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Concentration of CO2 in the Atmosphere

What’s the Difference Between 1.5°C and 2°C of Global Warming?

Global warning. Planet as melting ice cream under hot sun. (AdobeStock_209217051/sveta)

George Harvey

We have been hearing for some time that we need to stop temperature increases from climate change at 2°C (3.6°F) to avoid the worst catastrophes, but anything upwards of 1.5°C (2.7°F) will be pretty bad. The difference is so small. Why worry over such a small thing?

It’s partly about ice.

There are few chemicals more fascinating than water. Whole books have been published with nothing but pictures of snowflakes. They are pretty, but the science relating to the phase changes of water, as it melts and freezes, is nothing short of amazing. There is a small difference in temperature between the two, but our lives depend on it.

Ice can exist at 0°C (32°F), and if no energy is going into it, it does not melt. Water can exist at the same temperature, and if no energy is being extracted, it does not freeze. There seems to be some sort of balancing act going on here. How does that work?

A calorie (as used in physical sciences) is the amount of energy required to raise one gram of water by 1°C. The amount of energy it takes to melt a gram of ice at 0°C into water at 0°C, without changing the temperature, turns out to be about 80 calories. If you measure the amount of heat it takes to convert a given volume of ice into water, without raising the temperature, and then apply the same amount of heat to the water, you will raise its temperature to about 80°C (176°F). It takes a lot of heat to melt ice.

The converse is also true. When water freezes into ice, it releases a lot of heat. That is why ponds can have water under the ice, if they are deep enough.

We know that glaciers are melting. They have been retreating up valleys, and in some cases they have disappeared altogether. We have photographs recording glaciers melting all over the world for over a century, and the speed of the melting is clearly accelerating. This is happening because a lot of heat from the atmosphere is going into the glaciers.

Now, we are worrying about melting ice in the polar regions, especially on Antarctica and Greenland. The amount of ice melting is so great that the sea levels are increasing. The process removes a lot of heat from the atmosphere, but it is speeding up anyway. Without global warming, the whole process was balanced, but now, it is not.

The rising sea levels are threatening to put some places under water. The Marshall Islands are likely to be lost, and all their people will have to move to new homes in other countries. Miami is also likely to be lost, along with a large number of other places along the seaboards of the United States.

All of this is happening because carbon dioxide (CO₂) can trap sunlight. Please note here that the CO₂ does not have to react with anything to do this. As heat is trapped, the CO₂ stays in the atmosphere, trapping more.

So the heat will keep going up until CO₂ is removed from the atmosphere, a process that has been kept in balance by trees, grass, and other plants. But plants cannot remove the amount of CO₂ that we put into the air.

Things are out of balance. The amount of CO₂ is growing, and it is causing heat to be trapped faster and faster. To counter this, we must get things back into balance again. And to do that, we have to do two things. First, stop increasing the amount of CO₂ in the air, and then, reduce it to the point that balance has been restored. The longer we continue increasing the CO₂ in the air, the harder the job of restoring balance will be.

If we can do the job of reducing emissions of CO₂ sufficiently, then we will be able to limit global warming to 1.5°C through 2050. Otherwise, global warming can go to 2.0°C or even higher. The difference between these two may seem small, but it represents an amount of energy that is far beyond the abilities of most of us to imagine.

As small as the difference between 1.5°C and 2.0°C is, to get to the higher temperature, an almost unimaginable amount of ice would have to melt along the way. An article at Reuters quoted Dr. Michael Mann saying that melt would be enough to cause major ice shelves in the Arctic and Antarctica to collapse (www.reut.rs/3nBg7pH). And with that, the changes around the world would be catastrophic.

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