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Chapter 6
THE RELATIONSHIPS BETWEEN MARINE
PHYTOPLANKTON, DIMETHYLSULPHIDE AND THE
GLOBAL CLIMATE: THE CLAW HYPOTHESIS AS A
LAKATOSIAN PROGRESSIVE PROBLEMSHIFT
Nei Freitas Nunes-Neto*, Ricardo Santos do Carmo and
Charbel Niño El-Hani
Research Group on History, Philosophy, and Biology Teaching,
Institute of Biology, Federal University of Bahia
Salvador, Bahia, Brazil
ABSTRACT
In this chapter, we address the origin and development of a scientific hypothesis
about the connection between some species of marine phytoplankton, sulphur
compounds, and clouds over the oceans. This hypothesis is very relevant to the
understanding of the climate system. Investigations carried out by Lovelock and
colleagues in the beginnings of the 1970s were important to the construction of this
hypothesis. Those studies searched for a stable intermediary in the sulphur cycle, which
would be responsible for transferring this element from the oceans to the land surface.
Based on studies about the release of dimethylsulphide (DMS, a volatile sulphur
compound) by marine phytoplankton species, as well as the process of cloud formation
and its relationship with planetary albedo, Charlson, Lovelock, Andreae and Warren
proposed in 1987 what became known as the CLAW hypothesis. This hypothesis
proposes that the rapid oxidation of DMS in the atmosphere leads to the formation of a
non-sea-salt aerosol (NSS–SO42-), which, when oxidized, constitutes nuclei required for
the condensation of water vapor, and, thus, to cloud formation over the oceans. Since
* Correspondence Address
Rua Barão de Jeremoabo, 147, Campus Universitário de Ondina,
Instituto de Biologia, Departamento de Biologia Geral.
Salvador, Bahia, Brazil, 40170-290
Phone: +55 (71) 32836568.
Email Addresses: [email protected], [email protected], [email protected]
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Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
clouds reflect part of the solar radiation that reaches the planet, they contribute to cool the
planetary surface. Therefore, DMS has been pointed out as a negative greenhouse gas,
which could counterbalance the heating effects of greenhouse gases such as CO2 and
CH4. We should stress, however, that the degree in which DMS can contribute to cool the
Earth surface and the mechanisms responsible for DMS production by the phytoplankton
and other organisms of the marine biota are still open issues in the scientific community.
However, despite the controversies, Charlson and colleagues’ hypothesis gave rise to a
whole new area of interdisciplinary scientific research, known as the ‘cloud-algae link’.
Here, we intend to show how this hypothesis and the new research area resulting from it
have an impact on studies about climate change, and, also, about the relationships
between the biota and its physicochemical environment. We intend to do this from an
epistemological point of view, holding that the success of the CLAW hypothesis can be
qualified as a “progressive problemshift” in the sense of Imre Lakatos’ epistemology. We
also offer some considerations on the scientific status of Gaia.
Keywords: CLAW hypothesis, Cloud-algae link, Dimethylsulphide, Climate change,
Epistemology, Lakatos, progressive problemshift, Gaia.
Even if CLAW turns out to be utterly irrelevant climatically, it will leave a rich and
fundamentally important legacy in our perceptions of how the world works and in the way we
need to do our science in order to understand it.
Anonymous reviewer, quoted in Liss & Lovelock, 2007
1. INTRODUCTION
The quotation used above as an epigraph straightforwardly expresses the central
argument we will elaborate throughout this chapter, mainly because it is an ipsis litteris
quotation of an anonimous reviewer. Here, we will address the development of a scientific
hypothesis that, with little more than two decades of existence, has had a positive impact on
researches related to the planetary dynamics of sulphur and climate changes. The hypothesis
at stake was put forward in 1987 and became known in the literature as the “CLAW
hypothesis”, an acronym of the names of the four scientists that proposed it (Charlson,
Lovelock, Andreae, and Warren). Very briefly, it states that the synthesis and release of a
dominant volatile sulphur compound, dimethylsulphide (DMS), by oceanic algae originates
cloud condensation nuclei (CCN), which are particles that favors the formation of clouds
(Rissman et al., 2007. For more detailed explanations, see section 2 of this chapter). The
oceanic clouds resulting from the activities of algae can contribute to cool the planetary
surface, since they reflect a great deal of the incoming solar radiation.
In spite of the controversies raised by the hypothesis since it was proposed, it has been
relatively well received by the scientific community and had a significant influence on the
investigations done in several disciplines dedicated to the understanding of the climate. It also
contributed to a better understanding of the complex relationships between living beings and
their physicochemical environment, a central topic for the science of ecology. Between the
end of the 1980s and the beginnings of the 1990s, the CLAW hypothesis led to the
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 3
appearance of a new and interesting interdisciplinary research area, known as ‘algae-cloud
link’, or sometimes, “algae-cloud connection” (see Bell, 1986). The CLAW hypothesis and
this new area continue to be an enthusiastic topic to several researchers, even beyond the
natural sciences, given their sociopolitical implications to the problem of global warming.
This chapter begins with an explanation of the CLAW hypothesis, which is also situated
in a historical context and give room to some epistemological remarks. In the subsequent
section, we briefly consider the theory of science developed by Imre Lakatos, which will be
instrumental to the building of our central argument in the chapter. We hold there that CLAW
can be treated as a progressive problemshift on our understanding of the systems at stake,
from a Lakatosian perspective. Then, in the next section, we will move on to present the main
implications of the CLAW hypothesis to the understanding of the dynamical relationships
established between living beings and their physicochemical environments, sketching
important consequences to the problem of global climate change. Finally, we will offer our
concluding remarks.
2. FROM A GAP IN THE SULPHUR CYCLE TO A NEW RESEARCH AREA
Until the beginnings of 1970s, there were many doubts about the dynamics of the global
sulphur cycle. Indeed, our knowledge about the cycle of this fundamental element was quite
incomplete (Volk, 1998). One important gap was related to the chemical stable compound
that transported sulphur from the oceans to the land surface. As the English chemist James
Lovelock said:
The weathering of sulphur-bearing rocks, the sulphur extracted from the ground by
plants, and the amounts put into the air by the burning of fossil fuels, are not nearly enough to
compensate for the millions of tons washed into the sea each year (Lovelock, 2000, p. 122).
The mechanical action of water along the rivers and the transfer of sulphur to the oceans
in the form of sulphate ions make the land lose great amounts of this element. This explains
why sulphur is more abundant in the oceans than in the land. Since sulphur is an essential
element to all living beings, if there were no mechanism that could bring it back to the land
masses, terrestrial organisms would not be able to survive. Since these organisms are not
deprived of this element, then, what would be the reposition mechanism of sulphur to the
continental ecosystems? In the beginnings of the 1970s, this was an important focus of
research for several scientists interested in the dynamics of sulphur.
The conventional wisdom of that time ascribed to hydrogen sulphide (H2S) the role of
transferring sulphur from the oceans to the land. However, for this hypothesis to be true, huge
amounts of H2S should be released from the oceans, in order to compensate for the loss of
sulphur from the terrestrial environment. But this hypothesis could not be supported, as
Lovelock, Maggs and Rasmussen (1972) pointed out. They noticed that the seawater has such
an oxidative power that there could not be H2S in the oceans in a concentration enough to
carry out the transfer of the needed amounts of sulphur to the land (Lovelock et al., 1972).
Moreover, H2S has such a strong and peculiar smell that would have to be easily detected.
However, this compound was never detected in enough concentrations to be accounted
responsible for the transfer of sulphur.
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Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
It is important to notice that the hypothesis that H2S would be the intermediary chemical
compound in the transfer of sulphur derived from a traditional perspective on the cycles of
elements, namely, that only physicochemical sources could account for the huge amounts of
substances involved in such cycles. Non-biological sources of H2S that were already known,
such as volcanoes and fumaroles, were the main candidates to be the sources of sulphur, with
the exception of industrial human activities. According to Charlson et al. (1987), volcanoes
and fumaroles release about 10 to 20 % of the total natural flux of gaseous sulphur to the
atmosphere. But, as these authors argue, the emission of sulphur by volcanoes is highly
variable in space and time, and, consequently, the production of sulphate aerosol by oxidation
of volcanic sulphur during the quiescent stage of a volcano can be only regionally important.
In turn, large volcanic eruptions, which tend to impact huge areas, are very rare events, and
thus cannot play a substantial role in the explanation of the sulphur cycle.
All this shows that more consistent and acceptable models of the sulphur cycle were
required. James Lovelock, the main proponent of the Gaia theory (or, as we will call
throughout this chapter, ‘research programme’), gave major contributions to the construction
of such models from his theoretical perspective, according to which life is not a passive
player in the biogeochemical Earth system. This means that Gaia, albeit controversial, has
been providing far-reaching contributions to science since the 1970s.
Gaia proposes that a cybernetic system including the biota and the abiotic components of
the Earth regulates environmental variables at a global scale, keeping them within a range that
makes Earth inhabitable by living beings. From this perspective, life is an active and, even
more, a central player in the planetary dynamics of elements. Living beings are influenced by
the geological environment, but they also produce deep and long-lasting effects on this same
environment. This theoretical standpoint is part of the explanation of why Lovelock and
colleagues (1972) saw, in Fred Challenger’s observation that many marine organisms release
dimethylsulphide (DMS), a reason for casting doubt on the contemporary views about the
sulphur cycle. Based on Challenger’s studies, they proposed that the “DMS is the natural
compound of sulphur which fills the role originally assigned to H2S; that of transferring
sulphur from the seas through the air to land surfaces” (Lovelock et al., 1972, p. 452).
After all, one cannot escape from noticing that the suggestion of DMS as the
intermediary involved in the planetary dynamics of sulphur was grounded on a central thesis
of the Gaia research programme, namely, that all living beings are deeply and systematically
involved in regulatory mechanisms of the global physicochemical variables. From this
perspective, great emphasis is given to the role of living beings as sources of chemical
compounds that play a role in geochemical cycles, that is, these cycles tend to be generally
seen as biogeochemical cycles, in a quite strong sense.
After the publication of the 1972 paper by Lovelock and colleagues, new studies showed
that several species of marine algae release DMS to the atmosphere. As Andreae and
Raemdonck (1983, p. 746-7) observed, “DMS is the dominant source of biogenic volatile
sulfur compounds to the marine atmosphere” (For reviews, see Lovelock, 2000; Gabric et al.,
2001). It was also shown that DMS, as well as other compounds, could be involved in the
process of cloud nucleation (For further details, see Pham et al., 1995; Ayers & Cainey, 2007;
Liss & Lovelock, 2007). This additional role of DMS led to yet another key contribution from
Gaia to our understanding of the Earth system, to which we will turn our attention now.
The existence of a relationship between cloud albedo and the climate has already been
suggested by Twomey (1977). And Shaw (1983), in turn, proposed that biogenic atmospheric
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 5
sulphur aerosols could participate in the radiative balance of the planet, significantly affecting
the climate. However, neither Twomey nor Shaw constructed a hypothesis linking algae,
clouds, sulphate compounds and the global climate, as put forward by Charlson et al. (1987).
In their paper, taking as a starting point a series of previous works on sulphur dynamics and
cloud formation, and assuming a systemic perspective on Earth (such as that offered by Gaia),
Charlson and colleagues proposed what became known in the literature as the CLAW
hypothesis. In a very brief and schematic way, this hypothesis claims that there is a negative
feedback loop linking the algae, DMS and clouds.
According to Charlson et al. (1987, p. 656), “the warmest, most saline, and most
intensely illuminated regions of the oceans have the highest rate of DMS emission to the
atmosphere”. The DMS in the ocean water is ventilated to the atmosphere. In the atmosphere,
DMS is quickly oxidized, giving origin to, at least, three substances: (1) DMSO
(dimethylsulphoxide); (2) SO2 (sulphur dioxide) and (3) MAS (methane sulphonic acid). The
pathways of oxidation in the atmosphere are complex. However, we can say that the oxidation
of the SO2 produces ‘non-sea-salt sulphate (NSS-sulphate) aerosol particles’, which can form
sulphate particles (SO42-), that play the role of CCN for water vapor. These nuclei are known
as cloud condensation nuclei (CCN). The CCN are acidic particles that have properties that
make it possible that the water vapour molecules condensate. As a consequence, the CCN
derived from DMS lead to the growth of cloud droplets in the troposphere of the open oceans
(Rissman et al., 2007). As the concentration of clouds over the oceans increases, less solar
radiation reaches the surface waters, since clouds tend to reflect radiation back to space. As a
consequence, less DMS is released by the marine phytoplankton and this, in turn, reduces the
production of clouds, closing the negative feedback mechanism. This is, in sum, the
mechanism proposed by the CLAW hypothesis.
Today, we know more about the details of this process (Ayers & Cainey, 2007). The
investigations developed after the proposition of CLAW showed that not only the
phytoplankton species are important to the release of DMS to the atmosphere. Other species
of the marine community, including organisms of the zooplankton, bacteria and virus, are also
relevant to the release of DMS to the atmosphere.
As we will explain in more detail below, the algae synthesize DMSP, a sulphur
compound that has important functions in the algal metabolism. This substance is the
precursor of DMS. The convertion of DMSP into DMS, through a DMSP-lyase, occurs in the
interior of the algal cell; or in the marine environment (after cell lysis due to viral attacks or
through exudation of the substances by the cell); or in the guts of the zooplankton, which
feeds on the algae. These are alternative routes to the presence of DMS in the oceans and,
thus, to its atmospherical origin. Moreover, part of the DMS molecules undergo photolysis or
are consumed by bacteria, since they are a good source of sulphur and carbon. Thus, we can
notice that the DMS flux to the atmosphere depends on the interactions among the organisms
of the planktonic food web, in the ocean environment, and not only from the influence of
solar radiation and salt content on the phytoplanktonic organisms, as originally proposed in
the CLAW hypothesis (For a good review of this matter, see Simó, 2001; see also Figure 1).
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Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
Figure elaborated by the authors.
Figure 1. Schematic representation of the main mechanisms involved in the production of DMS and,
consequently, clouds over the oceans. The picture resulting from scientific research since 1987 is more
complex than that proposed by the original CLAW hypothesis. However, this hypothesis is the
historical source of the subsequent developments. DMSaq: dimethylsulphide in the marine water, DMSg:
dimethylsulphide
in
the
atmosphere,
DMSP:
dimethylsulphoniopropionate
DMSO:
dimethylsulphoxide, MSA: methane sulphonic acid, SO2: sulphur dioxide, SO4: sulphate ions, NSSsulphate: non-sea-salt sulphate, CCN: cloud condensation nuclei.
The CLAW hypothesis generated an intense debate since it was proposed, especially in
virtue of its implications to the problem of climate change (Ayers & Cainey, 2007; Vallina et
al., 2007; van Rijssel & Gieskes, 2002; Gabric et al., 2001; Andreae & Crutzen, 1997;
Schwartz, 1988). More than 1500 papers were published about this hypothesis since 1987,
according to Ayers and Cainey (2007). This indicates how it was deemed relevant by the
scientific community. Notice also that Charlson, Lovelock, Andreae, and Warren won, in
1988, the Norbert Gerbier-Mumm Award, given by the World Meteorological Organization
(associated to the United Nations) as an acknowledgement of their discoveries and the
elaboration of a mechanism to explain the sulphur cycle (WMO, 2007).
Nevertheless, in the scientific community, some doubts remain about the exact
relationships among the algae, other organisms of the marine biota, the sulphur compounds,
the clouds, and the climate. Some of them were highlighted by Charlson et al. (1987)
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 7
themselves. For instance, it has been debated by the scientific community whether the
influence of the solar radiation on the synthesis of DMSP by the algae is positive or negative.
The CLAW hypothesis proposes that the synthesis of DMSP is increased by the solar
radiation, in such a manner that the final result is a negative feedback (regulatory)
mechanism. But the authors themselves recognize that they did not have enough elements to
decide about this point at that time. If the signal of the feedback is positive, then the
mechanism that includes the marine organisms, the sulphur compounds and the clouds, is not
of control, but of amplification. This means that the more DMS is released by the marine
organisms, the more clouds are formed over the oceans. In sum, empirical data obtained since
the proposal of the CLAW hypothesis do not point to a single direction, pro or con the
hypothesis. The consequence is that even central features, such as whether the signal of the
feedback is negative or positive, are still open issues.
In fact, it was not possible to adequately test the CLAW hypothesis up to the present,
despite its impact on research about the process of cloud formation and its relationship with
the global climate, and, consequently, its potential role in the construction of a scientific
understanding of the Earth system. The reason lies in the overall complexity of the
atmospheric and oceanic processes involved in the proposed feedback mechanisms and, also,
in the lack of understanding about several aspects of DMS oxidation in the atmosphere (Ayers
& Cainey, 2007; Vallina et al., 2007; Malin, 2006; Andreae & Crutzen, 1997).
For the sake of our argument, however, it is a secondary issue whether the CLAW
hypothesis will be maintained or refuted by the scientific community. This is an empirical
issue, which will be solved in its due course. What most interests us here is the capacity
shown by the proposals of Lovelock et al. (1972) and Charlson et al. (1987) of generating
new predictions and research questions. The pioneering studies of these authors gave origin to
a whole new area of research, known as the ‘cloud-algae link’, which shows a strongly
interdisciplinary character, congregating researchers from a variety of disciplinary fields, such
as geochemistry, geophysics, biogeochemistry, climatology, meteorology, taxonomy,
oceanography, ecology and evolutionary biology, who work in close collaboration.
There are reasons to think that, despite the uncertainties that surround it and the necessity
of proper empirical testing, the CLAW hypothesis was able to point out to elements that are
likely to play a role in future models of the global climate, even if these models come to
diverge substantially from the specific content of that hypothesis. Micro- and macroalgae, for
instance, are likely to take part in the climate system, since they are, as the CLAW hypothesis
proposes, a source of chemical substances involved in the formation of CCN, without which
there would be no clouds (Ayers & Cainey, 2007). Christner et al. (2008) also highlight that
aerosols produced by living organisms (mainly bacterial plant pathogens and other
microorganisms) are ubiquitous and constitute the major source of active particles that induce
the formation of clouds, particularly at high temperatures.
In order to properly understand what is proposed by the CLAW hypothesis (and, for that
matter, also by the Gaia research programme as a whole), it is important to bear in mind that
the production of DMS by phytoplanktonic organisms (especially prymnesiophytes and
dinoflagellates) and other organisms of the marine biota, cannot and should not be interpreted
as some act of global altruism, with the alleged purpose of keeping Earth temperature at
adequate values to the survival of all the biota. First, consider that the algae synthesize only
DMSP. The synthesis of DMSP, the precursor compound of DMS, has metabolic costs for the
algae and, thus, in order to explain how the metabolic pathways leading to DMSP synthesis
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Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
evolved, we need to consider benefits for the algae themselves, which should more than
compensate for those costs, indeed increasing the fitness of the organisms exhibiting them. In
these terms, the influence of DMS over the global climate would be just a by-product of
biochemical mechanisms evolved as a consequence of their contribution to the fitness of the
individual algae, despite its overall importance to the rest of the biota.
Accordingly, we have now evidence that DMSP plays at least four roles in algae
physiology: (1) it is a solute that contributes to the cell’s osmotic equilibrium (Vairavamurthy
et al., 1985; Kirst, 1996; Stefels, 2000); (2) it is an antioxidant (Sunda et al., 2002); (3) it is an
inhibitor of cysteine and methionine, by means of an overflow mechanism1 (see Stefels,
2000); and (4) it is a mediator of chemical information involved in interactions with predators
(Steinke et al., 2002; Stefels, 2000; Wolfe et al., 1997). These four physiological functions are
important for the reproductive success of the algae, and, thus, explain why DMSP synthesis
was selected for, and, consequently, DMS came to be released, as a by-product, by the algae,
and could give rise to the feedback mechanisms proposed by the CLAW hypothesis. For a
further discussion about the evolutionary treatment of DMSP metabolism and its implications
to cloud nucleation, within the framework of Gaia, we refer the reader to Hamilton and
Lenton (1998).
We will now move on to discuss how the CLAW hypothesis and the emergence of the
cloud-algae link research area show the scientific status of the Gaia research programme, by
treating them as progressive problemshifts in the sense of Lakatos’ theory of science. But
first, in the next section, we will briefly explain some central ideas of this theory of science.
3. LAKATOS’ THEORY OF SCIENCE AND THE CLAW HYPOTHESIS AS A
PROGRESSIVE PROBLEMSHIFT IN THE GAIA
RESEARCH PROGRAMME2
The methodology of scientific research programmes, developed by the Hungarian
philosopher of science and mathematics Imre Lakatos, represents an important step toward
the goal of philosophy of science to solve – or dissolve – the “demarcation problem”. This is
the problem of how to distinguish science from pseudoscience, following Popper’s
terminology (1974, p. 35). To solve the demarcation problem, according to Popper, we need
to establish a criterion to distinguish, on the one hand, empirical sciences, and, on the other,
mathematics, logics, and metaphysics. In Popper’s view, this problem is the source of almost
all other problems in the theory of knowledge and, by this very reason, is central to
philosophy of science.
1
2
Stefels (2000) proposes the hypothesis that DMSP production is an overflow mechanism for excess reduced
compounds and, indeed, for every energy excess. An overflow mechanism is a reaction of the cell to a
condition of unbalanced growth. Compounds are produced and discarded in order to ensure the continuation of
other metabolic pathways. The continued production of DMSP keeps cysteine and methionine concentrations
at a low level. One advantage of this inhibition of methionine and cysteine is that it allows continued sulphate
assimilation even under nitrogen-limited conditions.
Here, we are following Hacking (1983), who uses “programme” to indicate scientific research programmes as
treated in Lakatos’ theory, rather than “program”, a word with a wider and not a very precise meaning.
Lakatos himself uses the word “programme”.
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 9
Although other philosophers of science have dedicated themselves to the problem of
demarcation, it was Popper who built the argument that the progress of science is
fundamentally based on a rigid strategy or rational method. This is tipically represented by a
set of well defined rules. Grounded on these assumptions, Popper formulates its theory of
science, known as Popperian falsificationism, and his criterion to distinguish science from
non-science, i.e., his demarcation criterion.
Popperian falsificationism, elaborated from such a rationalist perspective, was criticized
by Kuhn (1996) in the context of his own theory of science. Put in simple terms, one reason
that opposes Kuhn to such rationalist thesis is that, for him, other factors, besides the
cognitive ones, play crucial roles in the development of scientific knowledge, or in the
rejection or acceptance of a given theory by scientists. In other words, for Kuhn, it is not only
the relationship between theory and the empirical world that matters to the genesis and
development of scientific knowledge. Other very important factors concern the sociological
and historical aspects of the scientific community and, furthermore, the wider social
community in which scientific practice is embedded. These factors are not, in Kuhn’s view,
adequately taken into account from a Popperian perspective.
Lakatos himself, even though a follower of Popper, recognizes the relevance of this
criticism, but argues that there is more than such a naive perspective in Popper’s writings. For
him, there was a Popper1, a Popper2 and a Popper3, this sequence denoting increasingly
sophisticated versions of the Popperian doctrine. The more sophisticated version was called
by Lakatos (1978) “sophisticated methodological falsificationism”, which was the starting
point of his “methodology of scientific research programmes”.
Just like Popper, Lakatos assumes that scientific change is a rational process. For him,
Kuhn proposes that “scientific change is a kind of religious change” (Lakatos, 1978, p. 9) or
mob psychology. In Lakatos’ view, scientific change must be governed by rules and the
central problem of philosophy of science would be to make explicit the universal conditions
under which a theory can be taken as scientific (Lakatos, 1978). In this sense, Lakatos
rejected the relativist position, according to which there would be no logical universal
criterion to prescribe the decisions made by the scientists on what theory to choose. But,
ironically, Lakatos himself was not able to provide elements for the scientists to judge what
theories to choose. His theory of science was backward-, not forward-looking. In other words,
all Lakatos can offer – as said by his critics (e.g., Feyerabend, 1993) – is a model for
historical rational reconstructions of the past of a given research programme, not clues to
scientists to choose a theory to be accepted henceforth. However, it is possible to argue that
this is not necessarily a flaw of Lakatos’ theory, as Ian Hacking (1983) pointed out and we
will explain later.
It was important for Lakatos to offer a rationalist theory of science, because to judge a
theory based on the number, faith or vocal energy of its partisans was, in his view, to accept
that truth is derived merely from power (Lakatos, 1978). The fact that Lakatos adopted this
perspective was partly derived from his own political experience during the World War II, in
Hungary, where he was chased by the Nazi regime (Larvor, 1998, p. 2).
Lakatos’ theory differs from methodological falsificationist views which are rather naïve,
in the sense that they accept that a single counterevidence could be enough to falsify a theory.
He observed that this was not even a necessary condition for science to grow, because “no
experiment, experimental report, observation statement or well-corroborated low-level
falsifying hypothesis alone can lead to falsification” (Lakatos, 1978, p. 35). According to him,
10 Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
no falsification of a given theory takes place before another, better theory is available. This
means that falsification does not occur only because of a simple relationship between theory
and empirical data. Instead, it occurs because of the confrontation between rival theories,
even when empirical data also plays a role in theory change. In these terms, it is necessary to
the falsification of a theory T the proposition of an alternative theory, T’, which (i) has
exceeding empirical content3 with regard to T; (ii) explains the non-refuted content of T, and
(iii) has at least part of its exceeding content corroborated (Lakatos, 1978, p. 32).
In these terms, theory appraisal should necessarily take into account how theories are
modified during the historical process of their development. Here, we have to appreciate how
Lakatos uses the terms ‘theory’ and ‘research programme’. For this philosopher, a research
programme is a set of interconnected theories, which follow one another. These different
theories are gathered in a single research programme due to a set of shared propositions,
which constitute, in Lakatos’ terms, the hard core of the programme. These propositions
amount to a set of commitments assumed by the scientists working in a given programme,
which should not be rejected or modified for methodological reasons, since they provide the
grounds to the growth of knowledge within that research programme.
Another important notion in Lakatos’ theory of science will be central to our arguments
here, namely, that of a ‘progressive problemshift’. The discovery of improbable facts under
the light of new theories included in a research programme is regarded by Lakatos as a
theoretically progressive problemshift. These facts amount to an exceeding empirical content,
which, when corroborated, at least in part, by research oriented by the programme, leads to an
empirically progressive problemshift. The research programme that shows such progressive
problemshifts is, in turn, regarded as progressive in Lakatos’ theory, and this is what allows
us to demarcate it as scientific. Otherwise, it is a degenerating programme, at risk of losing its
scientific status. This view results from Lakatos’ assumption that the most basic and
important characteristic of scientific knowledge is that it has to grow, and, more than that, it
should be pregnant with the seeds of its own growth.
It is clear from the above account of progressive problemshifts in a research programme
that the corroboration of exceeding empirical content is more important than falsification in
Lakatos’ theory of science (see Lakatos, 1978, p. 36). Furthermore, in this account of science,
verification and falsification of propositions are not important in themselves. Their
importance has to be established, always, with regard to other propositions, which can be bold
or cautious. The verification of a well-supported, cautious scientific proposition or the
falsification of a proposition that is completely new does not contribute to the growth of
knowledge. In turn, the falsification of well-supported propositions and the verification of
bold statements predicting novel facts indeed contribute to the growth of knowledge. In these
cases, the scientific community may be led to abandon well-established knowledge, replacing
it by a potentially more powerful or promising alternative, which may become the new
established scientific content (Chalmers, 1999).
Lakatos gives the concept of ‘heuristic’ a central place in his theory (see Lakatos, 1978,
p. 47), inspired by the works of his mentor and countryman, the mathematician Georg Polya
(Hacking, 1983). Research programmes are characterized in terms of a negative and a
positive heuristic. It is the negative heuristic that determines a hard core, a set of
3
By ‘exceeding empirical content’, Lakatos means that the alternative theory predicts “some novel, hitherto
unexpected fact” (Lakatos, 1978, p. 33).
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 11
proposititions that are accepted by the scientists involved in a research programme as
methodologically unfalsifiable. This methodological decision allows that, on the grounds of a
number of central propositions, a research programme grows, leading to progressive
problemshifts.
To keep the integrity of the hard core of a programme, scientists make changes in a set of
auxiliary hypotheses and observational methods, which Lakatos calls the protective belt. The
protective belt has the function of protecting the hard core, supporting the impact of empirical
tests. As such, it should be adjusted, readjusted and even replaced, when necessary (Lakatos,
1978, p. 48). Indications about how to build, change and develop the protective belt constitute
the positive heuristic of the programme (Lakatos, 1978, p. 50). When the protective belt is
well-developed, there is a greater tendency that its modifications lead to the discovery of
novel facts, contributing to the progress of a research programme, and, thus, to its scientific
status.
As we said above, Lakatos’ theory has been criticized on the grounds that it only looked
backward, not forward. That is, it could offer a historical reconstruction of the past, but not
precise clues for scientists to make decisions about keeping or discarding a given theory. In
our view, this is undoubtedly a problem for Lakatos’ original goal of providing rationalist
criteria for theory change. His methodology of scientific research programmes was simply not
capable of providing such criteria.
But Hacking (1983) offers us a more positive appraisal of Lakatos’ theory, focusing on
what this theory can contribute to our efforts to understand the growth of scientific
knowledge. We agree that this theory can help in such efforts, even though it may not fulfill
Lakatos’ own expectations and intentions. Hacking says that, looking backward, Lakatos
offers an analysis of how we got here; he contributes to our understanding of how we arrived
at a given understanding of the natural world. He adds, indeed, to our understanding of the
very search for objectivity in science, something that can be taken as part of the duty of
philosophy of science. As to theory choice, it has been increasingly accepted in the last three
decades of science studies that it is not an entirely rational process, crucially depending on
sociohistorical circumstances both internal and external to the scientific community.
Here, we make use of Lakatos’ theory of science precisely to build such a retrospective
understanding of how we moved from the problem of the intermediary in the sulphur cycle in
the early 1970s to the CLAW hypothesis, as part of the Gaia research programme, and after to
the current state of knowledge about the relationships between planktonic food web, cloud
formation, and the global climate. The analysis of this movement also allows us to advance a
discussion about the scientific status of Gaia itself.
Since it was proposed, around the end of the 1960s (see Lovelock & Giffin, 1969), Gaia
was harshly criticized by the scientific community. Its scientific status was put into question
(Kirchner, 1989, 1993) and it was even cited as an example of antiscience or pseudoscience
(Postgate, 1988). Since the end of the 1980s and along the 1990s, the Gaia research
programme became more accepted by the scientific community. The increasing acceptance of
Gaia was mainly a result of two important advances – the Daisyworld model (Watson and
Lovelock, 1983; Lenton and Lovelock, 2000) and the CLAW hypothesis. Today, Gaia is
more accepted and indeed offered a substantial contribution to the development of the new
field of Earth System Science (for commentaries on this issue, see Jacobson et al., 2000;
Margulis, 2004; Tickell, 2004; Nunes-Neto, 2008; Carmo et al., in press).
12 Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
The central thesis of the Gaia research programme – its hard core – is the idea that Earth
exhibits a cybernetic system involving the biota and the physicochemical environment in
close interaction. These cybernetic interactions include both positive and negative feedback
loops, and result in a dynamical regulation of some important environmental variables, which
are kept in this manner in a range that makes Earth inhabitable by living beings. In our view,
it is this idea, and not that of a living Earth, the most important, central claim of Gaia (e.g.
Lima-Tavares & El-Hani, 2001; Lima-Tavares, 2002; Nunes-Neto & El-Hani, 2006; NunesNeto, 2008; Guimarães et al., 2008; Carmo et al., in press).
An examination of the CLAW hypothesis and the cloud-algae link research area can
contribute to establish the scientific status of the Gaia research programme. In the context of
Lakatos’ theory, this can be done by showing that this hypothesis amounted to a progressive
problemshift in the understanding of the sulphur cycle, leading to an increase of the empirical
content of Gaia.
Initially, the problem faced in models of the sulphur cycle was: What is the intermediary
chemical compound responsible for the transfer of sulphur from the oceans to the land
surface? To answer this question, it was necessary to elaborate a mechanism of sulphur
transference to continental environments. The assumptions about the role of living beings in
the cycles of chemical elements on Earth, which are an integral part of the Gaia research
programme, underlie Lovelock and colleagues’ approach to this problem. Thus, in 1972,
Lovelock and colleagues advanced the testable hypothesis that DMS was the compound
responsible for transferring sulphur from oceans to land. This proposal was well corroborated
by subsequent studies, as we saw above, and led to the proposition in 1987 of the CLAW
hypothesis, by Charlson and colleagues. This hypothesis not only advanced our understanding
of the sulphur cycle, but also proposed a completely new – and at that time unexpected –
relationship among phytoplankton (and, generally speaking, the marine food web), volatile
compounds of sulphur, clouds, and the global climate. The proposition of this hypothesis
opened up a whole new set of questions to be investigated by scientists from several fields,
such as marine ecology, atmospheric chemistry, climatology, among others. From this
positive heuristic of the Gaia programme, an entirely new research field emerged, the cloudalgae link.
Based on these considerations, we can say that Lovelock and colleagues’ investigations
about the sulphur cycle and, in particular, the CLAW hypothesis show a remarkable
exceeding empirical content. Moreover, it is important to notice that part of this exceeding
content was indeed corroborated, as discussed in section 2. It is quite clear, then, that these
achievements concerning the sulphur cycle can be interpreted as a theoretical and empirical
progressive problemshift in the Gaia research programme, contributing to its scientific status.
4. SOME IMPLICATIONS OF THE CLAW HYPOTHESIS
Lovelock and Rapley (2007), in a recent letter to Nature, proposed a geoengineering
mechanism in order to mitigate the effects of global warming. This mechanism is grounded
on the CLAW hypothesis, since it is related to the contributions of algae to the increase of
atmospheric DMS and CO2 capture. The authors proposed to build a “free-floating or tethered
vertical pipes to increase the mixing of nutrient-rich waters below the thermocline with the
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 13
relatively barren waters at the ocean surface” (Lovelock & Rapley, 2007, p. 403). These pipes
would have to be 100 to 200 meters long, 10 meters in diameter, and would pump the deep
waters to the surface. Since deep waters are richer in nutrients, this pumping would offer an
extra amount of food to the algae. As a consequence, they would release more DMS and this
would lead, in turn, to the production of more clouds. Moreover, the algae would capture
more CO2 from the atmosphere. These activities would contribute, then, to cool the planet.
Indeed, as Jones and Gabric (2006, p. 28) suggested, DMS can be treated, if the CLAW
hypothesis is correct, as a “negative greenhouse gas”. If its atmospheric concentration was
doubled, this might lead to a cooling of the planetary surface in up to 1.3 ºC.
According to Lovelock and Rapley (2007), although there are risks involved in this
geoengineering approach, we need urgently to stimulate the Earth system to regulate its
temperature. In their own words, “the removal of 500 gigatonnes of carbon dioxide from the
air by human endeavour is beyond our current technological capability. If we can’t ‘heal the
planet’ directly, we may be able to help the planet to heal itself” (Lovelock & Rapley, 2007,
p. 403).
Lovelock and Rapley’s letter was commented by Shepherd et al. (2007) in the subsequent
issue of Nature. According to them, the geoengineering approach proposed by Lovelock and
Rapley “… might cause, not cure, problems” (Shepherd et al., 2007, p. 781). Their arguments
are based on previous studies showing that, although some initial increase in the biomass of
producers would happen, this would not lead to the sequestration of carbon into the deep
ocean (below 1,000 meters), which is essential if the carbon dioxide captured is to be isolated
from the atmosphere for centuries or longer. Furthermore, we should notice that, when
phytoplanktonic organisms died, carbon would be released back to the oceans and,
consequently, to the atmosphere through ventilation. After death, the phytoplanktonic
organisms would sink and their captured carbon molecules would be rapidly degraded by
respiration and mostly remineralized within the upper ocean. As a consequence, it is likely,
according to Shepherd et al. (2007), that almost all the CO2 taken up through the increased
algal metabolism would be released back to the atmosphere within a year. Moreover, we
cannot lose from sight that interventions in poorly known ecosystems, such as the marine
ones, could cause great and unforeseen damages, for instance, by changing the trophic
structure in such a manner that the resulting problems could outweigh the potential benefits.
However, interventions in the Earth system such as those proposed by Lovelock and
Rapley (2007) are not the only way to derive contributions from researches on the cloud-algae
link to mitigate the effects of the current climate change. Indeed, a more interesting – and
safer! – contribution should be emphasized. It simply consists in emphasizing the role of life
on Earth, recognizing living beings as central players in the biogeochemical cycles and the
process of climate change. The CLAW hypothesis and the studies developed thenceforth
showed, since the end of 1980s, the great complexity of the biogeochemical cycles. It is also
clear that living beings should not be treated as secondary factors, but, rather, as critical
elements in models about the climate and its changes. Algae, for instance, capture CO2 and
release DMS and O2, quite important substances with regard to the climate dynamics. Models
that do not take in due account the role of the phytoplankton and the other components of the
marine biota in the global dynamics of climate are not only oversimplified models of the
14 Nei Freitas Nunes-Neto, Ricardo Santos do Carmo and Charbel Niño El-Hani
Earth System, but mistaken representations of this very system4. Works recently done on
climate modeling pointed to the importance of adequately incorporating the role of organisms
in the construction of the physicochemical environment (e.g. Iglesias-Rodríguez et al., 2002;
Moore et al., 2004; Iglesias-Rodríguez et al., 2008). As Ayers and Cainey (2007) argue, the
report of the Working Group I of the IPCC (International Panel on Climate Change),
published in February 2007 (see IPCC, 2007), does not take into account the CLAW
hypothesis and neglect the importance of the biological generation of clouds. Nevertheless, it
is clear that both micro- and macro-algae play a key role in the climate system by providing
precursor gases for CCN, without which there would be no clouds (Ayers & Cainey, 2007).
5. CONCLUDING REMARKS
In this chapter, we argued for the importance of investigations about the cloud-algae link
to the understanding of global ecological processes, such as the biogeochemical cycles and
climate changes. The CLAW hypothesis and the cloud-algae link research area offer
important lessons to the current science of climate change. Based on Lakatos’ theory of
science, we argued that this hypothesis amounts to a progressive problemshift in the Gaia
scientific research program. The CLAW hypothesis offers a systemic approach of global
phenomena and has become part of the scientific conventional knowledge in what is known
today as ‘Earth System Science’ (Kump et al., 1999; Jacobson et al., 2000). In the face of the
current environmental crisis, such an approach is indispensable, since climate changes are not
spatially localized, but are both affected by and affect the entire Earth system.
Many of the sociopolitical actions related to the issue of climate change are based on
models that need to consider the role of living systems in the construction of the
physicochemical environment. This role has already been recognized in the study of the
biogeochemical cycles, but has not been adequately incorporated into the modeling of the
planetary climate up to the present. The CLAW hypothesis and the cloud-algae link research
area contribute to fulfill this requirement, since they address the interconnections among
living and non-living components in the sulphur and water cycles.
Moreover, we should point here to another very important contribution of the CLAW
hypothesis to the construction of scientific knowledge, namely, that it offers a good example
of successful integration of biological subdisciplines related to ecological systems, such as
marine ecology, biogeochemistry, evolutionary biology, and cell physiology. This is indeed
one of the main goals assumed by contemporary ecologists and philosophers of ecology.
Moreover, the scientific trend resulting from the proposition of the CLAW hypothesis led to
even greater integration of scientific knowledge, since it involved not only fields of biology,
but also other scientific disciplines, such as atmospheric chemistry, geophysics, climatology,
etc.
Greater integration in science is a sine qua non condition to deal effectively with complex
problems such as global warming. Disciplinary science has made its contribution to provide
4
In different degrees, all models are, of course, simplified representations of some system. However, the point here
has to do with the degree in which some crucial elements are adequately incorporated into the model. What we
have in view here is the question of the significance of the models to the generation of reliable scientific
knowledge and sound sociopolitical decisions based on this knowledge.
Relationships between Marine Phytoplankton, Dimethylsulphide and the Climate… 15
us with explanations about the natural phenomena relevant to the understanding of the climate
crisis, but it is clear that this is not enough in the current state of affairs.
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