联合国称气候变化影响土地质量和粮食生产（在线收听）

UN: Climate Change to Affect Land Quality, Food Production

A new United Nations scientific report says that human-caused climate change is greatly reducing land quality worldwide. It also warns that the way humans use land is causing the Earth’s atmosphere to warm faster and could harm food production.

The Intergovernmental Panel on Climate Change (IPCC) published its latest report on Thursday. It examines the relationship between climate change and land use, agriculture and food security.

The report notes that the effects of climate change are already making food more costly and less nutritious and are worsening food shortages.

“The cycle is accelerating,” says NASA climate scientist Cynthia Rosenzweig. She was among the writers of the report. “The threat of climate change affecting people’s food on their dinner table is increasing.”

The scientists write that if humans change the way they eat, grow food and manage forests, it could help slow world temperature rise.

Land warming faster

About 30 percent of the Earth’s surface is land. But the report says that the land is warming two times faster than the planet as a whole. While heat-trapping gases are causing problems in the atmosphere, land has been less talked about as a part of climate change.

“The way we use land is both part of the problem and also part of the solution,” said Valerie Masson-Delmotte. She is a French climate scientist who was on one of the IPCC’s working groups. “Sustainable land management can help secure a future that is comfortable,” she added.

The report said climate change has worsened land degradation. It has caused deserts to spread and permafrost to partly melt, and made forests more easily harmed by fire, disease and lack of water.

The future could be worse, the report said.

Agriculture and forestry together account for about 23 percent of the heat-trapping gases that are warming the Earth. That does not include energy costs, food transportation and packaging. With those activities added, the amount grows to 37 percent.

But scientists also note that land is a good carbon “sink.” In other words, it can suck heat-trapping gases out of the air. From 2007 to 2016, for example, agriculture and forestry each year put 5.2 billion metric tons of carbon dioxide into the air. But the land pulled 11.2 billion metric tons out of it. Carbon dioxide is a main heat-trapping gas.

But one of the writers of the report, Luis Verchot, noted, “this additional gift from nature is limited.” He warned that the land will be less able to take in emissions in the future. Verchot is a scientist at the International Center for Tropical Agriculture in Colombia.

He said that total emissions from land are increasing, especially because of deforestation in places such as Brazil, Colombia and Peru.

Less-nutritious food

Scientists have long believed that one of the few good things about higher levels of carbon dioxide is that plants grow well in such conditions, NASA’s Rosenzweig said. But many studies show that the high levels of carbon dioxide reduce protein and nutrients in many crops.

For example, the studies show that high levels of carbon in the air cause wheat to have six to 13 percent less protein, four to seven percent less zinc and eight percent less iron, Rosenzweig said.

Food security

The IPCC also warned of more harmful effects to the global food supply as extreme weather becomes more common. It predicts an increase of 7.6 percent in cereal prices by 2050. Higher food prices, the report said, lead to an increased risk of hunger.

Changing farming, changing diets

The report noted that better, smarter farming methods could reduce carbon levels by up to 18 percent of current emission levels by 2050.

The report also suggested ways that carbon emissions could be reduced further. This could be done if humans reduce the amount of red meat they eat and instead eat more plant-based foods like fruits, vegetables and seeds. That would also make people healthier, Rosenzweig said.

More plant-based diets also would free up several million square kilometers of land by 2050.

“There are certain kinds of diets that have a lower carbon footprint and put less pressure on land,” said Jim Skea, a professor at London’s Imperial College. He spoke with Reuters reporters Thursday.

Reducing food waste

The report said that reducing food waste is an important part of fighting climate change. The report noted that almost one-third of food produced is lost or wasted. The causes of food loss and waste differ greatly between developed and developing countries.

Between 2010 and 2016, worldwide food waste accounted for eight to 10 percent of heat-trapping emissions. Reducing food waste would reduce emissions and improve food security, the report said.

However, the report urged that “the window for making these changes is closing fast.”

Stanford University’s environmental sciences chief, Chris Field, was not involved in the IPCC's report. But he told the Associated press that the report’s main message is that humans must “recognize that we have profound limits on the amount of land available.”

He added, “We have to be careful about how we utilize it.”

I’m Mario Ritter.

And I’m Anne Ball.

Words in This Story

accelerate - v. to move faster : to gain speed

comfortable - adj. not causing any physically unpleasant feelings : producing physical comfort

degradation - n. the act or process of damaging or ruining something

permafrost - n. ?a layer of soil that is always frozen in very cold regions of the world?

account for - phrasal verb. to be the cause of (something)

emissions - n. ? the act of producing or sending out something (such as energy or gas) from a source?

footprint - n. ?the area occupied or affected by something?

profound - adj. ?very great?; absolute or complete

utilize - v. ?to use (something) for a particular purpose