Take these Wikipedia statements:
"Historical geography is the study of the human, physical, fictional, theoretical, and 'real' geographies of the past"
"Environmental history can be divided into three key components... First, nature itself and its change through time... Second, how we use nature... Thirdly, how we think about nature"
"Historical geography studies a wide variety of topics. A common theme is the study of the geographies of the past and how a place or region changes through time"
"Environmental history, a relatively new branch of historiography, is the study of human interaction with the natural world over time"In reading these definitions over, I get somewhat lost and confused, but that's only because I have a tendency to want to build barriers around these 'fields' and differentiate them from one another - a tendency I imagine is shared by many in the modern academy who feel a need to systematize and categorize different forms of inquiry into disciplines, fields, subfields, schools of thought, etc.
"Historical geography seeks to determine how cultural features of various societies across the planet emerged and evolved, by understanding their interaction with their local environment and surroundings"
"Environmental history is history written with the acknowledgment that we shape our environment and it shapes us. Environmental historians maintain that as nature is a key influence on human affairs then it is both an appropriate and necessary subject for historical analysis"
However, arguably there is no real substantive difference in these two 'fields', aside from their name and perhaps the way their practitioners may refer to themselves. The reason why they are so similar is because they are both broadly focused on similar types of questions regarding both space and time. More particularly, the interest in space, in both of these fields, is particularly focused on the relationship of/between humans and nature, or as some would call it, 'society-nature relations'. In other words, for the most part, environmental historians and historical geographers share a similar approach. This doesn't mean that they hold the same presuppositions, but rather than the plane of focus upon which they presuppose questions of reality lies in a similar area.
Take, for example, the presuppositional level of ontology, as Harrison and Livingstone (1980) would call it. This is a level of presupposition at which theorists presuppose answers to questions on the character of reality. The point I am trying to make is that both environmental historians and historical geographers, in sharing a similar approach, tend to be attempting to answer the same types of questions (at an implicit level of cognition). The question might be something like "What is the real character of society-nature relations?"
While the question may be similar, the answers are quite diverse. Luckily, the introduction to Noel Castree and Bruce Braun's Social Nature is particularly helpful in characterizing three different types of answers to this question. In other words, Castree and Braun provide three types of ontological presuppositions regarding the reality of society-nature relations. They refer to these three perspectives as the 'people and environment', the 'ecocentric', and the 'social' approaches. The key word in the dominant 'people and environment' approach is the joiner 'and' - characterizing the interpreted disjuncture seen between humans and nature. This approach tends to equate nature with 'environmental problems', thereby often advocating technocratic solutions based in the 'management' of resources and ecological systems. The other two ontologies find fault with the 'people and environment' approach because it fails to incorporate the social processes and structures that have transformed nature itself. The dominant ontology thus "leads to policy geared to ameliorating environmental problems without ever addressing the deeper causes responsible for those problems in the first place" (3), suggests Castree (revealing his own allegiance to the 'social' approach).
In contrast, the 'ecocentric' approach offers a nature-first ontology wherein the environment is an overarching system of which humans are merely a small part (though admittedly with a large impact). A exemplary author of the ecocentric approach is James Lovelock (who came up with the Gaia hypothesis).
Finally, the 'social' approach, which Castree notes is becoming increasingly popular with critical human geographers, sees nature as inescapably social: "Nature is defined, delimited, and even physically reconstituted by different societies, often in order to serve specific, and usually dominant, social interests. In other words, the social and the natural are seen to intertwine in ways that make their separation - in either thought or practice - impossible" (3). Thus, drawing from Castree it is possible to typify three distinct categories of ontological presupposition that affect how a social scientist will interpret the reality of society-nature relations.
It is no wonder, then, that environmental historians and historical geographers seem to easily fade into the same crowd; while their methods, theoretical beliefs and ideological biases and presuppositions about reality may differ, the focus of interest upon which they make presuppositions in the first place is a shared space.