Killer heat fueled by climate change could cause an additional 150,000 deaths this century in the biggest U.S. cities if no steps are taken to curb carbon emissions and improve emergency services, according to a new report.

The three cities with the highest projected heat death tolls are Louisville, with an estimated 19,000 heat-related fatalities by 2099; Detroit, with 17,900, and Cleveland, with 16,600, the Natural Resources Defense Council found in its analysis of peer-reviewed data, released on Wednesday.

Reluctance to raise ambitions to cut greenhouse gas emissions due to economic constraints is threatening progress towards limiting global warming, delegates at United Nations' climate talks in Germany warned on Monday.

The talks in Bonn, which end on May 25, are partly to discuss ways of raising the level of ambition on cuts but the worsening eurozone crisis and battered global economy have increased reluctance to commit to more financially onerous cuts by the end of the decade, delegates told Reuters.

The number of extreme rainstorms - deluges that dump 3 inches or more in a day - doubled in the U.S. Midwest over the last half-century, causing billions of dollars in flood damage in a trend climate advocates link to a rise in greenhouse gas emissions.

Across the Midwest the biggest storms increased by 103 percent from 1961 through 2011, a study released by the Rocky Mountain Climate Organization and the Natural Resources Defense Council reported on Wednesday.

Rising carbon dioxide emissions will cause a global average temperature rise of 2 degrees Celsius by 2052 and a 2.8 degree rise by 2080, as governments and markets are unlikely to do enough against climate change, the Club of Rome think tank said.

Failing to tackle climate change in the first half of this century will put the world on a dangerous track to warming in the second half, even though global population should peak in 2042 at 8.1 billion and economic growth will be much slower than expected in mature economies, the Switzerland-based body said in a report on Tuesday.

EU nations have yet to come up with a plan on how to fill a multi-billion euro fund to help tackle climate change, even as the region's executive body hosts talks with countries likely to bear the brunt of extreme weather.

The European Union recommitted to providing 7.2 billion euros ($9.4 billion) for the fund over 2010-12, according to draft conclusions seen by Reuters ahead of a meeting of EU finance ministers next week.

Some of the main proposals in a draft text for negotiation at a U.N. sustainable development conference next month are being watered down at informal talks in New York, observers said on Tuesday, heightening fears the summit will fail to deliver.

The Rio+20 summit in Brazil from June 20-22 is expected to draw more than 50,000 participants from governments, companies and environmental and lobby groups.

It will try to hammer out sustainable development goals across seven core themes including food security, water and energy but is not expected to produce mandatory targets.

New research suggests that global warming is causing the cycle of evaporation and rainfall over the oceans to intensify more than scientists had expected, an ominous finding that may indicate a higher potential for extreme weather in coming decades.

By measuring changes in salinity on the ocean’s surface, the researchers inferred that the water cycle had accelerated by about 4 percent over the last half century. That does not sound particularly large, but it is twice the figure generated from computerized analyses of the climate.