Basically, I never understood why (or rather how) a global increase of 1.5° (Celsius) can have as big an impact on the world as it does. How is that seemingly small increase melting the poles so much so that the coastline of many countries in the world might even be pushed back?
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A great way to think about it is heat and energy side that’s the important factor. While the average temperature increase seems small, and 1.5 is barely noticeable in our every day lives, temperature is not the thing that matters here, it’s energy. The earth is big. The oceans are huge. A candle is hot, but doesn’t have a lot of energy. A stove top is also hot, but because it’s a lot more massive which one would you rather sleep your hand on? That seemingly small temperature change requires a massive amount of energy to achieve.
A little more, it’s not the temperature that we care about, it’s what that heat does. Storms are driven by heart energy, so more energy means bigger storms. Cuteness of air and water are driven by temperature gradients which can get disrupted by small differences in temperature, which can lead to things like the gulf stream weakening, the key stream heading south and messing up precipitation patterns, the monsoon seasons lengthening or shortening, a whole host of issues are caused by this massive influx of energy into the planets systems.
Keep in mind that the 1.5 degree number is the *global average* temperature. It does not mean everywhere will get 1.5 degrees warmer, some places will be less and others more. Due to [the way climate works]*, when the world’s climate changes the temperatures at the poles are affected more strongly than those near the equator.
When people are talking about a 1.5 degree global increase, that’s referring to a scenario where the equator only warms a little bit and the poles warm up much more than just 1.5 degrees, maybe like 5+ degrees. And if you add 5 degrees to the temperature of every day in the poles, you’ll find that way more of them get above freezing than before (melting more ice), and the days that were already above freezing are now farther above freezing (melting more ice). And ice is more reflective than water, so the more ice that melts, the faster the warming gets (melting more ice). You can see where this is going…
*non-ELI5
The average temperature of Earth is something like 290 kelvin. So a 1.5 C increase (which is also a 1.5 K increase) is something like half a percent.
I think the thrust of your question is “why does half a percent matter?”
Well, let’s look at sea level. Seawater doesn’t expand linearly with temperature, but let’s imagine for a sec that it did, and that the amount of water on Earth increased by 0.5%. That’s an amount equal to about 20% of the Earth’s total fresh water, an amount a little lower than the total volume of every lake, river, and aquifer on Earth. Or, in absolute terms, it’s about 7 million cubic kilometers of water.
If you added that 0.5% extra water into the ocean, you’d raise sea levels by (7 million cubic km) / (area of oceans) = about 20 meters. [Here’s a map of the state of Florida](https://i.pinimg.com/originals/59/3c/74/593c747813ee646c79b9227a50bd4443.jpg) – everything in blue and purple is underwater, and bright greens are now beachfront. If sea levels *dropped* by that much, a thin land bridge would connect Great Britain to continental Europe, Florida would be double or more the size it is today, and shallow seas all around the world would be new coastline.
In the long-term, worst-case climate scenarios, we end up melting all the ice in Earth’s ice caps and causing (over centuries) a sea level rise several times worse than that.
The earth’s climate is a very complicated system and some seemingly small changes to it can have huge consequences.
For example the last ice age was “only” [6 degrees colder than today](https://www.smithsonianmag.com/smart-news/ice-age-temperature-science-how-cold-180975674/), but during that time New York was covered in ice that was higher than the empire state building in some places.
This shows that just a few degrees change in average temperature can have massive impacts on the climate.
This is why we should work very hard to keep the warming as low as possible.
If it was just a flat 1.5 degree increase everywhere, it wouldn’t be THAT big of a deal. A lot of ocean stuff and bugs are highly sensitive, coral would be pretty screwed.
But it’s not just a flat rate. 1.5 is the average. Some places are a lot hotter, some places are actually cooler. Because weather patterns shift.
Small changes in the average can cause climate change. You know how Seattle and London are rainy? Or how Europe is temperate despite being so far north? Or how California has forests? All that is because of predominant weather patterns. The wind typically blows the wet air from the ocean over Seattle where the mountains squeeze it out. Warm ocean currants flow up to Europe. But with temperatures changing, those norms shift. California dies out, Texas gets freezes, Canada has really hot summers. Hurricanes are just another Tuesday in Japan, but they’re a big deal in NYC.
Because we’re not used to it. People, cities, plants, animals, bugs. Everything. Wheat country is a specific region and if it gets too wet or too hot, it better to grow different crops. Except the farmers in that area have all the stuff to farm wheat, not use it as ranch-land. Some places will actually become better farmland. They were previously too dry or whatever, but that changes and now they could grow better crops. Except there’s no grain elevators, tractor dealerships, farm and feed, rail lines, or whatever else goes into agriculture. Cities need to invest a whoooooole lotta money prepping for the storms of tomorrow rather than hoping everything is going to stay the same. And that’s expensive. But not as expensive as being devastated by things you’re not prepared for.
Birds can truly just go somewhere else. They’ve been through world-wide cataclysms and mass extinction before. They’re the dinosaurs that lived. And deer and such can probably follow the food. But it takes an ant a really long time to hike to a different biome. And forget about the migration speed of a forest. It depends on how far their branches reach and how fast a tree can grow. Temperatures have changed a lot in the past, but never this fast. The speed of the change is beyond anything any species has evolved to deal with. Possibly excepting birds. But when they got selected for that ability, everything else on the planet went through a mass extinction.
An average increase of 1.5 means it gets a lot hotter (10+) at the poles. Ya know, where all the unmelted ice is located?
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