Thoughts on climate change
Posted: 14 Aug 2012, 14:28
Fact: Both poles are warming much faster than the rest of the planet, and much faster than almost anybody expected.
Fact: For most of Earth's history, there was no polar ice.
Fact: Current climate change is mostly anthropogenic. Our influence far exceeds any natural variation.
Premise: Let's ignore the probable connection between natural climate change and the timing of the arrival of human civilisation. Let's imagine that civilisation could have appeared when there was no ice at all.
Are the poles warming faster because there is ice present?
Or would they have warmed faster even if there was no ice when humans got involved?
Or is there less difference between polar and tropical temperatures when the global average is warmer?
Or is there less difference between polar and tropical temperatures when there is no polar ice?
OR...is it because the poles are much smaller, in terms of area, than the tropics?? BINGO! This one makes perfect sense. It seems obvious that it will take much more energy to raise the average temperature of the tropics by one degree than it takes to do so at the poles, because there's far more of the tropics to heat up. Sure, there is also more energy arriving...but the poles are special. They are completed surrounded by a large area where the temperature is rising by a small amount, but this temperature rise is persistent and pervasive. From the POV of the poles, it just keeps on coming. There's no escape.
And the fact that we happen to have polar ice at the point in Earth's history when this is happening makes this worse, because several of the feedback mechanisms are directly related to ice loss.
So what can we conclude if I haven't got something wrong here?
I think the fate of humanity is as hard to predict as it ever was, because that depends on so many other things than climate change, but I think we can now say with a decent degree of certainty that by the time this episode of climate change is through, much of the polar ice will be gone and sea levels will be several metres higher. What happens in the arctic will depend on whether or not the Gulf Stream shuts down due to all that freshwater being dumped into the North Atlantic and Arctic oceans, but by the time the climate change has finished there will be very little permanent ice left in Greenland. That's a 7 metre rise in sea levels. All of the floating ice in antarctica will also go, and the rest of the antarctic ice sheet will start thining and retreating.
We must also take into account the fact that all the additional heat is being churned down into the ocean depths by the conveyor currents, which is going to cause further sea level rises driven by expanding water at depth - a process which would go on causing sea level rises for hundreds of years after atmospheric temperatures have stabilised.
So...
How fast are sea levels going to rise?
How far are they going to rise before they stop rising?
If the climate does what I'm expecting it to, which is rise by 10 degrees because of out-of-control feedback mechanisms, then all of the arctic ice and most of the antarctic ice will have gone by the time a new stable state is reached. That would translate into sea level rises of several tens of metres (if all the ice melted it would be 73m).
How long would this take though? The ten degree rise could easily happen with 100-200 years. The question is how long after a ten degree rise would it take for the antarctic ice sheet to either stop melting, or be reduced to a few glaciers in the Transantarctic Mountains?
1500 years maybe?
Fact: For most of Earth's history, there was no polar ice.
Fact: Current climate change is mostly anthropogenic. Our influence far exceeds any natural variation.
Premise: Let's ignore the probable connection between natural climate change and the timing of the arrival of human civilisation. Let's imagine that civilisation could have appeared when there was no ice at all.
Are the poles warming faster because there is ice present?
Or would they have warmed faster even if there was no ice when humans got involved?
Or is there less difference between polar and tropical temperatures when the global average is warmer?
Or is there less difference between polar and tropical temperatures when there is no polar ice?
OR...is it because the poles are much smaller, in terms of area, than the tropics?? BINGO! This one makes perfect sense. It seems obvious that it will take much more energy to raise the average temperature of the tropics by one degree than it takes to do so at the poles, because there's far more of the tropics to heat up. Sure, there is also more energy arriving...but the poles are special. They are completed surrounded by a large area where the temperature is rising by a small amount, but this temperature rise is persistent and pervasive. From the POV of the poles, it just keeps on coming. There's no escape.
And the fact that we happen to have polar ice at the point in Earth's history when this is happening makes this worse, because several of the feedback mechanisms are directly related to ice loss.
So what can we conclude if I haven't got something wrong here?
I think the fate of humanity is as hard to predict as it ever was, because that depends on so many other things than climate change, but I think we can now say with a decent degree of certainty that by the time this episode of climate change is through, much of the polar ice will be gone and sea levels will be several metres higher. What happens in the arctic will depend on whether or not the Gulf Stream shuts down due to all that freshwater being dumped into the North Atlantic and Arctic oceans, but by the time the climate change has finished there will be very little permanent ice left in Greenland. That's a 7 metre rise in sea levels. All of the floating ice in antarctica will also go, and the rest of the antarctic ice sheet will start thining and retreating.
We must also take into account the fact that all the additional heat is being churned down into the ocean depths by the conveyor currents, which is going to cause further sea level rises driven by expanding water at depth - a process which would go on causing sea level rises for hundreds of years after atmospheric temperatures have stabilised.
So...
How fast are sea levels going to rise?
How far are they going to rise before they stop rising?
If the climate does what I'm expecting it to, which is rise by 10 degrees because of out-of-control feedback mechanisms, then all of the arctic ice and most of the antarctic ice will have gone by the time a new stable state is reached. That would translate into sea level rises of several tens of metres (if all the ice melted it would be 73m).
How long would this take though? The ten degree rise could easily happen with 100-200 years. The question is how long after a ten degree rise would it take for the antarctic ice sheet to either stop melting, or be reduced to a few glaciers in the Transantarctic Mountains?
1500 years maybe?