This is purely my opinion, as always. Those with different opinions are free to challenge me at firstname.lastname@example.org . I reserve the right to publish your comments on this page and to offer my responses to them - if you don't agree to this, then don't waste my time.
I recently have had some personal contacts with some of the scientists who are considering various aspects of global climate change - its causes, the scientific evidence, and its possible consequences. Knowing personally a few of these people does not qualify me to offer an "expert" opinion about the science. Neither does my background as a severe storms meteorologist. However, I am in the position of being reasonably knowledgeable about the basic physics that governs the weather. Weather and climate are intimately connected but they aren't the same. The climate is the time integral of the weather - and it's a definite integral. That is, if the interval of the time integration is changed, the answer can depend strongly on the time interval chosen. I suppose I should establish some limits on what could reasonably be called the climate. If you do a time integral of the weather over some short interval - an hour, a day, a week, a month - then this integral is not very useful in discussing the climate. We know that weather evolves strongly over some key time periods. The average of the weather over a period of one day (the diurnal period) is not likely to represent the climate very well. The average of the weather over a period of 3 months (a seasonal period) would certainly look different from that of adjacent seasons but this wouldn't likely be considered a climate change. The seasons follow a more or less regular progression and those changes are very close to periodic. The average of the weather over a year (the annual period) is also expected to show similarities from one year to the next. It is only when the period of interest extends over perhaps several 10s of years or more that we begin to move away from the weather and enter the margins of what might be considered climate. Real climate scientists think in terms of no less than 100s of years and longer, perhaps much longer.
For many purposes, the notion of what is "normal" has been confined to the most recent 30-year average - see my essay about the meaning of normality as it pertains to the weather. It's what most people would consider as typical of the weather they've seen over their lives. Older folks might be able to recall the weather several decades before the most recent 30 year average, and might have some vague memory of the average being different then from what it is now. Their memory of the weather more than 30 years ago is typically rather fuzzy and may well be dominated by a few extreme weather events they experienced long ago. The weather more than 60 years ago is, for most people, the stuff of myths and legends.
During the most recent 100 years or so, perhaps longer in some parts of the world, we have direct weather measurements using thermometers, barometers, anemometers, and hygrometers (measuring, respectively, the temperature, pressure, wind, and humidity), as well as precipitation measurement. Before the period of direct instrumentation for weather variables, it's possible to make estimates of global temperature and other variables from various indirect means (tree rings, ice and sediment cores, and so forth), such that we have a fair idea of how the main variables may have varied over many thousands of years, and perhaps longer. The more removed the observations are from direct measurements of relevant atmospheric variables, the more problematic their interpretation becomes in terms of the actual weather that may have been occurring. From this so-called paleoclimatological work, we're aware that the climate has changed more or less continuously over the time period for which we have any information. The climate is not constant, so climate change is something that goes on at a slow pace - much slower than the weather - although it apparently can shift from one climate regime to another rather suddenly at times (e.g., over a period of 100 years or so).
Climate is fundamentally different from the weather in the following way: The physical laws that govern the weather are a set of coupled partial differential equations, the solution of which the mathematicians call an initial value problem: if we know the weather in terms of the basic set of variables at some time t = to, then these equations describe the time rate of change of the variables as a function of various physical processes. The weather at some time after to, say t = t1, is given by the weather at t = to + the change in the weather over the time from to to t1. The weather in the future depends directly on what was going on at the initial time, and the changes in the weather over the time from to to t1 also depend on what was going on at the initial time. If it was cloudy at the start, the temperature at some later time depends on that cloudiness that was there at the start.
The climate, on the other hand, is mostly what mathematicians call a boundary-value problem: the equations that govern the climate are also differential equations, but these are dominated by terms that represent the aggregate effects of so-called climate forcings. The climate changes when, for example, the input from the sun changes, or the surface of the earth changes its character, or the composition of gases in the atmosphere changes. These changes alter the transfer of energy that goes on within the atmosphere. On the average, the weather acts to redistribute energy both horizontally and vertically and the system remains approximately in balance as a result, so the time rate of change in the climate is much slower than the time rate of change in the weather. It's only when the balance is disturbed does the climate change - in the absence of changes, it should remain more or less constant. The change in the climate is an attempt by the atmosphere to achieve a new equilibrium after some change has occurred in the forcings.
For instance, we know that various wobbles in the orbit of the Earth cause climate change and can be used effectively to explain a lot of the variability between ice ages and interglacial eras. We also know that the concentration of greenhouse gases in the atmosphere is another driver for climate change - it's changed in the past owing to completely natural (i.e., in the absence of anthropogenic1 modification) processes. There are numerous other processes that can alter the climate, and they can be linked to one another in complex ways. Thus, we are about as far from a complete understanding of the climate as we are from a complete understanding of the weather. Because weather and climate are intimately connected (but not the same), we can't understand one without understanding the other.
1 Anthropogenic means caused by humans
At the moment, we humans are conducting an enormous experiment with our atmospheric environment, as part of an even larger experiment with the overall environment. Without any serious planning effort and certainly without much of any intention to do so, we're altering the balances with the system by our exponential population growth, our agricultural practices, our industrial production, and in particular, by spewing greenhouse gases, as well as pollution (particulates and aerosols) into the atmosphere at prodigious and constantly increasing rates. A few million hunter-gatherers roaming the savannas and forests of the world have minimal effects. The development first of agriculture and then of industrial mass production has magnified the impacts of every individual in our increasingly urban world, and allowed our numbers to increase enormously. Thus, a few million people using wood to cook with and to build primitive shelters with has little effect on the planet, whereas several billion people using wood and other fossil fuels to fill their urbane lives with technological conveniences that consume considerable energy is having a measurable and likely very detrimental effect on the planet. Detrimental to us, that is. Whatever we do to ourselves, the planet will go on (Unless, God forbid, we find a way to wreak an ultimate destruction on the planet itself).
This essay grows out of several recent email conversations. I thought it might be useful to summarize where I stand about global climate change, and particularly on the issue of the anthropogenic contribution, and offer my reasons.
In my essay about how science works, I've discussed this notion at some length - at any given time, science operates via consensus. That is, there is some set of principles by which the evidence we have is interpreted. The vast majority of scientists subscribe to this consensus understanding, but reserve the right to dispute any or all of it. Consensus is how a logical argument is able to proceed - if the individuals involved in an argument don't agree about anything, no logical argument is possible. There has to be an agreement about something for logical arguments to proceed. For science, there's a basic set of principles that evolve very slowly and when those are changed, the change is very profound and alters fundamentally the way scientists in that discipline, and possibly even in related disciplines, view the world. For example, the change from Newtonian physics to account for Einstein's relativity theories was such a "paradigm shift". Similarly, the development of quantum mechanics was another such major shift in consensus understanding. When you question the most basic principles, as Einstein did, your concepts will be attacked by the existing consensus, and you will need to find extraordinary evidence to back up your extraordinary claims. Less fundamental, but still major challenges to consensus understanding, are going to require compelling evidence before the consensus shifts. Make no mistake about it - the consensus can and does change, but until its tenets are successfully challenged by substantive evidence to back up such changes, the consensus remains the basis for most scientific understanding. Proposed changes to the consensus run the gamut from profound to near-trivial.
Many challengers to the current scientific consensus arise, for various reasons. One way to ensure fame in the annals of science is to succeed in challenging some aspect of consensus science. The more profound the change, the greater the fame of the successful challenger and, presumably, the more clever and insightful is the process by which the challenge became successful. Venal reasons for challenging the consensus might also be involved, such as being paid by someone to take a contrary position, or to secure funding for one's own research projects. In any case, if everyone agrees about some aspect of consensus science - that is, the concept is universally accepted - then that part of the science is effectively dead. We make progress in science by changing the consensus, in great leaps or in small increments, or somewhere in between. So while the consensus represents a sort of inertia in science, that inertia is a necessary part of the process. And scientific disagreements are not an indicator of something wrong with the process, but rather are a clear signal that the science is alive and prospering.
Why do I go on about this? What does this have to do with global climate change? When it comes to the existing consensus regarding global climate change, we have what amounts to an official statement of that consensus, which has been carefully distilled from the input of climate scientists around the world. It is a product of the Intergovernmental Panel on Climate Change (IPCC). They've been issuing periodic assessments of climate change, the most recently completed version of which was issued in 2001. An updated version is in progress as I write this. The reason for having such a formal document describing the consensus is that climate change has become politicized. Its implications regarding important decisions by national politicians demand that there be such an "official" consensus statement. In most other parts of weather and climate science, there is no such formal process, although the American Meteorological Society provides relatively brief (by comparison) statements about various topics on an irregular basis. These are arrived at by a much less formalized and rigorous procedure than the summaries of the IPCC. Given the controversial nature of global climate change science, it seems appropriate to make its consensus statements via such a process.
The upshot of this discussion is that despite my formal training in meteorology, I believe it would be inappropriate for me to challenge the IPCC's version of a consensus on the subject. I'm not so arrogant as to believe that even my relatively informed understanding of the weather would qualify me to dispute the consensus of a large group of people who actually do cutting edge research on global climate science. Many of those who seek to dispute the IPCC's findings are, of course, much less thoroughly educated and trained in atmospheric science than I am. Hence, in my opinion, they're entitled to their opinions but have essentially no substantive basis upon which to dispute the IPCC consensus. Of late, many "pundits" (typically, right-wing media stooges like Bill O'Reilly for the so-called conservatives) are being cited by ordinary citizens calling into question the conclusions of the IPCC. These pundits also have no basis for making any statement whatsoever about climate science - they aren't even scientists, much less specialists in climate change science. Where they obtain their information often is from the so-called "skeptics" who are climate scientists but who dispute some or all of the IPCC's findings. The pundits may have their own political reasons to discredit the scientific consensus and so are eager to publicize the skeptics, who by having at least some stature within climate science. lend an aura of undeserved credibility to the pundits. In turn, the pundits serve the needs of the skeptics by drawing attention to them.
I have no problem with skeptics, on the whole, when they keep their discourse focused on the science. On the whole, all scientists should be skeptics - we help one another by finding weak points in scientific arguments. However, it's not appropriate for scientific disagreements to be adjudicated by non-scientists. It isn't appropriate to engage in personal attacks when debating the issues of a scientific disagreement.
It is almost always possible to find some scientist who disputes the consensus in some way or another. An unfortunately common tactic being employed by some of these skeptics, for reasons of their own, is to call the motives of the consensus scientists into question. They assert that they (the skeptics) are being persecuted by the consensus, who are accused of engaging in a conspiracy to muzzle them in the scientific literature, and monopolizing research funding grants. Some of the skeptics have begun to whine publicly about this in the media, rather than in the scientific journals, where such disputes are most properly carried out. Conspiracy theories abound in the modern world, of course.
2 Ad hominem means appealing to personal considerations rather than to logic or reason. Literally, it is Latin for "to the man"
Unfortunately, some of the consensus-supporting scientists have lashed back in a comparable way (in the media) in retaliation for the ad hominem attacks by the skeptics. This is unfortunate because it lowers the standards of a professional disagreement, down to what amounts to unprofessional mudslinging. Frankly, I find such attacks being carried on via the media to be embarrassing to our profession. Retaliation in kind for ad hominem attacks is lowering yourself to the level of your attacker. We should be forcing the debate away from such tactics and toward a more professional discourse. If you see such things happening in media reports, be aware that this is simply an illogical and irrelevant mode of "winning" an argument. If you impugn my motives, it seems to me that it might be justifiable to impugn yours in response, but I would prefer to choose not to do so. By using such tactics, it seems to me that my detractors would be voluntarily surrendering the ethical high ground to me, and I'd always prefer to be on such high ground.
A related tactic is to seize upon some impropriety committed by a small number of scientists and use that as an excuse to discredit the entire group of scientists constituting the consensus. Such a method is particularly well-suited to implementation via the media. The recent "Climategate" episode is a classic example of the smear tactic. Via an illegal hacking of the computers at the University of East Anglia, some apparently damning evidence of unethical science was found and used to create a media blitz of pseudo-journalistic muckraking aimed at tarring all of global climate science with the same brush. The fact that the alleged perpetrators of the supposed improprieities have been exonerated of any misconduct in several independent investigations doesn't seem to get the same attention in the media. There's a seemingly endless array of ways to call the credibility of the whole of consensus global climate science into question by what amount to personal attacks on various participants in that consensus. Since most the deniers of anthropogenic global climate change are unqualified to carry on a meaningful scientific debate via the standard channels (i.e., peer-reviewed scientific publications), this sort of smear tactic is their only choice as a fall-back.
To be fair to the skeptics, not all of them are without some scientific credentials - some of them that have some legitimate claim to be a scientist at least, seem to be rationalizing that their inability to publish their work in refereed scientific journals is some sort of conspiracy by the participants in the consensus. This neatly ignores the principle that overthrowing the consensus is necessarily predicated on presenting convincing evidence. This is how science works! The larger the change in the consensus, the more compelling the evidence must be. Many of the scientist skeptics have little or no history of publishing contributions to global climate science, but rather come in from some other scientific subdiscipline. This doesn't preclude the logical possibility that such "outsiders" can contribute, but neither does it excuse them from being required to provide compelling demonstrations that the consensus needs to be changed. For the most part, these scientist skeptics have been unsuccessful in publishing their ideas in scientific journals, apparently because the journal reviewers consistently find that the skeptics have failed to make a compelling case for their ideas. Does this mean the skeptics are guaranteed to be absolutely wrong? No, of course not. But it doesn't mean there's a conspiracy muzzling them, either. To infer this is actually insulting to the professionals who are trying their best to understand the complex topic of the global climate and implies that they're collectively willing to be unethical simply to suppress honest scientific debate. Apart from their personal ethics, why would they want to do that? The only possibilities would be venal and we're right back to impugning their motives.
a. Global warming
There can be no dispute on the basis of the overwhelming evidence that supports the compelling reality of global warming. The skeptics out there have been engaging in such tactics as "cherry picking" which observations to show, selectively finding cases where cooling seems to be underway. The raw temperature observations that provide evidence for global warming have been carefully reviewed to remove biases that might mask the signal (such as urbanization about the observation point) and the resulting signal is very clear. The overall recession of glaciers and polar ice is also compelling evidence. The indisputable dramatic rise in the atmospheric concentration of greenhouse gases, notably CO2 must inevitably be associated with a rise in temperature, by physical mechanisms that are indisputable and even accepted by the majority of skeptics. And so on and on. Given that global warming is real, the issue then becomes one of whether or not this is a "natural" or an anthropogenic effect. Again, the IPCC offers what seems to me to be overwhelming evidence that this warming is clearly dominated by greenhouse gas increases which are anthropogenic. Note that the residence time for CO2 is on the order of 100 years, so a considerable amount of what we put in today will still be around in 50 years. Changing the course of global warming owing to greenhouse gas emissions is nearing the point where we simply have run out of chances to limit global warming to relatively low levels, but will have to deal with (adapt to, as best we can) continuing warming for decades, leading to potentially disastrous consequences. More on consequences later.
It turns out that recent evidence has suggested strongly that the contributions from greenhouse gases are being partially offset by another consequence of burning fossil fuels: particulates and aerosols. Whereas increasing greenhouse gases result in an overall warming, the contributions from the same burning that results in particulates and aerosols is an increase in the Earth's albedo3. This pollution is reflecting incoming solar radiation back before it reaches the surface. Of course, it also has other consequences, such as respiratory illness, haze and smog, more cloudiness, reduced precipitation, etc..
3 Albedo is the fraction of incident electromagnetic radiation reflected by a surface. In the sense of the Earth's albedo as a whole, it refers to the comparison between incoming solar radiation and that reflected at the abstract 'surface' that constitutes the 'top of the atmosphere'. The Earth's actual physical surface has an albedo, as well, that varies from place to place and would have some average value over the entire surface. At the surface, the incoming solar radiation would have been reduced by absorption in the atmosphere, as well as reflections from clouds, aerosols, and particulates - the reduction of the incoming radiation would be less at the top of a high mountain than at sea level, and less in a very clear atmosphere versus one contaminated with pollutants.
It now seems that this cooling effect from pollutants is larger than was anticipated and is reducing the impact of greenhouse gas emission on the increase in global temperature. Were it not for this offsetting effect, we might already have increased the global temperature by an additional 1.5 deg C beyond what has been observed (about 0.8 deg C) in the last century. Do two wrongs make a right? I don't think so. Pollution is definitely not good for anyone on the planet, so we can and are seeking to reduce the emission of particulates and aerosols. But if we could reduce their emission to zero (and their residence time in the atmosphere is much shorter than for gases, because they're washed out of the atmosphere relatively rapidly by precipitation, producing acid rain among other effects), this would simply magnify the impact of the greenhouse gases. Since the effect of the pollution is larger than we expected, it appears we might be underestimating the impact of the compensating greenhouse gas emissions and the scenario of rapid increases in temperature could be right around the corner. Simply reducing pollution from burning fossil fuels is not enough if we do nothing about the associated greenhouse gas emissions.
It is in the realm of consequences that my experience as a severe storm scientist has some relevance. There is considerably more to be understood about the relationship between weather and climate. But there are some important misconceptions. I'm told by someone whose views I respect a great deal (Dr. Susan Solomon, of NOAA) that in a globally warmer future, every place around the globe would be warmer, on average (except perhaps Antarctica, so long as the ozone hole remains). Nevertheless, I expect that not everyone around the globe would experience exactly the same amount of warming. Changes in the regional weather do not mirror exactly whatever changes occur in the global climate. Moreover, not every year would look exactly the same as the year before except being incrementally warmer. Natural variability of the weather is a strong signal that would not be drowned out by global warming. In some years, parts of the world would be colder than before, at least for that year. Perhaps in the following year, a different part of the world would experience a cold snap. This is why I spent time earlier discussing the difference between the weather and the climate. They're connected, but do not change in lockstep - the large variations in the weather are superimposed on the longer time scale, smaller changes associated with climate change. It's very hard to infer changes in the weather from changes in the climate. And it is logically false to draw conclusions about climate change based on the weather of the moment. As bad as heat waves are, for example, it's not possible to conclude that a heat wave, which is a regional weather phenomenon, is an indicator of global warming. Such heat waves are only indicative of global warming if their frequency increases consistently over relatively long time periods - decades and longer.
As always, the devil is in the details. Climate models don't predict the weather, so the weather must be inferred from the distribution of various atmospheric variables as resolved within the climate models. Note that "the weather" is not logically equivalent to, say, the temperature distribution. The latter is a component in inferring the actual weather and is an example of what can be predicted in a climate model. But the global, coarse resolution distribution of climate model variables is not equivalent to the weather! At most, we can try to interpret the model output in terms of the weather, but that interpretation is risky. The difficulty is partly a result from the inescapable limitations of any numerical model - no model is perfect! But the challenge is associated with more than model uncertainty.
As we currently understand global warming as a consequence of greenhouse gas emissions, for instance, the temperature in the Tropics would increase much less than the temperature of the polar regions. On the average, then, the temperature difference between the poles and the Equator would decrease. This might mean weaker midlatitude jet streams, which would imply that the large weather systems of midlatitudes (extratropical cyclones), would be weaker, on average. A decrease in vertical wind shear might favor the development of stronger tropical cyclones, however, which find vertical wind shear to be unfavorable for their development. There's also reason to believe that global warming will not be distributed uniformly in the vertical - if the warming makes the lower troposphere warm at a greater rate than the upper troposphere, this will result in more thermal instability, promoting thunderstorms. However, if the upper troposphere warms faster than the lower troposphere, the opposite would result. At this point, it's simply not possible to be absolutely certain of such details from the predictions of the global climate models. Our climate models give us some hints about what the future might look like in terms of weather, but no one is ready to accept them uncritically. They could be wrong, and perhaps dramatically wrong, in their current predictions regarding the likelihood of changes in the frequency and/or intensity of hazardous weather events such as tropical cyclones or severe thunderstorms and tornadoes. Various statements (pro and con) have been made about the possibilities for increased hazardous weather as a consequence of global warming, but the fact is we're necessarily much less confident in such "forecasts" for the overall weather that will result from anthropogenic climate change than we are in the likelihood of global warming itself.
For a host of reasons I actually know something about, the existing records of tropical cyclones or severe thunderstorms and tornadoes are simply inadequate to validate any hypothesized relationship between global mean temperature and the occurrence of such weather events. Numerous attempts have been made to use these occurrence data to relate these hazardous weather events to such long-period features of the general circulation such as the El Niño - Southern Oscillation (ENSO, for short). These attempts are, in my opinion, doomed to failure owing to the large secular trends in our occurrence data for such events. Even if we had a way to get 100% accurate knowledge of such events today (a very unlikely prospect), it would take at least 100 years of such perfect observations to begin to deduce confidently any relationships between observations of such events and global temperature changes on climatic time scales. I won't be around to see that happen. If we're to have confidence in a prediction of the weather based on climate change at any time in the next century, it will have to be because we have much more confidence in our models than we now have.
In any global climate change scenario, it seems clear that there will be winners - and losers. Areas that are now prosperous might be devastated by global warming, whereas other areas that are marginally favorable for us humans might become much more benign when the global temperature increases. At this point, it's difficult to be absolutely sure we know who will win and who will lose. As Susan Solomon recently asked (in a presentation paraphrasing Clint Eastwood as Dirty Harry) - "You gotta ask yourself, 'Do I feel lucky?' Well, do ya, punk?' " If, as it appears to be, we're gambling on being beneficiaries from global warming rather than being losers, on the average. This seems to me to be a dangerous game.
The GWB administration chose, likely for reasons of its own, to take a position that opposes any effort to reduce the impacts of global warming by reducing our consumption of fossil fuels. They have characterized the choice our society faces as being one of polar opposites - either (a) continuing "prosperity" through a business-as-usual policy, or (b) bankrupting our economy trying to reduce our dependence on fossil fuels. Given this choice, it's not surprising that many would choose (a) rather than (b). However, I dispute that this is actually a proper description of the situation. There is a range of choices between these extremes that stop well short of bankrupting our economy and accomplish far more than nothing toward reducing the impacts of greenhouse gas (and pollutant) emissions. Moreover, there's at least some chance that investing in alternatives to fuel will not only not bankrupt the economy but could invigorate it, instead. Unfortunately, the Obama administration has managed to do little or nothing to move our nation off the business-as-usual policy!
Even granting that there still might be negative consequences to shifting from our current dependence on fossil fuels, it seems to me that we have another choice to make: doing nothing virtually guarantees we will suffer whatever negative consequences come from global warming. It's impossible to imagine that those consequences are going to be trivial and it would only be by sheer happenstance that it might turn out we humans would be winners in the long run. The changes are coming, and some of them are already inevitable, owing to the long residence time for CO2 and some other greenhouse gases - if we do nothing, the consequences will no doubt be magnified and might include even more devastating effects. I'm trying not to be an "alarmist"- a Chicken Little, if you will - but any rational person has to accept that the reality of global warming is unlikely to be an unalloyed good for all of us. In a global world, what's bad for one large group is going to be bad for all. Like it or not, we humans are all in this together.
A policy of least regret, it seems to me is to begin to wean ourselves from fossil fuel dependence as soon as possible. There are several good reasons to do this, irrespective of any arguments about possible consequences of global warming:
There may well be others. It seems logical to me to begin this process at a serious level right now by establishing government subsidies, not for the oil oligarchy around the world, but for new technological exploration companies developing alternatives to fossil fuel.
It's not been discussed much, but at least some of the "green" alternatives to fossil fuel may have important unintended consequences of their own. For example, at some time in the future, the proliferation of wind farms to harvest the energy of atmospheric flow might grow into something that has a nontrivial impact on the global circulation. We used to think that we humans were incapable of affecting the global environment - the realization that dumping CO2 into the atmosphere without limit has some consequences when the scale of that reaches some limit is just now dawning on us. Removing low-level energy of the atmospheric flow to serve our energy needs (indirectly, a form of harnessing solar energy input) might also have important impacts on the environment when the scale of that reaches some currently unknown level. Tapping other "green" energy sources, such as tidal or geothermal energy, could also have some currently unforeseen consequences. It seems clear to me that having the majority of our energy from one source is going to become a thing of the past. The easiest way to avoid negative environmental consequences is to avoid overdependence on any single energy source. By keeping the scale of all the members of a diverse suite of energy sources relative low, then we might manage to avoid the adverse side effects of too much dependence on a single source. Energy is tricky - there are these nasty laws of physics to deal with. There is no free lunch, ever, and anyone saying that obtaining energy from this or that is essentially consequence-free is already either ignorant or a liar. Or both.
The big challenge to us all is somehow to get past the growing crisis associated with the loss of cheap oil and the technologies that it supports. Many people have not considered how pervasive the dependence on petroleum is. O.K. - so we all start running electric cars and using solar panels. How are we going to power heavy construction, or agricultural equipment, or the world's merchant fleets (to say nothing of military aircraft, as well as military land and sea vehicles)? The commercial aircraft industry consumes vast amounts of fossil fuel energy - how do we power the aircraft of the future without fossil fuels? All of the technology to do such things might already exist as ideas, but no support for testing and implementation of these ideas is forthcoming so long as we adopt a business-as-usual attitude.
Many of the fuel alternatives that have been proposed, such as ethanol from agriculture or hydrogen fuel cells, are presently completely impractical. As it now stands, unfortunately, it requires more energy to create such fuel alternatives than they're able to give back in the form of useful energy . The economics of that are pretty obviously dismal. These are at best stopgap measures that might serve to get us through a crisis but which ultimately cannot be considered viable long-term alternatives without considerable technological advances that are currently unforeseen.
The time to start exploring new technologies was decades ago, decades before we reached the global peak in oil production. We had a hint of things to come with the oil 'embargoes' in the early 1970s, but we seem to have failed to seize the initiative to reduce our dependence on cheap oil after that lesson. Oil has been a great gift from the Earth, but we've squandered that gift in stupid, greedy ways. We're leaving our children with a global crisis, not passing on a world of which we can be proud. My generation should be hanging our heads in shame for what we failed to accomplish with the gift of cheap energy from oil before it ran out. Now, it seems the prospects for a better future are dimming rapidly. The world is swimming in a pool of poisons and filth created by our greedy and selfish consumption of this great gift. Perhaps the best thing we leave our children with is the realization that their parents blew it and it's they and their children who will have to overcome the legacy we have left for them. The environment is rapidly being destroyed and plundered for short term profit - a few are living well, while the majority foots the bill. This is not an "accomplishment" in which I feel any pride whatsoever.
I admit it - I'm a child of my age. I sit here with my computer in my air conditioned home, just as dependent on the energy of fossil fuels as the next person. I wouldn't know how to deal with a world in which these comforts and conveniences didn't exist. Unfortunately, such a world might well be dawning, even though I may (or may not!) be fortunate enough to not live long enough to see it become reality. But my children likely will, and their children are even more likely to inherit such a world.
See here for some additional, rather dark thoughts about the possibilities for an apocalyptic end to modern global civilization. All things come to an end, after all. The fact that our current version of civilization has a limited future ought not to surprise anyone. There may still be time to save our global civilization, but that time is quickly running out. We can't simply stick our heads into the sand and go on as if everything's just grand. The saddest part of this is that the very people who are suffering the most as we head down the path toward the Apocalypse, the simple middle-class working stiffs, are being deceived by right-wing spinmasters into believing that business as usual is just what they need, even as the rich get richer off government subsidies of all sorts. The proponents of business as usual are in power because of votes from the deceived. What you don't know can hurt you, and our collective ignorance of science is likely to hasten our downfall.