Tens of millions of farmers in north and north-east China could face dramatic losses of income as a result of climate change, which is liable to exacerbate already serious droughts in those regions, according to a new study by consultants McKinsey.

As many as 35m farmers could lose more than 50 per cent of their incomes if measures are not taken to prepare for the impact of higher temperatures in the two regions, according to the study.

The north and north-east of China contain some of the main grain-growing regions of the country, making them part of the backbone of the country's huge agricultural sector, however they have already experienced some of the worst droughts in half a century this year. The latest in a series of stark warnings about the potential impact of climate change on China, the study underlines why Beijing has started to take more decisive steps over the past year to restrain the growth in Chinese carbon emissions.

The report, titled “From bread basket to dustbowl?”, was prepared in collaboration with the national development and reform commission, China's main planning body, and the Chinese Academy of Agricultural Sciences.

North China was less exposed to the risks of climate change because local governments had already taken a lot of steps to limit the impact from persistent droughts, the report said. However, even under more moderate scenarios for climate change, losses to farmers in the north-east from the effects of drought could rise by 50 per cent.

“The north-east is already at a critical stage,” said Martin Joerss, a McKinsey partner in Beijing, who was the main author of the study. “It is very exposed to further changes in the climate.”

McKinsey estimates that China will need to spend Rmb25bn ($3.7bn, €2.4bn, £2.2bn) a year between now and 2030 to reduce the impact of droughts, including investment in irrigation, seed engineering, soil conservation and reservoirs.

Although such measures could prevent as much as half of the expected crop losses, China also needed to expand agricultural insurance, which covers only 25 per cent of farmers.

Meanwhile, Wu Changhua, an expert on Chinese climate change policies, who is director of the China office of The Climate Group, said Beijing was considering announcing at next month's Copenhagen climate change talks a date for when Chinese emissions will peak.

Most advisers to the government had suggested dates of between 2030 and 2040 as a feasible target, she said.

China is expected to outline at Copenhagen its target for carbon intensity – the amount of carbon produced for each unit of economic output.

According to Ms Wu and several other sources with knowledge of the internal debate in Beijing, the government is considering a target of a 40 per cent reduction in carbon intensity by 2020.