Halfway through, this year is already the costliest on record for natural catastrophes, insurer Munich Re said Tuesday in its first-half review. Losses hit $265 billion in the first six months of 2011 – which exceeds the $220 billion in losses in the biggest previous year for natural disasters, 2005.

Most of the losses this year stem from the March earthquake and tsunami in Japan, which caused more than 15,000 deaths and accounted for $210 billion in economic losses. That is another record, beating out the $125 billion in losses caused by Hurricane Katrina in 2005.

Losses tied to the quake have already taken a toll on insurance industry profits. First-half insured losses hit $60 billion, Munich Re said – five times the annual average over the past decade.

Berkshire Hathaway (BRKA), which last year took a big stake in Munich Re, said in April that it would likely report an insurance underwriting loss this year for the first time in almost a decade, thanks to the Japanese disaster and other calamities, mostly in Asia.

That said, the Japan quake stands to be less costly than Katrina. Munich Re said insured claims from March’s disaster stand at around $30 billion, compared with the $44 billion the government estimated for Katrina. Insured losses on the World Trade Center terrorist attacks a decade ago have been estimated at around $40 billion, by comparison.

The question now is how high this year’s record toll might rise. Munich said first-half losses “are generally lower than second-half losses, which are often affected by hurricanes in the North Atlantic and typhoons in the Northwest Pacific.” Just another way in which the coming months promise to be eventful, and not in a good way.