Human activity causes global vegetation variation

Deforestation
...if you look at the spatial distribution as it appears on our map, you will clearly see that in certain areas, the human impact is much larger than the climatic influence.
Prof Dr Michael Schaepman
Human activity is responsible for more than a third of the changes in vegetation that have occurred over the last 30 years, a new study has revealed. An interdisciplinary team of geographers, headed by academics from the University of Zurich (UZH), has used computer models to illustrate the separate influences of human activity and climate variability on our planet’s vegetation. The scientists hope that their results will settle – once and for all – arguments over whether or not human activity is having a significant impact on the Earth’s vegetal makeup.

The team’s findings show that whilst climatological factors are responsible for over half of the changes that have taken place during the last three decades, human activity has caused more than 30 per cent of the observed variations. Around 10 per cent of changes could not be fully explained by either hypothesis, leading researchers to speculate that this portion is most likely the result of unknown human-climate interactions.

Seasonal vegetal trends are governed by our planet’s climate, but the climate is influenced by human activity. Whilst our overall influence on the Earth’s vegetation is thought to comprise around a third of the total impact, the effects of human activity are much more pronounced in some regions than they are in others.

Prof Dr Michael Schaepman, Head of the University of Zurich’s Remote Sensing Laboratories (RSL), told ScienceOmega.com that he and his colleagues had initially expected the human contribution to be higher.

Human impact lower than expected


"When we began our study, we actually expected the impact of human activity to comprise a larger share of the total," he said. "While refining our model, however, we realised that climatic variability was responsible for the highest proportion of vegetation changes. Of course, if you look at the spatial distribution as it appears on our map, you will clearly see that in certain areas, the human impact is much larger than the climatic influence."

Vegetation map
The above map, which was developed by RSL researchers, illustrates the relative contribution of climatic effects (in green) and other effects (in purple)
Analyses have revealed that since the early 1980s, vegetation activity has primarily declined to the south of Africa’s Sahal region – across countries such as Tanzania, Zimbabwe and the Democratic Republic of Congo. Although the Zurich-led study did not identify the specific activities that are responsible for such land degradation, Professor Schaepman was willing to proffer examples of the sorts of behaviour that might be contributing to the decline.

"Globally, we have seen significant changes in agricultural policy," he explained. "Pristine – or primary – forests are being changed into secondary types of vegetation. Typically, we are talking about palm oil plantations and similar operations. Urban sprawl is also a consideration: the expansion of megacities has intensified. In some areas, significant emphasis has been placed on the generation of biomass, and in other regions, logging activities have increased. Activities such as these appear to have contributed to a pronounced decline in vegetation throughout certain geographic locations."

It is well known that the vegetal makeup of the Earth’s surface is in a state of constant change. However, there have been arguments over the extent to which human activity is responsible for this alteration. In order to obtain concrete evidence to advance the debate, Professor Schaepman and his colleagues developed a system capable of differentiating between the vegetation changes caused by human action, and those that have resulted from climatic factors.

"We began by employing a measure known as the Normalised Difference Vegetation Index (NDVI)," he said. "Put simply, the NDVI identifies trends in greening and browning. The question then becomes: ‘How many of these changes can be explained by climatology?’ Essentially, we start by trying to explain everything from a climatological perspective. From here, we can calculate how many of the unexplained changes have been caused by human activity."

The model suggests that 54 per cent of the changes in global vegetation that have occurred during the last 30 years have been caused by climatological factors. 36 per cent are thought to have been human driven and approximately 10 per cent remain unaccounted for.

'Conclusive'


"The evidence is conclusive," Professor Schaepman commented. "We can confidently state that human activity is having a pronounced impact on vegetation. However, our research used a one-dimensional measure – greenness – yet the changes have resulted from a whole host of influencing factors. The next interesting step, therefore, would be to investigate the specific activities that lie behind particular variations. At present, we are unable to provide the exact reasons behind individual changes in vegetation."

I ended our interview by asking whether the information collected during the course of the study might be used to predict how the constitution our planet’s vegetation will alter over the coming decades.

"The model that we have developed is climatologically driven," Professor Schaepman concluded. "Our study is purely retrospective: the data runs from 1981 to the present. Let’s say that we wanted to implement a new model capable of forecasting. It would need to define how overall human activity is likely to change in the future. There are models that are trying to do this. However, there is much dispute over how best to integrate future human activities within climate scenarios. We have never tried to do anything like to this with our model. There are at least 70 types of documented ground degradation; our one-dimensional data would be insufficient to identify all of the effects that are at play. However, this focus could provide the basis for some extremely interesting research in the future."

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Governments need to stop pandering to the energy demand. We need to reduce our consumption. Even if energy is green the waste product is still heat, so we'll always be contributing to global warming.


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