Our weather is now profoundly different. For decades, warmer temperatures have altered the Earth’s metabolism, and now, the consequences are being felt worldwide.
In the United States, 2017 in particular has thrown the reality of climate change into sharp relief—featuring extreme heat, fires, precipitation, and floods. Among these, several recent events stand out, including a series of major, Category 4, landfalling hurricanes—Maria, Irma and Harvey—and the deadliest and most destructive fires in California’s history.
Climate change can look familiar—hurricanes in the Gulf, wildfires in California—but the hurricanes and fires of today are not like those from past decades. Hurricane Harvey unloaded over 60 inches of rain east of Houston, the greatest amount ever recorded—by 12 inches!—in the Lower 48 states from a single storm. One analysis finds climate change may have contributed as much as 30 percent to the extreme rainfall totals.
The wine country fires in northern California exploded, spreading 20,000 acres in 12 hours on October 9—which is more than a football field every three seconds. The rapid spread was due in part to exceptionally dense and dry fuel, the product of California’s record wet rainy season and record hot summer.
Extreme events offer numerous immediate teachable moments to engage the public. However, understanding the extent to which an extreme event is extreme requires historical context. It is with this in mind that Climate Nexus launched a new project in May 2016 called Climate Signals—a US-focused science education tool that places emerging extreme events, like the major 2017 Atlantic hurricanes and California wildfires, in the context of larger climate trends.
Climate Signals is designed to surface the immediate threat of climate change when the public is paying attention through real-time event attribution, thereby increasing public will for climate action. Attribution is done by identifying the chain of connections between greenhouse gas emissions and individual climate events.
As an example, let’s take a closer look at the climate connections to Hurricanes Maria, Irma and Harvey. Climate change is amplifying the damage done by hurricanes in three primary ways: increased storm surge, more extreme rainfall, and increased potential wind speed.
Seas are now higher due to global warming, allowing storm surge to drive dramatically further inland. Storm surge levels during Hurricane Irma exceeded 6 feet and set records in some parts of northern Florida up to coastal South Carolina. In some cases, Irma broke tide gauge records set just one year prior during Hurricane Matthew.
Global warming is also increasing water vapor in the air, which fuels extreme rainfall and increases the threat of hurricane-driven flooding. During Hurricane Maria, rainfall rates were as high as 6.44 inches per hour, and total rainfall over Puerto Rico exceeded 20 inches. For much of Puerto Rico, rainfall rates were so extreme that, based on statistics derived from old climate observations, they should occur just once every 1,000 years. Maria’s extreme rainfall is consistent with existing climate trends showing a 33 percent increase in very heavy rain events in Puerto Rico from 1958 to 2012.
As for Hurricane Harvey, which brought up to 60.58 inches of rain to the Houston area, rainfall totals were so extreme, they qualified as 25,000 to 500,000 year rains — rainfall with a very small chance of occurring in any given year. But again, these statistics are based on historical observations that no longer accurately characterize our climate. In fact, Harvey was Houston’s third 500+ year flood in three years.
Finally, as global warming heats sea surfaces, the energy available to power hurricanes increases, raising the limit for potential hurricane wind speed. Hurricane Irma grew in size amid nearly ideal circumstances for intensification, with low wind shear and sea surface temperatures 0.9°F to 2.25°F (0.5°C to 1.25°C) above average, relative to a 1961-1990 baseline. At full strength, Irma maintained maximum wind speeds of at least 180 mph for 37 hours, longer than any storm on Earth on record, passing Super Typhoon Haiyan, the previous record holder (24 hours). Irma’s maximum accumulated energy over 24 hours was also the highest for any Atlantic hurricane on record.
The record-breaking storm surge, rainfall, and intensity observed during Hurricanes Maria, Irma, and Harvey are what climate change looks like. To effectively communicate the emerging impacts of climate change, the most accurate and helpful thing is to show that many events are part of and extend some major trends that are consistent with human-caused climate change.
Climate Signals fills this gap, providing the interested public with resources to better understand and report on climate change connections to major events as they unfold and as people confront the impacts.