Nine scientists analyzed the article and estimated its overall scientific credibility to be ‘very low’. more about the credibility rating

A majority of reviewers tagged the article as: Flawed reasoning, Inaccurate, Misleading.

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SCIENTISTS’ FEEDBACK

SUMMARY

An article by Boston Globe columnist Jeff Jacoby argues that climate science is too “incomplete” to determine whether human-caused emissions of greenhouse gases like carbon dioxide could be responsible for global warming. The column defended US EPA Administrator Scott Pruitt’s recent statement that he “would not agree that [human activity is] a primary contributor to the global warming that we see”—a statement scientists reviewed and found to be incorrect.

Scientists who analyzed Jacoby’s column found that it is inaccurate, misleading, and uses flawed reasoning to support its central claims. In reality, CO 2 ’s role in the climate system is well understood, and this fundamental knowledge informs the determinations that humans are responsible for modern climate change, and that continued greenhouse gas emissions will cause further warming.

See all the scientists’ annotations in context

REVIEWERS’ OVERALL FEEDBACK

These comments are the overall opinion of scientists on the article, they are substantiated by their knowledge in the field and by the content of the analysis in the annotations on the article.

James Screen, Associate Professor, University of Exeter:

This is a highly inaccurate article that makes a number of false and intentionally misleading claims. The weight of scientific evidence (summarised in the IPCC reports) shows that greenhouse gas emissions are the dominant cause of observed global warming. The claim that climate models “always predict far more warming” is demonstrably false. The discussion of complexity is intended to mislead: the fact that the climate system is incredibly complex does not mean we don’t understand key aspects of how it functions.

Mitch Lyle, Professor, Sr. Research, Oregon State University:

Jacoby used a flurry of words to claim that models did not work. He set up a straw man about complexity that was irrelevant and never actually examined real climate models.

Dan Chavas, Assistant Professor, Purdue University:

The article is full of logical fallacies: just because a system has many moving parts does not mean it is unpredictable.

Alexis Tantet, Postdoctoral researcher, Hamburg University, Meteorologisches Institut:

The facts given by the author regarding the skills of climate models and the state of the art are mostly wrong. The most important processes are not understood by the author and his logic is flawed

William Seviour, Vice Chancellor's Research Fellow, University of Bristol:

This article combines tired and regularly-debunked climate myths with faulty reasoning to support a statement which is ungrounded in scientific reality.

James Renwick, Professor, Victoria University of Wellington:

One of the most egregious pieces of misinformation I have seen in the media in years.

Ilissa Ocko, Climate Scientist, Environmental Defense Fund:

This article employs flawed reasoning mixed with inaccurate statements to create a false impression of climate scientists’ state of understanding.

Andreas Schmittner, Associate Professor, Oregon State University:

The article contains major scientific inaccuracies and it omits important information.

Notes:

[1] See the rating guidelines used for article evaluations.

[2] Each evaluation is independent. Scientists’ comments are all published at the same time.

KEY TAKE-AWAYS

The statements quoted below are from the article; comments and replies are from the reviewers.

1. It is clear that humans are causing climate change through emissions of greenhouse gases like carbon dioxide, which acts as a control knob on the climate system.

“CO 2 is certainly a heat-trapping greenhouse gas, but hardly the primary one: Water vapor accounts for about 95 percent of greenhouse gases. By contrast, carbon dioxide is only a trace component in the atmosphere: about 400 ppm (parts per million), or 0.04 percent.” Christopher Colose, Postdoctoral Research Fellow, NASA GISS:

First, it is true that water vapor constitutes the bulk of Earth’s present-day greenhouse effect (measured in terms of infrared absorption). Quantitatively, however, Jacoby is off by quite a bit. In fact, water vapor constitutes ~50% of the terrestrial greenhouse effect, not 95% (see here*). Clouds (solid and liquid water that form when the vapor condenses) constitute another ~25%, but CO 2 contributes to almost all of the remaining fraction (only ~5% or so from all of the other combined gases). This is because CO 2 still absorbs well in spectral regions where water vapor doesn’t, and also because the upper troposphere is very dry; the ability to absorb intense surface emission and re-emit it at colder, higher layers of the atmosphere is critical for the maintenance of a planetary greenhouse effect. Secondly, the water vapor greenhouse effect is not independent of the CO 2 in the atmosphere.

Jacoby stresses that CO 2 is only a trace component of the atmosphere, an argument that is irritatingly unoriginal and provides useless context when describing the flow of radiation through the atmosphere. As before, CO 2 accounts for ~20% of Earth’s greenhouse effect. N 2 and O 2 account for nearly all of Earth’s atmospheric mass. However, if the atmosphere were purely N 2 and O 2 , the planet would likely be in a snowball state due to the lack of greenhouse trapping. This is where the equations of radiative transfer must be applied, rather than a naive intuition about proportions. Schmidt et al (2010) Attribution of the present-day total greenhouse effect, Journal of Geophysical Research: Atmospheres. Mark Zelinka, Research Scientist, Lawrence Livermore National Laboratory:

Another helpful quote comes from this article: “The contribution of CO 2 to the greenhouse effect, considerable though it is, understates the central role of the gas as a controller of climate. The atmosphere, if CO 2 were removed from it, would cool enough that much of the water vapor would rain out. That precipitation, in turn, would cause further cooling and ultimately spiral Earth into a globally glaciated snowball state. It is only the present of CO 2 that keeps Earth’s atmosphere warm enough to contain much water vapor.” I like to think of CO 2 as analogous to a military commander and water vapor as analogous to an army of foot soldiers. Even though the water vapor foot soldiers do most of the fighting, the CO 2 commander sends the army to battle. William Seviour, Vice Chancellor's Research Fellow, University of Bristol:

While it is true that carbon dioxide constitutes about 400 ppm (or 0.04%) of the atmosphere, the implication that this means it is insignificant in Earth’s climate is incorrect. It is the ability of a gas to absorb radiation, and so affect energy balance of the Earth, not its concentration, which is important. This effect on Earth’s energy balance can be quantified by the radiative forcing (RF); a positive RF means a surface warming effect and a negative RF a cooling. The figure below, from the 2013 IPCC report shows estimates of RF for a range of factors which have influenced climate from 1750-2011. As can be seen, increasing carbon dioxide concentrations have the largest RF and therefore the largest impact on climate. I also stress that knowledge of the important role of carbon dioxide (despite its low concentration) in Earth’s climate is not new, and dates back to the work of Tyndall, Arrhenius, and others in the 19th century.

“Moreover, its warming impact decreases sharply after the first 20 or 30 ppm. Adding more CO 2 molecules to the atmosphere is like painting over a red wall with white paint — the first coat does most of the work of concealing the red. A second coat of paint has much less of an effect, while adding a third or fourth coat has almost no impact at all.” Christopher Colose, Postdoctoral Research Fellow, NASA GISS:

Jacoby emphasizes the logarithmic nature of how CO 2 affects the energy balance of Earth, and hence surface temperature (i.e., going from 10 ppm of CO 2 to 11 ppm would have a much larger impact than going from 300 to 301 ppm). This is correct, but has been known for well over half a century now, and is fully accounted for in even simple estimates of future warming. This is therefore a distraction. Andreas Schmittner, Associate Professor, Oregon State University:

The effects of CO 2 do not decrease sharply after the first 20 or 30 ppm. The radiative effects of CO 2 are logarithmic, so they increase slightly less the higher CO 2 gets but they don’t decrease sharply. Ilissa Ocko, Climate Scientist, Environmental Defense Fund:

This is flawed reasoning as it is not a sensible analogy for how the greenhouse effect works. The science is more complex: Namely, radiation from the surface at a warmer temperature is absorbed in the layers above which are at a colder temperature; the colder layers emit less radiation so that there is a net loss of radiative energy escaping to space from the atmosphere-surface system as a whole, but coming about due to the “exchange” as formulated. This is true in absorption bands that are transparent and not opaque—i.e., in bands that are not saturated. In bands that are opaque, the radiation emanating from the layer to space represents a “cooling-to-space” and this too represents a “trapping”. In this regard, the lapse-rate and decrease of temperature with height (in the troposphere) are important. The more CO 2 that is added to the atmosphere, the more heat that is “trapped” in the climate system, although it is not 1:1 and is instead a logarithmic relationship. However, regardless of the rate, we still have more warming with more CO 2 —that is unequivocally true. William Seviour, Vice Chancellor's Research Fellow, University of Bristol:

Jacoby links to a blog page which explains the logarithmic relationship of CO 2 concentrations and radiative forcing. Contrary to Jacoby’s implication, this is actually a well accepted part of climate science. For instance, see Myhre et al 1998* (table 3), who give detailed estimates of this logarithmic relationship. However, as CO 2 concentrations rise, the fraction of CO 2 which remains in the atmosphere (rather than being absorbed by the ocean) is projected to increase (see Jones et al 2013*). The net effect is that the relationship between total CO 2 emissions and surface temperature is almost linear. See the figure below from the 2013 IPCC report. Myhre et al (1998) New estimates of radiative forcing due to well mixed greenhouse gases, Geophysical Research Letters

Jones et al (2013) Twenty-First-Century Compatible CO 2 Emissions and Airborne Fraction Simulated by CMIP5 Earth System Models under Four Representative Concentration Pathways,

Journal of Climate

“The science is far from settled.” James Renwick, Professor, Victoria University of Wellington:

The basic controls on the climate, sunlight and greenhouse gases, have been understood for over a century and are not disputed. The frontiers of climate research are where the debates lie, as with any branch of science. “[Pruitt’s statement] was an accurate and judicious answer” Ilissa Ocko, Climate Scientist, Environmental Defense Fund:

It is objectively not an accurate answer and is misleading at best. [Pruitt’s statement has been reviewed by scientists with Climate Feedback and found to be incorrect.] While it is certainly challenging to determine human influence on the climate, decades of research by tens of thousands of scientists from different institutions all over the world have yielded a nearly unanimous consensus with extreme confidence that humans are the dominant cause of climate change. In fact, scientists have been questioning and researching human influence on the climate for nearly 200 years. Further, we can use techniques similar to the smoking-cancer causality research to prove that humans are mainly responsible and to show that carbon dioxide is the primary control knob for today’s climate change. There is no “tremendous disagreement” or “debate” about this.

2. Earth’s climate system is complex, but the basic processes are well understood, allowing climate scientists to usefully project the impacts of continued greenhouse gas emissions.



“Earth’s climate system is unfathomably complex. […] The more variables there are in any system or train of events, the lower the probability of all of them coming to pass. Your odds of correctly guessing the outcome of a flipped coin are 1 in 2, but your odds of guessing correctly twice in a row are only 1 in 4 — i.e., ½ x ½ Extending your winning streak to a third guess is even less probable: just 1 in 8.” James Renwick, Professor, Victoria University of Wellington:

Yes, it is complex, but not unfathomable. The basics are simple—the energy budget at Earth’s surface is controlled by the intensity of sunlight reaching the ground and the amount of greenhouse gas in the atmosphere. That’s it. This analogy implies everything is happening randomly in the climate system. This is not the case. There is a great deal of structure imposed by the laws of fluid motion and energy transfer, and by the basic geometry and rotation rate of the Earth. Alexis Tantet, Postdoctoral researcher, Hamburg University, Meteorologisches Institut:

The Earth system is indeed complex with nonlinear interactions between various components on a large range of time and spatial scales. However, some processes are very robust, such as the response of the global energy budget to increased greenhouse gases, so that the surface of the Earth eventually has to warm up in order to reach a radiative balance. The distribution of the heating, the rate of melting of the ice sheets, the changes in the occurrence of extremes, etc. are more difficult to predict and that is why we need state-of-the art global climate models. Last, one should not confuse the weather prediction of an exact meteorological state, limited by the chaotic nature of the system, and climate projections of the statistics of variables in response to forcing, such as the global mean surface temperature sensitivity to greenhouse gases emissions.

“The list of variables that shape climate […] would run to hundreds, if not thousands, of elements, none of which scientists would claim to understand with absolute precision.” Mitch Lyle, Professor, Sr. Research, Oregon State University:

Jacoby is making a laundry list, not trying to understand the issues. He is also confusing the issue by trying to claim that since scientists cannot predict climate change at a given small location at a fixed point in future time that they do not have the ability to generally predict the the future trend. Climate scientists are after the trend. Most of the variables he mentions cause the local climate to deviate to a small extent from the trend. Some, like volcanic activity or El Niño, affect the climate for a small number of years, and then their effect disappears. Christopher Colose, Postdoctoral Research Fellow, NASA GISS:

The basic argument in the remainder of the article is one of “complexity” and the notion that climatologists cannot perfectly understand thousands of variables, and hence the behavior of the system under investigation. Jacoby is not completely wrong—climate is extremely complex, and poses no shortage of interesting research questions.

However, it is sometimes difficult for non-specialists to appreciate the emergent simplicity that can arise in an incredibly complex system. After all, how do we know summer will be warmer than winter, that the top of Mt. Everest is colder than the base, or that Arizona is expected to be on average drier than Florida, or that the equator ought to be hotter than New York, or that the climate will cool following a large volcanic eruption? These statements are not just based on prior observations, but in fact can be predicted by applying fundamental equations to a rotating planet. Part of the beauty in studying atmospheric science is in gaining an appreciation for where complexity is counterbalanced by an almost eerie predictability, much like how the outcome of a single spin in roulette is hopelessly unpredictable (and certainly influenced by every slight detail at the time the dealer releases the ball), but casinos have no problem with such complexity because the statistical behavior of the roulette wheel is well-posed. Similarly, the statistical behavior of the atmosphere, while unsolved, is not actually that complex. The appeal to complexity is a compelling one. Nonetheless, progress has been made in many complex sciences (astrophysics, geology) in which the system under investigation cannot be experimentally isolated, and yet where so much is known. However, it turns out to be incredibly simple to rule out El Niño, volcanic eruptions, soil quality, sunspot cycles, plate tectonics, etc. to the trend in global temperatures since 1950. Just as geologists can inform you of the glacial history of a region, sometimes with little more than a trained eye, CO 2 leaves behind “fingerprints” in the atmospheric warming that other “forcing agents” do not. Another perhaps surprising component is that this result is not extremely sensitive to unknown variables. Suppose, for example, that the Andes Mountains were abruptly flattened. This would almost certainly affect important aspects of the global and regional climate, but many of the critical phenomena of the climate system (e.g. that the equator is wet where air rises, that storm tracks develop in the mid-latitudes, the presence of a jet stream, etc.) would still remain. Furthermore, adding CO 2 to a “flat-Andes hypothetical Earth” would still result in warming. It’s physics, and it’s unavoidable. It is true that the exact magnitude of future warming, even if we knew future carbon emissions perfectly, is still not known to within even 10%. However, that uncertainty range does not overlap with “very little warming” or “make the planet uninhabitable warming.” In any case, if one’s argument is based on how complex the system is, surely perturbing that complex system is not something they ought to advocate for!

“What are the odds that a climate model built on a system that simple would be reliable? Less than 50/50. (Multiplying .95 by itself 15 times yields 46.3 percent.)” James Renwick, Professor, Victoria University of Wellington:

Again, this assumes that all variables are independent and everything is happening randomly. This is just not the case. Winds, temperatures, pressures, cloud formation, and so on are all bound together in coherent ways by the laws of physics. Alexis Tantet, Postdoctoral researcher, Hamburg University, Meteorologisches Institut:

This is absolutely not how prediction skills are and should be measured. Assuming that each variable is given the same weight, the initial error would be of 5%. How this error grows with the prediction is a nontrivial problem, which cannot be explained by kindergarten probabilities, but requires observations, theory and modeling. Moreover, the problem of the predictability of fast weather fluctuations become irrelevant for long-term climate projections of statistics in response to forcing.