The biggest health insurers in the U.S. show little understanding or concern about the risks to their business posed by climate change, even though warmer winters and springs are already causing spikes in conditions such as allergies, asthma and Lyme disease.

That’s one of the findings of a report from non-profit Ceres that ranks the 148 largest insurance companies in the U.S. on their response to climate risks, including severe weather events. The report is based on a climate risk survey developed by the National Association of Insurance Commissioners, or NAIC, and first conducted in 2014.

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“ “We have no choice. A 2°C world might be insurable, a 4°C world certainly would not be.” ” — Former Axa CEO Henri De Castries

The survey polled insurers such as AIG AIG, +1.33% , MetLife Inc. MET, -1.28% , and Travelers Cos. TRV, -0.18% that write more than $100 million in premiums, and then ranked their responses using a four-tier scoring system of high quality, medium quality, low quality and minimal. The companies polled represent about 71% of the U.S. insurance market measured by direct premiums written.

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Ceres found that while property and casualty insurers and life and annuity insurers have made some progress in engaging with climate change and attempting to evaluate the risks to their business, health insurers appear to be in a state of denial.

“Every segment can improve, but health insurers are just not engaged much and that really came through in their disclosures,” said Max Messervy, manager of the Ceres insurance program and one of the authors of the report. “ A few actually said they do not believe climate change is a material business risk.”

The companies were evaluated on five core themes, including governance, climate risk management, the use of catastrophe modeling or other modeling to evaluate and manage risk, greenhouse gas management and stakeholder engagement. The latter includes the extent to which climate risk is discussed at board level and among senior managers, as well as external parties such as shareholders and regulators, and elected lawmakers, who could work on carbon-reducing legislation.

A full 64% of those surveyed scored either the low quality or minimal ranking with health insurers faring worst. Not one health insurer earned a high quality ranking and only four garnered medium quality ratings, while 89% were low quality or minimal. Yet health insurers are facing serious exposure to some of the worst climate trends, namely the impact on human health and well being.

“The Zika virus may have been exacerbated by the fact that higher latitudes are warmer than they were, so mosquitoes can go further north,” said Masservy. “It’s the same with Lyme disease, which is arriving earlier in parts of the U.S.”

If temperatures rise, air pollution will increase, making it easier for airborne pathogens to thrive. The study found that as of 2011, the ragweed pollen season is 11 to 27 days longer than it was in 1995, weighing on the roughly 6.8 million children who suffer from asthma and allergies. Higher temperatures also have implications for food safety.

Property and casualty insurers demonstrated better awareness of and engagement with climate risk, to which they are exposed through policies written for homeowners, cars and businesses. Disasters such as the recent Hurricane Matthew can be expensive for those companies as they pay up for damage to homes, vehicles and commercial properties.

Sixteen, or 25%, of the 64 property and casualty insurers polled earned a high quality rating, while 27% earned a medium quality rating. Only 19% of the group earned a high quality rating for stakeholder engagement. FM Global won praise for disclosing that it had brought together a team of climate scientists for a workshop on observed climate impacts. The team produced a white paper on the issue that the company distributed to clients.

“While the majority of P&C insurers’ disclosures are of at least moderate quality, there is still significant room for improvement,” said the report.

In the life insurance segment, the focus shifted to investment strategies and a look at how well companies are managing longer-term liabilities for climate-related impacts. Life insurers have large real-estate investments and are further exposed to property through their holdings of mortgage-backed securities.

Companies should be working to ensure they are investing in such things as energy efficiency, reducing water usage and fortifying buildings against events like hurricanes.

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“Life insurers need to match their liabilities with long-term assets, so they will invest in corporate bonds, they’ve really stepped up in green bonds,” said Masservy. “But they can also do things like take direct stakes in renewable energy companies, they can help fund wind farms. And some are beginning to take more action.”

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Still, just 6 of the life insurers polled disclosed strong climate risk governance practices. MetLife and Prudential PRU, -1.57% stood out for identifying special board committees to oversee corporate climate and sustainability policies.

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Ceres is now calling on the whole insurance industry to take a more proactive role in shaping climate policy at government level, and to step up their efforts to educate and update management and other stakeholders on the risks.

European insurers are more advanced in their efforts to combat and adapt to climate change, said Masservy, citing former AXA SA Chief Executive Henri de Castries as a leader in the field.

De Castries was behind Axa’s AXA, +2.23% decision to sell its fossil fuel-related assets and revamp its investment strategy with a clear focus on sustainability and has been a champion of the Paris climate treaty goal of limiting global warming to 2 degrees a year.

“ We have no choice,” he said in a May 22, 2016 speech. “A 2°C world might be insurable, a 4°C world certainly would not be.”

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