In February this year, the Oscar award for the best documentary film went to An Inconvenient Truth. The film was based on a lecture by former US Vice President Al Gore on the perils of global warming and is already the third-highest grossing documentary ever. It is to be hoped that the message within reaches an ever wider international audience. Seen as a complex statement, the title of the film has relevance in all walks of life, including research in plant science on the impacts of global change. Increasing concentrations of CO2 in the atmosphere can drive complex changes in climate beyond the undesired warming potential of CO2 itself. However, an inconvenient truth is that, in experiments, increasing concentrations of CO2 are generally beneficial for plant growth, although with quite some variation among species and experimental designs (Körner, 2006). The simple plant perspective is that more CO2 increases photosynthesis and reduces water loss, a double benefit (Ainsworth & Long, 2005), but with novel changes in CO2-dependent gene expression still to be investigated in depth (Taylor et al., 2005). Further, CO2 enrichment can reduce the impact of the pollutant tropospheric ozone (O3) on plant productivity (King et al., 2005; Ashmore et al., 2006; Morgan et al., 2006), resulting in unique changes in gene expression that are found only when plants are exposed jointly to O3 and CO2 (Gupta et al., 2005). These experimental results clearly indicate a productivity benefit of rising CO2 concentrations. Evidence that this is occurring naturally is less easy to obtain or to attribute unequivocally to rising CO2. However, some long-term analyses of tree growth (Soulé & Knapp, 2006) show greater growth in the latter half of the 20th century, when CO2 was rising most quickly. The growth responses also tended to be greater during drier years, as expected from CO2 enrichment experiments, but it is inconvenient that these changes can not be ascribed with certainty to rising concentrations of CO2 concentration. Research on the influence of global change on plants growing in the field is dominated by the impacts of CO2 enrichment, with the most natural conditions being present within Free Air CO2 Enrichment designs. Unfortunately it is inconvenient to enrich plants to the gradual rate of increase of CO2 observed in the atmosphere – that is the other human-controlled experiment that controlled systems are trying to predict. Instead, plants are treated to a step change in CO2 concentration, probably no problem for plants starting from seeds, but a likely and unknown problem for existing plants, particularly those that are long-lived, where the persistence of pretreatment effects is poorly understood. Assessment of the impact of CO2 enrichment on vegetation succession would be a natural way to identify the manner in which observed species-specific responses influence community composition, but few studies have adopted this approach (Dijkstra et al., 2002). The problems of securing long-term funding are a bothersome limitation to a more general application of such an approach. The future survival of plant species is unlikely to be dominated by rising concentrations of CO2 directly but rather by the negative impacts of climatic change, such as reductions in precipitation and extremes of temperature, where the beneficial effects of CO2 enrichment may be less. Projections of the future changes, generally reductions of plant biodiversity, are based on models that are only concerned with changes in climate (Thomas et al., 2004). Any inconvenient impacts of CO2 enrichment are not considered, although CO2 experiments often demonstrate species-specific responses to CO2, not only by higher plants (Körner, 2006) but also by mycorrhizal mutualists in the soil (Alberton et al., 2005). The many model simulations that address the impacts of changing temperature on vegetation are in direct contrast to a very small number of field-based warming experiments (Musil et al., 2005). Warming vegetation is difficult and inconvenient but necessary to understand the range of future species responses that may well be latitude or location specific. There is a troublesome distance between practical experiments and the need to understand and predict the future responses of plants in the field. This has not prevented brave attempts to use empirical understanding within simulation models to predict future scenarios for plants in uncharted environmental conditions. However, models most generally agree closely in their simulations of the carbon and water cycles up to the present day but then begin to differ increasingly into the future (Cramer et al., 2001). It is an inconvenient truth that such uncertainty needs to be assimilated in some way (Midgley & Thuiller, 2005) for those policy makers that have the capacity to influence emission controls, but it's difficult.