WASHINGTON—Governments must take steps to limit greenhouse gases and enact "stricter and enforceable zoning and building codes" to deal with the impact of climate change, a reinsurance executive told the Senate Homeland Security and Government Affairs Committee last week.

But governments should not provide a financial backstop to natural catastrophe risks, Andrew Castaldi, senior vp and head of catastrophe perils, Americas, for Swiss Reinsurance America Corp. told the committee during a hearing regarding the impact of climate change on private and federal insurance programs.

Mr. Castaldi reiterated Swiss Re's contention that climate change cannot be ignored.

"It's quite clear that if left unchecked, (carbon dioxide) emissions will alter the natural variations of climate changes and will affect U.S. weather patterns and some natural catastrophes," he said. "Preventive action, therefore, must be taken today. If we wait until we have achieved absolute certainty, we run the risk of acting too late."

Mr. Castaldi noted that some insurers have cut back on their exposure on the Gulf Coast, and that Florida property owners are facing increased insurance costs. Those developments have led lawmakers and others to suggest that natural catastrophes cannot be insured by the private market and that a government backstop is needed.

Swiss Re does not share that view, he said. "Because these risks can be modeled by the private sector and are random in nature, they are insurable," he said, adding that the "largest events can and have been absorbed" by the private market.

"A government backstop for such risks is inappropriate public policy," said Mr. Castaldi. Instead, governments should take steps to mitigate future damage, such as enforcing better zoning and building codes, he said.

"We must all grapple with this new weather environment. We must recognize that we can no longer always build what we want or where we want."

The Government Accountability Office released a report during the hearing on how private insurers and federal insurance programs are responding to climate change.

It found that while many "large insurers are incorporating climate change into their annual risk management practices, and some are addressing it strategically by assessing its potential long-term industrywide impacts," federal insurance programs such as the National Flood Insurance Program and Federal Crop Insurance Corp. have not developed comparable "information on long-term financial impacts."