NEW YORK (Reuters) - A top U.S. banking regulator has found that major lenders are in the early stages of assessing and managing the risks climate change poses to their businesses, and that significant work is needed in some areas, three people familiar with the matter said.

The Office of the Comptroller of the Currency conducted a review last year including 22 large banks to see how they account for the impact of climate change on their loan books and businesses.

In a letter sent in recent days to the banks' chief executives, the OCC said it found all had completed some level of risk identification, but approaches and stages of development varied widely. The letter, the contents of which were described to Reuters by sources, has not been previously reported.

It sheds more light on the shortcomings regulators have identified in many banks' preparations to manage climate risks, which some industry experts argue puts trillions of dollars of assets in jeopardy.

The OCC found that most banks were early in the process of incorporating climate risk into functions such as strategic and operational planning, internal audit and assessments of their risk appetite, the sources said.

It also found that several had not started working with climate scenario analysis and that significant work was needed to implement planned governance frameworks around climate risk, the sources said.

An OCC spokesperson said the agency does not comment on supervisory activities. The sources requested anonymity to talk about confidential regulatory matters.

Banks and regulators around the world are grappling with how to measure and manage the consequences a warming climate and alterations to energy policy will have for the financial system.

Some industry executives question, though, whether the long-term process of climate change poses a severe immediate threat to bank stability in the same way that a recession could.

The OCC carried out its first review in 2023, conducting multiple meetings with banks, and published guidance on managing risks alongside the Federal Deposit Insurance Corporation and Federal Reserve.

The Fed led its own exercise in which the six biggest banks were asked to simulate what extreme weather and a shift to cleaner energy could do to their assets and investments.

The OCC's letter describes a range of practice observations and does not spell out specific actions it wants the banks to take, the sources said.

It said it will continue to conduct risk-based supervisory activities, the sources added.