are supposed to be feeding lakes. The great salt lake is dying, because 62% of the river water that used to feed the lake, is now used for irrigation. Most irrigation as currently practiced by humans is unsustainable.
Farmers and governments know this. So how do they respond? Well, one solution is drip irrigation. Instead of just spraying a lot of water on your land, you slowly drip water on your crops. This causes less water to be lost through evaporation. This is great for the farmer and for the local aquifer, but think about the consequences.
Less water is used for irrigation. This means less water now evaporates. This mean you get less cloud formation, less reduction in temperatures over the land, less rain further downwind. All the positive externalities from irrigation are basically eliminated, when the farmers switch to drip irrigation. The farmers however, don’t have much of a choice. A lot of these farmers can’t just keep using the large amount of water they’re using right now.
The Water Situation in the Indian Subcontinent
After a terrorist attack, the government of India suspended the Indus water treaty, which requires India to share water with Pakistan. The Indian minister of water declared that not a drop of water will flow into Pakistan. India doesn’t have the infrastructure yet, to follow up on that threat. They’re now working on building the infrastructure, to deny Pakistan any water.
First they started dredging their dams. They have also now started planning the construction of new dams. They’re also building new canals, where the water can be used. They’re also diverting water to the northern Indian states, with a new tunnel that is supposed to be operational by 2029.
So, what happens to Pakistan? Well for starters, the Pakistani government is not happy. Their climate change minister has threatened to “chop off the hand” that tries to control its water. Pakistan was supposed to receive 80% of water from the Indus, under the Indus water treaty.
Pakistan has two main sources of water: They have the water from the Indus river system and they have groundwater from their aquifers. I can’t really find consistent reliable estimates on what percentage they derive from the Indus river system and what percentage they derive from their aquifers. Pakistan’s minister says half the population depends on the Indus river system. Some sources say 90% of agriculture in Pakistan depends on the Indus river system.
Other sources say that more than half of Pakistan’s water use in agriculture, comes from groundwater. The problem however, is that they’re using their groundwater much faster than nature can replenish it. Most cities in Pakistan have rapidly declining groundwater tables. A study recently estimated when groundwater extraction will peak in Pakistan. They arrived at 2040 as the most likely year when groundwater extraction from the Indus aquifer would peak. But that was before India suspended the Indus water treaty.
So, why is India doing this? The official reason is because of the terrorist attack. In reality however, they simply need the water themselves. Estimates are that by 2030, 40% of India’s population will have no access to drinking water. Estimates are that lack of water will reduce cropping intensity in India by 20%, with a reduction of 68% in the most water-scarce regions.
When an aquifer is depleted, the grains of sand that used to leave room for water are gradually compacted by the pressure from the soil above. As a result, after depleting an aquifer, it tends to be unable to properly recharge, even once you stop using the aquifer.
India’s recent heatwave was much worse than anything we faced in Europe. During these heatwaves, if you live in a city like New Delhi, there is just not any water coming out of the tap. Drinking water has to be driven into the city, by a “water mafia”, that bores illegal well holes. Then the population has to stand in a cue, to buy water from these tankers.
In Bangladesh, it’s the same problem. They just declared 5,000 villages as “water-stressed areas”, meaning the people are just not allowed to use the ground water to irrigate their crops anymore, they can only use the water to drink it themselves. In 1950, Bangladesh had 40 million people. Today, Bangladesh has 178 million people.
In Bangladesh, you have 20 million people living in the capital city, Dhaka. In Dhaka, the groundwater table is declining by 2 meters per year. By 2030, they’re looking at the groundwater table declining by 4 meters per year. As you have to delve deeper, there’s more arsenic and other pollutants in there. But eventually, it just gets so deep that it costs you too much energy to get the water up.
In other parts of the country, their problem is that when they use up the water beneath their feet, salty seawater infiltrates the groundwater. Salt water infiltration is threatening drinking water and water for agriculture, for more than 20 million people in Bangladesh. That’s more people than live in the entire Netherlands.
So, is there a technofix? Could India’s government just deliver desalinated water to Northern India instead? No, the math doesn’t math. Desalinated water would be about three times more expensive than the wheat it produces, so your food would become four times as expensive.
This is just the cost of desalinating the water at the coast. To transport all the water inland all the way from the coast to Northern India would roughly equal the cost of desalinating the water. In other words, your bread would be seven times as expensive as it is today.
The Water Situation In California
California produces huge amounts of food, the valley is said to produce a quarter of all food in the United States. The problem is, they depend on an aquifer that’s being depleted to produce that food, but the ground has now compacted, so that it has become physically impossible for the aquifer to be refilled by nature.
In parts of California, the situation with the aquifer is so bad, that the government has simply instructed farmers to stop using groundwater like the government did in Bangladesh, so the farmers are just leaving their land dry.
So with these new rules that means California is going to struggle to produce as much food from now on, as it did in the past. But think about all the feedback effects we now start to get as a result:
- Local temperatures get higher
- Less clouds are being generated
- The rest of the United States now gets less rainfall
Through irrigation we’re both increasing rainfall when it is most needed and reducing the amount of water our plants need, by reducing peak heatwave temperatures.
If you take this into consideration, you’ll realize that when we have to stop irrigating our crops, we’ve got one hell of a feedback coming.
One study looked at what we can actually expect, in regards to groundwater depletion. They looked at 235 groundwater basins and found that total global human groundwater extraction will peak at 625 km3 yr−1 around mid-century, followed by a decline through 2100.
The peak and decline occur in about one-third (82) of basins, including 21 that may have already peaked. This will result in exposing about half (44%) of the global population to groundwater stress. The countries that are worst affected, are the United States, Mexico, Pakistan, India, China, Saudi Arabia and Iran.
There are also places, where groundwater use just doesn’t really seem to be an issue. Global warming is an easier environmental problem to understand, we’re all suffering from the pollution of the global commons. But groundwater is a stranger one: There are places that have already exhausted their groundwater, there are places busy exhausting it and there are other places where the groundwater reserve is actually increasing.
Soil erosion is a similar problem, there are places where we’re losing our fertile soil to erosion and there are other places where this is just not a serious problem.
Add the whole picture together however, and you see the problem: There are parts of the world where we’re running out of the soil our crops need, there are parts of the world where we’re running out of the water our crops need and there are parts of the world where the temperatures are simply getting too hot to properly grow crops.
Finally, there are places where the soil is good, the water we need is available and the temperatures are acceptable, but we’re running out of people who can grow the crops! Japan is a good example of this. They’re shrinking their farmland from 4.2 million hectare in 2020 to just 2.7 million by 2050. Their caloric self-sufficiency, will decline from 37% in 2020, to just 29% by 2050. The reason is because their farmers are old and they have nobody to inherit the farm.
Russia is another example. You have all these climate models, that predict that although food production will decrease as a result of climate change in countries near the equator, it’s no big deal because food production will increase in Russia and that will compensate on a global level. Here’s an example of what I mean:
This is what the World Bank published, back in 2010. Most of the world sees yields go down by 2050, but don’t worry, because Russia, Canada, New Zealand and Scandinavia will bail the rest of us out!
Well, that’s not going to happen, because the Russian government has been stupid enough to spend the past few years invading Ukraine. By now, a fifth of Russian farmers face bankruptcy. They don’t have the diesel they need. Russia is not going to increase its food production, they’re struggling to hold onto what they have.
Nobody seems to bother accurately modeling the situation that lies ahead of us, by incorporating all variables. Example, there’s much ado now, about a study that claims 1 degree of global warming reduces rice yields by 8.1%, rather than 3.8%.
But read the study and they admit:
Our estimates should be interpreted within the context of physiological effects. The temperature-yield relationships are derived from single-factor warming experiments, which allow us to isolate high-temperature effects from confounding water and nutrient stresses. However, these experimental conditions may differ from farmer-managed fields, where yield outcomes also depend on complex interactions among temperature, water availability, crop physiology, and canopy energy balance.
They’re looking at one variable in isolation. Globally, 75% of rice agriculture is irrigated. If you can’t irrigate your rice anymore, yields don’t drop 8.1%, they collapse.
But let’s take a look again, at the study that predicts what’s going to happen to our groundwater. At the end they write:
Our model does not include an explicit physical representation of processes such as recharge, capture or lateral flows. However, these dynamics are embedded in the historical depletion datasets we use to calibrate our model, and alternative depletion limits (described above) allow us to capture a range of plausible future groundwater availabilities resulting from changing human-induced or naturally varying fluxes.Alright, so you’re not properly modeling how the aquifer recharges. Well that’s a problem, because the recharging of our aquifers changes too. As our climate changes, what happens is that you get longer periods of drought, followed by an increase in rain that falls all at once.
That’s a problem. Dried up land, struggles to absorb water. What is now happening in practice all across the world, is that we get a bunch of rain all simultaneously on dried land, that ends up in the rivers and is eventually dumped into the ocean. It no longer recharges our aquifers!
So again, when they say we will hit peak groundwater around 2050, that fails to take into consideration that our aquifers are no longer getting properly recharged.
And in fact, aquifers that now look sustainable to these scientists, that look like they are not being overexploited, may turn out to be overexploited after all, because the rain will stop refilling these aquifers for us, because it all falls simultaneously on dried-out soil that can’t absorb the water!
This is just lack of water that I’ve talked about. Your crops will get the opposite side of the coin too: Too much water, all at once. When your farmland is flooded for an extended period of time, your crop yields drop to zero, because the plants die and rot.
You can look at what happened to Pakistan’s rice production in 2022, when the country suffered severe flooding. They lost a third of their rice output that year.
And then there are the dense plumes of wildfire smoke, which can be enough to wipe out your harvest in their own way. If your crops don’t get sunlight, they don’t grow.
Our entire system of food production, depends on cereal grains. Two thirds of all the calories we consume, directly or through the animals we eat, come from grasses.
And when you understand that, you understand our problem. Grass ecosystems on this planet, are new.
The first true grass biomes (grasslands) did not form until the Miocene epoch, roughly 20 to 30 million years ago. Although individual grass species and tiny plants evolved over 100 million years ago during the Cretaceous period, they only grew as rare forest-edge or moist patches.
Why is that? You’re finding out as we speak. A forest is good at generating its own rain, because it releases water during periods of drought and absorbs massive amounts of water during periods of heavy rainfall.
Grassy ecosystems, which our entire system of food production depends on, can’t do that.
The last time CO2 concentrations in the air were as high as they are now, was between 14-16 million years ago.
The tropical grassy biomes only developed into expansive, dominant regional biomes roughly 8 to 3 million years ago. Today they support a fifth of the world’s human population.
With the climate trajectory we are on, there is essentially no guarantee, that the Earth will be capable of sustaining grassland ecosystems, including the artificial ones we depend on for our food.
If we stopped our greenhouse gas emissions today, you would be left with the kind of climatic circumstances, where grasses as we know them today, were minor plants on the outskirts of our forests.
Back then, the grasslands that now cover 27% of the Earth’s surface and 70% of our agricultural area, did not exist.
Under the climate we’re now creating, grasses could not survive, except as a kind of pioneer species that lived on the outskirts of forests.
The atmosphere can hold 8% more moisture with every degree of warming, so during summer the air now ruthlessly sucks up all the water out of the soil until the grasses start dying, then in autumn when it cools down, this massive amount of water is dumped onto these poor grasses with tiny roots that struggle to let all the rain flush down into the soil.
You can see this happening in England today. England has recorded its driest July on record, in a series since 1836, with just 6.5mm of rainfall recorded – just 10% of its long-term meteorological average for the month, and less than half of the previous record of 13.4mm set in 1911. That’s why England now looks like this:
Our animals are not safe either. A healthy young adult can survive a wet-bulb temperature of about 31 °C for a few hours in the shade. Cattle standing in an open pasture, with no shade and no relief overnight, start dying around 26 °C. They just don’t have bodies that can sweat as effectively as ours.
These conditions we are now dealing with, are not conditions under which we can sustain agriculture.
This only becomes obvious, once you start to look at multiple interacting variables. If you just look at heatwaves, rice yield goes down by 8.1% per degree of warming. If you actually take into consideration that rice dies when exposed to too little or too much water, you realize 1 degree of warming leads to a collapse in agriculture.
And then we haven’t even looked at what happens to your crops because of pest species yet. In India, they lose a fifth of their crop to rats. In other parts of the world, you lose your crop to insects. Plant defenses against insects are shut down, when CO2 concentrations in the air are increased. The plants you eat, can no longer defend themselves against insects. And because the winters get warmer, those insects no longer die off during winter.
What we also haven’t looked at yet, are the dust storms. Climate change causes dust storms to increase, but what’s particularly worrisome, is when you have arid soils that you can no longer use for agriculture, because once you abandon those soils, it takes years before nature can stabilize them for you. That’s the risk they now face in Arizona for example.
When you have dust storms, the leaves of your young plants are damaged by the dust. This can dramatically reduce yields. In other cases, your soil is damaged by large amounts of salt deposited by the dust storms. Again, nobody really tries to put a proper number on this.
So, could we just block the sun instead? Would that bail us out? I wouldn’t count on it. There are numerous studies that take a look at what happens when you block the sun. When you start blocking the sun, you start changing everything. How much rain falls, where the rain falls, where the wind blows, all this stuff starts changing.
And to make matters worse, we don’t even known if blocking the sun would even work to reduce warming. When you spray these sulfate aerosols in the stratosphere, they can react with ammonia in the atmosphere to form ice-nucleating particles such as ammonium sulfate. Those particles then give rise to cirrus clouds, which have the effect of causing further global warming.
And keep in mind, the effect of these aerosols in the stratosphere that block the sun is not symmetrically opposed to the greenhouse effect. You will reduce warming more during summer than during winter, you reduce warming more during the day than the night, you reduce it more near the equator than near the poles. This is all opposite of how the greenhouse gasses affect the climate, so when you try to compensate for it by blocking the sun, you still just create a whole new global climate. There’s no real guarantee it will work.
The most likely outcome of what we are doing, is that we simply end up with a climate in which agriculture just no longer works. The methods we’ve so far used to mask the damage we’ve caused to our climate, the unsustainable use of irrigation, the blocking of the sun through air pollution, are falling away. The ecosystems we depend on for our food today simply did not exist, in the climatic circumstances we are now creating.
No comments:
Post a Comment