This paper studies how homeowners insurance markets respond to growing climate losses and how this impacts mortgage market dynamics. Using Florida as a case study, we show that traditional insurers are exiting high risk areas, and new lower quality insurers are entering and filling the gap. These new insurers service the riskiest areas, are less diversified, hold less capital, and 20 percent of them become insolvent. We trace their growth to a lax insurance regulatory environment. Yet, despite their low quality, these insurers secure high financial stability ratings, not from traditional rating agencies, but from emerging rating agencies. Importantly, these ratings are high enough to meet the minimum rating requirements set by government-sponsored enterprises (GSEs). We find that these new insurers would not meet GSE eligibility thresholds if subjected to traditional rating agencies’ methodologies. We then examine the implications of these dynamics for mortgage markets. We show that lenders respond to the decline in insurance quality by selling a large portion of exposed loans to the GSEs. We quantify the counterparty risk by examining the surge in serious delinquencies and foreclosure around the landfall of Hurricane Irma. Our results show that the GSEs bear a large share of insurance counterparty risk, which is driven by their mis-calibrated insurer eligibility requirements and lax insurance regulation.