Global climate change is the much-dreaded “kill shot” for all humankind and all other life forms on Earth. The risk is very real, if the planet heats up too much, all life on Earth would die out.
There is absolutely no doubt that C02 levels are rising and are a key contributer to the rising temperatures. The latest ice cores from the Antarctic have been dated back to over 800,000 years ago. This provides scientists with a significant timeline in which to measure C02 levels.
Not surprisingly, C02 levels are directly related to Antarctic temperatures, and that of the rest of the planet. The new data says that the correlation between Antarctic temperatures and CO2 continues unabated.
However, efforts to discredit this finding abound, most notably directed at the movie, “An Inconvenient Truth” and Al Gore. Others point to Al Gore almost as if he is the actual cause of climate change, which is an absurdly ridiculous argument.
[the following is excerpt from RealClimate.org, my comments included – Admin]
Congressman Joe Barton was one of those who have attempted to discredit these finding during Al Gore’s congressional testimony. Barton said:
In your movie, you display a timeline of temperature and compared to CO2 levels over a 600,000-year period as reconstructed from ice core samples. You indicate that this is conclusive proof of the link of increased CO2 emissions and global warming. A closer examination of these facts reveals something entirely different. I have an article from Science2 concentrations did not precede a rise in temperatures, but actually lagged temperature by 200 to 1,000 years. CO2 levels went up after the temperature rose. The temperature appears to drive CO2, not vice versa. On this point, Mr. Vice President, you’re not just off a little. You’re totally wrong.
This subject has been very well addressed in numerous places. First of all, saying “historically” is misleading, because Barton is actually talking about CO2 changes on very long (glacial-interglacial) timescales. On historical timescales, CO2 has definitely led, not lagged, temperature. But in any case, it doesn’t really matter for the problem at hand (global warming). We know why CO2 is increasing now, and the direct radiative effects of CO2 on climate have been known for more than 100 years. In the absence of human intervention CO2 does rise and fall over time, due to exchanges of carbon among the biosphere, atmosphere, and ocean and, on the very longest timescales, the lithosphere (i.e. rocks, oil reservoirs, coal, carbonate rocks). The rates of those exchanges are now being completely overwhelmed by the rate at which we are extracting carbon from the latter set of reservoirs and converting it to atmospheric CO2. No discovery made with ice cores is going to change those basic facts.
Second, the idea that there might be a lag of CO2 concentrations behind temperature change (during glacial-interglacial climate changes) is hardly new to the climate science community. Indeed, Claude Lorius, Jim Hansen and others essentially predicted this finding fully 17 years ago, in a landmark paper that addressed the cause of temperature change observed in Antarctic ice core records, well before the data showed that CO2 might lag temperature. In that paper (Lorius et al., 1990), they say that:
…changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing
What is being talked about here is influence of the seasonal radiative forcing change from the earth’s wobble around the sun (the well established Milankovitch theory of ice ages), combined with the positive feedback of ice sheet albedo (less ice = less reflection of sunlight = warmer temperatures) and greenhouse gas concentrations (higher temperatures lead to more CO2 leads to warmer temperatures). Thus, both CO2 and ice volume should lag temperature somewhat, depending on the characteristic response times of these different components of the climate system. Ice volume should lag temperature by about 10,000 years, due to the relatively long time period required to grow or shrink ice sheets. CO2 might well be expected to lag temperature by about 1000 years, which is the timescale we expect from changes in ocean circulation and the strength of the “carbon pump” (i.e. marine biological photosynthesis) that transfers carbon from the atmosphere to the deep ocean.
Several recent papers have indeed established that there is lag of CO2 behind temperature. We don’t really know the magnitude of that lag as well as Barton implies we do, because it is very challenging to put CO2 records from ice cores on the same timescale as temperature records from those same ice cores, due to the time delay in trapping the atmosphere as the snow is compressed into ice (the ice at any time will always be older than the gas bubbles it encloses, and the age difference is inherently uncertain).
Still, the best published calculations do show values similar to those quoted by Barton (presumably, taken from this paper by Monnin et al. (2001), or this one by Caillon et al. (2003)). But the calculations can only be done well when the temperature change is large, notably at glacial terminations (the gradual change from cold glacial climate to warm interglacial climate). Importantly, it takes more than 5000 years for this change to occur, of which the lag is only a small fraction (indeed, one recently submitted paper I’m aware of suggests that the lag is even less than 200 years). So it is not as if the temperature increase has already ended when CO2 starts to rise. Rather, they go very much hand in hand, with the temperature continuing to rise as the the CO2 goes up. In other words, CO2 acts as an amplifier, just as Lorius, Hansen and colleagues suggested.
Now, it there is a minor criticism one might level at Gore for his treatment of this subject in the film (as we previously pointed out in our review). As it turns out though, correcting this would actually further strengthen Gore’s case, rather than weakening it. Here’s why:
The record of temperature shown in the ice core is not a global record. It is a record of local Antarctic temperature change. The rest of the globe does indeed parallel the polar changes closely, but the global mean temperature changes are smaller. While we don’t know precisely why the CO2 changes occur on long timescales, (the mechanisms are well understood; the details are not), we do know that explaining the magnitude of global temperature change requires including CO2. This is a critical point. We cannot explain the temperature observations without CO2.
But CO2 does not explain all of the change, and the relationship between temperature and CO2 is therefore by no means linear. That is, a given amount of CO2 increase as measured in the ice cores need not necessarily correspond with a certain amount of temperature increase. Gore shows the strong parallel relationship between the temperature and CO2 data from the ice cores, and then illustrates where the CO2 is now (384 ppm), leaving the viewer’s eye to extrapolate the temperature curve upwards in parallel with the rising CO2. Gore doesn’t actually make the mistake of drawing the temperature curve, but the implication is obvious: temperatures are going to go up a lot. But as illustrated in the figure below, simply extrapolating this correlation forward in time puts the Antarctic temperature in the near future somewhere upwards of 10 degrees Celsius warmer than present “” rather at the extreme end of the vast majority of projections (as we have discussed here).
Global average temperature is lower during glacial periods for two primary reasons:
1) there was only about 190 ppm CO2 in the atmosphere, and other major greenhouse gases (CH4 and N2O) were also lower
2) the earth surface was more reflective, due to the presence of lots of ice and snow on land, and lots more sea ice than today (that is, the albedo was higher).
As very nicely discussed by Jim Hansen in his recent Scientific American article, the second of these two influences is the larger, accounting for about 2/3 of the total radiative forcing. CO2 and other greenhouse gases account for the other 1/3. Again, this was all pretty well known in 1990, at the time of the Lorius et al. paper cited above.
What Gore should have done is extrapolated the temperature curve according this the appropriate scaling “” with CO2 accounting for about 1/3 of the total change “” instead of letting the audience do it by eye. Had he done so, he would have drawn a line that went up only 1/3 of the distance implied by the simple correlation with CO2 shown by the ice core record. This would have left the impression that equilibrium warming of Antarctica due to doubled CO2 concentrations should be about 3 °C, in very good agreement with what is predicted by the state-of-the-art climate models. (It is to be noted that the same models predict a significant delay until equilibrium is reached, due to the large heat capacity of the Southern ocean. This is in very good agreement with the data, which show very modest warming over Antarctica in the last 100 years). Then, if you scale the Antarctic temperature change to a global temperature change, then the global climate sensitivity to a doubling of CO2 becomes 2-3 degrees C, perfectly in line with the climate sensitivity given by IPCC (and known from Arrhenius’s calculations more than 100 years ago).
In summary, the ice core data in no way contradict our understanding of the relationship between CO2 and temperature, and there is nothing fundamentally wrong with what Gore says in the film. Indeed, Gore could have used the ice core data to make an additional and stronger point, which is that these data provide a nice independent test of climate sensitivity, which gives a result in excellent agreement with results from models.
A final point. In Barton’s criticism of Gore he also points out that CO2 has sometimes been much higher than it is at present. That is true. CO2 may have reached levels of 1000 parts per million (ppm) “” perhaps much higher “” at times in the distant geological past (e.g. the Eocene, about 55 million years ago). What Barton doesn’t bother to mention is that the earth was much much warmer at such times. In any case, more relevant is that CO2 has not gone above about 290 ppm any time in the last 650,000 years (at least), until the most recent increase, which is unequivocally due to human activities.
The new 800,000 year ice core data reveals that the CO2 concentrations were generally lower than average between 800,000 and 650,000 years ago. The lowest CO2 value ever measured in an ice core is now 172 ppm, from 667,000 years ago. Current levels are more then twice as high at 384 ppm and climbing.
“Alarmism” is a term that gets bandied about a lot. It is often said that one should not call out “fire” in a crowded building. But it really depends, one might say, on whether the “calling out” is done in such a way as to simultaneously prevent a stampede and prevent anyone getting burned.This riddle was very much on my mind as I sat down to write my thoughts on Mark Lynas’s book, Six Degrees: Our Future on a Hotter Planet (London: Fourth Estate, 2007).
I don’t read much popular science literature, and I doubt I would have read this book if I hadn’t made the mistake of referring to it (in a negative manner) in the comments section of a RealClimate post. I don’t think my error was very grave. What I actually said was that if what I had heard about the book from the press materials were true, then the book was probably alarmist and not worth reading. But I don’t blame the author for asking me to read the book and see for myself. He said that the press (in this case Sunday Times (London)) had misconstrued what he says in the book, and he assured me that is was all based on very careful review of the scientific literature. I was thus both curious and obligated to read the book.
Mark Lynas will no doubt be pleased that I very much like the book. To be sure, it is alarming, but the question of whether it is alarmist is a more difficult one, and I don’t think the answer lies in debating the book. Rather, it lies in looking closely at the underlying science the book builds on. I don’t intend to do that here, but I do think that all climate scientists (particularly those that talk to the public) ought to read this book, and ask themselves a question. I’ll get to that question at the end, after saying a bit more about the book.
Six Degrees, as the title suggests, is comprised of six main chapters (plus an introduction and a conclusion). Each of the main chapters examine what the earth might look like as we raise the planet’s temperature by 1o, 2o, etc. degrees Celsius, based on what the scientific literature has to say about it. Laying out the book this way makes for a good logical progression of ideas, and a fair bit of suspense. Very few people, Lynas says, have got “the slightest idea what two, four or six degrees of average warming actually means in reality, and I’m sure he is right.
In Chapter 1, at 1o, we have predictions of, for example, an annually ice free Arctic ocean [this means Arctic resource wars – Admin]. Yes, quite plausible and supported by the literature, and perhaps occurring a little sooner than expected. At 2o, we have, “so whilst southern China can expect more flooding as the two-degree line is approached, the oceanic time lag means that it may take much longer for the rain-bearing summer monsoon to reach the drought-stricken north.” [now think what that will mean to the food production – Admin]
Yes, certainly plausible based on the studies Lynas cites. At 4o, we have “with global sea levels half a meter or more above current levels, [the Egyptian city of] Alexandria’s long lifespan will be drawing to a close. Even in today’s climate, a substantial part of the city lies below sea level, and by the latter part of this century a terminal inundation will have begun. “¦ a rise in sea levels of 50 cm would displace 1.5 million people and cause $35 billion of damage.”
Alarmist? Hardly. A 50 cm rise in sea level, is well within the conservative IPCC projections, even for temperature rises less than four degrees.
At 5o and 6o, the book really does start to sound alarmist, with the analogy to Dante’s Inferno ““ used to good literary effect throughout the book ““ coming very much to the fore. At five degrees, we have “an entirely new planet is coming into being ““ one largely unrecognizable from the Earth we know today. At six degrees, “”¦ the pump is primed “¦ not for flourishing palm trees in Alaska, but for the worst of all earthly outcomes: mass extinction.
Aha, say the skeptics! It is alarmist after all. But is it? Lynas’s reference to the “entirely different planet” actually refers to the fact that at five degrees, the “remaining ice sheets are eventually eliminated from both poles.” That’s entirely true. And unlike in Gore’s discussion of sea level in Inconvenient Truth Lynas does emphasize the long timescales (thousands of years) in this case [please note that all previous estimates have been wrong and are being updated daily – Admin].
Furthermore, there is published research that raises the likelihood of the significant loss of ice sheets at lower temperatures, and Lynas could have claimed certainty of a disappearing Greenland ice sheet in an earlier chapter. That he doesn’t do that is characteristic of the book: it doesn’t tend to go beyond the published literature. This is what Lynas claims at the outset “” “all of the material in the book comes from the peer-reviewed scientific literature” ““ and I think he does an admirable job.
And that brings us back to the question I promised to raise at the beginning, which is this:If a reading of the published scientific literature paints such a frightening picture of the future as Six Degrees suggests ““ even while it honestly represents that literature ““ then are we being too provocative in the way we write our scientific papers? Or are we being too cautious in the way we talk about the implications of the results?
Many scientist are now questioning this issue. If they have been too cautious, what might they do to warn the world? And they recognize the importance and probably response, many think nothing will be done until the Greenland ice literally disappears. This has long been my personal “take” on the entire issue, we’re simply too entrenched to change and refuse to recognize the signs all around us.
What will happen, for example, if 100 million Bangladeshis “inundate” neighboring areas of Myanmar and India, as their near-sea level homes are inundated by a rising sea? What will happen in the USA if California’s central valley is flooded, and the midwest dries up? Will Canada build a fence and try to thwart an “invasion” of starving US citizens? In light of the current US attitudes many hold on immigration, some might see such a situation as poetic justice. I see the potential for major social and political upheavals with truly sobering consequences [this is a huge understatement, typical of the scientific mindset – Admin].
Comment by Gene Hawkridge “” 25 November 2007 @ 5:22 PM
I also read 6 Degrees recently, and was impressed by the clear and unemotional writing style. I don’t have the knowledge to critique the science quoted though I try and keep very informed on the subject, but found the book very frightening.
In terms of your question I believe that the scientific consensus is inevitably somewhat late and is, in climate circles, maybe still anticipating the scorn of the deniers which used to be heaped on anything they didn’t like. As such it often reads as if it’s a bit tentative.
One of the major problems is how to give a sense of urgency without being alarmist. One option would be to combine the simpler book conclusions for each degree rise, with a percentage based chance of reaching that rise within various periods. So as an example each year after the UNFCCC report on emissions, RealClimate could produce a document which assumes these emissions and growth in emissions and states:-
Under the current growth case we see a
75% chance of a 1 degree rise over 25 years
25% chance of a 2 degree rise over 25 years
5% chance of a 3 degree rise over 25 years
75% chance of a 2 degree rise over 50 years
25% chance of a 3 degree rise over 50 years
5% chance of a 4 degree rise over 50 years
1 degree rise = Ice free Artic..
2 degree rise Monsoon disruption..
4 degree rise Good chance Australia becomes uninhabited etc”¦
Even if the science is still a bit vague on the percentages, this allows a rational decision on how quickly we must change, which is, now that the deniers are all but dead or in exile, the major remaining issue.
I think that focusing on the next 50 years (rather than 100 years as often seen) allows people to think within their own lifetime, and I don’t believe most understand the extent of the worst case disruption within 50 years. Thus while not being sensationalist it clearly brings the worst case to the fore.
Policy-makers need to carefully consider the implications of scientific reticence for climate change policies.
Even the most stringent international policy responses on the table at present set a course to stabilize mean global temperature rises at 2-3°C above pre-industrial levels.
The stated objective of the EU is to stabilise mean global temperature rises at 2°C, but the emission reduction targets they propose (most significantly, 60% by 2050) appear more likely to lead to a 3°C rise [which means no ice at either pole, and irreversible climate change – Admin]. The IPCC (2007a) report suggests a global reduction of emissions of 60% by 2050 will put the world on track to stablise around a 2.4°C rise.
If the world adopts an objective of stabilising mean global temperature rises at 2-3°C above pre-industrial levels, Hansen et al (2006) comments have a nagging logic on likely sea level rises:
“Sea level was 25-35m higher the last time that the Earth was 2-3°C warmer than today, i.e. during the Middle Pliocene about three million years ago.”
While the IPCC (2007b) estimated sea level rises of 0.18-0.59cm this century it acknowledges, “Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking.”
In the light of the IPCC’s caveat, Hansen’s point about sea level rises suggests trying to stabilize mean global temperature rises at 2-3°C above pre-industrial levels is lunacy and we need to do much better.
[Frankly, I think it is incredulous to think we can “stabilize” at ANY temperature, since we have so little direct control over the climate and given our actual behavior (denial and business as usual). All feedback mechanism are decades, if not centuries behind their cause and effects. The assumption that we can accurately predict and enforce some sort of human industrial standards that will guarantee our climate to “only” increase in temperate by 2-3°C is patently absurd. We can’t do this, it is impossible. Therefore, climate temperatures will rise significantly higher then our best estimates because we consistently fail take into account these huge time lags and our contributed cause and effect. All of the current measurements and late-breaking news indicates this, as estimates and predictions are constantly revised to take into account the actual, real on-the-ground measurements now pouring forth.
There is also a very real and extreme danger to all of humanity, and that is simply this: we are only willing to do (maybe) what is minimally required of us and nothing more. And this is exactly why we will fail.
This is also in part, why I proclaim the collapse of civilization is now upon us. Collapse will come, either “naturally” by the forces of nature, or by design, by the forces of mankind, as we desperately attempt to “save ourselves” from our own contribution to collapse. Either by global die-off (genocide) or resource collapse, we will have absolutely no choice, collapse is happening now as evidenced by the daily news and scientific reports documenting this fact – Admin]
THERE ARE ZERO HUMAN AUTHORITIES.
Scientists do not vote on what is the truth. There is only one vote and Nature owns it. We find out what Nature’s vote is by doing Scientific [public and replicatable] experiments. Scientific [public and replicate] experiments are the only source of truth. [To be public, it has to be visible to other people in the room. What goes on inside one person’s head isn’t public unless it can be seen on an X-ray or with another instrument.]
Science is a simple faith in scientific experiments and a simple absolute lack of faith in everything else. Do not trust any human, not even yourself. Trust only the experiments that you personally perform. Otherwise, you will be misled.