Vivian on 12/8/2012 at 16:41
So we're like 3 standard deviations below the average for the last 20 years (when a StDev is about 0.5 million km2), and we're following what looks like the same curve as five years ago. Nice. Be more conclusive to see it for the last 200 years/since serious anthropogenic carbon emissions, but I guess that data is unavailable?
edit: duh, like you said. long term. yeah.
demagogue on 13/8/2012 at 04:58
For the record, as I learned it, a really slam dunk piece of evidence for the link between carbon level & climate change was the experiments on bubbles in ice cores, because then then could correlate the level of carbon in the bubbles with the layering of the ice at that level, which was apparently a signal of snowfalls & temperature (sort of like tree rings)... But it was such a good piece of evidence because the correlation was a surprisingly 1:1 curve, and the cores went back for 1000s of years, over a really wide spread of carbon levels & temperatures, roughly maintaining that correlation throughout. I don't know that it's the best for the era of anthropomorphic emissions, but I can't think why it wouldn't be (edit: I mean, why it couldn't be extrapolated to that), and I was impressed when my prof walked through it all anyway.
faetal on 13/8/2012 at 09:48
The really good news is that reduction in ice coverage lowers the earth's albedo, meaning that less of the sun's light is reflected back out into space and ends up being absorbed and upping the heat, which means more rapid ice loss and so on and so forth. The real problem with anthropogenic climate change isn't the progressive trends we see from graphs like this, it is the tipping point we are going to cross at some stage past which the change goes into free-fall when the positive feedback mechanisms get going. Sub-oceanic methane clathrate stores being released is going to be the real killer. It was the release of sequestered methane which is thought to be responsible for the Permian mass extinction. To help us on the way though, we have ice albedo loss, release of methane from permafrost thaws and tundra warming up etc... There are a load of potential positive feedback mechanisms waiting to pass that crucial threshold.
The other real worry is the rate at which this is occurring. The warming which preceded the Permian mass extinction occurred over the course of about 250,000 years - 5 degree rise caused the release of underwater methane which led to the further 5 degrees which killed off most life on earth. We have seen nearly 2 degrees of change in only 200 years. So while we wait for positive feedback to take the issue out of hour hands, we have some serious potential issues on the horizon for the biosphere if temperature flux causes e.g. any number of pollinating insects' life cycles to desynchronise from the plants they pollinate. Serious probs ahead, yo.
jay pettitt on 13/8/2012 at 11:14
An extinction event from ocean acidification eating the exoskeletons of oxygen producing planktons will get us long before the methane [/extinction event top-trumps]
Don't get me wrong, I'm not espousing extinction events - but I think the projected mild impacts are scary (and persuasive) enough. Because climate change will be something we're stuck with for a long time, even relatively slight economic impacts produce a big net economic loss over time.
I'm actually getting a little bit sensitive to sticking things with different time scales next to each other in a sentence. Extinction events probably (I'm supposing) take a long time to happen, even if we cause the conditions that could set the ball rolling very quickly. We could geo-engineer our way out of an extinction event. If we wanted to.
But that assumes a buoyant economy that won't mind taking on additional planet sized projects. If we're left with a limp from land use changes and less predictably weather - that's the bit that bugs me.
But yeah - I'm pretty sure my Fisher Price Encyclopedia of the Solar System said the average temp of planet earth was 14C. Changing that to 20C is going to be interesting in lots of different ways.
Vivian on 13/8/2012 at 11:48
I dunno, I wouldn't be too surprised if someone could show the K/T event happened pretty quickly. Post-impact, there's some evidence of global snap-freezing (fossil plants with ruptured xylem) and ashfalls, massive spikes in fungus and fern spore deposits, all of which is cogent with a nuclear-winter scenario and a large amount of dead biomass. Of course, it's impossible to date stuff anywhere near that accurately, but it seems plausible that something like that could have only taken a few years to kill off most things.
faetal on 13/8/2012 at 11:57
Yes, but I'm not sure what a large object impact has to do with global warming as they are essentially random. The Permian mass extinction event is more relevant here since it was effectively warming followed by positive feedback over the course of around 250,000 years.
jay pettitt on 13/8/2012 at 12:55
Most (not all) of the Methane is a long way down - there's a lot of frozen ground to thaw before you get a really massive release. It's a bit like the thing with Glaciers. It won't take us long at this rate to heat the planet up enough to cause the melt, but it's still going to take a 1000 years or so to do the actual melting.
Just as a communication thing I think it's befuddling for the rest of us when human sized time scales and things that happen over millennia and longer are muddled together.
faetal on 13/8/2012 at 13:29
Quote Posted by jay pettitt
...it's still going to take a 1000 years or so to do the actual melting.
1) [citation needed]
2) At current temperatures? projected temperatures? taking into account intervening factors such as various positive feedback mechanisms?
3) 1000 years is a long time for an individual, but for a species, it's the blink of an eye. Not having to deal with the consequences shouldn't circumvent any feeling of urgency, especially considering that positive feedback loops passing a crucial equilibrium stage are likely to take matters out of our hands at some stage. I don't want the legacy of my children and their children etc.. to be an ever increasing sense of concern until it is too late to do anything.
Quote:
Just as a communication thing I think it's befuddling for the rest of us when human sized time scales and things that happen over millennia and longer are muddled together.
I'm not sure how it is muddling together when the time scales are explicitly mentioned. If people are unable to tell the difference between 250,000 years and 200 years, I'm not sure that communication is necessarily the issue.
Another thing to mention is that as certain environmental and economical factors begin to have effects, social structures become less stable. So for example, if food resources start to be more adversely affected than they already are - and they will - you can bet that it will exacerbate the already simmering antipathy between the "haves" and the "have nots", particularly since it is not too much of a stretch to assume that the former will use their resources in order to ensure that they are not the ones feeling the effects. The only way catastrophe in X years time can be averted is if the problem is dealt with now. In many ways this "yeah, but it won't happen for ages" attitude is the biggest danger, since it allows people to emotionally distance themselves from the consequences.
