Tipping point one: Complete global deglaciation.
This looks like it happened in the last Interglacial 120 000 yrs ago.
The Arctic Sea ice went completely. Most if not all of Greenland and west Antarctic ice sheets went too. Theres 30m above current sea level ancient beaches all around the world proving that.
With recent observations of coastlines receding by Thermokarst/coastal erosion (wave action and warm water melt the coastal land permafrost layer, accelerated by thermokarst lakes drilling with warm water through the coastal tundra permafrost) in Siberia, Alaska, and Nth Canada by up to 200m, mostly in the last 10yrs, and accelerating...
Example of Coastal Thermokarst lakes on the East Siberian Arctic Shelf coastline:
Pan around, Zoom in, its quite scary.
I think its fair to say that most, if not all of the ESAS, and most of other arctic basin continental shelves may have been created by this process in that last interglacial.
|International Bathymetric Chart of the Arctic Ocean - from: ibcao.org|
Shelves in these places are flat, 40-100m below sealevel, flat, the glacial channels mostly filled with sediments from the eroded coasts. Some of this erosion has happened in the last 10 thousand years around Norway, Greenland, and to a lesser extent Nth Canadian Archipelago, and Svalbard.
But its unlikely that prior to mans intervention, that much coastal permafrost got melted in the ESAS, because the surface seawater stayed -1.8C to 0C probably up until the last 30 years.
The reason the arctic shelves, and particularly the ESAS are the most dangerous pieces of geology on the planet is, that while they have been frozen for at least the last 90 000 years. They have been collecting methane produced by baking oil shale layers, subducted under the edges of the continents, mostly as water-methane crystal hydrates in their bottom layers.
If this happens under land permafrost, its more porous and there isn't enough pressure for hydrates to be stable. Under not frozen submarine shelves the temperature isn't low enough for hydrate stability.
Now, Earths vulnerable Carbon stores are:
Carbon in the Arctic
500 Gton C organic
1000 Gton C hydrate
700 Gton C free methane
total: 2200 Gton C
+other submarine arctic permafrost:
2200/0.8=2750 Gton C
+1700Gt in land permafrost= 4450 Gton C
A large part of this is Vulnerable to being lost rapidly into the Ocean/Atmosphere system if the Arctic defrosts, polar ocean warms, heavy rainfalls hit the Tundras.
Carbon in soils and Living Biomass:
Total organic C in soil and living biomass is approx: 1000 Gton C living + 1500 Gton soil.
= 2500Gton C
A large part of this is Vulnerable to being lost rapidly into the Ocean/Atmosphere system if the Arctic defrosts, Global weather systems change, Rainforests and/or peat deposits burn, desertification and/or heavy rainfalls hit the Tropical, Temperate, Boreal forests.
So tha'ts the vulnerable surface Carbon stores. Total about 7000 billion tons of carbon.
There's never been this much in the history of planet earth, that we know of.
Carbon in Deep sea Clathrates:
estimates range from 5000 Gton C to 78000 Gton C
A large part of this is Vulnerable to being lost into the Ocean/Atmosphere system if the oceans warm a few degrees, reaching the bottom in a few hundred to a few thousand years, causing the stability to be lost.
There's never been this much in the history of planet Earth, that we know of.
Now if Mankind hadn't got in the way by dumping 500 Gton C of Organic carbon from soil and living biomass into the Ocean-Atmosphere system before the Industrial revolution, and most particularly by dumping a further 500 Gton C of fossil fuels there as well since, what might have happened is this:
The Arctic sea ice would have gone slowly, over a period of centuries, and the Arctic shelf methane would have fizzed off slow enough to be all converted into CO2, without raising methane and its product ozone levels in the atmosphere significantly.
The Weather patterns wouldn't have changed much so the tundras wouldn't have melted fast, and the prospect of heavy rain there wouldn't be looming. The ecosystems would have had time to shift the boreal forests north onto the tundras as they slowly got wetter. The frozen Tundra peats would have been stabilised by roots, and the tundra permafrost methane, would have fizzed off slowly, all safely converted to CO2 and a little organic carbon/nitrogen would have been decomposed into safe CO2 and soil Nitrates.
The Release of CO2 would have been slow enough for the biological ocean system to bury it on the sea bottom, the 300 year duration of carbonate/silicate weathering getting it on the way to safe limestones, and clays.
We probably would have been up for a hundred odd million years of no ice on the planet. Subduction techtonics around the polar shelves would have gradually broken off the ESAS etc, and a lot of the ex-permafrost peats, turning them thru submarine landslides into polar basin sediments. As that happened slowly, the carbon would have all been buried and turned to stone. The CO2 would have stayed high enough throughout this time to keep the planet ice free.
Eventually in maybe 100 million years the earth might have gone back into a glaciation.
|Image from: http://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png (click to enlarge)|
Instead, Mankind got in the Way.
Now we have today this:
This chart showing the present day situation, the effect of an extra 4.5 Gton C methane in the atmosphere, and the tipping point line for "super-greenhouse/Anoxic ocean" mass extinction events like the end Permian 252 million years ago, and the more recent PETM 56 million years ago. About 20 of those we know about in earths history.
Unfortunately it doesn't stop there.
It looks like Nature has conspired to set up a perfect Eco-Geospheric beartrap, that we have sprung by slamming together a WHOLE LOT of tipping points into such a short space of time that what we have probably done is created a perfect planetary environmental storm, and lined ourselves up for, in a few decades from now THIS:
And with water vapour feedback kicking in, the Megacyclones kicking vast quantities of warm moist air high into the stratosphere, warming it from -40C to well above Zero....
It doesn't look like stopping there.
The good news though is that we have all the knowledge now, just in time, and all the tools to stop it quickly and relatively easily. Provided we act within the next few months.
If we don't, We might have no chance whatsoever of stopping this cascade of tipping points.