London (CNN Business) Airlines ordered tens of billions of dollars worth of new aircraft from Airbus and Boeing at the Paris Air Show this week. But there was also huge interest in the planes of tomorrow.

The rise of hybrid and electric aircraft was on full display at the biannual aviation showcase , where startups competed with industry giants to show off technology that's more efficient and better for the environment than traditional designs.

The focus on electrically-propelled aircraft reflects a rush to develop urban flying taxis (coming soon) and longer range fully electric planes (coming later).

According to the consultancy Roland Berger, the number of electric aircraft in development increased by roughly 50% over the past year to 170. The number could swell to 200 by the end of 2019.

There are two big factors driving increased investment: The global aviation industry produces up to 3% of all carbon dioxide (CO2) emissions, a share that's projected to increase sharply in coming years; and it spends roughly $180 billion a year on jet fuel.

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