For billions of people on Earth, a vast array of fruits and veggies is available all year long. Gone are the days when you could only eat what was in season. Nowadays, you can get everything, any time. But plants don’t grow all the time — not normally, at least. To ‘trick’ plants into growing regardless of season, we plant them in greenhouses that mimic the plants’ preferred conditions.

But we may be going too far.

A different greenhouse effect

According to new research that used satellite imagery and deep learning, researchers quantified the area covered by greenhouses. They conclude that 1.3 million hectares of Earth are covered by greenhouses, three times more than previously estimated, or 18 million football fields.

In the 1970s and 1980s, large clusters of greenhouses were set up in North America and Europe. Now, however, greenhouse expansion is coming mostly from China. China’s greenhouses account for a whopping 60.4% of the total greenhouse coverage, followed by Spain (5.6%) and Italy (4.1%). Mexico, Turkey, Morocco, and South Korea follow. Overall, there are now 2.7 times more greenhouses in the Global South than elsewhere.

China’s surge in greenhouses seems to be linked to the country becoming more affluent. People in China are creating demand for fruits and vegetables all year, and they have the means to pay for it.

“The boom in China seems is closely linked to its strong economic performance over the past decade and the rise of an urban population with purchasing power that demands tomatoes, cucumbers, and other types of fresh fruit and vegetables. At the same time, farmers who would otherwise be unable to finance this form of cultivation receive government subsidies and support to build greenhouses and learn cultivation techniques,” says Xiaoye Tong, a postdoc at the Department of Geosciences and Natural Resource Management and first author of the research article published in Nature Food.

Greenhouses offer another advantage. Because of their controlled environment, they offer stable yields and conditions. This makes them more predictable, which enables farmers to make long-term plans. Subsidies for greenhouses also exist in countries, providing an additional incentive.

However, global estimates of greenhouses have been few and far between.

Regulation and tracking may be needed

“Greenhouse cultivation has become a global phenomenon and there is every indication that it will continue to expand. Until now, however, this phenomenon is rapidly rising under the radar and we have had large gaps in our knowledge of the dynamics that drive this phenomenon,” says Xiaoye Tong.

We also don’t know all that much about the environmental effect of this greenhouse surge. Associate professor and co-author Marianne Nylandsted Larsen from the Department of Geosciences and Natural Resource Management says it’s very easy for greenhouses to lead to an overexploitation of resources. Furthermore, greenhouses are not regulated at all in most countries.

“In low- and middle-income countries, which account for 70-80% of the total area, there is a lack of regulation in greenhouse cultivation. This needs to be addressed,” says Xiaoye Tong.

Another challenge is estimating the impact that greenhouses are having on society. Are they helping local societies, or is it just a way to make more money?

“I hope this mapping serves as a point of departure for studies related to the consequences of greenhouse cultivation. For example, has it alleviated rural poverty? Does greenhouse cultivation affect the demand and quality requirements for fruit and vegetables in both national and international markets? And what consequences does this have on the consumption of groundwater resources, fertilizers and chemicals? These types of questions are important to answer if we are to ensure sustainable and socially responsible development within the sector.”

The research article about the study has been published in Nature Food.