The Human Fingerprints on Extreme Weather
This post originally appeared on Nexus Media News. Read it here.
Hurricane Michael broke records Wednesday, when it became the most powerful cyclone ever recorded to make landfall along the Florida Panhandle. Abnormally warm waters fueled winds up to 155 miles per hour, which laid waste to homes and businesses caught in the storm’s path. As multiple outlets noted, climate change likely fueled the record-breaking wind speeds. That fact is notable given that both reporters and researchers have historically been reticent to link any one storm to climate change.
Five or ten years ago, if you asked a scientist how climate change figured into a particular hurricane, she would demur, saying that it was impossible to blame any single event on the overall warming trend. Those days are over. In the last decade, scientists have developed sophisticated tools for finding the human fingerprint on extreme weather. The emerging field of attribution research, as it’s known, investigates the role of climate change in specific events. A newly published report amassing more than 200 attribution studies makes clear that heat-trapping carbon pollution is already making the weather measurably more severe.
“Since the initial days of detecting the fingerprint of human activities in 20th century warming, scientists are now able to attribute the specific influence of climate change on many events, disasters, and trends,” notes the report from Climate Signals, a project connecting the dots between carbon pollution and extreme weather. The report details the numerous links between rising temperatures and recent weather disasters in the United States and around the world. Here are a few of the highlights.
Three different studies, using varying methods, found that climate change made rainfall during Hurricane Harvey between 15 and 20 percent more severe. Warmer seas are more prone to evaporation, delivering more water to the air. Warmer air holds more water, producing more rain during storms. With the help of all that extra heat, Hurricane Harvey shattered the U.S. rainfall record.
Warmer weather means that more precipitation comes down as rain instead of snow. It also means that what little snow accumulates melts earlier than it would have otherwise. This is significant because melting snowpack feeds the rivers and streams that deliver water to the rest of California. Between 2011 and 2015, climate change diminished Sierra Nevada snowpack by 25 percent. Making matters worse, extra heat dries out the soil, worsening drought. Between 2012 and 2014, rising temperatures accounted for up to 27 percentof the severity of the drought.
Climate change isn’t just responsible for unusual heat. Paradoxically, it is often responsible for unusual cold. The jet stream divides cold Arctic air from warmer air at lower latitudes. The greater the difference in temperature, the firmer the barrier — think of warm and cold air like oil and vinegar, separating according to their different densities. Now, because the Arctic is heating up faster than the rest of the planet, the jet stream is growing weaker and more wobbly, allowing cold Arctic air to reach further south. That’s what happened in February of 2015, according to two studies, when the eastern half of North America saw its second-coldest month since 1900. In Chicago, which saw its coldest month since 1875, the average February temperature was below 15 degrees F.
Miami has seen more and more floods on sunny days. This can sometimes happen when the moon drifts near the Earth, producing extra-large tides, and it is made worse by rising seas. Sea levels have creeped up about 8 inches since the preindustrial age, making floods more severe. The probability of a 22-inch tidal flood in Miami has increased by more than 500 percent since 1994.
“Human greenhouse gas emissions have profoundly impacted the global climate, natural systems and human infrastructure,” notes the report. “These impacts are clear, costly and widespread.” Authors noted, “As the the science has become stronger, it has become clear that human activities are primarily, if not exclusively, responsible for the global warming trend.”
It’s remarkable how much damage human-caused climate change has already inflicted given how little the planet has warmed. Temperature data show that temperatures have risen around 1 degree C on average since around the turn of the 20th century. That doesn’t mean that every day in every place is 1 degree warmer. Some years are hotter, while others are cooler. And some places have shown little warming, while others are broiling. Parts of the Arctic, for example, have warmed as much as 4 degrees C. The 1 degree average is merely an indictor of planetary health, a way of showing the Earth is running a fever.
A new report from an international body of climate scientists warns that fever is only going to get worse. Rising temperatures, they say, are fueling all manner of mayhem and will prove increasingly deadly in the years to come. At just 1.5 degrees of warming, hundreds of millions of people will suffer severe heat waves and lasting drought, while tens of millions more will face flooding from rising seas. And that’s the best-case scenario.
It only gets worse from here.
Under the Paris Agreement, countries adopted a goal of keeping warming “well below 2 degrees” and agreed “to pursue efforts to limit the temperature increase even further to 1.5 degrees.” It’s now evident that even at 2 degrees of warming, climate change will be catastrophic. And 2 degrees is a formidable goal. Even if countries fulfill their pledges under the Paris Agreement, the planet will heat up by 3 degrees, and virtually no one is taking those goals seriously. At the current rate, Earth is headed for 4 degrees of warming by the end of this century, a level of geophysical chaos that climate scientist Kevin Anderson has called “incompatible with an organized global community.”
Even small differences in temperature can produce vast changes to the global climate. The difference between 1.5 degrees of warming and 2 degrees of warming is the difference between decimating coral reefs and killing them off altogether. At 2 degrees, the average drought doubles in length, and the world can expect to losing trillions of dollars more to coastal flooding by the end of the century.
While the goal of limiting warming to 2 degrees C has some crude basis in science, that science is severely outdated. Yale economist William Nordhausargued for a 2-degree limit in 1975, with the goal of keeping temperatures within the “normal range of long-term climatic variation.” But there is nothing particularly significant about 2 degrees, as opposed to 1.8 or 2.2 degrees. The number stuck because it is big and round, and it looked to be an attainable goal.
In the decades since Nordhaus made his back-of-the-envelope calculation, the science has significantly improved, and researchers now have a much better idea of what to expect at various levels of warming. They learned, for example, that at just 2 degrees, rising seas would inundate low-lying islands in the Pacific, effectively wiping entire countries off the map. It now seems that countries should have been gunning for 1.5 all along.
To keep warming to 1.5 degrees, countries need to overhaul the global energy system in just a few short years, phasing out gas-powered cars, trucks and planes, as well as shuttering coal- and gas-fired power plants. Scientists say the world must cut emissions in half by 2030 and bring emissions down to zero by 2050, at which point they need to actively remove carbon dioxide from the atmosphere.
The scale of the change is unprecedented in human history, but without radical transformation, history-making weather disasters like Hurricane Michael will start to feel routine. The research is clear. Climate change is already taking a massive toll and, as the new report on the 1.5 degree target shows, it’s only going to get worse. How much worse is up to us.