Is climate change responsible for the devastation caused by Super Typhoon Haiyan – the strongest tropical cyclone to make landfall in recorded history?
Was it responsible for Superstorm Sandy, which caused billions of dollars of damage to New York City and New Jersey? More broadly, is climate change starting to have an impact today on such extreme weather events?
The answer to those questions is a complicated one, but it starts with the word "yes".
Scientists have spent years researching climate change's role in specific, extreme events such as Haiyan and Sandy. But what climate scientists know today, with a high degree of certainty, is that all extreme weather events are now occurring in a world where the oceans are warmer, sea levels are higher and temperatures are rising. So the odds of more intense, devastating storms like Haiyan and Sandy are increasing every year.
The first decade of this century was the hottest ever recorded, and there is a scientific consensus that man-made greenhouse gas emissions are significantly responsible. There are fluctuations from one year to the next – and new studies show that temperatures for the planet were likely hotter than we know if we take the accelerated warming in the polar regions into account – but temperatures continue to rise decade-by-decade even in the face of natural climate influences such as the La Nina/El Nino and solar minimum/maximum cycles.
What's more – and this is critical in understanding the impact on superstorms like Haiyan and Sandy – recent peer-reviewed studies show that much more substantial warming is occurring in the oceans. At some point, that ocean warming will rise to the surface and accelerate land temperatures further – but it is almost certainly having an impact right now on superstorms that gather strength over those warmer ocean waters.
"We no longer live in a world without warming," climate scientist Michael Mann wrote Nov. 17 in EcoWatch about the climate impact on Haiyan. "Given that 1985 was the last year with temperatures below the 20th century average, and 2000-2010 was the hottest decade on record, it has become impossible to say for certain that any given storm is free from the influence of our warmed world. The bottom line is this: climate change makes tropical storms more damaging - not only through increased wind speed and rainfall, but most notably through rising sea levels. This means greater damage and loss of property and life."
While scientists are still researching whether superstorms will be more frequent – a draft of the Intergovernmental Panel on Climate Change's most recent report says that we still don't know yet - the science is much clearer and certain on the intensity of such storms. They will be more intense – and super storms like Haiyan and Sandy are almost certainly more intense today than they would have been otherwise. (The winds of Haiyan, for instance, surged well above the starting point for Category 5 designation for hurricanes and typhoons.) There are a number of ways in which climate change strengthens typhoons like Haiyan and their impacts.
In Sandy's case, the climate impact was three-fold: a record 13-foot storm surge that swept across lower Manhattan and caused massive damage was exacerbated by the elevated sea levels near the city, and the superstorm's fury was likely fueled offshore by warmer waters and an altered jet stream pattern that caused two systems to collide.
In the case of Haiyan, a combination of sea level rise and considerably warmer ocean waters at both the surface and the sub-surface (100 meters below the surface) likely contributed to the massive strength and depth of the typhoon before it struck land.
Sea level rise increases the destructive power of storm surges. The city of Tacloban experienced a storm surge of 17 feet during Haiyan, which caused some of the most deadly flooding. These elevated levels will continue to worsen the impacts of typhoons through higher storm surges because climate change has already contributed about eight inches to global sea level rise.
At the same time, sea surface temperatures also fueled Haiyan by increasing the available energy and water vapor – the two critical elements that drive superstorms in the first place. Hurricanes and typhoons can form if the sea surface temperature is above 28 degrees Celsius (or about 82 degrees Fahrenheit). Sea surface temperatures near the Philippines were 30 degrees Celsius - nearly one full degree C above the 1985-1993 average for the region.
While scientists are racing to more fully understand correlations between ocean warming and extreme events, the fact that sea surface temperatures have been steadily increasing around the world's oceans means that climate impacts will continue to intensify super storms.
In one of the most overlooked pieces of science related to Haiyan, the ocean waters at a depth of 100 meters below the surface during the super typhoon's rapid intensification phase were a somewhat shocking 4-5 degrees Celsius (or up to 9 degrees Fahrenheit) above average. These deeper temperatures are important because as a storm passes over water, it pushes warm surface water down and brings cool deep water up.
Normally this cools the surface and causes a storm to gradually lose intensity. However, if the deep water is unusually warm – as it was in Haiyan's case - a storm will maintain its intensity longer, or even increase. The sub-surface temperatures for waters at a depth of 100 meters have risen in the Eastern Pacific in recent decades, and scientists believe this could play an increasingly important role in the rapid intensification of superstorms like Haiyan. The scientific significance of this still needs to be assessed, but it's an anomaly that demands attention. And finally, because climate change has already added perhaps as much as 5 percent more water vapor to the Earth's climate system – and is projected to increase the precipitation associated with tropical cyclones by 20 percent by the end of the century, studies show - extreme rainfall in superstorms is also now a new, emerging threat in mountainous areas such as the Philippines because it can cause dangerous flash floods and landslides.
Haiyan covered a huge swath of the Philippines with more than 19 inches of rain (with an almost unimaginable peak of 27 inches in the southeastern part of the country). That sort of extreme precipitation in the middle of superstorms such as Haiyan will only grow in intensity as climate impacts are felt in the coming years around the planet.
So, is climate change responsible for superstorms like Haiyan and Sandy? The better question, as science is beginning to show, may be this one: is any superstorm from this point forward not connected in a variety of ways to climate change due to higher sea levels, warmer oceans (at the surface and the sub-surface), greater levels of water vapor in Earth's climate system and altered atmospheric patterns like the Arctic jet stream?