It's easy to believe that humankind's earliest cities existed sustainably within the natural ecosystem, unlike modern megalopolises, fed and sustained by vast tracts of farm land and a global economy. But, as a team of researchers studying the ancient city of Akko found out, human cities have been radically transforming the environment since at least 6,000 years ago.

Writing for Nature's Scientific Reports, a team led by David Kaniewski showed that the development of Akko, a port city along what is now Israel's northern shores, coincided with a collapse of the local ecosystem, with dense coastal forests transforming into a dry, shrubby grassland. In their paper, the scientists describe how the growth of Akko, one of the world's oldest cities, reshaped the local environment:

The city rapidly developed with ramparts, buildings and industrial areas. The anchorage, in connection with the Na’aman River fluvial system, was the focus of the economy and trade, and the main driver behind urban population growth. The spatial concentration of agricultural, industrial and commercial activities led to increased demands on local ecosystems, and to an encroachment on and a loss of natural biotopes in and around the tell. Fragmented proto-urban ecosystems only persisted as small patches within a matrix of urban and agricultural expansion, or even disappeared. … Accelerated population growth since 4000 [before present] and unsustainable development generated by socio-economic demands dramatically increased water needs. Higher water uptake from watercourses and water tables, associated with the intentional or unintentional anthropogenic pressures on the fertile alluvial plains of the Na’aman River, the main source of freshwater at Akko, may further explain the expansion of an urban-adapted shrub-steppe.

Ancient peoples' overuse of the local water supply made the local plant life less able to withstand shocks, like dry years, and not long after humans' arrival at Akko the coastal forest disappeared, permanently, in favor of a grassland.

On top of those changes, the construction of the city itself caused shifts in the local climate. Through what's known as the “urban heat island” effect, the city became slightly warmer than the neighboring countryside—a climate dynamic that affects cities today, though on a much larger scale. The changes in temperature, coupled with the changes in water availability, further spurred the collapse of the coastal forests.

Now, the extent of the changes to the local ecosystem because of early human cities like Akko pales in comparison to the global effects of modern civilizations. But, when viewed in the proper context, says Liviu Giosan, a scientist who edited a recent book on the subject of ancient climate change, the differences seem less stark:

I think “the world” was defined very differently for ancient civilizations. The world, if we look at the ancient Greeks, ended in the Mediterranean. For the Egyptians, it was largely around the Nile. If we look at their definition and adopt their point of view, their world was as affected as ours by what they did.

Kaniewski and his team's work at Akko isn't the first evidence of ancient humans' effect on the ecosystem, or on the climate. But as evidence on the subject grows, say Kaniewski and his colleagues, it forces us to rethink our idyllic understanding of ancient peoples, and of what we can expect from our cities:

This questions the long-held belief of a ‘‘golden age’’ of sustainable early urban development. The same mechanisms that degrade or overexploit the ecosystems nowadays were already at work, even if technologies and agroinnovations were markedly different during the pre-industrial era. Accepting large urban concentrations might need to concede an intrinsic impossibility to produce locally sustainable development.

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