Many of the world's biggest companies are failing to meet their own targets on tackling climate change, according to a study of 25 corporations.

They also routinely exaggerate or misreport their progress, the New Climate Institute report says.

Google, Amazon, Ikea, Apple and Nestle are among those failing to change quickly enough, the study alleges.

Corporations are under pressure to cut their environmental impact as more consumers want green products.

Some of the companies told BBC News they disagreed with some of the methods used in the report and said they were committed to taking action to curb climate change.

The firms analysed account for 5% of global greenhouse-gas emissions, the report says - which means although they have a huge carbon footprint, they have enormous potential to lead in the effort to limit climate change.

"The rapid acceleration of corporate climate pledges, combined with the fragmentation of approaches, means that it is more difficult than ever to distinguish between real climate leadership and unsubstantiated," the study says.

Study author Thomas Day told BBC News his team originally wanted to discover good practices in the corporate world, but they were "frankly surprised and disappointed at the overall integrity of the companies' claims".

John Stulp was born on the Eastern Plains. Fifty years ago he began farming with his father-in-law near Lamar. Together he and his wife, Jane, brought up five children in southeastern Colorado, raising cattle and dryland wheat.

Along the way Stulp was elected as a Prowers County commissioner, and later served as Gov. Bill Ritter’s commissioner of agriculture and Gov. John Hickenlooper’s water policy adviser. When his service to the state was done in 2019, he headed back home to the prairie.

But the prairie is changing.

Winter wheat crops are becoming more unpredictable as hot, dry weather lasts longer. Where it once took 30 acres of pasture to support a cow and calf, it now takes 40 or more. As farming the prairie becomes a more marginal enterprise, ranchers are selling off cattle, farms are consolidating and families are leaving. Year after year, the area sets records: Driest summers. Driest winters. The last six months of 2021 were the hottest in Colorado’s recorded history, beating records set nearly a century ago in the Dust Bowl.

“We’re in trouble,” said Stulp, 73. Wheat planted in the fall in anticipation of being watered by winter snow is performing poorly, he said.

“The topsoil is so dried out, when we do get moisture, it doesn’t go very far. The wind sucks up the rest. It’s climate change, no question about it. If we get 3-4 degrees warmer like they say we might, it’ll look more like Albuquerque around here, and they don’t do a lot of farming around Albuquerque.”

Meanwhile, in Colorado’s high country, scientists monitoring snowpack in the mountains are noticing a strange phenomenon: even in strong snowpack years, it’s translating into less spring runoff into rivers and streams, as soils left parched by long stretches of hot weather drink first before any water runs on.

With Colorado facing a warmer future, scientists are looking at how increasingly dry soils could spell big trouble for reservoirs, agriculture, forest health and pose greater risk of wildfire.