Russia's agriculture sector contributes about 5% of the country's total GDP, although the sector employs about one-eighth of the total labour force. It has the world's third-largest cultivated area, at . However, due to the harshness of its environment, about 13.1% of its land is agricultural, and only 7.4% of its land is arable. The main product of Russian farming has always been grain, which occupies considerably more than half of the cropland. Russia is the world's largest exporter of wheat, and is the largest producer of barley, buckwheat, oats, and rye, and the second-largest producer of sunflower seed. Various analysts of climate change adaptation foresee large opportunities for Russian agriculture during the rest of the 21st century as arability increases in Siberia, which would lead to both internal and external migration to the region.