What exactly is irreversible in climate change? – Sinan Eden

People use a bunch of words like “irreversible”, “run-away” and “lock-in” to underline the urgency for climate action. They use these words in different contexts applied to different phenomena. Then other people criticize these uses for being alarmist. All of this is rather confusing. So here’s a short summary to clear it up for you.

The warming itself:

We already reached a 1.1ºC increase in global average surface temperatures. That won’t be reverted, not during this century anyway. In fact, there is a decades’ long delay between emissions and warming. A carbon dioxide molecule released to the atmosphere today will remain there for hundreds of years. So, current emissions do actually lock us into more warming.

That’s also why there is such a thing as a “carbon budget”. So for instance, you can calculate that if emissions continue as they are now, by 2030 we will already have emitted all the CO2 sufficient for 1.5ºC warming (by 67% probability).

This means that after the emissions, the warming is irreversible.

The emissions:

Whatever was emitted was emitted. CO2 will remain the atmosphere for centuries (causing future warming). There is some talk about geoengineering, capturing the carbon dioxide in the atmosphere and then storing it. So, in paper, the emissions would be reverted this way. These technologies are nonexistent for all practical purposes. They may have an incremental effect after we reach zero real emissions, but that would be decades from now.

The infrastructures:

Some people are talking about an “investment lock-in”. This is a stranger use of the term, unless you are an economist. It goes like this. You contract a company for the construction of a gas pipeline. That triggers investment in gas power plants and other infrastructure where the pipeline goes to. Once the construction of the pipeline ends, the company needs to run it to make profit and thereby recover the costs of construction. That takes decades. So, the decision to build the pipeline locks us into using it, therefore causing emissions.

These are decisions made by the society and there is no rigid reason to believe they cannot be changed. The act of reverting can be difficult though: some companies may lose profits or go bankrupt, the people who were hired for the job may need support, other resources that were allocated to the site will have to be reallocated, etc. Yet, there is nothing irreversible in any of this.

The impacts of climate change:

We live in a world 1.1ºC warmer than pre-industrial times. The heatwaves, the storms, the droughts and the hurricanes that belong to this warmer planet are here to stay. That’s one thing.

Then, the warming so far is already causing ice to melt in the Arctic as well as in the glaciers. Even if we stop emissions now and even if warming itself stopped now, the oceans will continue absorbing heat and thereby expanding, causing sea levels to rise. So, sea level rise (not just the rise that already happened, but the continuous rise in the sea levels) is irreversible.

There are other ecosystem collapse scenarios, for instance in the coral reefs, that are also irreversible even if global warming stopped now. The new acidity in the oceans will continue killing the corals.

So there are irreversible impacts of climate change which will continue.

Continuous warming:

Finally, people talk about run-away climate change. This is the serious lock-in that makes climate change categorically different than any other issue we are dealing with.

It’s the feedback mechanisms embedded in the Earth systems.

Very briefly, here’s how they work:

Warming melts the Arctic ice. Ice is then replaced by water. That’s a blue surface substituting a white surface. Sea absorbs more energy than ice. So that means more warming. More warming causes more melting, and more melting causes more warming. This is a positive feedback mechanism. The tipping point for this mechanism is predicted to be 1-3ºC warming.

Another example is the forests. Warmer climate means stronger and more frequent forest fires. Burning trees release the carbon they have. That causes even more greenhouse effect, hence more warming, hence more wildfires. This is another positive feedback mechanism. The tipping point for this one to kick off is predicted to be 3-5ºC warming.

My last example is the permafrost, the soil in the North that is permanently frozen. With warming, the permafrost starts to thaw. And it has methane fixed in it, that gets released. Methane is a greenhouse gas, meaning more warming, hence more permafrost melting, hence even more warming. This is another positive feedback, and the tipping point for it is >5ºC warming.

Now look at this map produced in an article published in the Nature.

You see that certain ecosystems collapse with 1-3ºC warming and cause further warming, which then tips off other ecosystems at 3-5ºC warming that causes even further warming, which then launches other positive feedback mechanisms at >5ºC warming. This is the domino effect. This is the run-away climate change.

The latest IPCC report mentions such non-linear cases to be kicked off when we cross from 1.5ºC to 2ºC warming.

This is what climate activists are scared the hell out of and are trying to warn people about: if we emit sufficient CO2 to guarantee more than 1.5ºC warming, then warming may become irreversible in the sense that physical and chemical processes make sure that we reach 2ºC, 3ºC, 4ºC, 5ºC, 6ºC even if we stop the emissions.

There is a problem with this situation that makes it harder to communicate: The tipping points for each degree are still decades away while the carbon budget to cross the tipping point will be consumed globally before 2030. So if we don’t cut emissions to zero now, then global warming – the continuous warming of the planet – will be irreversible.

This is why we must stop whatever we are doing and start stopping climate change. Now. Not next year. Not next month. Not next week. Now.

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