Australian cities with a high biogenic influence will see higher pollution levels in a warmer climate. We show that four Eucalyptus species grown in future-climate conditions can emit isoprene at temperatures 9 K above the peak temperatures capping isoprene in biogenic-emission models. With these measurements, we predict up to 2 ppb increases in isoprene in 2050, causing up to 21 ppb of ozone and 0.4 µg m⁻³ of aerosol in Sydney. The ozone increase is one-fifth of the hourly air quality limit.