The link between smoking tobacco and cancer was first established in the 1930s, and it took about 60 years for a good fraction of the world to accept the need to limit smoking.
The climate change debate is of similar character – some of the same players are even involved. The tactics, not surprisingly, are similar. Promote the view with a combination of bought off scientists and fake grassroots (astroturf) movements that there is more debate about the science than there really is. Promote the view that there is a mafia who attack anyone who opposes the mainstream scientific position. Argue that the mainstream is "junk science" as opposed to opinions of non-specialists, who do not do any real scientific work, who somehow have it right. Position dissenters from the mainstream as Galileos.
No one would be happier than me if the link between CO2 and climate could be convincingly debunked, because the tobacco example shows just how hard it is to change government policy, not matter how convincing the science, in the face of a determined industry lobby. For this reason, I've been taking a skeptical view of the climate change "skeptics": trying to find evidence that they may just be right. This has been pretty heavy going, because a lot of them are clearly uninformed and a lot of "skeptic" commentary is plain garbage. Some of course is valid. In an area as complex as this, there have to be errors and omissions in the accepted models. A genuine scientific skeptic will of course validly explore these problem areas and either find improvements, or overturn the whole model.
So far, in my reading of this work, I've not managed to find anything better than nitpicks. Some details of the models may not be totally accurate, not that anyone ever claimed they were. All of the models used by climate modelers of any worth are reported as representing a range of values, allowing for uncertainties – as they should.
The thing which troubles me about the self-appointed (being kind and not assuming they are not industry shills) "skeptics" is that they all insist that the range of values in IPCC projections are "alarmist", i.e., that the "skeptical" position is that things are better. I have not seen one person in the group widely touted as representing correction to the "mainstream" arguing that science could be badly wrong in the other direction. There are climate scientists in the "mainstream" who argue that some numbers could be optimistic, e.g., James Hansen at NASA argues that we don't have good data to support the view that sea level rise will be within the relatively benign range the IPCC accepts for 2100 (or more recently, 2099).
A true skeptic has to look at the whole range of possibilities for error in the modeling. So, what evidence is there that the modeling could be radically wrong in the direction of optimism?
A popular "skeptic" argument revolves around looking in the paleoclimactic record for instances of temperature-CO2 coupling, and demonstrating that temperature change leads the trend. This is not particularly useful, because such instances do not mirror the current scenario, where gigatonnes of CO2 are being added to the atmosphere independently of a temperature trigger. It is more useful to look for past events where a massive infusion of greenhouse gases was not triggered directly by a temperature increase, i.e., something bigger than can be explained by reduced solubility of CO2 when the oceans warm up.
The best candidate is the Permian-Triassic extinction event (I cite WikiPedia because it's easy to read and accessible, but I have read relevant literature in academic journals as well to check; I encourage other genuine skeptics to read further). Let's call this one the PTE for brevity. PTE is the biggest extinction event since the fossil record began, and wiped out 90% of all life. it took 3-million years for coal to form in significant quantity, so severe was the die-off. What triggered it? That far in the past, exact mechanisms are hard to pin down, but it is known that massive volcanos, the Siberian Traps, spewed out millions of cubic kilometres of lava. Some of this lava landed in coal beds; much also landed in a shallow sea. Seas contain methane clathrates (also called methane hydrates), methane trapped in water molecules in relatively cold water. If the temperature increases, the methane is released. These two effects combined to have a significant greenhouse effect, and the resulting rapid temperature rises may have made the oceans become anoxic. The dominant life form in the oceans became sulfur-reducing bacteria, which exhale toxic sulfur dioxide, which poisoned life on land. How quick was the die-off? One study [Rampino et al 2000] shows that it could have taken under 8,000 years, but definitely less than 60,000 years, for most animals to die off.
How close is this scenario to what is happening today? The Siberian Traps eruptions occurred over a much longer time period, of the order of hundreds of thousands of years at least. The continental configuration was different – this was the era of the single supercontinent, Pangea, so ocean circulation would have been very different. The presence of a significant polar land mass in the south today means we have a larger buffer against warming (sea ice is much less stable than land ice). On the other hand, the atmospheric CO2 levels were very similar to today's before being elevated over a relatively short period by a factor of 5 to 10.
So on balance, I can't say that what is happening today is cause for much optimism. The fact that we are adding CO2 to the atmosphere so much faster cannot be good for the environment. The worst-case IPCC scenario has CO2 levels rising by a factor of 5 on pre-industrial by 2100, scarily close to what happened at the end of the Permian – but thousands of times faster. Time is of course a critical variable in biosphere adaptation. Evolution does not work on decadal time-scales. If forced change in thousands of years was catastrophic, where are we headed now?
Then there's the Paleocene-Eocene Thermal Maximum (PETM), around 55-million years ago. Methane clathrates have also been implicated in this one, as has a release of between 2000 and 5000 gigatons of carbon into the atmosphere over 10,000 to 20,000 years. There is also the possibility of volcanic events causing the greenhouse gas releases. As with the PTE, the key issue is the rapid deployment of greenhouse gases, followed by global warming, then a large-scale die-off. In the case of PETM, the die-off was more restricted, with some molluscs heavily reduced (over 90%); this was the time when many older mammal forms died off, and precursors to modern life forms appeared. As with PTE, the time-scale was much longer than today's. Since PETM is much more recent, it is an easier target for study, and figures in IPCC reports. What is particularly worrying about PETM is that the rate of warming is outside the range of climate models, suggesting that contrary to the common "skeptic" position that cliamte models are alarmist, the opposite may be true.
In conclusion, from what I've found so far, there is a strong relationship between relatively rapid increases in greenhouse gases, similarly rapid climate change, and mass extinctions.
If anyone can find an example of this scale of increase in greenhouse gases (doubling or more, with a baseline similar to today's levels), over a time period short enough to cause problems with biosphere adaptation, which is not associated with a significant extinction event, let me know.
So, to answer the question in the title: are we doomed? On the evidence I've found so far, yes. Until I turn up something better, it seems we have no option but to fight the fossil fuel industry, futile though that may seem. Meanwhile, this all reminds me of one of my favourite Far Side cartoons: "The Real Reason Dinosaurs Became Extinct". A bunch of dinosaurs are seen smoking. Larson tied the two issues together nicely.
In case you can't find references on the net and have a library:
[Rampino et al 2000] Rampino, M. R., A. Prokoph, and A. Adler, 2000. Tempo of the end-Permian event: high-resolution cyclostratigraphy at the Permian-Triassic boundary. Geology, 28: 643-646.