# Isoprene Emissions, Oxidation Chemistry and Environmental Impacts
## 7 Deforestation and Reforestation and Their Environmental Impacts  
Deforestation has increased over time due to the pressure of population growth, which can have a significant impact on isoprene emissions. The world's temperate zones experienced high rates of deforestation throughout the nineteenth and twentieth centuries; however, in contrast, the tropics did not see deforestation on this scale until after 1950. Rates of deforestation in the tropics reached 12 million hectares per year in the 1990s [165], before beginning to slow slightly in the twenty-first century. The overall rate of deforestation in the tropics is still approximately 9 million hectares per year, with the exception being in Amazonia, where deforestation rates have declined by nearly 80% since a peak in 2004, and an increase in planted forests (reforestation) is helping to offset the overall rate of deforestation. [PERSON] et al. [166] showed that the simulated global deforestation can reduce isoprene emissions by 87%: most of the reduction in emissions (72%) is occurring from tropical deforestation. There has been an increasing amount of evidence to support observations that show that, in temperate and tropical regions, the surfaces of forests are cooler than grasslands and croplands in these regions. A recent analysis, carried out by [PERSON] and [PERSON] [167] identified that the cooling effect on surface temperature in temperate forests also, albeit to a lesser extent, cools the air. Cooling was found to be of the order of 0.5 to 1 \({}^{\circ}\)C at the annual timescale, and, during the daytime growing season periods, a significantly greater effect was observed, with cooling between 2 and 3 \({}^{\circ}\)C.  
Land cover and temperature have long been theoretically linked, which is recognized and incorporated into climate models [168; 169; 170]. Deforestation often causes increased atmospheric CO\({}_{2}\), which results in a positive radiative effect on the climate (i.e., the climate warms). However, forests are darker in color than grass or croplands, and so their albedo (the reflectivity of the land surface) is increased with deforestation, thus producing a negative radiative effect [166]. Overall, the balance of these impacts tends to mean that the climates of tropical forests are warmed by deforestation, whereas forests at high latitudes are cooled [171; 172; 173]. In the tropics, this can be explained by relatively large evapotranspiration [174], whilst in temperate regions, albedo-driven warming is outweighed by the combined surface temperature-reducing effects of evaporative cooling and emitted longwave radiation [175]. Models by [PERSON] et al. [166] looked at the effects of complete global deforestation and found that this could lead to a net global warming of 0.8 \({}^{\circ}\)C after 100 years. In their simple scenarios, tropical deforestation contributed 0.6 \({}^{\circ}\)C to this warming; however, boreal deforestation cooled the climate by around 0.3 \({}^{\circ}\)C. In addition, deforestation can reduce ozone and SOA formation, as the loss of vegetation results in lower isoprene and other biogenic VOC emissions and can contribute to global warming. [PERSON] et al. [166] also investigated the effect of reduced isoprene emissions on SOA and found the reduction of SOA production by 91%, with the majority of this global reduction being accounted for by tropical deforestation accounted (80%). The paper published by [PERSON] et al. [176] estimated that by 2050, the global potential canopy cover (where \"canopy cover\" refers to an area of land that is covered by tree crown vertically projected to the ground) could shrink by as much as 223 million hectares. The majority of this loss is projected to occur in the tropics. The study also stated how over 50% of global reforestation potential could be found in just 6 countries: Russia, the UnitedStates, Canada, Australia, Brazil, and China. Under the current climate, [PERSON] et al. [176] estimated that in total, 4.4 billion hectares of canopy cover could be supported on land.