August 2003 gave a possible taste of likely effects, with present day emissions. The high temperatures and stagnant air led to a serious photochemical smog episode, with elevated concentrations of both ozone and PM. Excess deaths during this short period in the UK were ~ 2000, of which about one third were cause by poor air quality, the rest by the more direct effects of elevated temperature. Under the anticyclonic conditions experienced, the VOCs and NOx required for smog formation were transported from the continent, but there was an additional source of the elevated ozone. Vegetation emits isoprene which had a very short lifetime of only ~ 20 minutes under the conditions that applied and so travelled only short distances from its sources in the still air (wind speed ~ 1 m s-1).