B.L. Batten
an area (including territorial seas) of roughly 377,000 square kilometers, slightly less than the
U.S. state of Montana. Japan is located on the Pacific Ring of Fire at the juncture of several tec-
tonic plates and is thus prone to volcanic eruptions, earthquakes, and tsunami. Topography is
rugged and mountainous except where rivers flow into the ocean; most of the larger plains are
located on the Pacific (east) side of Honshu. Climate ranges from subarctic in the north to sub-
tropical in the south but is temperate in most parts of the archipelago, with four distinct seasons.
Climate is strongly affected by ocean currents such as the warm Kuroshio (Black Current or Jap-
anese Current), flowing from the south, and the cold Oyashio (Parent or Okhotsk Current),
flowing from the north. Another factor is the East Asian monsoon, which brings rain in early
summer. Typhoons are common in the fall. Mineral resources, formerly abundant, are today
largely exhausted. The islands are heavily forested (mainly with broadleaf trees in the south and
conifers further north), and marine resources such as fish are also abundant.
Viewed in the fullness of time, few of these geographical facts are set in stone (so to speak).
The archipelago itself did not exist before 15 million years ago, when it detached from the Asian
continent.^4 Since then, the shape of the islands, the climatic conditions they experience, and their
resource endowments have changed, and continue to change.^5 Some of these changes, particu-
larly in recent centuries, are anthropogenic, but over the long term most are of natural origin.
Here I will not attempt a comprehensive account but will focus on one specific issue: climate
change. There are three reasons. First, climate change is one of the important causes of other
observed changes in Japan’s natural environment, for example rising or falling sea levels or
changes in flora and fauna.^6 Second, climate change operates on a scale that is relevant to human
history. Climate following the end of the Ice Age has been generally stable, but there have been
many short- term (annual to decadal) fluctuations, as well as some longer- term (centennial) ones,
most notably the Little Ice Age of the sixteenth through mid- nineteenth centuries. Third,
research on past climate change is of intrinsic interest and importance for the light it may cast on
contemporary issues.
The reconstruction of past climates is an important and growing field of study in Japan as
elsewhere. Reconstructions fall into two major categories: those based on written records and
those based on physical evidence. Research of both kinds tends to focus on the Little Ice Age,
which falls outside the scope of this book (although I will touch upon it again). Nevertheless, a
number of studies extend to earlier times.^7
For whatever reason, Japanese people from ancient times have shown great interest in weather
and the seasons, which as a result figure prominently in diaries and other historical sources.^8
Courtier diaries, for example, contain records of cherry- blossom viewing parties held each year
in Kyoto when the trees achieved full bloom. The dates vary somewhat from year to year, reflect-
ing variations in mean temperature in early spring. This data has been mined by many scholars,
most notably Aono Yasuyuki, who has published temperature reconstructions for Kyoto going
back to the ninth century.^9 Another example of the use of written records concerns winter freez-
ing dates of Lake Suwa in Nagano prefecture in the mountains of central Honshu. Mikami Take-
hiko and his colleagues used records of freezing kept by Suwa Shrine to calculate mean winter
temperatures going back to 1444.^10
The other type of reconstruction makes use of physical evidence or “proxies.” One such
proxy is pollen. Perhaps the best known pollen- based study is that by Sakaguchi Yutaka, who
analyzed a peat column collected at Ozegahara Moor in the mountains of Gunma prefecture.^11
The analysis centered on the relative frequency of pollen from two species of pine, one favoring
colder growing conditions than the other. As a result, Sakaguchi was able to construct a temper-
ature curve extending back approximately 8,000 years. Tree rings, typically of Japanese cedar
(Cryptomeria japonica; sugi) and cypress (Chamaecypress obscura; hinoki), are another popular object