spot's beginner's guide to Global Warming
Posted: Wed Jan 14, 2009 5:20 am
Now that President Dissocial Personality Disorder is returning to private life and new ER staff take over the White House to treat the nation he mugged I thought we might have another look at Global Warming.
Compared to the huge amount of energy reaching the Earth every day from the sun there's nothing in nature which comes remotely near it as an energy store. The oceans can be warmer or cooler, the air can be warmer or cooler, water stays at freezing point while it releases latent heat becoming ice, ice won't warm past its melting temperature until it's absorbed the right amount of latent heat and melted and the same principle applies to evaporation and condensation; these are all feeble batteries compared to the daily blast of energy from the sun.
What happens to that energy from the sun, though, is it's either reflected or absorbed, trapped or free to leave easily. There's a whole set of switched states which either promote a colder or a warmer Earth. Lots of clean white Polar ice cover promotes a cooler steady state. Lots of white fluffy clouds promote a cooler steady state. Lots of greenhouse gas in the atmosphere promotes a warmer steady state.
Each of these switched steady states has a traditional energy diagram.
Random fluctuations from time to time push any switch condition some way up the hill dividing on from off. Lots are small and go only a bit of the way and fall back. Some get further. In time eventually, despite everything else being equal, a random fluctuation will flip the switch. Once a system has enough activation energy to pass the transition state it automatically falls to the other side. Getting back is a lot of work, an unlikely event, it needs another rare heavy random fluctuation.
One switch in Global Warming is whether there's an oceanic conveyor system dumping tropical hot water in polar regions and bringing cold water back to cool the tropics. Another is whether the Arctic is reflective, covered in ice, or it's absorbing energy because it's all water and no ice. There are lots of switches.
If one of the switches flips, the new steady state is a warmer or a cooler planet. Flipping one state can push conditions so far from where they were that another switch is flooded with so much transitional energy that it flips too. They can fire each other off in turn if they overlap. Switching the Arctic Ice Cover to Off has, in the past, shut down the ocean heat conveyor current. That in turn might melt the clathrate methane deposits under the Tundra, giving a new steady state which traps far more of the solar energy and leaves the planet a lot warmer still. The warmer the oceans, the more sea water ejects its dissolved carbon dioxide (which is less soluble in warm water) and, the more it ejects, the warmer the oceans end up because of greenhouse effects from the additional carbon dioxide.
The burning of fossil fuels over the last few hundred years is pushing a number of these steady state conditions toward transition.
The effects are mitigated by increased reflectivity of more cloud cover. Just as there are positive feedback systems in which adding transition energy applies pressure to add more transition energy (gradually losing ice cover is an example) so there are negative feedback systems which make adding more transition energy harder (increasing cloud cover might be an example of that).
The Doomsday argument is that triggering one switch fires off a second which in turn passes the threshold for a third and so on. Venus and Mars were arguably Earth-like at earlier stages and went to their current extremes by such a process, passing transition points which allowed no way back but led instead to the next.
The argument against Doomsday is that all the known switches have been thrown back and forth since life started on Earth and life's still here. The planet's been mostly snowball, it's been entirely ice-free, it's had thicker greenhouse gases than now, even the methane clathrates may have all entered the atmosphere in the past.
What's certainly the case is that there's two hundred feet of extra ocean stored up in the existing ice on Earth. Melting the Arctic ice cap won't add to the rise because that's already floating. Melting Greenland and the Alps and Antarctica would. Melting the Arctic icecap is a switch because the subsequent steady state absorbs more sunlight and makes the planet warmer, pushing more transitional energy against the other switches.
What's suggested is the world's ice is all going to melt if greenhouse emissions aren't reversed. Nobody, yet, has even started to discuss reversal of greenhouse gas concentrations, it's all just talk of slowing the rate of increase.
Compared to the huge amount of energy reaching the Earth every day from the sun there's nothing in nature which comes remotely near it as an energy store. The oceans can be warmer or cooler, the air can be warmer or cooler, water stays at freezing point while it releases latent heat becoming ice, ice won't warm past its melting temperature until it's absorbed the right amount of latent heat and melted and the same principle applies to evaporation and condensation; these are all feeble batteries compared to the daily blast of energy from the sun.
What happens to that energy from the sun, though, is it's either reflected or absorbed, trapped or free to leave easily. There's a whole set of switched states which either promote a colder or a warmer Earth. Lots of clean white Polar ice cover promotes a cooler steady state. Lots of white fluffy clouds promote a cooler steady state. Lots of greenhouse gas in the atmosphere promotes a warmer steady state.
Each of these switched steady states has a traditional energy diagram.
Random fluctuations from time to time push any switch condition some way up the hill dividing on from off. Lots are small and go only a bit of the way and fall back. Some get further. In time eventually, despite everything else being equal, a random fluctuation will flip the switch. Once a system has enough activation energy to pass the transition state it automatically falls to the other side. Getting back is a lot of work, an unlikely event, it needs another rare heavy random fluctuation.
One switch in Global Warming is whether there's an oceanic conveyor system dumping tropical hot water in polar regions and bringing cold water back to cool the tropics. Another is whether the Arctic is reflective, covered in ice, or it's absorbing energy because it's all water and no ice. There are lots of switches.
If one of the switches flips, the new steady state is a warmer or a cooler planet. Flipping one state can push conditions so far from where they were that another switch is flooded with so much transitional energy that it flips too. They can fire each other off in turn if they overlap. Switching the Arctic Ice Cover to Off has, in the past, shut down the ocean heat conveyor current. That in turn might melt the clathrate methane deposits under the Tundra, giving a new steady state which traps far more of the solar energy and leaves the planet a lot warmer still. The warmer the oceans, the more sea water ejects its dissolved carbon dioxide (which is less soluble in warm water) and, the more it ejects, the warmer the oceans end up because of greenhouse effects from the additional carbon dioxide.
The burning of fossil fuels over the last few hundred years is pushing a number of these steady state conditions toward transition.
The effects are mitigated by increased reflectivity of more cloud cover. Just as there are positive feedback systems in which adding transition energy applies pressure to add more transition energy (gradually losing ice cover is an example) so there are negative feedback systems which make adding more transition energy harder (increasing cloud cover might be an example of that).
The Doomsday argument is that triggering one switch fires off a second which in turn passes the threshold for a third and so on. Venus and Mars were arguably Earth-like at earlier stages and went to their current extremes by such a process, passing transition points which allowed no way back but led instead to the next.
The argument against Doomsday is that all the known switches have been thrown back and forth since life started on Earth and life's still here. The planet's been mostly snowball, it's been entirely ice-free, it's had thicker greenhouse gases than now, even the methane clathrates may have all entered the atmosphere in the past.
What's certainly the case is that there's two hundred feet of extra ocean stored up in the existing ice on Earth. Melting the Arctic ice cap won't add to the rise because that's already floating. Melting Greenland and the Alps and Antarctica would. Melting the Arctic icecap is a switch because the subsequent steady state absorbs more sunlight and makes the planet warmer, pushing more transitional energy against the other switches.
What's suggested is the world's ice is all going to melt if greenhouse emissions aren't reversed. Nobody, yet, has even started to discuss reversal of greenhouse gas concentrations, it's all just talk of slowing the rate of increase.
