Greening Our World

Over the last twenty years, the planet has become greener with China and India leading the way. Data courtesy of NASA Earth Observatory.

We’re so used to seeing headlines about humans destroying the rainforests, swaths of deforestation and our activities affecting the climate; seeing a report suggesting we are making the planet the greener caught our attention.

China and India lead in greening of the world through land-use management’ by Chen et al was published in Nature Sustainability this month, and it shows that the world has become greener over the last 20 years, or more precisely that there has been a greening of land over the last 20 years due to tree planting and increased croplands with China and India heading these developments.

The research is based on satellite data from NASA’s MODIS (Moderate Resolution Imaging Spectroradiometer) instruments from which they were able to create a global 20-year time series looking at the leaf area of the canopy. MODIS is carried on board both the Terra and Aqua satellites, with the former launched in 1999 and the latter in 2002. With a swath width of 2 330 km and a spatial resolution of 500 m for the wavebands used; the two satellites image the whole Earth every day enabling this dataset to be created.

Leaf Area Index (LAI), to give its exact name, is an indicator defined as the one-sided green leaf area per unit ground area in broadleaf canopies and as half the total needle surface area per unit ground area in coniferous canopies. As it characterises the canopy structure, it’s a good predictor of primary productivity and crop growth and is it is often used as an input into ecosystem models. The USGS and NASA have an interesting video here showing the changes in the greenness of the United States during a couple of years.

Satellite image and LAI of around the Loch Doon area of Scotland. Data Courtesy of Copernicus/ESA.

It’s an interesting piece of research for us, as we’re using LAI in one of our international projects, for a much smaller area, and looking at specific crop growth with farmers to try and help them understand their growing seasons and how to develop their yields. Rather than MODIS, we’re using Sentinel-2 to create our LAI based on NDVI, and to the left is one of our images for an area of the Dumfries and Galloway region of Scotland, where the freshwater Loch Doon can be seen in the bottom left corner. The satellite image has the LAI next to it, where the greener the colour on the LAI the greener the land is – this is most noticeable in the two left-hand corner corresponding to fields. It’s also worth noting that Sentinel-3 that also offers LAI as part of its land monitoring products.

The image at the top of the blog shows that the world has become greener, with darker colours indicating a greater increase in foliage. The research determined that there are two million square miles of additional green leaf area, a five percent increase on what was around in the early 2000s. If that does not sound much, it actually equates to the area covered by the Amazon rainforest.

Whilst this sounds a positive story, the researchers also sound a cautionary note. The increase in greening is due in large part – 42% – from tree planting and other forest conservation activities; although a third – 32% – comes from food production. The map shows that this greening is most pronounced in China and India. In terms of tree-planting India began a large-scale afforestation campaign in the 1980s, and China has been working on the so-called ‘Great Green Wall’ project since 1978. Given the two countries size and population, it is unsurprising that they are also increasing food production. In India, where 82% of the greening comes from food production, this development is supported by groundwater irrigation which will have a limit on what it can support. The increased use of fertilizer to support these crops will also have an impact on the local ecosystem. The impact on the climate of these changes is also complex, as the forests are good for capturing carbon in the atmosphere, whereas farmland tends to release it with harvests.

The team also highlight that this increase in greenness doesn’t offset the loss of natural vegetation in tropical areas such as Brazil and Indonesia, which are still threatened. It does, however, demonstrate that human activities do have a direct effect on the greenness of the planet, and we can make a positive difference.

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