Assessing ExxonMobil's climate change communications (1977–2014)

Tailoring the approaches of Cook et al, Feldman et al, and Elsasser and Dunlap, each document is coded by assigning 'Endorsement Points' (EP1 to EP4b, defined in table 2) to pertinent text and figures based on whether each acknowledges or doubts the scientific evidence that AGW is real and human-caused (intercoder reliability of Endorsement Points: percentage agreement = 93%; Krippendorff's (Kripp.) α = 0.84) [22, 27, 28]. We recognize that all science involves uncertainties, and therefore that doubt is not, ipso facto, an inappropriate response to complex scientific information. Uncertainties are an innate and important part of reasonable scientific discourse. However, it has also been shown that uncertainty may be amplified or exaggerated in ways that are misleading and unreasonable, sustaining doubt about claims that are scientifically established [42, 52, 57, 69]. Therefore, to distinguish reasonable and unreasonable doubt, we apply two first-order filters to our Endorsement Point codings. First, in documents published on or before 1990, we exempt expressions of doubt that AGW is real (i.e. we deem such expressions to be reasonable at that time). Second, in documents published on or before 1995, we exempt expressions of doubt that AGW is human-caused. 1990 and 1995 are when the Intergovernmental Panel on Climate Change (IPCC) first concluded that AGW is real and human-caused, respectively (these are conservative thresholds insofar as many scientists had arrived at these conclusions prior to the IPCC reports; indeed, IPCC reports are based only on already-completed work) [70, 71]. Finally, based on its individual Endorsement Points, each document is assigned one overall Endorsement Level (EL) (intercoder reliability of Endorsement Levels: 89%; Kripp. α = 0.85): 'No Position' (all text and figures are EP4a only); 'Acknowledge' (EP1–3 only); 'Acknowledge and Doubt' (EP1–3 and EP4b); 'Reasonable Doubt' (EP4b only, deemed reasonable as defined above); or 'Doubt' (EP4b only, deemed unreasonable). 'Acknowledge and Doubt' reflects the fact that some communications acknowledge aspects of AGW yet emphasize other areas of doubt or uncertainty.

Our filtering of reasonable doubt (see also section S1.4.2, supplementary information) helps address the challenge of characterizing the positions of documents published during a period of rapidly evolving scientific opinion. Otherwise, however, our coding scheme is agnostic to each document's publication year.

We assign 'Impact Points' (IP1 to IP3, defined in table 2) throughout each document based on its positions on AGW as having known or predicted negative impacts (for example, geophysical, economic, or sociopolitical) (intercoder reliability of Impact Points: 94%; Kripp. α = 0.86). Each document is then assigned one of four overall Impact Levels (ILs): 'No Position' (all text and figures are IP2 only); 'Acknowledge' (IP1 only); 'Acknowledge and Doubt' (IP1 and IP3); or 'Doubt' (IP3 only) (intercoder reliability of Impact Levels: 89%; Kripp. α = 0.77).

We identify documents that express 'Doubt' (SP1, defined in table 2) as to whether AGW can be mitigated or whether the costs of doing so exceed the benefits (intercoder reliability: 97%; Kripp. α = 0.84). While the question of AGW's solvability is not resolvable on purely technical grounds, the relative extent to which documents promote doubt on the matter remains relevant to the character of climate communications, insofar as assertions that AGW cannot be stopped are a common component of contrarian claims [42, 72].

Figures 1(a) and 2(a) show that ExxonMobil's peer-reviewed publications overwhelmingly acknowledge AGW as real and human-caused ('Acknowledge'). Of the 65% (47/72) of peer-reviewed documents that express a position, more than three-quarters hold an 'Acknowledge' position (39/47 = 83%). Table 3 provides sample quotations (see section S7, supplementary information, for substantiating quotations for all documents). ExxonMobil's listed publications include chapter 8 of the 1995 IPCC report (ExxonMobil's principal climate scientist, Haroon Kheshgi, was a contributing author), which observed a 'discernible human influence on global climate' [15, 76]. Kheshgi also co-authored the Summary for Policymakers and several chapters of the next IPCC report in 2001, which found 'there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities' [77–80]. Of the minority of peer-reviewed documents holding a position of 'Acknowledge and Doubt' (5/47 = 11%), 'Reasonable Doubt' (2/47 = 4%), or 'Doubt' (1/47 = 2%), we judge that most of the expressed doubt constitutes normal scientific discussion about uncertainties; for example, 'the estimation of the uncertainty of this causal chain [linking human activities to changes in climate]' [81].

The predominant stance taken in non-peer-reviewed communications is also 'Acknowledge', although compared to peer-reviewed work, it loses ground to the 'Acknowledge and Doubt' and 'Doubt' stances in roughly equal measure (p = 0.044, FET). Figures 1(a) and 2(a) show that, of the 74% (35/47) that take a position, 66% (23/35) 'Acknowledge', 17% (6/35) 'Acknowledge and Doubt', and 17% (6/35) 'Doubt' that AGW is real and human-caused. The more frequent expressions of doubt in non-peer-reviewed documents, compared with peer-reviewed ones, reflect the mixed nature of these documents. Some are technical, academic analyses, while others are industry-targeted speeches, reports, conference proceedings, company pamphlets, etc (see sections S2, S3, and S6, supplementary information).

The bulk of ExxonMobil's internal documents also take the 'Acknowledge' stance. Figures 1(a) and 2(a) show that, of the 63% (20/32) that take a position, 80% (16/20) adopt 'Acknowledge', with most of the rest expressing 'Reasonable Doubt' (3/20 = 15%). Unlike other document categories, however, our characterization of internal documents shifts dramatically if we remove filters for reasonable doubt from our analysis (see section 2). Then, 61% (11/18) take the mixed position ('Acknowledge and Doubt'), with the remainder split between 'Acknowledge' and 'Doubt' (3/18 = 17% and 4/18 = 22%, respectively).

These results are explained by the early publication period of internal documents: all but two were published before the 1990 IPCC report, and are therefore subject to our filters for reasonable doubt. These results also reflect the predominant nature of the internal documents: they acknowledge the likelihood of AGW based on internal and external research, while also highlighting uncertainties.

In 1979, for instance (table 3), an internal Exxon study concluded that:

The most widely held theory is that:

• The increase [in atmospheric CO₂] is due to fossil fuel combustion
• Increasing CO₂ concentration will cause a warming of the earth's surface
• The present trend of fossil fuel consumption will cause dramatic environmental effects before the year 2050.

However, the memo notes: 'It must be realized that there is great uncertainty in the existing climatic models because of a poor understanding of the atmospheric/terrestrial/oceanic CO₂ balance' [82]. Likewise, an internal briefing on the 'CO₂ "Greenhouse" Effect' from 1982 states: 'There is currently no unambiguous scientific evidence that the earth is warming. If the earth is on a warming trend, we're not likely to detect it before 1995' (see table 3). Yet, the authors say, 'Our best estimate is that doubling of the current concentration could increase average global temperature by about 1.3 °C to 3.1 °C' [83]. Several internal documents make this distinction, acknowledging that increased CO₂ would likely cause warming, while expressing (reasonable) doubt that warming was already underway and large enough to be detected.

This cautious consensus is also evident in charts in internal ExxonMobil presentations and reports. (Due to copyright restrictions prohibiting the reproduction of figures owned by ExxonMobil, we instead provide hyperlinks to third-party websites at which relevant figures can be viewed.) For example, in a 1978 presentation to the Exxon Corporation Management Committee, Exxon scientist James Black showed a graph (see https://perma.cc/PJ4N-T8SC) of projected warming 'model[ed] with the assumption that the carbon dioxide levels will double by 2050 A.D.' [95]. Another case is the 1982 Exxon primer already mentioned, which includes a graph (see https://perma.cc/PH4X-ZJBA) showing 'an estimate of the average global temperature increase' under the 'Exxon 21st Century Study-High Growth scenario' [83]. A third example is a table (see https://perma.cc/9DGQ-4TBW) presented by Exxon scientist Henry Shaw at a 1984 Exxon/Esso environmental conference, which showed that Exxon's expected 'average temperature rise' of 1.3 °C–3.1 °C was comparable to projections by leading research institutions (1.5 °C–4.5 °C) [96]. This shows that ExxonMobil scientists and managers were well informed of the state of the science at the time. But they also tended to focus on the prevailing uncertainties: Black stressed the alleged shortcomings of extant climate models before showing his results; Shaw emphasized the variable and 'unpredictable' character of some values.

We conclude that ExxonMobil's recent defense accurately characterizes the situation with respect to its peer-reviewed, non-peer-reviewed, and internal documents: 'Our researchers recognized the developing nature of climate science at the time...[and] mirrored global understanding' [14]. On several occasions during the early 1980s, the company's peer-reviewed and internal documents went as far as to refute 'calculations on a more limited scale by a number of climatologists' that projected much less global warming than the rest of the scientific community, including ExxonMobil [97–99]. 'In summary,' said a 1982 memo, 'the results of our research are in accord with the scientific consensus on the effect of increased atmospheric CO₂ on climate...and are subject to the same uncertainties' [99]. As a scientific consensus emerged in the early 1990s that AGW was underway, a 1995 'Primer on Climate Change Science' co-authored by Mobil as part of the Global Climate Coalition explicitly rejected contrarian claims that were beginning to circulate: 'Contrarian theories...do not offer convincing arguments against the conventional model of greenhouse gas emission-induced climate change' [100].

The predominant stance taken in ExxonMobil's advertorials is 'Doubt'. In essence, these public statements reflect only the 'Doubt' side of ExxonMobil's mixed internal dialogue. Figures 1(a) and 2(a) show that of the 72% (26/36) of climate change advertorials that take a position, 81% (21/26) take the position of 'Doubt', with the remainder split between 'Acknowledge' (3/26 = 11.5%) and 'Acknowledge and Doubt' (2/26 = 7.5%). A characteristic example is a 1997 Mobil advertorial (table 3), which stated: 'Let's face it: The science of climate change is too uncertain to mandate a plan of action that could plunge economies into turmoil...Scientists cannot predict with certainty if temperatures will increase, by how much and where changes will occur. We still don't know what role man-made greenhouse gases might play in warming the planet' [92]. Another, also from 1997, referred to a 'high degree of uncertainty,' 'debate,' and a 'knowledge gap,' and the need for further 'fact-finding' and 'additional knowledge' before UN negotiators in Kyoto could make decisions [94]. The advertorial stressed the goal 'of achieving a consensus view,' two years after the IPCC had presented one.

Our analysis is limited to advertorials in the NYT because those pertaining to climate change have already been compiled and are readily available. Brown et al report that ExxonMobil also ran advertorials in eight other major newspapers [19]. Some of these appear to have been the same or similar to those in the NYT. For example, in an advertorial in The Washington Post in 2000, ExxonMobil criticized a US National Assessment report on climate change as putting the 'political cart before a scientific horse' and being based 'on unreliable models' [101]. The advertorial was condemned by the former director of the National Assessment Coordination Office: 'To call ExxonMobil's position out of the mainstream is...a gross understatement' [102].

Our analysis shows that ExxonMobil's scientists and executives were, for the most part, aware and accepting of the evolving climate science from the 1970s onwards, but they painted a different picture in advertorials. The majority of ExxonMobil's peer-reviewed publications acknowledge that climate change is real and human-caused, and internal documents reflect this scientific framework. Uncertainties are mentioned or even highlighted, but usually in the context of broader scientific understandings and broadly consistent with the evolving science. In contrast, ExxonMobil's advertorials overwhelmingly focus on the uncertainties, casting doubt on the growing scientific consensus (e.g. peer-reviewed publications versus advertorials: p = 4.1 × 10⁻¹³, FET).

The contrast between advertorials and other documents is particularly evident in their accompanying figures. For instance, in a chapter of a 1985 US Department of Energy report co-authored by Exxon scientist Brian Flannery [103], a graph (see https://perma.cc/A5WN-LKLS) presents the results of future warming modeled for different CO₂ scenarios. 'The foregoing results, with all their caveats,' the report summarizes, 'can be construed as an approximate bracketing of the consensus of transient model predictions for the next century's CO₂ greenhouse effect. In this restricted sense, they are consistent with the EPA's estimate of a 2 °C warming from fossil fuel CO₂ and other greenhouse gases by the middle of the next century.' Their conclusion is entitled 'Consensus CO₂ Warming.' Compare this with figures from ExxonMobil advertorials in 1997 and 2000 (see https://perma.cc/39CC-JTES and https://perma.cc/74BL-KL8A, respectively), which downplay the human contribution to AGW and emphasize natural variability instead [104, 105]. Featured in an advertorial entitled 'Unsettled Science' in the NYT and The Wall Street Journal, the latter figure was taken from an article in Science by Lloyd Keigwin of the Woods Hole Oceanographic Institution [105–107]. Keigwin called the use of his data 'very misleading' [106]. They were a historical reconstruction of sea-surface temperatures in the Sargasso Sea and, in his words, 'not representative of the planet as a whole [as the advertorial could be taken to imply]. To jump from the western North Atlantic Ocean to the globe is something no responsible scientist would do...There's really no way those results bear on the question of human-induced climate warming....'

The contrast across document categories is also clear when analyzed at a year-to-year scale (figure 1(a)). The majority of advertorials promoting doubt follow a decade of numerous acknowledgments in the other three document categories. Between 1977 and 1996, of all peer-reviewed, non-peer-reviewed, and internal documents that take a position, 83% fully or partly (81% and 2%, respectively) acknowledge that AGW is real and human-caused (if we remove our filter for reasonable doubt, still 83% fully or partly (43% and 40%, respectively) acknowledge this). Thereafter, in 1997 alone, we see nine advertorials promoting 'Doubt'. Significantly, throughout the late 1990s and early 2000s, ExxonMobil peer-reviewed publications and advertorials in the same years contradict one another (figure 1(a)).

ExxonMobil's 72 peer-reviewed publications focus almost exclusively on methods and mitigation (section S3, supplementary information). Only 10 discuss the potential impacts of AGW (figure 1(b)), of which 60% (6/10) take a position of 'Acknowledge', 30% (3/10) of 'Doubt', and 10% (1/10) of 'Acknowledge and Doubt' (figure 2(b)). Hoffert et al (2002), for example (see table 4), warned that unchecked greenhouse gas emissions 'could eventually produce global warming comparable in magnitude but opposite in sign to the global cooling of the last Ice Age...Atmospheric CO₂ stabilization targets as low as 450 ppm could be needed to forestall coral reef bleaching, thermohaline circulation shutdown, and sea level rise from disintegration of the West Antarctic Ice Sheet' [108]. A 1994 paper defined 'mean global warming of 2 °C from preindustrial time to 2100 as Illustrative Reference Values for climate and ecosystem protection,' two years before the EU adopted this limit [109, 110].

Non-peer-reviewed documents offer a mix of positions (figures 1(b) and 2(b)). Among the 47% (22/47) that take a position, 45% (10/22) 'Acknowledge', 41% (9/22) 'Doubt', and 14% (3/22) 'Acknowledge and Doubt'. As with Endorsement Levels, several of the expressions of doubt in non-peer-reviewed documents reflect the industry-targeted communications included in this category (see sections S2, S3, and S6, supplementary information).

Internal documents typically acknowledge the potential for serious impacts but also highlight uncertainties. Of the 53% (17/32) of documents with a position, 35% (6/17) 'Acknowledge' and 47% (8/17) 'Acknowledge and Doubt' (figure 2(b)). A characteristic acknowledgement is found in a 1980 Exxon memo, which says, 'There are some particularly dramatic questions that might cause serious global problems. For example, if the Antarctic ice sheet[,] which is anchored on land, should melt, then this could cause a rise in the sea level on the order of 5 meters. Such a rise would cause flooding in much of the US East Coast including the state of Florida and Washington D.C.' [98] (see also [83]). An example of doubt is a 1981 report stating 'that it has not yet been proven that the increases in atmospheric CO₂ constitute a serious problem that requires immediate action' [111] (table 4).

In contrast, ExxonMobil advertorials overwhelmingly take the position of doubt (e.g. peer-reviewed publications versus advertorials: p = 0.045, FET). Of the 58% (21/36) of advertorials that take a position, 62% (13/21) express 'Doubt' (figure 2(b)). Most of the remainder express a mixed position (5/21 = 24%). Often, they express the opinion that concern over climate impacts is alarmist, such as a 1995 advertorial entitled 'The sky is not falling,' which asserted, 'The environment recovers well from both natural and man-made disasters' [112] (table 4).

These discussions imply limitations on fossil fuel use because of greenhouse gas limits or climate mitigation. 'Mitigation of the "greenhouse effect",' says the 1982 internal Exxon primer, 'would require major reductions in fossil fuel combustion' [83]. Likewise, an internal 1979 Exxon study found that 'should it be deemed necessary to maintain atmospheric CO₂ levels to prevent significant climatic changes...coal and possibly other fossil fuel resources could not be utilized to an appreciable extent' [82].

These discussions introduce, with varying degrees of detail, ideas of 'cumulative fossil fuel use,' 'cumulative CO₂ emissions,' and 'carbon budgets...for CO₂ stabilization' and/or climate mitigation [81, 127]. Five of these ExxonMobil studies–one internal, three peer-reviewed, and one non-peer-reviewed–include data (see, for example, https://perma.cc/EJ5A-EAZ7) that indicate 2015–2100 CO₂ budgets consistent with limiting warming to 2 °C and/or stabilizing CO₂ concentrations below 550 ppm in the range of 251–716 GtC [81, 83, 127–129]. These budgets are within a factor of two of contemporary estimates of roughly 442–651 GtC [130] (see caption, table 6).