As Hurricane Sandy moves out of the region, people in affected areas are beginning to take stock of the damage. Flooding in parts of New Jersey and New York from the storm surge hit record levels. The 13.8-foot surge measured at Battery Park in Lower Manhattan surpassed the all-time record of 11.2 feet set in 1821, flooding the New York subway system and two major commuter tunnels.  Along the Eastern Seaboard, an estimated 7.5 million people lost power. Farther inland, blizzard conditions dropped as much as 2 feet of snow as Sandy crashed into arctic air over the Midwest. While early estimates indicate direct damages from the hurricane may be as much as $20 billion, the total economic losses, including losses in consumer and business spending, could be more than twice that amount.

A number of climate change-related factors may well have intensified the storm's impact: higher ocean temperatures, higher sea levels, and an atmospheric traffic jam that may be related to Arctic melting.  Hurricane Sandy is also a clear reminder of how vulnerable our homes and infrastructure already are to extreme weather — and this risk is growing.

Scientists know that warmer atmospheric temperatures and higher ocean temperatures are increasing the frequency and severity of heavy precipitation events on average, and Sandy spent significant time over water that was as much as 5 degrees Celsius above normal.

Globally, climate change is increasing sea levels, and in the Northeast U.S., the ocean is rising at a level much faster than the global rate. When Sandy’s storm surge combined with  an extra-high tide caused by the full moon and sea level rise, the results were devastating for coastal areas.

Sandy might have avoided some of the most expensive real estate in the country if the storm had not encountered a “traffic jam” in the North Atlantic that halted weather from moving out to sea. Instead, Sandy veered into a winter storm developing over the Midwest, resulting in an unusual hybrid storm that brought hurricane-like conditions to the coast and blizzard conditions to interior areas. While traffic blocks  have occurred historically from time to time in the North Atlantic, an emerging area of research is indicating that blocks and cold outbreaks are becoming more common during the fall, as arctic sea ice extent declines and the barrier between arctic and lower latitude weather erodes.

While we may never know how each of these elements specifically contributed to the path, severity and subsequent damage that Sandy caused, we do know that climate change will result in deviations from the normal weather of the past.    Hurricane Sandy is just one data point in the observational record that shows a trend of increasing risk from extreme weather. The most important lesson to take away from the terrible damage that Sandy caused is that we must be more prepared for extreme weather in the future and be aware of the changes in risk that are underway. This means taking action to adapt to increases in risk that are already exist, and acting now to reduce carbon dioxide emissions in order to avoid a risk level in the future that is simply too costly to cope with.