Climate change is already a heavily charged issue, fraught with political tension. But complicating the mix are a slew of misconceptions about exactly how it will affect the planet and its inhabitants.
One confusion involves plant growth. Some skeptics have argued that rising carbon dioxide levels could actually benefit agriculture, and in fact, research shows that rising temperatures and more carbon dioxide can be a boon to plants — up to a point. But that’s not the whole story, according to researcher Camilo Mora, a professor of geography at the University of Hawaii at Manoa. And in a new paper, published today in the journal PLOS Biology, he and his colleagues attempt to set the record straight.
The study examines not only the effects of rising temperatures, but also how solar radiation and water availability impact plant productivity — specifically, their effects on the number of “suitable growing days” for plants worldwide. The researchers looked at these variables under several different climate change scenarios: The worst of these is the “business-as-usual” trajectory, which is the amount of warming the planet will experience if humans do nothing to cut down on carbon emissions. The scientists also evaluated scenarios where there was a strong or moderate reduction in emissions.
The results indicate that climate change may not be the net positive to plants that some prior research has suggested. If humans allow global warming to go on unmitigated under a business-as-usual scenario, the Earth could lose a significant number of suitable growing days per year by the end of the century. And that’s bad news for people as well as plants, with the potential for widespread food shortages and economic downturns.
On the other hand, strong and even moderate efforts to cut down on global carbon output could reduce the impact of climate change and hardly hurt plant growth. The study underscores the importance of heading off climate change, says Mora, the paper’s lead author, while providing a look at what could happen if we don’t.
The researchers are among the first to analyze how factors aside from temperature—including sunlight and water—affect plant growth, says Steven Running, senior author of the paper and regents professor of ecology at the University of Montana.
For example, it makes sense that global warming will extend the growing season in cold places at high latitudes. But when you factor in less sunlight in these regions, which plants also need to grow, you find that the number of growing days added isn’t actually that high. High northern latitudes get less light in the winter due to the Earth’s axial tilt, and no amount of warming can change that. In this case, limited light becomes the factor that cuts the growing season short, even if temperatures continue to rise.
Some water-scarce areas may experience similar trade-offs, says Running. If a high-latitude area is short on water and runs out, the plants are going to suffer even if temperatures are improving for them. Taking these factors into account has helped the authors come up with a more realistic, if less optimistic, view of how climatic changes will affect growing seasons around the world.
That said, the findings do indicate that some parts of the world, particularly areas of Russia, China and Canada, will gain suitable growing days throughout the year. However, it turns out the rest of the world won’t be quite so lucky — and the places that lose growing days will far outweigh the places that gain. In fact, on a global scale, the authors predict that the Earth will lose a whopping 11 percent of its annual suitable growing days by the year 2100 under a business-as-usual scenario.
Tropical areas are likely to contribute to these net losses in a big way. “Warming at high latitudes may be good, but the same warming in the tropics can be devastating,” says Mora. This is because even plants have a limit on the amount of heat they can endure.
In the tropics, climatic conditions are already very close to this threshold, so it won’t take too much warming before the plants there start to decline, Mora says. In fact, the authors predict that tropical parts of the world could lose up to 200 growing days out of the year by the end of the century under a business-as-usual scenario — that’s a loss of more than half a year’s growing days.
Declines in suitable growing days could affect humans in some major ways, the authors caution. Food shortages are an obvious effect. And in areas where agriculture suffers, job losses and economic problems are sure to follow. The authors note that the areas likely to be hit worst are poor and developing countries. In fact, they predict that approximately 2.1 billion people in low-income countries will be “highly vulnerable” to changes in plant-related goods and services. It’s an outcome that highlights the “issue of unfairness when it comes to climate change,” Mora says.
These inequalities could result in mass human migrations in the future, Mora predicts, as people start moving to more fertile areas in order to survive. And Running adds that while more research is needed to predict future migration patterns, this paper could provide a “first look at where global human migration patterns might develop in the coming decades” by pointing out which areas of the world are likely to come out on top.
Luckily, there’s still some hope at the end of this story. There are ways to prevent the doomsday scenarios described so far — and this, according to the authors, is the study’s most important message.
“Our objective with this paper was to try to illustrate that reducing carbon emissions really will matter, it will make a difference,” Running says. “And that it will make the biggest difference to the most vulnerable, low-income people of the world.”
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