Why does just 1.5C° of heating make such a significant difference on Earth’s climate and environment?
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That’s the *average* across the *whole* planet, which means in some places it will be higher than that, and in some places it might be lower than that. But if we’re talking about things like massive formations of ice, you don’t need to raise the temperature too high to accelerate the process of melting.
And life on earth has adapted to a certain range of temperatures. As the temperature changes, the environment changes, things (animals and plants alike) start to move to what is familiar and comfortable and eventually that might not be an option.
Also there are many other processes going on behind the scenes, not just temperature raising. For example, as more carbon dioxide is released and absorbed into the ocean, the water in the ocean becomes more acidic, and that can wreak havoc on the wildlife there, which can cause a ton of problems for the things on land.
Imagine the Earth is like your body. If your body temperature rose by 1.5C°, you would have a fever, and all the systems in your body that normally work at your average body temperature would be thrown out of wack. It is not much different for the Earth.
Because it’s an average over the entire year, and it’s doubly so an average across the entire globe.
So places in the equator will only increase 1.2 degree, but for example Europe will increase 2.4 degrees. The North Pole will increase even more, which is particularly problematic. (these are made up numbers but not far from the truth, I don’t remember the exact temperature distribution from equator)
When you remove the averages from the yearly data what you’ll get is a lot of abnormal spikes far above 2.4 degrees for Europe, so we’re talking 5 or even 10 degree heat waves or cold snaps in areas outside the euqator, all because of that 1.5 degree average increase.
While heat waves and cold snaps get the most news, the biggest problem with these weather events is that they annihilate crops and lead to sudden mass food shortages. These most affect the poorest parts of the world who simply cannot afford to pay more for food. Europe and America can always stop buying the latest iPhones and Teslas, but poor nations living on the edge of falling into famine have no financial safety net. They need global food crops to be steady to live.
Well, when you’re talking about a very large object like a planetary surface, even a small rise in temperature corresponds to a *lot* of extra heat.
Just to give one example of how “quantity has a quality all its own”: thermal expansion of the oceans. Warm water takes up slightly more space than cool water. We don’t usually think about that because it’s only a slight difference: if you take 1 gallon of 20°C water and heat it up to 21.5°C, the result is about 1.0003 gallons. The extra 0.0003 gallons corresponds to an extra quarter-teaspoon or so; barely noticeable. But if you take 100 *quintillion* gallons of 20°C water (e.g., the Atlantic Ocean) and heat it up to 21.5°C, the result is about 100.03 quintillion gallons. The extra 30 quadrillion gallons, which do have to *go somewhere*, correspond to maybe ten extra Lake Superiors; *very* noticeable.
And that’s just one example. There are dozens of different effects that warming produces. The effects are mostly pretty tiny on a planetary scale, but that doesn’t stop them from potentially being very big on a human scale.
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You’re looking at the average global temperature. Which is the average temperature everywhere all year long.
However the 1.5 won’t be a 1.5 increase to everywhere all year long.
It will be minimal increases in many places (possibly decreases) and turbo increases for short periods in some places, and really bad increases for long periods in other places.
For comparison, the last ice age had Chicago covered in an ice sheet a mile thick.
The global average temperature was only 6 C cooler than now.
So 1.5 C is about a quarter Ice age in temperature change.
Warning, personification is used repeatedly for ease of discussion. I am NOT suggesting that the world has thoughts and feelings.
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Temperature and heat are two different things.
If you were to increase the temperature of a small mug of water by 1.5°C you would need a certain amount of heat.
If you wanted to increase the temperature of TWO mugs, then you’d need TWICE as much heat. Likewise, a full bath would need much much more heat. I think most people have an intuitive sense of this (even if they don’t know the distinction in terminology).
Now, heat is a form of energy. In simple terms, energy is a measure of an object’s capacity to “do stuff”. You use energy to walk. Tornadoes use energy to destroy buildings. The sun uses energy to melt your ice-cream.
Now, suppose you wanted to heat THE WORLD, all of it, by 1.5°C. Such a temperature increase would require A LOT of energy. A temperature change of 1.5°C is not a big temperature change, but a small change across the entire planet is indicative of an unthinkable amount of new energy that we’ve added to the atmosphere. No telling what the atmosphere will do with that energy and it’s not forced to spread it’s usage evenly.
Nature (for all her virtues) enjoys the sport of killing us. Giving her more energy with which to buy our destruction is not going to help us in the long run. Floods, heat waves, storms, droughts, you name it. Anything that nature has done to us in the past, she will gladly do more often as we feed her the necessary funds (energy) to pay for it.
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As it happens, 1.5°C is not as concerning as people make out. It’s simply the lowest round number that we realistically might stay below. We are already at 1.2°C and (while we have our problems) the environment isn’t too harsh yet. 1.5°C would be worse but not too much worse.
The original concern was 4°C, which very few people believe we will hit (not within the next 100 years at least). 3°C is still a real possibility in 2100, but there is reason to be optimistic about getting that number lower.
It’s not really just the heating
Plants and animals can adapt to temperatures, and can move to the poles if they need cold.
The big problem is how fast is happening.
Animals and plants simply die to heat in a place without having the time to adapt or colonize a colder place.
Some will probably go extinct. And there’s no quick replacement.
Same for humans, if you live in a city that will lose its source of water (mountain-stored snow) that city is gonna die. For example, north Italy has never built water storage as the alps have plenty of rivers feeding the plains alla year long thanks to melting snow. This year the lack of snow on mountains has caused massive loss of crops, and scarcity of drinkable water. Other places are subject to sea rise that will soon cover part of maritime cities.
Another problem is that higher average temperatures, even 0.5 degrees, will massively boost the force of storms, hail, hurricanes and tornadoes. If you live in an area built for a quiet weather, your buildings will have no built in defense for hail, hurricanes or tornadoes. Rivers will lack proper flood barriers for prolonged heavy rain.
Most of the above problems would not be a big challenge if the change would take a century to happen. But 10 years… that’s no time to adapt.
Think of all the places with snow.
If the average temperature increases by 1,5°C, all snowy places with an average between -1.5°C and 0°C will no longer have any snow as the temperature will be above 0°C and the snow will melt. (I’m aware this is average temperature and actual effects can be very local.)
It happens snow is white and is very good at reflecting sunlight back into space preventing that same sunlight from warming the earth.
Loosing a large amount of “white” snow, ensures the sunlight is no longer reflected and trapping additional heating from the sun. Then the average temperature will increase more, more snow will melt, etc… causing a runaway effect.
1.5°C has been put as a limit of when such a runaway effect will occur.
(This is just one of the many reasons, 1,5°C has a very large effect. This one is just easy to comprehend as it doesn’t go into the complex and intricate mechanisms of dependencies in ecosystems; which can cause food shortages, etc…)
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