In a stable climate, the ratio of new record highs to new record lows is approximately even. However in our warming climate, record highs have begun to outpace record lows, with the imbalance growing for the past three decades. This trend is one of the clearest signals of climate change that we experience directly.
Winter sea ice in the Arctic typically reaches its maximum extent in March. After three consecutive record lows in March of 2015, 2016 and 2017, maximum extent is on track to set yet another new record low this year. Monthly average extent in February 2018 was the lowest ever recorded for a February.
The Arctic is warming at about twice the rate of the Northern Hemisphere, largely due to anthropogenic global climate change. Arctic sea ice has shown a dramatic decline since at least 1979—when satellite measurements began—due to climate change.
The Arctic just finished its warmest winter on record. North of 80° latitude (i.e. near the North Pole), temperatures have averaged approximately 10°F (6°C) above normal since January 1. The northernmost weather station in the world, Greenland's Cape Morris Jesup, recorded above-freezing temperatures for over 60 hours in February.
Snow melt provides a sustained source of water for over one billion people globally and is a critically important resource in the western US and in California where the Sierra Nevada snowpack supplies one-third of the state's water supply. In recent years, snow water equivalent (SWE)—the amount of water stored in the snowpack—in the western US has significantly diminished.
Long-term climate warming is strongly correlated with declining snow water equivalent. And shifts in stream flow throughout the American West have been driven by decreased spring accumulation and/or increased spring melt. The fingerprint of warming temperatures has been found in these trends at both broad scale and in California in particular.
SWE is measured on approximately the first of each month in the mountains of the western US during the winter season and reaches its basin-wide maximum on approximately April. These measurements indicate the condition of water resources. At the February 1, 2018, measurement, water resources in several states were a fraction of the historical average.
Many western states including California, Utah, Oregon, Washington, and Colorado are in the midst of a warm, dry winter. In January, almost all of the open resorts in New Mexico, Arizona, Colorado, Utah, Nevada, and California were relying on man-made snow to operate. These states have also experienced worsening drought in recent months.
The intense cold hitting the United States during the first week of 2018 continued with a heavy snowstorm that inundated the Northeast seaboard beginning the night of January 3 through January 4. The combined impact of the arctic outbreak and the intensified nor’easter landed a double whammy in which new record low temperature records were set.
Science studies and models report that the outbreak of arctic air bringing freezing temperatures to the lower United States is consistent with the climate disruption expected on a warming planet where the Arctic heats up faster and cold air is displaced to the south.
Unusually warm offshore waters also amplified the temperature contrast between land and ocean surfaces. This temperature contrast is what generally fuels nor’easters. These conditions over the Atlantic are consistent with the long-term climate change trends that intensify nor’easters.
While climate change warms the planet as whole, it also disrupts regional weather patterns, sometimes displacing cold air to the south. The overall warming trend continues but cold conditions can move. The record setting heat events recently observed further north in parallel to cold conditions in the continental US are consistent with this pattern of disruption.
Higher temperatures, drier conditions, increased fuel availability, and growing warm seasons—all linked to climate change—are increasing wildfire risk in California.
In 2017, the combination of a wet winter followed by extreme heat and dry conditions has fueled record wildfires in many Western states.
In early December, a series of fires extended this trend when they erupted in the mountains north of Ventura and Los Angeles, California.
The Thomas Fire, which began on the evening of December 4, is the largest blaze and grew quickly to nearly 31,000 acres (50 square miles) in less than 12 hours. As of January 1, 2018, the Thomas Fire was 92 percent contained and had burned 281,893 acres establishing it as largest fire in California recorded history. A mixture of dry foliage, low humidity and high sustained winds of more than 30 miles per hour led to its explosive growth, according to Fire Sgt. Eric Buschow. Other major fires included the Creek and Rye events.
Research indicates a direct causal link between human-induced climate change and increased wildfire risk in California. Climate change has contributed to California's longer fire seasons, the growing number and destructiveness of fires and the increasing area of land consumed.
Trends in California driven by climate change—including higher temperatures and drier conditions—are elevating the risk of dangerous and destructive wildfires across California and the western United States.
On October 8, a group of fires exploded across a wide swath of Northern California. Taken as a group, the fires are among the worst on record in the state in terms of lives and property lost. After just one week, the fires have killed at least 41 people, burnt more than 200,000 acres, destroyed or damaged more than 5,500 homes, and displaced 100,000 people. Governor Jerry Brown declared a state of emergency in Butte, Lake, Mendocino, Napa, Nevada, Orange, Sonoma and Yuba counties.
By the end, the Wine Country fires killed 42 people, destroyed 8,700 homes and buildings, and burned 245,000 acres. The event was deadliest, most destructive, and one of the largest fires in California history.
The combination of a wet winter followed by extreme heat and dryness has fueled record wildfires in many Western states. Climate change compounds the risks of wildfires by extending the length of the fire season and adding to the intensity of droughts and heat waves. Park Williams, a climate and drought expert, noted, “... the combination of dry fuel, extreme heat and climate change is a recipe for what we are seeing."
A vast area of high pressure brought unusual heat and humidity to the Great Lakes and Ohio Valley after the end of astronomical summer. This late-season heat wave occurred the same year and in much of the same region that experienced record hot and unseasonably early temperatures in February. Formal attribution work has identified the fingerprint of global warming in February's record hot temperatures, as climate change increased the likelihood of such heat by threefold.
Chicago had seven days in a row of record daily high temperatures, with the mercury reaching or passing the 92 degree-mark each day from September 20th to 26th. This is the latest stretch of seven consecutive 90-degree days on record in Chicago. Further east, Cleveland had a five-day streak of daily record highs, and Lansing, Michigan had a five-day streak of highs that tied or broke the previous records set in 1891 and 1895. A handful of other cities saw their highest temperatures on record for this late in the year, and Burlington, Vermont warmed above 90°F for the first time since 1939.
The fingerprint of global warming has been firmly identified in the increasing intensity, duration and frequency of extreme heat events globally. Heat waves exacerbate the risks associated with heat exposure, and urban residents are particularly vulnerable to threats of heat waves due to the urban heat island effect.
The record-breaking rainfall and flooding driven by Hurricane Maria—as well as Hurricanes Harvey and Irma just weeks before—is consistent with the long-term trend driven by climate change. Hurricane Maria made landfall in Dominica as a Category 5 hurricane on September 18, then hit southeast Puerto Rico on September 20 with 155 mph winds and a central pressure of 917 millibars. It was the third strongest storm to make landfall in the United States. "1,000-year" rains inundated much of eastern and northwestern Puerto Rico. The storm knocked out power to the entire island of Puerto Rico, home to 3.5 million people, leading to a prolonged humanitarian crisis.
Extreme rainfall is increasing worldwide due to climate change. In Puerto Rico, rain falling in very heavy events increased at least 33 percent from 1958-2012. Seas are now higher due to global warming, so storm surge drives much further inland. There has also been a global increase in the observed intensity of the strongest tropical cyclones, correlated with observed trends in sea surface temperatures in recent decades.
NFIP claims rise alongside upward trends in extreme storm frequency . . .
The increasing frequency of US National Flood Insurance Program (NFIP) claims parallels the increasing frequency of extreme rainfall and flooding in the United States.
Higher temperatures and drier conditions—both linked to climate change—are increasing wildfire risk in California.
The La Tuna Fire erupted north of downtown Los Angeles and, at more than 7,000 acres, the fire is the largest to burn within Los Angeles' city limits.
While small compared to the biggest fires in California's history, the La Tuna Fire is notable for its proximity to a major city and its rapid growth amid unseasonably warm temperatures. The fire also erupted at the edge of the Angeles National Forest, a region where bark beetle activity has increased in recent years of extreme heat and drought.