New Climate Models Fall Short
The IPCC is working up to releasing pieces of its next climate report, starting in 2013. This has the world's climate scientists scrambling to get their latest work included in that dubious document. Foremost among those struggling for primacy of place are the computer modelers, those who study their own created worlds instead of the natural one around them. This report promises to be more contentious than the last one (AR4) in that the modelers have been racing to incorporate the effects of aerosols, soot and other airborne particulates that had previously been give scant attention. Early results suggest that aerosols have a much greater impact on regional climate than scientists had realized and that aerosols and clouds are providing some big surprises.
From space parts of Earth's surface appear pristine, white clouds painted on deep blue oceans or tan and green continents. But not all areas come into such clear focus—others are obscured by haze, clouds of a different nature made of fine particles known as aerosols. Airborne particulates do more than just obscure our planet's surface. By reflecting, absorbing and emitting radiation, they play a major role in regulating Earth's temperature, a role that has proved maddeningly difficult to simulate in computer models. A new crop of global climate models is in the offing, trying to reflect an increasing understanding of aerosols while at the same time climate scientists are discovering that they do not know as much about their old boogieman, CO2, as some would have us believe.
Smoke gets in their eyes
For decades, airborne particulates have been the biggest sources of uncertainty in forecasts of future climate. Arguments have raged as to whether aerosols primarily caused cooling or warming. The skies of Asia are muddled by the infamous Brown Clouds that poison the air, alter the climate and impact the monsoon cycle. Not all airborne particulates are man made either. From the southern edge of the Sahara Desert, the dustiest place on Earth, come dust clouds that modify conditions as far away as North America.
The Asian “Brown Cloud” taken by a NASA satellite.
New papers are constantly popping up in scientific journals discovering some amazing new impact of dirty air. In a news focus article, “A break in the clouds,” Nature reporter Jeff Tollefson provides a recap of recent investigations into aerosols and the efforts to add aerosol effects into climate models. “Researchers have yet to fully analyse the new results,” he reports, “these are just the first wave of a deluge in modelling data.”
“This is fundamentally new science,” says Ben Booth, a climate modeler at the UK Met Office Hadley Centre. Booth is investigating how aerosols affect surface temperatures in the North Atlantic Ocean and the weather on the surrounding continents. “The new generation of models is changing the kinds of questions we face as scientists.”
Scientists have discovered that aerosols not only affect temperature directly but also have many indirect effects on cloud properties. Unfortunately, these interactions take place on too fine a scale to simulate directly in a global model, even on the largest computer systems. Instead, scientists are forced to represent such factors by statistical equations derived from more detailed regional and local models. In other words, as important as aerosols are believed to be they are still simulated by statistical guesswork, not actual computation.
The Hadley Centre team reported last month that, in their new model, the aerosols had an exceptionally large effect on North Atlantic sea surface temperatures. In an article entitled “Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability,” Booth et al. report:
Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean. These links are extensive, influencing a range of climate processes such as hurricane activity and African Sahel, and Amazonian droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures, but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear.
Using their new set of models, the crew from Hadley Centre have concluded that changes in volcanic and aerosol forcing are capable of driving variability in North Atlantic sea surface temperatures ( NASSTs) much like that observed over recent decades. Scientists have hypothesized that aerosols and other forms of man made pollution are carried north out of North America, eastward across the North Atlantic and then southward, down the coast of France. “Scientists have proposed that this arc of aerosols could block enough sunlight to cool sea surface temperatures in the Atlantic Ocean and alter the regional climate,” states Tollefson.
The Hadley Centre's results seem to overturn the prevailing wisdom in climate circles, which holds that the ups and downs in sea surface temperatures result from a natural ocean cycle dubbed the Atlantic multidecadal oscillation (AMO). Effectively, aerosols have added a significant cooling effect to the North Atlantic, masking some of the expected warming (or at least warming predicted by the older models). Perversely, the success of efforts to reduce air pollution since the 1960s has reduced this cooling and led to more warming according to the new model.
Researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, report similar results from their newly rejiggered models, but not all researchers agree. According to NCAR climate scientist Kevin Trenberth satellite observations do not find the indirect aerosol effect to be as strong as the models indicate. Trenberth says. “It would be surprising to me if the ocean is not playing a substantial role” through natural cycles.
Elsewhere on planet Earth the new data are sometimes contradictory and often surprising. Simulations with one of NOAA's Geophysical Fluid Dynamics Laboratory's (GDFL's) new models, with aerosols and clouds impacting inter-hemispheric energy exchange, showed that aerosols are creating a major disruptions. “Aerosol emissions are like putting up a sunscreen over the Northern Hemisphere, and that reduces the solar imbalance that drives the system,” says Yi Ming, a GFDL climate modeler and an author of the study “Anthropogenic Aerosols and the Weakening of the South Asian Summer Monsoon” in Science. “We're trying to argue this from a larger spatial scale.”
Under some conditions the new models suggest not additional warming or a wholesale movement of heat energy between hemispheres but general cooling. According to researcher Sandrine Bony, a model at the Pierre Simon Laplace Institute near Paris produces less warming in response to greenhouse gases than did the previous generation. It seems that climate modelers are finding surprises galore with their new play toys—warming and cooling, drying and increased precipitation—all linked to aerosols.
Other researchers at GFDL find that new more complex cloud and aerosol simulations could help to provide an explanation for the wide fluctuation in arctic ice seen over the past few decades—something that current models fail miserably at. NCAR's new atmospheric model produced more warming and sea-ice loss than the previous estimates with the main difference being due to cloud cover. It seems that high, gauzy clouds allow more sunlight through in the summer, melting more ice and exposing more open water.
Bottom line on all of this renewed modeling madness is a rush of activity as various modeling teams from around the scientific world compete for inclusion in the incipient fifth IPCC report. Scientists in the IPCC's physical science working group have until 31 July 2012 to submit papers for the IPCC process, and observers expect the literature to explode with results from climate simulations over the coming year. Inundated by a wave of new results, confusion reigns. “What we need now is to really understand what the models are doing, and why they differ,” says Bony. Did someone say “settled science?”
The mystery of carbon dioxide
If the new excitement over aerosols has led to greater variability in modeling results there are also interesting happening regarding that old bugaboo CO2. One would think that climate science would have a fairly firm handle on carbon dioxide, since it is the original smoking gun in the whole anthropogenic global warming scare. A perspective article in Science by Edward Brook introduces the subject this way:
Between about 24,000 years ago and today, the large ice sheets covering most of Canada and parts of Europe and Asia melted away, sea level rose by 120 m, Earth warmed by about 5°C, and rainfall and vegetation patterns shifted, sometimes abruptly. This dramatic natural climate experiment was set in motion by cyclic variations in the geometry of Earth's orbit, but a complex system of feedbacks governed the transition from a glacial to an interglacial state. One of the most important of these feedbacks was a well-documented change in the atmospheric greenhouse gas carbon dioxide (CO2).
The article, “The Ice Age Carbon Puzzle,” goes on to describe what is a major conundrum for climate scientists: just where did the carbon dioxide all come from since the world started warming? This is a more important question that it may sound. After all, if the sources (and sinks) of CO2 remain in question the mechanisms that effect its release and absorption also remain unknowns—and it has been upon these “feedbacks” that the case for the whole AGW crisis has been made. According to Brook:
Multiple studies of air trapped in polar ice have shown that ∼17,500 years ago CO2 levels started to rise from ice age levels of about 180 parts per million (ppm), reaching about 265 ppm 10,000 years ago (see the figure). Over the next 10,000 years, CO2 slowly rose by another 20 ppm, until the rapid increase that started in the industrial age took over. Looking farther back in time, CO2 variations appear to be a fundamental characteristic of ice age cycles
Exactly why CO2 changed like this has been vexing geochemists for decades. The carbon cycle involves uptake and release of CO2 from both land and oceanic reservoirs, and these processes operate on many time scales. No one unified theory fits all available evidence, nor is the available evidence sufficient to test all hypotheses.
Scientists have been able to make some guesses about the sources of CO2 by measuring the ratios of carbon isotopes trapped in times past. Carbon, like other elements, comes in a number of variants called isotopes: 12C, 13C and radioactive 14C. As the numbers indicate, each isotope has a different number of particles in its nucleus. The differences can be found in the number of neutrons, the number of protons remaining fixed at six. Since the number protons, and hence the number of surrounding electrons, remains the same the isotopes are chemically the identical, only varying slightly in mass. Still, that slight variation in mass is enough to cause different physical and biological processes to treat one isotope different than another.
For example, plants preferentially remove 12C from the atmosphere. Physical process can partition CO2 containing different carbon isotopes between the atmosphere and ocean. The radioactive isotope 14C, which is kept at a roughly constant level in the atmosphere due to incoming radiation, slowly disappears from fixed samples stored in the lithosphere or deep oceans. This depletion of 14C in fossil fuels gives human emissions a clear isotopic signature. A new study, “Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores,” sheds light on the isotropic history of carbon dioxide during the last transition from glacial to interglacial conditions.
Carbon isotope fluctuations since the last glacial maximum.
As can be seen from the figure above, starting 24,000 years ago, the isotopic pattern resembles a distorted letter W. The first event is a rapid 0.3 per mil depletion in 13C between about 17,500 and 14,000 years, a time when the CO2 concentration rose by about 60 ppm. The authors call this period the “mystery interval,” stating that it “is arguably the most enigmatic carbon cycle change in the course of the transition.” Schmitt et al. attribute this to a release of CO2 from a previously isolated deep-ocean reservoir. Precisely how and when the reservoir initially formed remains an open question.
At the other end of the W-shaped pattern is a slow rise between about 12,000 and 7000 years ago. Schmitt et al. suggest that this increase may reflect a resurgent terrestrial biosphere, growing plants which preferentially remove 12C from the atmosphere. The report itself offers a multitude of speculative sources for various “flavors” of CO2 being released at various times during the warming. The thing is, this is all really guesswork—educated guesswork, but guesswork nonetheless.
The inescapable conclusion? Science does not understand the sources of carbon dioxide that have contributed to the rise in atmospheric concentrations in the past. Different sources respond differently to climatic conditions—not just to temperature but to current atmospheric concentrations, the interaction of shifting ocean and wind currents, release from newly unfrozen tundra and absorption by resurgent forests across the northern continents. We were asked to believe that CO2 is at the heart of climate change yet science does not understand the carbon cycle—where the carbon is coming from and where it is going to—with sufficient clarity to describe the events of the last 24,000 years. Certainly not clearly enough to capture in a global climate model.
Climate science on the bias
Lastly, I would like to mention an interesting piece of commentary that appeared in Nature in the same issue as the Tollefson report. In “Beware the creeping cracks of bias,” Daniel Sarewitz, co-director of the Consortium for Science, Policy and Outcomes at Arizona State University, talks about one of those subjects that is usually taboo in scientific circles: the threat to science by researcher's own bias.
Sarewitz issued this blunt warning: “Alarming cracks are starting to penetrate deep into the scientific edifice. They threaten the status of science and its value to society. And they cannot be blamed on the usual suspects — inadequate funding, misconduct, political interference, an illiterate public. Their cause is bias, and the threat they pose goes to the heart of research.”
Though Sarewitz is specifically concerned with biomedical research, his warning should be taken as a general one. All areas of scientific endeavor can be affected by peer pressure, by group think, by consensus. When an idea becomes generally accepted, there is a natural tendency for the scientific community to respond positively to new results that reinforce current thinking. Conversely, papers that present a negative result, attacking or diminishing the currently held theory, often find a cold welcome and may not be published at all. Bias is natural and pervasive, and antithetical to good science. Here is how Sarewitz describes it:
How can we explain such pervasive bias? Like a magnetic field that pulls iron filings into alignment, a powerful cultural belief is aligning multiple sources of scientific bias in the same direction. The belief is that progress in science means the continual production of positive findings. All involved benefit from positive results, and from the appearance of progress. Scientists are rewarded both intellectually and professionally, science administrators are empowered and the public desire for a better world is answered. The lack of incentives to report negative results, replicate experiments or recognize inconsistencies, ambiguities and uncertainties is widely appreciated — but the necessary cultural change is incredibly difficult to achieve.
The presence of bias in the global warming debate should be obvious to the most casual of observers. The paucity of published articles that contradict the existing paradigm, the reliance on “consensus” when arguing for the accepted dogma and the ad hominin attacks on scientists bold enough to decry the AGW party line all highlight the bias of the climate science community. Yet as we have seen above there are still gaping holes in our knowledge of Earth's climate system. The old models have been shown to be inadequate and the new ones are not in agreement—unsurprising given that aerosol effects are only crudely estimated and we still do not understand the carbon cycle in sufficient detail.
Beware the bias of group think.
All of this confronts climate science with some fundamental questions. “In the end, the climate community must confront a basic question about models,” reports Tollefson. Michael Winton, a modeler at the GFD puts it more succinctly: “If you made a model and it matched the observations perfectly, would you claim success?” What can be said for a model that matches recent climate fluctuation accurately but does so for the wrong reasons? More fundamentally, how do you know what the right answer is? As we have seen in the past, the right answer is decided by “consensus,” which is to say by the bias and expectations of the clique of climate scientists.
“A biased scientific result is no different from a useless one,” states Sarewitz, “neither can be turned into a real-world application.” Yet that is precisely what the IPCC modelers are claiming, that we should accept the uncertain output of incomplete models, created to satisfy the bias of the greater climate science community, as a factual representation of the Earth system. Starting in 2013, the IPCC will strive to achieve consensus, basically the same consensus they promoted in the previous report, but all they will be doing is codifying the bias of a group of scientists with no real answers.
Be safe, enjoy the interglacial and stay skeptical.