Human fingerprints on extreme weather conditions

Hurricane Michael broke records on Wednesday when it became the most powerful hurricane of all time to touch Florida. Abnormally warm waters supplied winds of up to 155 km / h, which devastated homes and businesses caught in the storm. As many outlets point out, climate change has probably fueled the record wind speed. This is remarkable in that both journalists and researchers have always been reluctant to associate any storm with climate change.

Five or ten years ago, if you asked a scientist why climate change was in a particular hurricane, it would be confusing to say that it was impossible to blame a single event for the general warming trend. . These days are over. Over the last decade, scientists have developed sophisticated tools to retrieve the human footprint of extreme weather conditions. The emerging field of attribution research, as it is known, studies the role of climate change in specific events. A recently published report of more than 200 attribution studies clearly shows that heat-trapped carbon pollution is already worsening weather conditions considerably.

"Since the early days of fingerprinting of human activities in the twentieth century warming, scientists are now able to attribute the specific influence of climate change to many events, disasters and trends," notes the report. of Climate Signals, a project linking the points between carbon pollution and extreme weather conditions. The report details the many links between rising temperatures and recent weather disasters in the United States and around the world. Here are some highlights.

Three different studies, using different methods, revealed that climate change had caused higher rainfall during Hurricane Harvey by 15 to 20%. Warmer seas are more prone to evaporation, which frees more water in the air. Hot air retains more water, producing more rain during storms. With the help of all this extra heat, Hurricane Harvey broke the record for precipitation in the United States.

The warmer the weather, the more precipitation is abundant instead of snow. It also means that the little accumulated snow melts earlier than expected. This is important because the melting snowpack feeds the rivers and streams that supply water to the rest of California. Between 2011 and 2015, climate change decreased the snowpack in Sierra Nevada by 25%. To make matters worse, the extra heat dries up the soil, aggravating the drought. Between 2012 and 2014, the rise in temperatures was at the origin of 27% of the severity of the drought.

Climate change is not just responsible for the unusual heat. Paradoxically, he is often responsible for an unusual cold. The jet stream divides the cold air of the Arctic into warmer air at lower latitudes. The greater the difference in temperature, the firmer the barrier: think of hot air and cold air, such as oil and vinegar, separating them according to their density. Now, because the Arctic is warming faster than the rest of the planet, the jet stream is becoming weaker and more flickering, allowing the cold air of the Arctic to reach more to the south. That's what happened in February 2015, according to two studies, when the eastern half of North America had its second coldest month since 1900. In Chicago, which had its coldest month since 1875, the average temperature in February was below 15 degrees F.

Miami has seen more and more floods on sunny days. This can sometimes happen when the moon approaches Earth, producing very large tides, and the rising waters aggravate the situation. Sea level has increased about 8 inches since the pre-industrial era, worsening flooding. The probability of a 22-inch tidal wave in Miami has increased by more than 500% since 1994.

"Human emissions of greenhouse gases have profoundly affected the global climate, natural systems and human infrastructure," the report notes. "These impacts are clear, costly, and widespread." The authors noted, "As science grew stronger, it became clear that human activities were primarily, if not exclusively, responsible for global warming."

It is remarkable the damage caused by climate change caused by man given the low global warming. Temperature data show that temperatures have risen by about 1 degree C on average since the beginning of the 20th century. This does not mean that every day, in every place, is 1 degree warmer. Some years are warmer, while others are cooler. And some places have shown little warming, while others are grilling. Arctic regions, for example, have warmed up to 4 degrees C. The average of 1 degree is just one indicator of the planet's health, a way of showing the Earth that it is fever.

A new report from an international group of climatologists warns that the fever will only get worse. Rising temperatures, they say, is fueling all kinds of unrest and will prove increasingly deadly in the years to come. With a warming of only 1.5 degrees, hundreds of millions of people will experience severe heatwaves and persistent drought, while tens of millions of other people will be exposed to flooding caused by rising water levels. And it's the best scenario.

Under the Paris Agreement, countries aimed to keep warming "well below 2 degrees" and "continue their efforts to further limit the temperature rise to 1.5 degrees". It is now obvious that even with a 2 degree warming, climate change will be catastrophic. And 2 degrees is a great goal. Even if countries fulfill their commitments under the Paris Agreement, the planet will warm up by 3 degrees and hardly anyone takes these goals seriously. At the current rate, global warming is expected to reach 4 degrees by the end of the century, a geophysical chaos that climate scientist Kevin Anderson has described as "incompatible with an organized global community".

Even small differences in temperature can lead to profound changes in the global climate. The difference between 1.5 degree warming and 2 degree warming is the difference between decimating the coral reefs and killing them completely. At 2 degrees, the average drought doubles in length and the world can expect to lose billions of dollars more because of coastal flooding by the end of the century.

Although the goal of limiting warming to 2 ° C is based on a basic scientific basis, this science is extremely outdated. William Nordhaus, an economist at Yale, advocated a 2-degree limit in 1975 to keep temperatures "within the normal range of long-term climate change." But nothing particularly significant around 2 degrees, as opposed to 1.8 or 2.2 degrees. The number stuck because it's big and round, and it seemed like a workable goal.

In the decades since Nordhaus made its final calculation, science has improved considerably and researchers now have a much better idea of ​​what to expect at different levels of warming. They learned, for example, that at only 2 degrees Celsius, the rising waters would overwhelm the low-lying Pacific islands, effectively wiping entire countries off the map. It now seems that the countries should have aimed 1.5 from the beginning.

To keep warming to 1.5 degrees, countries need to rethink the global energy system in just a few years, phasing out cars, trucks and gas-fired aircraft, as well as shutting down coal and gas-fired power plants. . Scientists say the world must halve its emissions by 2030 and bring them back to zero by 2050. At this point, they must actively remove carbon dioxide from the atmosphere.

The magnitude of this change is unprecedented in the history of humanity, but without radical transformation, meteorological disasters such as Hurricane Michael, which have made their history, will begin to feel routine. The research is clear. Climate change is already having serious consequences and, as the new 1.5 degree goal report shows, it will only get worse. How much worse is ours.

Disclosure: Climate Signals and Nexus Media are both affiliated with Rockefeller Philanthropy Advisors. Jeremy Deaton writes for Nexus Media, a subscribed wire covering climate, energy, politics, art and culture. You can follow him @deaton_jeremy.