According to a recent research, mapping tree density at the global level, there are 3.04 trillion trees covering 87% of ice-free land on Earth, with a ration of trees-to-people of 422:1. The mainstream opinion about climate change claims that the vegetation on the planet has been reduced by human activity and it is true that since the beginning of human civilisation around 45.8% of trees have fallen with 15.3 billion of trees cut for a total area of 192000 km2 every year.  However, surprisingly, the scientific findings reveal that there is an ongoing opposite trend defined global greening.

It is a gradual but large increase in trees and leaves on plants, particularly significant in northern extratropical land surface, which in the last 35 years covered an area equivalent to 2 times continental United States. Natural forces and internal climate variability are not enough to explain such a huge phenomenon. Conversely, the research carried out by T. W. Crowther, H. B. Glick and M. A. Bradford showed that it can rigorously be attributed with high statistical confidence to anthropogenic forcing. More specifically, 70% of it depends on the atmospheric concentration of greenhouses gas, 9% to nitrogen deposition and the remaining to other causes like rural to urban migration transforming abandoned lands in efficient industrial-scale agriculture or in marginal green areas, the green revolution spreading ecological techniques, and the regulated reduction of deforestation.

As the first cause is concerned, many studies investigated the so-called CO2 fertilisation determining human-induced greening. It is estimated that every year 10 billions of carbon emitted remains in the atmosphere and it promotes photosynthesis spurring plants and leaves growth. This peculiar fertilising effect begins with enhanced photosynthetic CO2 fixation, where non-structural carbohydrates, such as starch, soluble carbohydrates and polyfructosans, tend to accumulate in leaves and in other organs. Then, in the process of growth, photoassimilates are allocated to the vegetative shoots, root system or reproductive organs, but in some cases, more photoassimilate of CO2-enriched plants is partitioned to the root system than to the shoots. Above ground, more photoassimilate usually goes into stems and supporting structures than into leaves. This phenomenon may not be an inherent response to elevated CO2, but may be a by-product of the larger size of plants often found in CO2-enriched atmospheres, especially by species that produce branch stems along the aerial mainstems (Allen et al., 1991). As a result, reproductive biomass and vegetative biomass growth are induced by elevated CO2 concentration and produce the global greening effect.

1. Selection of plants that can better utilize carbohydrates produced with elevated CO2 concentration;
2. . Selection of plants producing less structural matter and more reproductive capacity under CO2 enrichment;
3. Search for germplasms that are adapted to higher temperatures to improve flowering and seed set;
4. Optimise planting periods and other crop management procedures under new climatic conditions;
5. Select species that have more stable production under high temperatures or drought;
6. Where needed or possible, develop irrigation systems for crops.