Externalities have a long history in economics. The concept has always been a somewhat slippery and controversial, but remains an important analytical tool for discussing market failures and government intervention [0].
The prospect of ecological collapse has drawn a lot of attention to the idea of negative externalities, but it's worth mentioning that positive externalities are also important in economic theory. For example, positive externalities to knowledge creation have been modeled as the engine of long-term growth by endogenous growth theorists since the 1980s (starting with Paul Romer and Robert Lucas), based on precursory work from the 1960s (e.g. Kenneth Arrow and Hirofumi Uzawa), and ideas reaching-at least-back to the work of Alfred Marshall in the late 19th c.
Still, let's hope that the global economic order doesn't depend on what economists are doing in their models :)