I've been asked to comment on an essay by Freeman Dyson written in 2007 in which Dyson proposed some heresies about climate science. It seems unfair to criticize an essay from 8 years ago, but some of what he said was demonstrably wrong in 2007 and a recent interview from 2015 suggests his opinion hasn't evolved since then. A physicist with his reputation has the potential to influence a lot of people, so it's worthwhile to examine if his sphere of influence should extend to the realm of climate science. The recent interview with Dyson coincides with a release of a report by the special interest group The Global Warming Policy Foundation in which Freeman Dyson wrote the introduction. The latter two items appear to be in preparation for the upcoming climate talks in Paris, possibly with the goal of influencing public opinion.
- Dyson 2007, an essay for The Edge: Heretical Thoughts about Science and Society
- Dyson 2015, a recent interview: The Register, Oct 11, 2015
- Oct 11, 2015: The Global Warming Policy Foundation report on the benefits of CO2.
This is part 1 of two or more posts in which I'm commenting on the following:
This is part 1 of two or more posts in which I'm commenting on the following:
- Dyson should acknowledge the entire scope of climate science before downplaying it's conclusions.
- The greenhouse effect is often described inadequately, even by physicists.
- Ocean acidification, a result of our rate of CO2 emissions, is a well-acknowledged problem and missing from Dyson's commentary.
- It's dangerous to use regional climate change to justify global climate change.
- What does land-use management and genetic engineering offer for mitigating our CO2 emissions?
Under-stating the scope of climate science
Dyson refers to his positions as "heresies", so I use his term with no intended bias.
"My first heresy says that all the fuss about global warming is grossly exaggerated...
.... It is much easier for a scientist to sit in an air-conditioned building and run computer models, than to put on winter clothes and measure what is really happening outside in the swamps and the clouds. That is why the climate model experts end up believing their own models."
--Freeman Dyson, Heretical Thoughts about Science and Society, 2007Dyson made a severe omission in the above paragraph. He implied that climate science is based solely on computer modelling. If true, such a statement would undermine arguments that global warming is real, is caused by humans, and is potentially dangerous -- in other words, the fuss would be grossly exaggerated. He also implies that computer modelers do not test their work against empirical evidence, such that "they end up believing their own models". Based on my routine reading of climate research papers, I see three categories of climate science:
- Computer modelling
- Instrumental observations
- It's happening. We know from world-wide weather stations that average surface temperatures are rising. Three different agencies publish this data: NASA, NOAA, Hadley Research Center, and recently, a prominent skeptic of the temperature record, Richard Muller, produced his own assessment (BEST). All four data sets agree that there is a global rise in surface temperature of almost 1 degree C since the onset of industrialization. In addition to surface temperatures, which represent a small fraction of the earth's energy budget, ocean temperatures are rising and surface ice and sea ice are decreasing.
- It's unprecedented. Various paleoclimate studies have reconstructed temperatures going back hundreds of thousands of years. These studies show our current warming is unprecedented in the Holocene (our current interglacial) and suggest that we may be on the way to warming that is unprecedented when compared to the past 900,000 years.
- It's dangerous. Paleoclimate research has shown that global temperatures in the previous interglacial period (the Eemian interglacial, about 115,000 years ago) peaked about 2 degrees C higher than temperatures did in our current, pre-industrial interglacial. Paleoclimate research shows the trigger of this higher temperature to be an orbital configuration that slammed the northern hemisphere with greater sunlight than what it received in the Holecene. Paleoclimate research also shows that Eemian sea levels were 6-9 meters higher than in the Holocene. Now take the observational evidence (from bullet 1) showing that global temperatures have ticked upward one degree since industrialization, and this gives us 1 degree C wiggle room between now and the sea level of the Eemian. If it is not already happening, one more degree should be enough to set loose the ice sheets of Greenland and West Antarctica, which would account for at least 5 meters of sea level rise.
Yes. I've read many studies indicating where modelers need to constrain certain variables in their models qualify their results. Conveniently, I was reading an example of this type of research a few weeks ago:
--Nature, 1 Oct 2015This paper analyzed the initial leafing out of plants in spring and determined that plants in their study were becoming less sensitive to warmth as a trigger for when to leaf out. From the paper's summary:
We found that the apparent sensitivity of spring phenology to warming for seven temperate tree species in Central Europe has declined significantly as winter and spring temperatures increased over the past three decades. These findings indicate that the early spring phenologically driven increases in carbon uptake may slow down for temperate forests under future conditions of climate warming.In other words, estimates of how much the biosphere will absorb additional CO2 (a good thing) are too high (a bad thing).
A review article in the same publication made this paper's connection to climate modeling more explicit (Spring greening in a warming world):
The relationship between spring temperatures and leaf emergence has allowed scientists of the Intergovernmental Panel on Climate Change to use changes in the timing of emergence as a key indicator of the ecological impact of climate change. Apart from resulting in a greener spring, earlier leaf emergence affects various aspects of ecosystem function, and generates multiple feedbacks to the climate system. It has thus been built into state-of-the-art Earth-system models, which predict a large advance in the timing of leaf emergence under future climate warming. To test the relationship between leaf emergence and warming, Fu and colleagues examined 33 years of observations of 7 forest species across 1,245 sites in Europe. Surprisingly, they discovered that spring leaf emergence has been getting less sensitive to temperature over time (Fig. 1). Their observation-based results call into question current model projections, and suggest that spring leaves might not emerge as early under future warming as had been previously expected.In other words, climate models need to scale back their estimates of how much CO2 the biosphere will absorb via an earlier start to the growing season.
This one example, a paper and review of the paper published in one issue of one journal, is not complete proof of the empirical testing of climate modelling, but it shows that such research is an on-going activity and supports my dismay that prominent individuals like Dyson suggest that modelers do not study the work of others who do test climate models.
Do climate modelers believe everything their models tell them?
No. A common saying in field is attributed to Jason Box:
"All models are wrong, but some are useful."Climate models test our understanding of basic physics, but it is well known that resolution and computing speed are inadequate, and the dynamics of many processes, such as the behavior of clouds and aerosols, are not well understood and therefore are not modeled correctly.
It should be noted that in paleoclimate research nature takes care of the aerosol and cloud calculations for us. If you can find evidence that CO2 rose in the past, and then find evidence that temperatures rose and storms intensified, then you don't have to model the poorly understood behavior of aerosols and clouds. Nature took care that part.
This passage is from Dyson's discussion of Climate and Land Management:
"Everyone agrees that the increasing abundance of carbon dioxide in the atmosphere has two important consequences, first a change in the physics of radiation transport in the atmosphere, and second a change in the biology of plants on the ground and in the ocean
.--Freeman Dyson, Heretical Thoughts about Science and Society, 2007Dyson does mention an influence on the ocean ecology, but doesn't mention that as the oceans absorb nearly half of our CO2 emissions, the CO2 is making ocean water more acidic. This is a worldwide problem which alone may justify halting our CO2 emissions. A recent paper summarizes issues of ocean chemistry:
Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions, Proceedings of the National Academy of Sciences
Rising anthropogenic CO2 emissions are anticipated to drive change to ocean ecosystems, but a conceptualization of biological change derived from quantitative analyses is lacking. Derived from multiple ecosystems and latitudes, our metaanalysis of 632 published experiments quantified the direction and magnitude of ecological change resulting from ocean acidification and warming to conceptualize broadly based change. Primary production by temperate noncalcifying plankton increases with elevated temperature and CO2, whereas tropical plankton decreases productivity because of acidification. Temperature increases consumption by and metabolic rates of herbivores, but this response does not translate into greater secondary production, which instead decreases with acidification in calcifying and noncalcifying species. This effect creates a mismatch with carnivores whose metabolic and foraging costs increase with temperature. Species diversity and abundances of tropical as well as temperate species decline with acidification, with shifts favoring novel community compositions dominated by noncalcifiers and microorganisms. Both warming and acidification instigate reduced calcification in tropical and temperate reef-building species. Acidification leads to a decline in dimethylsulfide production by ocean plankton, which as a climate gas, contributes to cloud formation and maintenance of the Earth’s heat budget. Analysis of responses in short- and long-term experiments and of studies at natural CO2 vents reveals little evidence of acclimation to acidification or temperature changes, except for microbes. This conceptualization of change across whole communities and their trophic linkages forecast a reduction in diversity and abundances of various key species that underpin current functioning of marine ecosystems.
I couldn't resist adding bold face to every instance of "acidification" in the paper's summary, but the real emphasis should be on the last line that says
"...forecasts a reduction in diversity and abundances of various key species that underpin current functioning of marine ecosystems".The health of our ocean is fundamental to the health of our world, so ocean acidification warrants close attention. (Note: I'll also return to the part that says "shifts favoring novel community compositions" in part 2)
I wonder if Dyson is using the same greenhouse effect I'm using?
Dyson alludes to the greenhouse effect in this passage:
Opinions differ on the relative importance of the physical and biological effects, and on whether the effects, either separately or together, are beneficial or harmful. The physical effects are seen in changes of rainfall, cloudiness, wind-strength and temperature, which are customarily lumped together in the misleading phrase “global warming”. In humid air, the effect of carbon dioxide on radiation transport is unimportant because the transport of thermal radiation is already blocked by the much larger greenhouse effect of water vapor. The effect of carbon dioxide is important where the air is dry, and air is usually dry only where it is cold. Hot desert air may feel dry but often contains a lot of water vapor. The warming effect of carbon dioxide is strongest where air is cold and dry, mainly in the arctic rather than in the tropics, mainly in mountainous regions rather than in lowlands, mainly in winter rather than in summer, and mainly at night rather than in daytime. The warming is real, but it is mostly making cold places warmer rather than making hot places hotter. To represent this local warming by a global average is misleading. "
--Freeman Dyson, Heretical Thoughts about Science and Society, 2007If I understand correctly, he is describing the greenhouse effect that we would have if the atmosphere were a uniform layer that differed only by location on the globe, some regions being warmer, others cooler, some more humid, others not. According the Dyson, CO2 should enhance warming only where the air is dry and cool. He fails to mention that the air is dry and cool everywhere above the planet. The lower layers of the atmosphere may be hot and humid, but if you go up a few miles, the atmosphere dries out and is cool. The entire earth is surrounded by higher layers of the atmosphere that represent an inexhaustible storage capacity for additional CO2. Climatologists say the atmosphere warms from the top down, and as you enhance the greenhouse effect, the top of the atmosphere rises-- the top being the average height at which energy radiates to space. This rise correlates with more heat in the climate system. A proper understand of the greenhouse effect is beyond this post, so I recommend the following:
- Physics Today: Infrared Radiation and Planetary Temperature (by Ray Pierrehumbert)
- Skeptical Science: How we know the greenhouse effect isn't saturated? (full disclosure: I contributed to this article)
Additionally, I've read two studies that tried to observe the enhanced greenhouse effect. One study from 2001 used satellites to look down at the upward emission of wavelengths affected by greenhouse gases. The other from 2015 looked up from the surface at backscatter of wavelengths affected by greenhouse gases. The first study examined the region over the Pacific Ocean, a place where you'd find plenty of tropospheric warmth and humidy. Another was using two locations, the Alaskan North Slope and the Great Plains of the United States.
(Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 , Nature, 2001)
The evolution of the Earth's climate has been extensively studied, and a strong link between increases in surface temperatures and greenhouse gases has been established. But this relationship is complicated by several feedback processes—most importantly the hydrological cycle—that are not well understood. Changes in the Earth's greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation, which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect. Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997. We find differences in the spectra that point to long-term changes in atmospheric CH4, CO2 and O3 as well as CFC-11 and CFC-12. Our results provide direct experimental evidence for a significant increase in the Earth's greenhouse effect that is consistent with concerns over radiative forcing of climate.
(Observational determination of surface radiative forcing by CO2 from 2000 to 2010, Nature 2015)Both studies claim to have detected the enhanced greenhouse effect, and I bolded text that alludes to the greenhouse effect as described by Ray Pierrehumbert in Physics Today. My basic argument is that the greenhouse effect as Dyson described it is not the same effect that climatologist describe and measure.
The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing, calculated as the difference between estimates of the Earth’s radiation field from pre-industrial and present-day concentrations of these gases. Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 ± 0.19 W m−2. However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO2. Here we present observationally based evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO2. The time series of this forcing at the two locations—the Southern Great Plains and the North Slope of Alaska—are derived from Atmospheric Emitted Radiance Interferometer spectra together with ancillary measurements and thoroughly corroborated radiative transfer calculations. The time series both show statistically significant trends of 0.2 W m−2 per decade (with respective uncertainties of ±0.06 W m−2 per decade and ±0.07 W m−2 per decade) and have seasonal ranges of 0.1–0.2 W m−2. This is approximately ten per cent of the trend in downwelling longwave radiation. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.
Additionally, reading Pierrehumbert's description and the above passages, one should reason that the enhanced greenhouse effect due to rising CO2 is based on fundamental physics. If you wish to invoke feedback mechanisms that will mitigate warming, and this will happen, you need to invoke behaviors of clouds and aerosols, physics that by general agreement (including Dyson) are not as well understood.
A bit of hindsight
It's interesting to compare Dyson's description of global average with current temperatures:
The warming is real, but it is mostly making cold places warmer rather than making hot places hotter. To represent this local warming by a global average is misleading. "
--Freeman Dyson, Heretical Thoughts about Science and SocietyIt is fair to say that that in 2007, it looked like surface temperatures were at a pause, another topic beyond the scope of this post. But let's jump forward to 2015. Here's an example of how world temperatures of 2015 compare to previous years:
We see a lot of red, meaning warmer, much warmer, or record warmth, and some blue, meaning cooler, much cooler, and record cooling. Some regions are warmer. Some are cooler. Would it be misleading to call this a global warming? Note that the cool areas are what one would expect if ice melt from Greenland and West Antarctica, the two sheets most vulnerable to melting, were indeed cooling the oceans.
I'll cover the next items in a follow-up post:
- It's dangerous to use regional climate change to rationalize global climate change.
- What does land-use management and genetic engineering offer for mitigating our CO2 emissions?