[Vision2020] The Economist: "Science of Climate Change: The Clouds of Unknowing"

[Ted Moffett]

> http://www.economist.com/opinion/displaystory.cfm?story_id=15719298
>
> The science of climate change
> The clouds of unknowing There are lots of uncertainties in climate
> science. But that does not mean it is fundamentally wrong
> Mar 18th 2010 | From *The Economist* print edition
>
> FOR anyone who thinks that climate science must be unimpeachable to be
> useful, the past few months have been a depressing time. A large stash of
> e-mails from and to investigators at the Climatic Research Unit of the
> University of East Anglia provided more than enough evidence for concern
> about the way some climate science is done. That the picture they painted,
> when seen in the round—or as much of the round as the incomplete selection
> available allows—was not as alarming as the most damning quotes taken out of
> context is little comfort. They offered plenty of grounds for both shame and
> blame.
>
> At about the same time, glaciologists pointed out that a statement
> concerning Himalayan glaciers in the most recent report of the
> Intergovernmental Panel on Climate Change (IPCC) was wrong. This led to the
> discovery of other poorly worded or poorly sourced claims made by the IPCC,
> which seeks to create a scientific consensus for the world’s politicians,
> and to more general worries about the panel’s partiality, transparency and
> leadership. Taken together, and buttressed by previous criticisms, these two
> revelations have raised levels of scepticism about the consensus on climate
> change to new heights.
>
> Increased antsiness about action on climate change can also be traced to
> the recession, the unedifying spectacle of last December’s climate-change
> summit in Copenhagen, the political realities of the American Senate and an
> abnormally cold winter in much of the northern hemisphere. The new doubts
> about the science, though, are clearly also a part of that story. Should
> they be?
>
> In any complex scientific picture of the world there will be gaps,
> misperceptions and mistakes. Whether your impression is dominated by the
> whole or the holes will depend on your attitude to the project at hand. You
> might say that some see a jigsaw where others see a house of cards. Jigsaw
> types have in mind an overall picture and are open to bits being taken out,
> moved around or abandoned should they not fit. Those who see houses of cards
> think that if any piece is removed, the whole lot falls down. When it comes
> to climate, academic scientists are jigsaw types, dissenters from their view
> house-of-cards-ists.
>
> The defenders of the consensus tend to stress the general consilience of
> their efforts—the way that data, theory and modelling back each other up.
> Doubters see this as a thoroughgoing version of “confirmation bias”, the
> tendency people have to select the evidence that agrees with their original
> outlook. But although there is undoubtedly some degree of that (the errors
> in the IPCC, such as they are, all make the problem look worse, not better)
> there is still genuine power to the way different arguments and datasets in
> climate science tend to reinforce each other.
>
> The doubters tend to focus on specific bits of empirical evidence, not on
> the whole picture. This is worthwhile—facts do need to be well grounded—but
> it can make the doubts seem more fundamental than they are. People often
> assume that data are simple, graspable and trustworthy, whereas theory is
> complex, recondite and slippery, and so give the former priority. In the
> case of climate change, as in much of science, the reverse is at least as
> fair a picture. Data are vexatious; theory is quite straightforward.
> Constructing a set of data that tells you about the temperature of the Earth
> over time is much harder than putting together the basic theoretical story
> of how the temperature should be changing, given what else is known about
> the universe in general.
> Absorb and reflect
>
> The most relevant part of that universal what-else is the requirement laid
> down by thermodynamics that, for a planet at a constant temperature, the
> amount of energy absorbed as sunlight and the amount emitted back to space
> in the longer wavelengths of the infra-red must be the same. In the case of
> the Earth, the amount of sunlight absorbed is 239 watts per square metre.
> According to the laws of thermodynamics, a simple body emitting energy at
> that rate should have a temperature of about –18ºC. You do not need a
> comprehensive set of surface-temperature data to notice that this is not the
> average temperature at which humanity goes about its business. The
> discrepancy is due to greenhouse gases in the atmosphere, which absorb and
> re-emit infra-red radiation, and thus keep the lower atmosphere, and the
> surface, warm (see the diagram below). The radiation that gets out to the
> cosmos comes mostly from above the bulk of the greenhouse gases, where the
> air temperature is indeed around –18ºC.
>
> Adding to those greenhouse gases in the atmosphere makes it harder still
> for the energy to get out. As a result, the surface and the lower atmosphere
> warm up. This changes the average temperature, the way energy moves from the
> planet’s surface to the atmosphere above it and the way that energy flows
> from equator to poles, thus changing the patterns of the weather.
>
> No one doubts that carbon dioxide is a greenhouse gas, good at absorbing
> infra-red radiation. It is also well established that human activity is
> putting more of it into the atmosphere than natural processes can currently
> remove. Measurements made since the 1950s show the level of carbon dioxide
> rising year on year, from 316 parts per million (ppm) in 1959 to 387ppm in
> 2009. Less direct records show that the rise began about 1750, and that the
> level was stable at around 280ppm for about 10,000 years before that. This
> fits with human history: in the middle of the 18th century people started to
> burn fossil fuels in order to power industrial machinery. Analysis of carbon
> isotopes, among other things, shows that the carbon dioxide from industry
> accounts for most of the build-up in the atmosphere.
>
> The serious disagreements start when discussion turns to the level of
> warming associated with that rise in carbon dioxide. For various reasons,
> scientists would not expect temperatures simply to rise in step with the
> carbon dioxide (and other greenhouse gases). The climate is a noisy thing,
> with ups and downs of its own that can make trends hard to detect. What’s
> more, the oceans can absorb a great deal of heat—and there is evidence that
> they have done so—and in storing heat away, they add inertia to the system.
> This means that the atmosphere will warm more slowly than a given level of
> greenhouse gas would lead you to expect.
>
> There are three records of land-surface temperature put together from
> thermometer readings in common use by climatologists, one of which is
> compiled at the Climatic Research Unit of e-mail infamy. They all show
> warming, and, within academia, their reliability is widely accepted. Various
> industrious bloggers are not so convinced. They think that adjustments made
> to the raw data introduce a warming bias. They also think the effects of
> urbanisation have confused the data because towns, which are sources of
> heat, have grown up near weather stations. Anthony Watts, a retired weather
> forecaster who blogs on climate, has set up a site, surfacestations.org,
> where volunteers can help record the actual sites of weather instruments
> used to provide climate data, showing whether they are situated close to
> asphalt or affected by sources of bias.
>
> Those who compile the data are aware of this urban heat-island effect, and
> try in various ways to compensate for it. Their efforts may be insufficient,
> but various lines of evidence suggest that any errors it is inserting are
> not too bad. The heat-island effect is likely to be strongest on still
> nights, for example, yet trends from data recorded on still nights are not
> that different from those from windy ones. And the temperature of waters at
> the surface of the seas shows similar trends to that on land over the past
> century, as does the record of air temperature over the oceans as measured
> at night (see chart 1).
>
> A recent analysis by Matthew Menne and his colleagues at America’s National
> Oceanic and Atmospheric Administration, published in the *Journal of
> Geophysical Research*, argued that trends calculated from climate stations
> that surfacestation.org found to be poorly sited and from those it found
> well sited were more or less indistinguishable. Mr Watts has problems with
> that analysis, and promises a thorough study of the project’s findings
> later.
>
> There is undoubtedly room for improvement in the surface-temperature
> record—not least because, at the moment, it provides only monthly mean
> temperatures, and there are other things people would like to know about.
> (When worrying about future heatwaves, for example, hot days and nights, not
> hot months, are the figures of most interest.) In February Britain’s Met
> (ie, meteorological) Office called for the creation of a new set of
> temperature databases compiled in rigorously transparent ways and open to
> analysis and interpretation by all and sundry. Such an initiative would
> serve science well, help restore the credibility of land-surface records,
> and demonstrate an openness on the part of climate science which has not
> always been evident in the past.
> Simplify and amplify
>
> For many, the facts that an increase in carbon dioxide should produce
> warming, and that warming is observed in a number of different indicators
> and measurements, add up to a *primafacie* case for accepting that
> greenhouse gases are warming the Earth and that the higher levels of
> greenhouse gases that business as usual would bring over the course of this
> century would warm it a lot further.
>
> The warming caused by a given increase in carbon dioxide can be calculated
> on the basis of laboratory measurements which show how much infra-red
> radiation at which specific wavelengths carbon dioxide molecules absorb.
> This sort of work shows that if you double the carbon dioxide level you get
> about 1ºC of warming. So the shift from the pre-industrial 280ppm to 560ppm,
> a level which on current trends might be reached around 2070, makes the
> world a degree warmer. If the level were to double again, to 1,100ppm, which
> seems unlikely, you would get another degree.
>
> The amount of warming expected for a doubling of carbon dioxide has become
> known as the “climate sensitivity”—and a climate sensitivity of one degree
> would be small enough to end most climate-related worries. But carbon
> dioxide’s direct effect is not the only thing to worry about. Several types
> of feedback can amplify its effect. The most important involve water vapour,
> which is now quite well understood, and clouds, which are not. It is on
> these areas that academic doubters tend to focus.
>
> As carbon dioxide warms the air it also moistens it, and because water
> vapour is a powerful greenhouse gas, that will provide further warming.
> Other things people do—such as clearing land for farms, and irrigating
> them—also change water vapour levels, and these can be significant on a
> regional level. But the effects are not as large.
>
> Climate doubters raise various questions about water vapour, some trivial,
> some serious. A trivial one is to argue that because water vapour is such a
> powerful greenhouse gas, carbon dioxide is unimportant. But this ignores the
> fact that the level of water vapour depends on temperature. A higher level
> of carbon dioxide, by contrast, governs temperature, and can endure for
> centuries.
>
> A more serious doubting point has to do with the manner of the moistening.
> In the 1990s Richard Lindzen, a professor of meteorology at the
> Massachusetts Institute of Technology, pointed out that there were ways in
> which moistening might not greatly enhance warming. The subsequent two
> decades have seen much observational and theoretical work aimed at this
> problem. New satellites can now track water vapour in the atmosphere far
> better than before (see chart 2). As a result preliminary estimates based on
> simplifications have been shown to be reasonably robust, with water-vapour
> feedbacks increasing the warming to be expected from a doubling of carbon
> dioxide from 1ºC without water vapour to about 1.7ºC. Dr Lindzen agrees that
> for parts of the atmosphere without clouds this is probably about right.
>
> This moistening offers a helpful way to see what sort of climate change is
> going on. When water vapour condenses into cloud droplets it gives up energy
> and warms the surrounding air. This means that in a world where greenhouse
> warming is wetting the atmosphere, the lower parts of the atmosphere should
> warm at a greater rate than the surface, most notably in the tropics. At the
> same time, in an effect that does not depend on water vapour, an increase in
> carbon dioxide will cause the upper stratosphere to cool. This pattern of
> warming down below and cooling up on top is expected from greenhouse
> warming, but would not be expected if something other than the greenhouse
> effect was warming the world: a hotter sun would heat the stratosphere more,
> not less.
>
> During the 1990s this was a point on which doubters laid considerable
> weight, because satellite measurements did not show the warming in the lower
> atmosphere that theory would predict. Over the past ten years, though, this
> picture has changed. To begin with, only one team was turning data from the
> relevant instruments that have flown on weather satellites since the 1970s
> into a temperature record resolved by altitude. Now others have joined them,
> and identified errors in the way that the calculations (which are complex
> and depend on a number of finicky details) were carried out. Though
> different teams still get different amounts and rates of warming in the
> lower atmosphere, there is no longer any denying that warming is seen.
> Stratospheric cooling is complicated by the effects of ozone depletion, but
> those do not seem large enough to account for the degree of cooling that has
> been seen there, further strengthening the case for warming by the
> greenhouse effect and not some other form of climate perturbation.
>
> On top of the effect of water vapour, though, the clouds that form from it
> provide a further and greater source of uncertainty. On the one hand, the
> droplets of water of which these are made also have a strong greenhouse
> effect. On the other, water vapour is transparent, whereas clouds reflect
> light. In particular, they reflect sunlight back into space, stopping it
> from being absorbed by the Earth. Clouds can thus have a marked cooling
> effect and also a marked warming effect. Which will grow more in a
> greenhouse world?
> Model maze
>
> It is at this point that detailed computer models of the climate need to be
> called into play. These models slice the atmosphere and oceans into stacks
> of three-dimensional cells. The state of the air (temperature, pressure,
> etc) within each cell is continuously updated on the basis of what its state
> used to be, what is going on in adjacent cells and the greenhousing and
> other properties of its contents.
>
> These models are phenomenally complex. They are also gross
> oversimplifications. The size of the cells stops them from explicitly
> capturing processes that take place at scales smaller than a hundred
> kilometres or so, which includes the processes that create clouds.
>
> Despite their limitations, climate models do capture various aspects of the
> real world’s climate: seasons, trade winds, monsoons and the like. They also
> put clouds in the places where they are seen. When used to explore the
> effect of an increase in atmospheric greenhouse gases on the climate these
> models, which have been developed by different teams, all predict more
> warming than greenhouse gases and water-vapour feedback can supply unaided.
> The models assessed for the IPCC’s fourth report had sensitivities ranging
> from 2.1ºC to 4.4ºC. The IPCC estimated that if clouds were not included,
> the range would be more like 1.7ºC to 2.1ºC. So in all the models clouds
> amplify warming, and in some the amplification is large.
>
> **However, there are so far no compelling data on how clouds are affecting
> warming in fact, as opposed to in models. Ray Pierrehumbert, a climate
> scientist at the University of Chicago who generally has a strong way with
> sceptics, is happy to agree that there might be processes by which clouds
> rein in, rather than exaggerate, greenhouse-warming effects, but adds that,
> so far, few have been suggested in any way that makes sense.
>
> Dr Lindzen and a colleague suggested a plausible mechanism in 2001. They
> proposed that tropical clouds in an atmosphere with more greenhouse gas
> might dry out neighbouring parts of the sky, making them more transparent to
> outgoing infra-red. The evidence Dr Lindzen brought to bear in support of
> this was criticised in ways convincing enough to discourage other scientists
> from taking the idea further. A subsequent paper by Dr Lindzen on
> observations that would be compatible with his ideas about low sensitivity
> has also suffered significant criticisms, and he accepts many of them. But
> having taken them on board has not, he thinks, invalidated his line of
> research.
>
> Arguments based on past climates also suggest that sensitivity is unlikely
> to be low. Much of the cooling during the ice ages was maintained by the
> presence of a large northern hemisphere ice cap reflecting away a lot of
> sunlight, but carbon dioxide levels were lower, too. To account for all of
> the cooling, especially in the southern hemisphere, is most easily done with
> a sensitivity of temperature to carbon dioxide higher than Dr Lindzen would
> have it.
>
> Before the ice age, the Earth had a little more carbon dioxide and was a
> good bit warmer than today—which suggests a fairly high sensitivity. More
> recently, the dip in global temperatures after the eruption of Mt Pinatubo
> in the Philippines in 1991, which inserted a layer of sunlight-diffusing
> sulphur particles into the stratosphere, also bolsters the case for a
> sensitivity near the centre of the model range—although sensitivity to a
> transient event and the warming that follows a slow doubling of carbon
> dioxide are not exactly the same sort of thing.
> Logs and blogs
>
> Moving into data from the past, though, brings the argument to one of the
> areas that blog-based doubters have chosen as a preferred battleground: the
> temperature record of the past millennium, as construed from natural records
> that are both sensitive to temperature and capable of precise dating. Tree
> rings are the obvious, and most controversial, example. Their best known use
> has been in a reconstruction of temperatures over the past millennium
> published in *Nature* in 1998 and widely known as the hockey stick,
> because it was mostly flat but had a blade sticking up at the 20th-century
> end. Stephen McIntyre, a retired Canadian mining consultant, was struck by
> the very clear message of this graph and delved into the science behind it,
> a process that left him and followers of his blog, *Climate Audit*,
> intensely sceptical about its value.
>
> In 2006 a review by America’s National Research Council endorsed points Mr
> McIntyre and his colleagues made on some methods used to make the hockey
> stick, and on doubts over a specific set of tree rings. Despite this it
> sided with the hockey stick’s overall conclusion, which did little to stem
> the criticism. The fact that tree-ring records do not capture recent warming
> adds to the scepticism about the value of such records.
>
> For many of Mr McIntyre’s fans (though it is not, he says, his central
> concern) the important thing about this work is that the hockey stick seemed
> to abolish the “medieval warm period”. This is a time when temperatures are
> held to have been as high as or higher than today’s—a warmth associated with
> the Norse settlement of Greenland and vineyards in England. Many climate
> scientists suspect this phenomenon was given undue prominence by
> climatologists of earlier generations with an unduly Eurocentric view of the
> world. There is evidence for cooling at the time in parts of the Pacific.
>
> Doubters for the most part are big fans of the medieval warm period, and
> see in the climate scientists’ arguments an attempt to rewrite history so as
> to maximise the drama of today’s warming and minimise the possibility that
> natural variation might explain the 20th-century record. The possibility of
> more climatic variability, though, does not, in itself, mean that greenhouse
> warming is not happening too. And if the medieval warmth were due to some
> external factor, such as a slightly brighter sun, that would suggest that
> the climate was indeed quite sensitive.
>
> Looking at the more recent record, logged as it has been by thermometers,
> you might hope it could shed light on which of the climate models is closest
> to being right, and thus what the sensitivity actually is. Unfortunately,
> other confounding factors make this difficult. Greenhouse gases are not the
> only climatically active ingredients that industry, farming and land
> clearance add to the atmosphere. There are also aerosols—particles of
> pollution floating in the wind. Some aerosols cool the atmosphere. Other,
> sootier, ones warm it. The aggregate effect, globally, is thought to be a
> cooling, possibly a quite strong one. But the overall history of aerosols,
> which are mostly short-lived, is nothing like as well known as that of
> greenhouse gases, and it is unlikely that any of the models are properly
> capturing their chemistry or their effects on clouds.
>
> Taking aerosols into account, climate models do a pretty good job of
> emulating the climate trends of the 20th century. This seems odd, since the
> models have different sensitivities. In practice, it appears that the way
> the aerosols are dealt with in the models and the sensitivity of those
> models tend to go hand in hand; sensitive models also have strong cooling
> aerosol effects.
>
> Reto Knutti of ETH Zurich, an expert on climate sensitivity, sees this as
> evidence that, consciously or unconsciously, aerosols are used as
> counterweights to sensitivity to ensure that the trends look right. This is
> not evidence of dishonesty, and it is not necessarily a bad thing. Since the
> models need to be able to capture the 20th century, putting them together in
> such a way that they end up doing so makes sense. But it does mean that
> looking at how well various models match the 20th century does not give a
> good indication of the climate’s actual sensitivity to greenhouse gas.
>
> Adding the uncertainties about sensitivity to uncertainties about how much
> greenhouse gas will be emitted, the IPCC expects the temperature to have
> increased by 1.1ºC to 6.4ºC over the course of the 21st century. That low
> figure would sit fairly well with the sort of picture that doubters think
> science is ignoring or covering up. In this account, the climate has natural
> fluctuations larger in scale and longer in duration (such as that of the
> medieval warm period) than climate science normally allows, and the Earth’s
> recent warming is caused mostly by such a fluctuation, the effects of which
> have been exaggerated by a contaminated surface-temperature record.
> Greenhouse warming has been comparatively minor, this argument would
> continue, because the Earth’s sensitivity to increased levels of carbon
> dioxide is lower than that seen in models, which have an inbuilt bias
> towards high sensitivities. As a result subsequent warming, even if
> emissions continue full bore, will be muted too.
>
> It seems unlikely that the errors, misprisions and sloppiness in a number
> of different types of climate science might all favour such a minimised
> effect. That said, the doubters tend to assume that climate scientists are
> not acting in good faith, and so are happy to believe exactly that.
> Climategate and the IPCC’s problems have reinforced this position.
>
> Using the IPCC’s assessment of probabilities, the sensitivity to a doubling
> of carbon dioxide of less than 1.5ºC in such a scenario has perhaps one
> chance in ten of being correct. But if the IPCC were underestimating things
> by a factor of five or so, that would still leave only a 50:50 chance of
> such a desirable outcome. The fact that the uncertainties allow you to
> construct a relatively benign future does not allow you to ignore futures in
> which climate change is large, and in some of which it is very dangerous
> indeed. The doubters are right that uncertainties are rife in climate
> science. They are wrong when they present that as a reason for inaction.
>
------------------------------------------
Vision2020 Post: Ted Moffett
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.fsr.com/pipermail/vision2020/attachments/20100421/0cbe4656/attachment-0001.html