Optimism, they all tell us, is a precondition of effective political action. And they are no doubt quite correct. Despair, after all, hardly motivates sustained political engagement. Drinking, more like it.

Optimism, unfortunately, is a problem, for enviros in particular but in fact for anyone determined to look, hard and critically, at the truth of our predicament. Few of us are able to consistently follow Antonio Gramsci's advice, to combine "pessimism of the intellect" with "optimism of the will." Most of the time, it seems more like a choice between one and the other. Or, even worse, a choice between paralyzing pessimism and idiot, right-wing confidence.

We, for our part, still believe that realism (the real thing, not the ersatz neo-con variety) is the best ground for an honest optimism, and in that spirit we'd like to start off this issue of Climate Equity Observer with an effort to look reality in the eye.

It's getting easier to do so, or at least harder to avoid the challenge. For the drumbeat is clearly becoming louder. A multi-year, globally synchronized drought continues, and while there's no proof, it's easy to argue that it (along with what Mike Davis called "stupid development") played an key role in the recent southern California firestorm. Looking back just a few months further, we come to a summer heat wave that killed 35,000 in Europe and untold others in India and the rest of the developing world, a heat wave that many took, with excellent justification, as a sign of things to come. And with stories of rapid Arctic melting become suddenly common, it's even starting to seem like global warming may have finally found its "ozone hole," the smoking gun that makes denial, if not impossible, at least unprofitable.

None of this, though, is the subject here. Instead, we wish to reach past the news to the deeper regions where science itself is the central drama. For though you might not know it from the chattering of the "balanced" mainstream media, global warming is slowly but clearly taking on a new air of scientific urgency. It's not just the drought and the heat wave, or even that these are just the sorts of events that the science tells us to expect. It's not even that, at least in Britain, the scientists have become brave enough to clearly say that natural processes, such as sunspots or volcanic activity, cannot account for the observed temperature increases. It's rather than the climate models are now actually quite good, and that the scientists have gotten down to the job of more carefully calibrating the remaining uncertainties. And that, as they do so, they seem to be discovering that the situation is even worse than we'd feared.

And, frankly, we'd feared it would be pretty bad.

Grim Science

At the risk of oversimplifying a complex and ever-evolving picture, we're going to take the liberty of categorizing the recent bad news into three piles:

• The climate sensitivity factor now looks likely to come in on the high side of the range delimited in the IPCC's Third Assessment Report, and might even be outside the "conventional" 4.5ºC upper bound.
• It appears that there's more global warming going on than we thought, but that it's being masked by a surprisingly large aerosol cooling effect.
• Some of the positive feedbacks that scientists have long worried about are now looking to be all too plausible, even in the short term.

Moreover, and importantly, the Earth's climate can and does change quite rapidly. Given this, and given as well that the carbon concentration of the atmosphere is now greater than it's been in over 420,000 years, it seems quite reasonable to worry. As Columbia's Wallace S. Broecker recently put it in the pages of Science (1), the "Earth's climate system has proven itself to be an angry beast. When nudged, it is capable of a violent response."

The Climate Sensitivity Factor

You may recall that last November, back at COP8, the Climate Action Network steeled itself to draw a clear line in the sand: if our goal is Preventing Dangerous Climate Change, then "global mean warming needs to be limited to a peak increase of below 2°C (above pre-industrial times)."

It was a tough line to draw, for by conventional reckonings it is all but unreachable. But the firming science made it possible and, for CAN, necessary. CAN, after all, is an NGO network, and as such it stands for precaution and sustainability or it stands for nothing at all. And while the politicians (those few who follow the details) have come to assume that, even in the best possible case, we'll see 3°C or even 4°C of warming before we manage to stabilize the climate, such a future would virtually guarantee intolerable impacts and suffering. Even 2ºC would be a death sentence for tens of thousands and perhaps millions of people, a commitment to catastrophic losses of species and ecosystems, and, frankly, an invitation to a sharp exacerbation of geopolitical and military instability that we hardly seem likely to manage with aplomb, particularly since, in the worse case (see below), 2°C would be enough to set the waters rising in earnest.

Even a peak warming of 2°C, then, would be a miserable and possibly unacceptable compromise. We must do everything in our power to ensure that we don't overshoot it, and, indeed, that we come in lower. Given this, the real question is an ugly one: How much greenhouse pollution can we, all of us together, emit without pushing the total global warming past the 2°C line? Such a calculation is necessarily uncertain, and debatable in innumerable ways, but if we did it, what would it show?

The answer would, first of all, depend on the value of the climate sensitivity factor, a variable by which scientists specify how much the average global temperature would increase if the CO2 concentration of the atmosphere was to reach twice its pre-industrial level. The actual value of this all-important number is still unknown (it is, in fact, one of the most important remaining uncertainties) but the bad news, and it is bad indeed, is that respected members of the scientific community are becoming more pessimistic about what we'll finally find.

Back in the dim past, in 1995, when its Second Assessment Report estimated the value of the climate sensitivity, the IPCC was so bold as to give a "best estimate" of 2.5ºC. In 2000, however, when the Third Assessment Report was released, the IPCC declined to give anything like a best estimate or even a probability distribution, choosing instead to simply estimate that the climate sensitivity was in the range of 1.5ºC to 4.5ºC.

This is the conventional estimate of the sensitivity's likely range. Here are some things to keep in mind when considering it:

• The low end estimate, 1.5ºC, dates back to 1990's First Assessment Report. Few current models and little evidence corroborate it.
• Reasonable assumptions about the behavior of the climate system indicate that a 2.5ºC sensitivity could well lock-in 2ºC warming when the CO2 concentration reaches 500 ppm (as against the preindustrial level of 275 ppm and the current level of about 373 ppm). But this number assumes that CO2 is the only major greenhouse gas, and it's not, not by a long shot.
• Non-CO2 greenhouse gases add an additional radiative forcing, even when you consider that aerosols are cooling pollutants. The IPCC's latest scenarios estimate that, in 2050, the non-CO2 greenhouse gases will add a warming equivalent to between 20 to 75 ppm of CO2. Take a midpoint estimate of 50 ppm, hold it constant, factor it into the equation, and you find that a 2.5ºC sensitivity would propel us across the 2ºC line when the CO2 concentration reaches a mere 450 ppm.
• It gets worse. The IPCC's classic estimate for the range of likely climate sensitively values puts the high end at 4.5ºC, but the scientific trend is to raise that upper limit. In fact,recent research (2) suggests that there are large tails of the probability distribution outside the classic range, and that the real 90% probability range is about 1ºC to 9.3ºC. And if this result is borne out, there's actually a 54% likelihood that the sensitivity lies outside the IPCC's conventional range.
• The IPCC's high estimate of 4.5ºC may turn out to be higher than the actual climate sensitivity, but it's hardly the upper bound, and it should not be taken as a hysterically high estimate. So note well that if the sensitivity is in fact 4.5ºC, we cross the 2ºC line at about 400 ppm, only 30 ppm above today's CO2 concentration level. And, again, that's without the non-CO2 gases. Add our 50 ppm estimate of their cumulative effect, and we've already crossed the 2ºC line, back when we shot past 350 ppm, though for a variety of reasons (the absorption of heat by the oceans, and the fact that past emissions have "locked in" but not yet delivered their contribution to future warming) we don't yet know it.

The bottom line: The actual climate sensitivity may not be as high as 4.5ºC, but neither is 4.5ºC a crazy, low-probability upper bound. Indeed, many scientists believe that there are substantial risks that the sensitivity is even higher.

Let's hope that they're not right.

Aerosol Masking

Let's start, again, with the IPCC's 2000 consensus, which tells us that today's climatic changes - the droughts, the floods, the migrating ecological zones, the melting ice - correspond to an average rise in global temperatures of 0.6ºC, a single degree Fahrenheit.

Are these changes serious? Perhaps not when weighed against all our other problems, not yet in any case. But there is that small matter of the future - the consensus among climatologists is that the century will see a temperature rise of between 1.4ºC and 5.8ºC: up to ten times the increase we've suffered so far (3). And that's the consensus, which is lagging the science, and which a number of scientists no longer accept.

The reasons for this shift take us back to non-CO2 forcing. Our 50-ppm estimate of that forcing, you'll recall, was a midpoint estimate for the sum for all non-CO2 greenhouse gases, some of which (sulfate aerosols) are cooling pollutants that mask global warming. But what if the cooling effect of these aerosols is actually stronger, perhaps much stronger, than was previously thought? What if, in effect, this cooling effect is masking a stronger warming? And what if, despite this masking, we're compelled to eliminate them - sulfates aerosols, after all, are extremely deadly, while others (like black carbon) appear to be radically amplifying the Arctic melting - but find that, by so doing, we radically accelerate the overall warming?

Consider, for example Strong carbon cycle feedbacks in a climate model with interactive CO2 and sulphate aerosols, which was published in Geophysical Research Letters this past May. (The press release has the snappier title of New Climate Model Predicts Greater 21st Century Warming. Here we learn of an "all-forcings experiment," ALL, recently completed by Chris Jones and colleagues at Britain's Hadley Centre. The point of this experiment was to incorporate everything: CO2 emissions, non-CO2 greenhouse gases, human-produced sulphate aerosol levels, the reflection of solar radiation associated with sulphate in the atmosphere (the "albedo effect"), atmospheric ozone levels, levels of solar radiation, the effects of volcanic eruptions, and climate-carbon cycle feedbacks into one integrated model.

The punch line:

"ALL shows that predicted reductions in human sulphate emissions will cause a reduction in the cooling effect associated with sulphates in the atmosphere, or a net warming. The model predicts that the resultant warming will enhance soil respiration, meaning that the increased amounts of carbon stored in the soil during the 20th century will be released into the atmosphere, causing a faster rise in atmospheric carbon dioxide. By the end of the 21st century, the authors state, the increase in carbon dioxide and decrease of sulphates will cause a substantially higher global warming of 5.5 degrees Celsius [9.9 degrees Fahrenheit] compared with 4 degrees Celsius [7 degrees Fahrenheit] when these interactions are neglected."

A second development, Global warming's sooty smokescreen revealed, is, if anything, worse, or will be if borne out by further research. Here we learn of a workshop in Berlin where a group of top atmospheric scientists, including Nobel laureate Paul Crutzen and Swedish meteorologist Bert Bolin, former chairman of the IPCC, concluded that the aerosol masking effect could be far stronger than was previously thought. Here's how Fred Pearce summarized the situation in New Scientist:

"It looks like the warming today may be only about a quarter of what we would have got without aerosols," Crutzen told New Scientist. "You could say the cooling has done us a big favour. But the health effects of many aerosols in smog are so great that even in the poor world, they are already cutting emissions." For good reasons, aerosol levels look set to fall.

Moreover, most aerosol emissions only stay in the atmosphere for a few days. Most greenhouses gases remain for a century or longer. So as time goes on, aerosols will protect us less and less from global warming. "They are giving us a false sense of security right now," said Crutzen.

One tentative estimate put warming two or even three times higher than current middle-range forecasts of 3 to 4°C based on a doubling of greenhouse gases in the atmosphere, which is likely by late this century.

That suggests global warming well above the IPCC maximum forecast of 5.8°C. Back-of-the-envelope calculations now suggest a "worst case" warming of 7 to 10°C."

This result is speculative, but if it's even partially borne out, it will announce big trouble in no uncertain terms. George Monbiot, writing in The Guardian, is not waiting to draw conclusions, arguing instead that "We are not contemplating the end of holidays in Seville. We are contemplating the end of the circumstances which permit most human beings to remain on earth." It would be unfortunate indeed if we find ourselves compelled to agree.

Plausible Non-Linearities

And then there's the problem of positive feedback, the fact that global warming will, more than likely beget more global warming. Check out, for example, this little paper from London's Global Commons Institute. Its goal is to reconcile the Hadley Centre's modeling of the global carbon cycle - which indicates that, with the warming, there will be a serious "die back" in the tropical forests of northern South America, and thus a positive feedback (dead trees release carbon) that amplifies the warming - with oil and gas depletion data published by the Association for the Study of Peak Oil. GCI's immediate point here is that, contrary to some recent glib optimism, the climate problem will not be solved by the depletion of easily accessible oil stocks; but put that aside for a moment and just look at the first graph, which presents Hadley's data in a form more accessible than Hadley does itself.

(For one of Hadley's own presentations of its carbon-cycle feedbacks analysis, see pages 8 and 9 of www.met-office.gov.uk/research/hadleycentre/pubs/brochures/B2002/global.pdf ).

What you have here is a fossil-fuel emissions projection that's consistent with a 450-ppm scenario. So recall that, as noted above, 450 ppm would likely force us across the 2°C line even without the carbon cycle feedbacks that so concern the Hadley Center. Now notice that, once you add those feedbacks, you radically reduce the size of the future carbon budget consistent with 450-ppm stabilization. In so doing, you make it even more difficult to imagine that we're going to make it by anything even remotely like a business-as-usual path.

Nor is Hadley's carbon-cycle feedback analysis the only one to worry about. Which takes us back to the Arctic ice cap, which has recently shrunk by two hundred and fifty million acres, an area the size of California and Texas combined. And, according to NASA's latest calculations, it is continuing to shrink at a rate of nine percent per decade.

We've already heard about this, though we'll soon hear a whole lot more. The Arctic melting could even emerge, and soon, as the "ozone hole" of the climate issue, and even today, few tasks could be more important than helping this process along by advertising the coming consequences of the Arctic melting. There are plenty, from the rapid erosion of the Inuit way of life to the almost inevitable doom of major species like walrus and polar bears.

But while such impacts are noteworthy for being current, not future/speculative, and for being directly linked to global warming, we cite them, here, as emblems of a greater danger. For just as we know that the Arctic ice is quickly thinning, we know too that water reflects less of the sun's energy than ice. And that the real Arctic nightmare may not be in the Arctic at all, but in the radical reduction of the Earth's albedo, the amount of solar energy reflected from the surface, that will follow from the melting.

Thus, the "worst case scenario," in which Arctic warming, by melting icecaps and increasing freshwater flows into the North Atlantic, shuts down the circulation of the Gulf Stream and ices northwestern Europe, even while accelerating the overall global warming by setting off other positive feedbacks around the world.

There are plenty of possibilities: the heat-triggered forest die-off that so concerns the Hadley Center; a rapid, large-scale release of the methane bound in the permafrost; the now clearly observed decline in phytoplankton productivity, a decline that thins the phytoplankton blooms crucial to the oceanic carbon sink; and a whole set of other possibilities besides. Maybe, in the very worst case, we'll live to see them all!

Or we may be lucky. Lomborg and Limbaugh and Liddy may turn out to be correct. This entire essay may be little more than a derivative, eco-apocalyptic screed, a waste of bits and bandwidth. On the other hand, the scientists now straining against their professional reticence to tell us to worry may, in fact, deserve a hearing, or more than a hearing. For one of their increasingly prominent messages is that something really terrible could happen very rapidly indeed.

It's clearly true that the Earth's climate can flip flop with remarkable alacrity. It may even be fair to say, as Mike Davis did in Our Summer Vacation: 20,000 dead that "abrupt climate change is one of the fundamental scientific discoveries of our lifetime." What we know for sure is that The Discovery of Rapid Climate Change has become a story in itself, and that the research community's perception of the risks of rapid climate change is itself changing rapidly. And why not? Something very much like the much-feared collapse of the thermohaline circulation actually happened 12,000 years ago (it's called the Younger Dryas event) and very suddenly indeed.

The Return of the 2C Standard

This has been a quick tour, but if you've read this far you probably get the point - if we're going to give our descendents a fighting chance of avoiding an all-out climate catastrophe, we have to hold the line at a maximum peak warming of 2°C. And less would be a whole lot better! But it isn't going to be easy, and there's no good reason to think that there's much slack in the situation.

The 2°C standard is, of course, somewhat arbitrary. But it's a line in the sand, and we're starting to see lots of other people, NGOs and research groups, work to draw it. And, frankly, we want to help, because having a reasonable line concentrates the mind by making a whole long list of fascinating questions quite unavoidable: How, for example, can a 2°C goal possibly be met? What's the transition story? How much time do we have before global emissions have to peak? And what needs to happen, and when, to make these peaks possible?

Look, next, at the kinds of answers these sorts of questions usually receive. These are well represented by a paper recently published in Science, by a team led by Ken Caldeira, of the Energy and Environment Directorate at the Livermore National Labs, under the title Climate Sensitivity Uncertainty and the Need for Energy Without CO2 Emission. Here we learn that, under mildly optimistic economic assumptions [IPCC IS92a], climate stabilization at a 2°C warming demands that "large amounts of carbon emissions-free energy will be required by mid-century," and that this is true even if climate sensitivity is low. The paper is well worth reading, and contains interesting projections of the need for carbon-free energy. And it includes this:

"For climate stabilization at a 2°C warming under IS92a economic assumptions, large amounts of carbon emissions-free energy will be required by mid-century, regardless of likely climate sensitivity. By the end of the century, between 75 and 100% of total power demand will need to be provided by non-CO2-releasing energy sources...a 2°C warming with a 1.5°C climate sensitivity has allowable carbon emissions equivalent to a 4°C warming with a 3°C climate sensitivity. Hence, even for a 4°C warming and climate sensitivity in the middle of the IPCC accepted range, stabilization of climate would require 75% of our primary power to be generated by non-carbon emitting sources."

Which is, if you think about it, a terrifying little paragraph. After all, the various studies noted above give us good reason to fear that the climate sensitivity will come in above the IPCC midpoint (3°C), though even at that midpoint we'll need 75% of our primary power to be carbon free by the end of the century if we want to hold the line at 4°C total warming! And if our goal is "preventing dangerous climate change," if we're trying for 2°C instead of 4°C, then we're already being pressed, hard, against a very rough wall, and it's way past time to admit it.

Which is, in the optimism/pessimism department, the heart of our problem. Because when you try to go beyond Caldeira's sort of disciplined scientific objectivity to the politics of the case, when you try to contrive a believable transition story of the kind you need if you're to sustain an honest optimism ("of the will" or otherwise), you rapidly find that you need to do a whole lot more than raise your hand to speak for a crash global program of clean energy development. You also have to explain why reasonable people, people who are free to pursue the lineaments of their own, personal, no-doubt well-justified skepticism, might nevertheless conclude that we have more than a snowball's chance in hell.

After all, the need for a crash clean-energy transition is hardly news. Caldeira's numbers are useful, but only because they quantify, and thus "prove," what we already suspect. The real question is how we're going to catalyze that crash clean-energy transition, and the answer, to be believable, is going to have to makes its way though American landscapes dominated by media monopolies, SUVs, real estate developers and Republican true believers.

A believable transition story has to seem relevant outside the conference halls and the ministries. And it has to tell us why, in a post-Cold War world where the United States has morphed into a wounded superpower intent on blindness, privilege, and empire, a world in which not only the green transition storylines, but even the nicer business-as-usual storylines seem increasingly implausible, we might nevertheless hope that the transition is there to be won.

The "two degree standard" is, increasingly, a factor in the climate debate. The question is how to reconcile it with lived reality, with US control of the Iraqi oil fields, and with the fact that the International Energy Agency is projecting that, "if present trends continue," over six trillion dollars will be invested in oil and gas production between now and 2030 (4) . The question, in other words, is how we tell the tale in which we manage to hold the line.

The pressure is great - say on an FM talk show, up against some well-rehearsed servant of the fossil cartel - to insist that it wouldn't be that hard, that the technology is here, or on the horizon, that drawing the line would entail no painful realignment of either our lifestyles or our identities. Hell, I've done it myself.

After all, despair is the enemy.

So What Counts as Good News?

Given all this, what counts as good news? A tough question, though one thing at least is clear: for anything to qualify, it has to presume an honest appraisal of the real situation. Which is why we'll turn, now, to James Hansen's recent work. Hansen, the head of the Goddard Institute for Space Studies, is best known for the 1980s congressional testimony in which he separated himself from the scientific pack by carefully declaring that anthropogenic global warming was an established fact. He is, in other words, a brave man, and one capable of speaking hard truths clearly, without either hyperbole or excessive equivocation.

Which is, no doubt, why he's now prominent among those calling attention to the rapidly of the Arctic melting, and, in particular, arguing that its speed cannot be explained without stepping beyond the IPCC consensus and drawing difficult conclusions. His recent meditation on Arctic melting, "Black Carbon" aerosols, and the limits of the scientific consensus, Can we defuse the Global Warming Time Bomb?, is a must read, and worth quoting at rather exorbitant length:

"The current planetary energy imbalance of about 3/4 Watt/m2 implies that global warming already "in the pipeline," about another 0.5 °C, will take us about halfway to the global temperature that existed at the peak of the Eemian period (5).

Sea level during the Eemian is estimated to have been 5-6 meters (16-20 feet) higher than it is today. Although the geographical distribution of climate change influences the effect of global warming on ice sheets, paleoclimate history suggests that global temperature is a good predictor of eventual sea level change. The main issue is: How fast will ice sheets respond to global warming?

The IPCC predicts only a slight change in the ice sheets in 100 years. However, the IPCC calculations include only the gradual effects of changes in snowfall, sublimation and melting. In the real world, ice sheet disintegration is driven by highly nonlinear processes and feedbacks. The peak rate of deglaciation following the last ice age was a sustained rate of melting of more than 14,000 km3/year, about 1m of sea level rise every 20 years, which was maintained for several centuries. This period of most rapid melt coincided, as well as can be measured, with the time of most rapid warming.

Given the present unusual global warming rate on an already warm planet, we can anticipate that areas with summer melt and rain will expand over larger areas of Greenland and fringes of Antarctica. This will darken the ice surface in the season when the sun is high, promote freeze-thaw ice breakup, and, via ice crevasses, provide lubrication for ice sheet movement. Rising sea level itself tends to lift marine ice shelves that buttress land ice, unhinging them from anchor points. As ice shelves break up, this accelerates movement of land ice to the ocean...

These considerations do not mean that we should expect large sea level change in the next few years. Preconditioning of ice sheets for accelerated breakup may require a long time, perhaps many centuries. However, I suspect that significant sea level rise could begin within decades, if the planetary energy imbalance continues to increase. Whatever that preconditioning period is, it seems clear that global warming beyond some limit will create a legacy of large sea level change for future generations. And once large-scale ice sheet breakup is underway, it will be impractical to stop. The same inertia of the ice sheets, which discourages rapid change, is a threat for the future. It will not be possible to build walls around Greenland and Antarctica. Dykes may protect limited regions, such as Manhattan and the Netherlands, but most of the global coastlines will be inundated.

I argue that the level of DAI [dangerous anthropogenic influence] is likely to be set by the global temperature and planetary radiation imbalance at which substantial deglaciation becomes practically impossible to avoid. Based on the paleoclimate evidence discussed above, I suggest that the highest prudent level of additional global warming is not more than about 1°C. In turn, given the existing planetary energy imbalance, this means that additional climate forcing should not exceed about 1 Watt/m2.

Pretty grim, huh? So why then does Hansen not despair? Because he thinks we still have the time to make the needed transition, and because, crucially, he's a strong "no regrets" man. Hansen believes that an emergency effort to stabilize the climate would have so many non-climate related benefits, and that these are becoming so obvious and pressing, that we might actually be moved to give it a try:

"A million people die every year from air pollution, with large economic cost. Actions to improve air quality have been initiated already in the United States and Europe, and still stricter standards are likely. In developing countries, such as India and China, air pollution is already about as bad as can be tolerated. Discussions among scientists from developed and developing countries suggest that cleaner air is practical, and achievement could be speeded if there were concerted efforts to develop and share cleaner technologies.

In addressing air pollution, emphasis should be placed on the constituents that contribute most to global warming. Methane, a precursor of O3, is a substance expected to contribute much to future global warming. If human sources of CH4 are reduced, it may even be possible to get the atmospheric CH4 amount to decline, thus providing a cooling that would partially offset the CO2 increase. Reductions in black carbon aerosols would help counter the warming effect of reductions in sulfate aerosols. O3 precursors besides CH4, especially nitrogen oxides and volatile organic compounds, must be reduced to decrease low-level O3, the prime component of smog, which damages the human respiratory system and agricultural productivity."

There's plenty more to be said about all this, but little of it is needed here. And while our sense of the practicalities may differ from Hansen's, his efforts to quantify the potential of the no regrets approach, and to articulate it into an "alternative scenario" that arrests the further growth of fossil fuel CO2 emissions, is a virtuoso performance indeed. We recommend it particularly for its embrace of completeness, its willingness to connect the dots.

Of course Hansen may be too optimistic. Most importantly, his alternative scenario assumes a climate sensitivity factor of about 3°C and, as we noted above, this may be low, particularly if the aerosol masking effect turns out to be higher than the current consensus estimate. But the realities here will come clear soon enough, and optimism, the right kind of optimism, is in any case a virtue.

As is the right kind of ambition, which Hansen has. His goal, after all, is not merely to reverse the growth in traditional air pollutants and thus avoid death by soot and sulfate. It is also to draw the line, and clearly. He wants, in particular, to keep the additional climate forcing below 1 W/m2, low enough, by his calculations, to avoid a fatal rising of the waters. He may be wrong about this precise figure, but, just now, this is a secondary consideration. It's the drawing of the line that counts.

The situation is dire, and we had best admit it. Because even if you're an optimist, the facts now speak clearly enough for all those who have not, already, decided to ignore them. Something big has to happen, and soon.

-- Tom Athanasiou

1. W. S. Broecker, " Does the Trigger for Abrupt Climate Change Reside in the Ocean or in the Atmosphere?," Science, pp. 1519-1522, 6 June 2003, Vol. 300   Return to text.

2. For discussions of the likely probability distribution across the range of possible climate sensitivity values, see N. G. Andronova and M. E. Schlesinger, "Objective Estimation of the Probability Density Function for Climate Sensitivity," Journal of Geophysical Research 106 (2001):22,605-22; R. Knutti, et. al., "Constraints on Radiative Forcing and Future Climate Change from Observations and Climate Model Ensembles," Nature 416 (2002):719-23; and C. E. Forest et. al., "Constraining Climate Model Properties by Using Optimal Fingerprint Detection Methods," Climate Dynamics (2001):18:277-295.   Return to text.

3. Intergovernmental Panel on Climate Change, 2001. Climate Change 2001, Synthesis Report.   Return to text.

4. "World Energy Investment Outlook Sees Need for $16,000 billion of Energy Investment through 2030, Highlights Major Challenges in Mobilizing Capital," International Energy Agency press release, November 4, 2003.   Return to text.

5. We're living in an interglacial period known as the Holocene. The Eemian was the last interglacial period.   Return to text.

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