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A paper from Nature Geoscience (reported by the BBC here) claims that the carbon dioxide humanity has pumped into the atmosphere is holding off a new Ice Age.

This has revived an old idea best described by Hoyle and Wickramasinghe in 1999 (full text) that we are more at risk from cold than heat. As they argue:

The renewal of ice-age conditions would render a large fraction of the world's major food-growing areas inoperable, and so would inevitably lead to the extinction of most of the present human population

Given that the earth has mostly had more carbon dioxide in its atmosphere and has been significantly warmer than today (see here), could warming be a net positive in the long term? An alternative and perhaps more vivid way to phrase this question in a way that highlights the issue could be: is the current world climate optimal for humanity or biodiversity?

N.B. It might be worth distinguishing gains to life in general from gains to humanity as we emerged in a cold climate and tend to live near coastlines which might change as warming happens.

Edit: Recent statistical palaeontology studies have resulted in a change of mind about biodiversity over geological history. Mayhew's group had previously argued that warm periods had low biodiversity (despite the opposite being the norm across today's world where the tropics teem with biodiversity). A reanalysis has reversed the original result (see nature news story). It is also worth noting that one author of the work doesn't think this is relevant to current warming (though this is opinion is not derived from his current results).

  • We tend to live near coastlines which might change as warming happens. I understand the use of the word "flood" to describe this, but "flood" is a weather phenomenon. Used to describe the effects of climate change, it implies a natural emergency that we would not expect to occur. – MetaEd Jan 9 '12 at 17:56
  • @MetaEd Please feel free to correct my terminology. – matt_black Jan 9 '12 at 17:57
  • Fred Hoyle? In the 90's? Wouldn't a link to those much denigrated climate scientists of the 70's who were predicting global cooling be more appropriate here? Astronomer Hoyle is a bit of a Johnny come lately to the climate change field. see skepticalscience.com/ice-age-predictions-in-1970s.htm – user951 Jan 9 '12 at 18:24
  • @matt_black I am not sure what you are skeptical of. They can be both bad right? It is like saying, "Hey I got cancer, but at least I didn't have a heart attack" – Sklivvz Jan 9 '12 at 20:34
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    "Good for life" isn't a clear term. (Some species of life would thrive in Ice Age conditions; some would be wiped out.) Do you mean, perhaps, "maintain biodiversity"? – Oddthinking Jan 9 '12 at 22:33
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If you're referring to human life, there are recent studies from the Europe and Australia regarding the effects of temperature changes on humans.

They figure that initially warming will actually reduce deaths due to cold (i.e. fewer people will succumb to hypothermia during cold spells) but in future decades the number of deaths due to more frequent and more extreme heat waves will far outweigh the reduction in hypothermia cases.

Logically speaking, any time weather events become more extreme, some life forms are going to be adversely affected and some will find new niches. Better or worse? Hard to say with certainty. Life will definitely be different. If you're one of the species who finds new/expanded habitat, then climate change may be good for you. If you're one of the species that loses habitat, well, now would be the time to buy a nice helmet.

You mention previous climate change but that sort of comparison isn't really relevant. The nature of the changes due to AGW are unprecedented. We simply don't have any detailed knowledge of any natural precedent where massive quantities of sequestered CO2 where released into the atmosphere in the geological equivalent of a microsecond. That's one of the reasons AGW is so problematic, there isn't any "Opt Out" check box that a species can tick to be left alone, every living species (including humans) are lab rats in this global experiment. The correct answer to your question can only be determined by evaluating the experiment when it's over. (casts a wary eye on Venus...)

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    Welcome to Skeptics, Dan! That's a lot of reading homework that you have assigned us. Any chance you could extract and quote a key passage or two that supports your claims? – Oddthinking Feb 8 '12 at 16:46
  • The nature of the changes from AGW should be the forecast nature of the changes. The actual changes observed so far are far from unprecedented. Also, it is not clear that sudden change (even in CO2 levels) is geologically unprecedented. AGW could be really bad for us but that needs to be proved by showing why and how it is different from previous episodes of change (most of the last 500m years was warmer than now and there were many rapid climate shifts). – matt_black Feb 10 '12 at 14:20
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    @matt_black: science isn't about proving anything. Science can only say what is most likely to be the correct theory. The best it can say is that a theory has not been contradicted by any of the evidence. That includes what the most likely consequences for species are. BTW there are no predictions coming from climate science, there are projections. Projections are conditional, predictions/forecasts are unconditional and therefore unscientific. This may help you: Feynman on scientific method: link – Dan Haynes Feb 11 '12 at 14:58
  • @Oddthinking Thanks! The site seems like a good idea given the current levels of anti-science hysteria and politicization in the USA. I'll put more specifics in my response. Cheers. – Dan Haynes Feb 11 '12 at 16:26
  • @Oddthinking I can't save my edits because you expanded my second pair of links. I don't have enough cred to post more than two links so it rejects the save. I'll update when I'm worthy :) – Dan Haynes Feb 11 '12 at 16:38
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Yes; it is valid to say that it could be "good for life" since extinction opens niches for new species:

On the theory of natural selection, the extinction of old forms and the production of new and improved forms are intimately connected together....[T]he appearance of new forms and the disappearance of old forms, both those naturally and artificially produced, are bound together.

Origin of Species,"On Extinction"

However, it is likely that global climate change will be very bad in human timescales for biodiversity:

[W]e predict, on the basis of mid-range climate-warming scenarios for 2050, that 15–37% of species in our sample of regions and taxa will be ‘committed to extinction’.

Extinction Risk from Climate Change

The question of whether biodiversity or total biomass is a better measure of what is "good for life" is subjective, although I suspect most would say a coral reef is "better" than a mat of algae.

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    I'm aware of the conventional view from climate science that warming is bad. I'm interested in how that stacks up against the fact that the world has had long periods of warmth and high atmospheric CO2 since the precambrian and they are not usually periods of mass extinction. How is geological history reconciled with climate models? – matt_black Jan 9 '12 at 23:41
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    I think it is part of the evidence that should feed into a really good answer of the question I asked. If life has thrived in a warm high-CO2 past, why do current models say we are doomed with moderate increases in CO2 and temperature? It is not the only relevant factor though. – matt_black Jan 10 '12 at 0:19
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    @matt_black - It is not ONLY global warming that we are up against. It is global warming, PLUS things like over-fishing, over-farming, deforesting, depleting aquifers. These other factors complicate things to the point that this period of warming is different from every other period of warming in the history of this planet. – user3344 Jan 10 '12 at 8:24
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    @woodchips I'll sign up to protect the forests and stop overfishing anyday. I know we have a tendency to despoil our environment (at least until we are locally rich enough to care). Those facts are irrelevant to my question which is whether high CO2 and warming are a net positive or negative. – matt_black Jan 10 '12 at 8:54
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    @LarryOBrien Wikipedia says "In a 4 °C world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved" This sounds like a good summary of the consensus and not far from a statement that "we are doomed" at least within the bounds of allowable rhetoric. – matt_black Jan 10 '12 at 10:24
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In summary

At human timescales? No, global warming is very bad for life on the whole.

At geological timescales? It could be very good for life. Or neutral. Or extremely bad.

At human timescales

Looking at a scale of decades to a century or two, global warming is very bad for life as a whole: both human life, and global biodiversity.

That's not to say that there won't be individual winners, as well as individual losers. As one habitat shrinks, so another habitat extends. Oceans warm, and acidity increases, meaning that species such as coral which are highly sensitive to temperature and acidity, will suffer hugely (DOI:10.1126/science.1152509, and pdf). This will open up new ecological niches, that will allow some other species to expand in the very short term, and evolve to suit the new niches, over centuries. The problem, as with changing sea levels and other ecosystem shifts, is not that the final equilibrium result is necessarily worse than the starting point: it is that we have built our civilisation based on the existing ecosystem; and the climate and ecosystem are now changing faster than our civilisation can adapt.

At the scale of decades, short by evolutionary standards, environmental change is more rapid than genetic change. Whereas previously the Earth has seen periods of warming and cooling that have raised or lowered the temperature by several Kelvin, those have happened over thousands of years or longer. Now, all the evidence is that this is happening over decades. This, combined with humankind's other environmentally degrading activities, means that Earth's ecology is now going through its sixth mass extinction.

So it's an issue of rate of change of climate.

The IPPC's 4th assessment report (AR4) presents the state of knowledge as of 2006-7. Specifically Working Group 2 (WG2) reported on Impacts, Adaptation and Vulnerability. This was watered down by a round of political editing. That dilution not withstanding, the following image appears in the report:

IPCC AR4 summary

At the moment, with a "business as usual scenario", we're on course for a global mean temperature change of 5-7°C or so, which would mean a loss of 40% or more of species. If we succeed in rapid mitigation, we can lessen the biodiversity impact so that there's a risk of losing "only" 30% of species.

At longer timescales

Looking at a scale of thousands of years upwards, things become much more speculative. We know that there are positive and negative feedbacks in the system. At some point, positive feedbacks will get balanced by negative feedbacks. However, we don't know how hot things will have got before then. Or what sort of life might be viable. However, some forms of life do seem extraordinarily tenacious even at the very extremes.

  • It is only bad for those that do not survive. Those that survive are going to find less competition from their competitors that did not survive. – Chad Sep 10 '12 at 19:16
  • Yes, that's right. I think that's what I say, a little more verbosely, in the second paragraph of the "At human timescales" section. – EnergyNumbers Sep 10 '12 at 19:31

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