London (AFP) - Climate change threatens global financial crises and long-term declines in wealth unless world leaders urgently seal a deal to limit it, the head of the Bank of England said on Tuesday.

"The challenges currently posed by climate change pale in significance compared with what might come," Mark Carney told business leaders in a speech in London.

"The far-sighted amongst you are anticipating broader global impacts on property, migration and political stability, as well as food and water security."

Speaking as world leaders scramble to lay the groundwork for a new United Nations agreement to limit climate change at talks in Paris starting in November, Carney warned that "the window of opportunity is finite and shrinking".

His comments come the day after French President Francois Hollande warned that if no deal was reached in Paris, "it will be too late for the world," in an address to the UN General Assembly in New York.

Scientists have underlined the urgency of preventing temperatures rising more than two degrees Celsius (3.6 Fahrenheit) from pre-industrial times, although analysts warn the world is heating far faster.

Several nations and private sector bodies have promised to cut greenhouse gas emissions, blamed for the severe weather and rising temperatures, but there remain deep international divisions over a long-awaited deal.

A Canadian economist who has been the governor of the central bank since 2013, Carney said that scientific evidence indicated "climate change will threaten financial resilience and longer-term prosperity".

He said the number of weather-related loss events for insurers had tripled since the 1980s, while inflation-adjusted losses for the sector had increased five-fold to $50 billion a year.

The "catastrophic impacts of climate change" -- including floods and storms and financial costs of shifting to a low-carbon economy -- will only be felt over a longer period than the three to 10 year horizon used in the financial industry, he warned.

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"In other words, once climate change becomes a defining issue for financial stability, it may already be too late," Carney said.

The Earth is currently on track for temperatures to rise 3.5 degrees (6.3 Fahrenheit), with a range of uncertainty between 2.1 and 4.6 Celsius, according to Climate Interactive, a Washington-based group used by leading governments.

A 3.5 degree rise would mean "a world we cannot adapt to", according to the body's co-director Andrew Jones.