The slippery concept of 'climate'

Reproduction of Johannes de Sacrobosco's zonal world map of 1230 

Warren Pearce has an interesting post over at the Making Science Public blog (see here) in which he explores the debate over the attribution of specific extreme weather events to climate change. He argues that when it comes to events like Hurricane Sandy, public and media discourse about links to climate change can quickly depart from the scientific line. While climate scientists prefer to say 'we can't attribute it directly to climate change, but it is consistent with the patterns we expect', some media outlets opt for the Bloomberg approach: 'it's global warming, stupid!'

Pearce also reports how internet interest in climate change peaked in the aftermath of Hurricane Sandy, suggesting that people were taking to the web to find their own answer to that quite profound ontological question: 'is the weather outside my window caused by humans, or not?'

Part of this debate revolves around the question of what distinguishes weather from climate. The regular back-and-forths of the blogosphere on this very question suggest that the majority of commentators are quite confident in their own understanding of the distinction. However, prompted by Pearce's post, I was decided to go and take another look at a great article published by Matthias Heymann in WIREs Climate Change in 2010 (see here).

Heymann presents a conceptual history of 'climate', from Ancient Greek philosophers to present-day Earth System modellers. His main thesis is that climate has always been a slippery term, with different understandings existing within different groups at any one time, within a history punctuated by radical conceptual shifts and ruptures. Heymann argues that "probably never in human history a single and universal understanding of climate existed" (p593).

Michel Foucault drew on Gaston Bachelard to describe the kind of epistemological thresholds evident in the history of climate: "they suspend the continuous accumulation of knowledge, interrupt its slow development, and force it to enter a new time, cut it off from its empirical origin and its original motivations, cleanse it of its imaginary complicities" (Archaeology of Knowledge, p4). Bachelard's focus on ruptures and breaks in the history of the sciences would go on to heavily influence Thomas Kuhn's notion of a 'paradigm shift'.

Among the most interesting shifts described by Heymann is the changing spatiality of the concept of climate. For Erathosthenes, climate meant a narrow strip of land defined by the angle of inclination to the sun. In contrast to this 'geographical climatology', Hippocrates adopted a 'causal climatology' which linked the dominant weather of a location to the character and health of its inhabitants (a precursor of the environmental determinism espoused in the early 20th century by people such as Ellsworth Huntingdon).

Humboldt's isotherms. From http://www.mappingthoreaucountry.org/maps/alexander-von-humboldt/

During the Enlightenment era, such deterministic thinking could mostly be observed in political philosophy, while the nascent meteorological sciences  - cleansed of these 'imaginary complicities' with academic racism - engaged themselves with weather observations at fixed points in space. Alexander von Humboldt continued this focus on place-based climate, but with some quite expansive additions. He defined climate as "all the changes in the atmosphere which noticeably affect the human organs". In this formulation, Humboldt maintains a locational logic but binds it to human experience. We can detect the emergence of the kind of holism which characterises much recent thinking, and Humboldt's studies also developed the tendency to search for universal laws. An interest in location was therefore supplemented with a drive for spatial synthesis.

Fast-forwarding to the 20th century, we can observe one of climate's most radical conceptual breaks. In the first half of the century, climatology existed very much as a geographical science. Men like Hann and Köppen pursued quantitative studies of climatic regions or zones, and established the language of the "polar climate", "sub-tropical climate" and so on. However, the emergence of dynamic meteorology - spurred on by Bjerknes' insistence that all meteorological process could be described by a few parameters and differential equations - quite radically altered the concept of climate.

From: http://koeppen-geiger.vu-wien.ac.at/present.htm

The climate became a system; a globe-spanning set of physical mechanisms which could be mathematically described, calculated and - with the later emergence of the computer - predicted. Norman Phillips' experiments with a simplified weather model in the 1950s paved the way for the general circulation models (GCMs) and earth system models (ESMs) which would eventually come to dominate the climate change debate. These models simulate not only meteorological phenomena, but also link the atmosphere to the biosphere, the geosphere, the cryosphere and so on, emphasising the beguiling interconnectedness of such physical systems (for a great history of these developments, see Paul Edwards' A Vast Machine).

The rise of dynamic meteorology and computational climatology saw the spatial relations of earlier conceptions fade into the background of scientific interest, as the temporal pattern of global climatic change became the research priority. I find it interesting how the spatial and temporal aspects of climate have come in and out of focus during the history of the atmospheric sciences, and I think some current debates point towards possible new shifts in conception and comprehension.

The furore about extreme weather event attribution brings climate back 'down to earth' with a renewed spatial logic which challenges the global framing of climate found in GCMs and ESMs. The climate of the latter is one of synthetic spatial averages and temporal trends, which doesn't sit comfortably with questions about human experiences at particular points in space. It's almost like two epistemes (in Foucault's sense of the term) are sitting side-by-side, with different rules of what constitutes an acceptable scientific statement.

The questions go beyond epistemology however. Mike Hulme, Saffron O'Neill and Suraje Dessai recently countered arguments made by a number of prominent climate modellers, who suggested that models could be used to help determine which extreme events had been caused or enhanced by climate change, thereby aiding the distribution of international funding for climate adaptation. Hulme et al. (see their piece in Science here) countered that this would be an unproductive effort to depoliticize an inherently political debate about societal vulnerability to meteorological hazards. They stress that funding and assistance is required by those regions with high levels of vulnerability to meteorological hazards of all kinds, rather than just those regions where hazards are most attributable to human actions.

What is at stake here is whether we choose to try and live with the elements of a climate which represent a departure from a pre-industrial, pristine state, or whether we embrace the ineradicable hybridity and ambiguity of a climate influenced by human actions in a way which transcends our abilities to reasonably categorise, predict and control*. These are ontological and epistemological questions; about where we draw the line between 'human' and 'natural', 'climate' and 'weather', and about how we integrate the spatial and temporal ambiguities of the environment into our political decision making.

An interesting shift has taken place: despite the detour into climatic globalism, the notion of 'region' has again come to the fore. Regional climate models (RCMs) do not perform universally well in all areas of the globe, thus limiting their use in global political mechanisms to distribute funds to those areas most impacted by human-induced climate change. RCMs have nonetheless gained great prominence in nation-state government efforts to know and manage the impacts of climate change on their own territories (I wrote an earlier post on this here). Heymann's historical tour stops at the emergence of comprehensive GCMs and ESMs, but maybe the spatial relations of 'climate' are again undergoing transformation. Regions, points and spatial distributions have become key epistemic objects in the struggles over the risks of and responsibilities for climate change, while the distinction between weather and climate has once again blurred; an artefact perhaps of a scientific episteme not wholly suited to the new hybridity of the atmosphere.


*Such ambiguities are also evident in the conceptual history of 'climate change'. For example, the Intergovernmental Panel on Climate Change defines climate change as any change in climate over time, whatever the cause. The UN Framework Convention of Climate Change by contrast defines climate change as  "a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods" (Article 1).