Category: Weather

Is climate change to blame for the recent weather disasters? 2 things you need to understand

Evidence connects human-caused climate change to heat waves. Ties to some other extremes aren’t as clear cut. AP Photo/Alessandra Tarantino

by Scott Denning (Colorado State University)

Summer isn’t even half over, and we’ve seen heat waves in the Pacific Northwest and Canada with temperatures that would make news in Death Valley, enormous fires that have sent smoke across North America, and lethal floods of biblical proportions in Germany and China. Scientists have warned for over 50 years about increases in extreme events arising from subtle changes in average climate, but many people have been shocked by the ferocity of recent weather disasters.

A couple of things are important to understand about climate change’s role in extreme weather like this.

First, humans have pumped so much carbon dioxide and other planet-warming greenhouse gases into the atmosphere that what’s “normal” has shifted. Extreme heat waves that were once ridiculously improbable are on their way to becoming more commonplace, and unimaginable events are becoming possible.

Second, not every extreme weather event is connected to global warming.

Shifting the bell curve

Like so many things, temperature statistics follow a bell curve – mathematicians call these “normal distributions.” The most frequent and likely temperatures are near the average, and values farther from the average quickly become much less likely.

All else being equal, a little bit of warming shifts the bell to the right – toward higher temperatures. Even a shift of just a few degrees makes the really unlikely temperatures in the extreme “tail” of the bell happen dramatically more often.

NASA mapped the changing temperature bell curve year by year starting in 1951.

The stream of broken temperature records in the North American West lately is a great example. Portland hit 116 degrees – 9 degrees above its record before the heat wave. That would be a once-unimaginable extreme at the end of the tail, but it’s now inching closer.

The width of a bell curve is measured by its standard deviation. About two-thirds of all values fall within one standard deviation of the average. Based on historical temperature records, the heat wave in 2003 that killed more than 70,000 people in Europe was five standard deviations above the mean, so it was a 1 in 1 million event.

Without eliminating emissions from fossil fuels, heat like that is likely to happen a few times a decade by the time today’s toddlers are retirees.

So, is climate change to blame?

There’s a basic hierarchy of the extreme events that scientific research so far has shown are most affected by human-caused climate change.

At the top of the list are extreme events like heat waves that are certain to be influenced by global warming. In these, three lines of evidence converge: observations, physics and computer model simulations that predict and explain the changes. At the bottom of the list are things that might plausibly be caused by rising levels of greenhouse gases but for which the evidence is not yet convincing. Here’s a partial list.

1) Heat waves: Studies show these are certain to increase dramatically with global warming, and indeed that’s exactly what we’re observing.

Map showing cities in the Southeast in particular will see the longest heat seasons
The hot season is getting a lot longer in some places. Michael Kolian/U.S. Global Change Research Program

2) Coastal flooding: Heat is causing ocean waters to expand, pushing up sea levels and melting ice sheets around the world. Both high-tide flooding and catastrophic storm surge will become much more frequent as those events start from a higher average level because of sea level rise.

3) Drought: Warmer air evaporates more water from reservoirs, crops and forests, so drought will increase because of increased water demand, even though changes in rainfall vary and hard to predict.

4) Wildfires: As the western U.S. and Canada are seeing, heat dries out the soils and vegetation, providing drier fuel that’s ready to burn. Forests lose more water during hotter summers, and fire seasons are getting longer.

A greenhouse surrounded by dry brush with fire in the forest on the hill behind it
The Tamarack Fire spread through dry forest and grass near Lake Tahoe on July 17, 2021. AP Photo/Noah Berger

5) Reduced spring snowpack: Snow starts accumulating later in the fall, more water is lost from the snowpack during winter, and the snow melts earlier in the spring, reducing the flush of water into reservoirs that supports the economies of semiarid regions.

6) Very heavy rainfall: Warmer water can transport more water vapor. Damaging rainstorms are due to strong updrafts that cool the air and condense the vapor as rainfall. The more water is in the air during a strong updraft, the more rain can fall.

7) Hurricanes and tropical storms: These derive their energy from evaporation from the warm sea surface. As oceans warm, larger regions can spawn these storms and provide more energy. But changes in winds aloft are expected to reduce hurricane intensification, so it’s not clear that global warming will increase damage from tropical storms.

8) Extreme cold weather: Some research has attributed cold weather than moves south with the meandering of the jet stream – sometimes referred to as “polar vortex” outbreaks – to warming in the Arctic. Other studies strongly dispute that Arctic warming is likely to affect winter weather farther south, and this idea remains controversial.

9) Severe thunderstorms, hail and tornadoes: These storms are triggered by strong surface heating, so it’s plausible that they could increase in a warming world. But their development depends on the circumstances of each storm. There is not yet evidence that the frequency of tornadoes is increasing.

A warning that can’t be ignored

The catastrophic impacts of extreme weather depend at least as much on people as on climate.

The evidence is clear that the more coal, oil and gas are burned, the more the world will warm, and the more likely it will be for any given location to experience heat waves that are far outside anything they’ve experienced.

Disaster preparedness can quickly fail when extreme events blow past all previous experience. Portland’s melting streetcar power cables are a good example. How communities develop infrastructure, social and economic systems, planning and preparedness can make them more resilient – or more vulnerable – to extreme events.

Scott Denning, Professor of Atmospheric Science, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Human activity influencing global rainfall, study finds

Read the full story in The Guardian.

Anthropogenic warming of climate has been a factor in extreme precipitation events globally, researchers say.

‘We live in a desert. We have to act like it’: Las Vegas faces reality of drought

Read the full story in The Guardian.

Water investigators track down wasteful homeowners and public turf torn up to conserve scarce water supplies

Colorado’s water scarcity may finally be coming for your local duck pond

Read the full story from KUNC.

Water supplies are so tight in the West that most states keep close watch over every creek, river, ditch and reservoir. A complex web of laws and rules is meant to ensure that all the water that falls within a state’s boundaries is put to use or sent downstream to meet the needs of others.

To prevent waste and avoid sparking an interstate legal battle, Colorado has started cracking down on what may seem like a drop in the proverbial bucket — illegal ponds.

Realtime Climate

Realtime Climate monitors local weather and events across the U.S. and generates alerts when certain conditions are met or expected. These alerts provide links to science-based analyses and visualizations—including locality-specific, high-quality graphics—that can help explain events in the context of climate change.

Climate Central launched this tool to help meteorologists and journalists cover connections between weather, news, and climate in real time, and to alert public and private organizations and individuals about particular local conditions related to climate change, its impacts, or its solutions.

The drought in the western U.S. is getting bad. Climate change is making it worse

Read the full story from NPR.

By almost every measure, the drought in the Western U.S. is already one for the record books…That’s creating a fundamental threat to the way Western water systems operate, because they were built around the idea that the climate would remain constant. Historical climate data such as river flows and rainfall totals told engineers how big to build reservoirs and canals. The data also told them how much water was available to divide up among cities and farms.

There’s a danger in over-simplifying water conservation

Read the full story from Morning AgClips.

You hear it every time drought returns to California: “Turn off the faucet when you brush your teeth.” “Collect shower water in a bucket before it warms up.”

While valuable, these tried and true drought resilience strategies can also deflect attention from the monumental challenges posed by droughts to natural areas, waterways, agriculture and people in California. Far-sighted and discerning management of the state’s annual precipitation and groundwater is critical, particularly as droughts become more frequent due to climate change, said Faith Kearns, the academic coordinator of UC’s California Institute for Water Resources.

Another dangerous fire season is looming in the Western U.S., and the drought-stricken region is headed for a water crisis

Dry conditions across the West follow a hot, dry year of record-setting wildfires in 2020. Communities were left with scenes like this, from California’s Creek Fire. Amir Aghakouchak/University of California Irvine

by Mojtaba Sadegh (Boise State University), Amir AghaKouchak (University of California, Irvine), and John Abatzoglou (University of California, Merced)

Just about every indicator of drought is flashing red across the western U.S. after a dry winter and warm early spring. The snowpack is at less than half of normal in much of the region. Reservoirs are being drawn down, river levels are dropping and soils are drying out.

It’s only May, and states are already considering water use restrictions to make the supply last longer. California’s governor declared a drought emergency in 41 of 58 counties. In Utah, irrigation water providers are increasing fines for overuse. Some Idaho ranchers are talking about selling off livestock because rivers and reservoirs they rely on are dangerously low and irrigation demand for farms is only just beginning.

Scientists are also closely watching the impact that the rapid warming and drying is having on trees, worried that water stress could lead to widespread tree deaths. Dead and drying vegetation means more fuel for what is already expected to be another dangerous fire season.

U.S. Interior Secretary Deb Haaland and Agriculture Secretary Tom Vilsack told reporters on May 13, 2021, that federal fire officials had warned them to prepare for an extremely active fire year. “We used to call it fire season, but wildland fires now extend throughout the entire year, burning hotter and growing more catastrophic in drier conditions due to climate change,” Vilsack said.

As climate scientists, we track these changes. Right now, about 84% of the western U.S. is under some level of drought, and there is no sign of relief.

Color-coded map showing drought
The U.S. Drought Monitor for mid-May shows nearly half of the West in severe or extreme drought. National Drought Mitigation Center/USDA/NOAA

The many faces of drought

Several types of drought are converging in the West this year, and all are at or near record levels.

When too little rain and snow falls, it’s known as meteorological drought. In April, precipitation across large parts of the West was less than 10% of normal, and the lack of rain continued into May.

Rivers, lakes, streams and groundwater can get into what’s known as hydrological drought when their water levels fall. Many states are now warning about low streamflow after a winter with less-than-normal snowfall and warm spring temperatures speeding up melting. The U.S. Bureau of Reclamation announced it would cut off water to a canal serving farms in the Klamath Project on the Oregon-California border because of low water supplies. It also warned that Lake Mead, a giant Colorado River reservoir that provides water for millions of people, is on pace to fall to levels in June that could trigger the first federal water shortage declaration, with water use restrictions across the region.

Dwindling soil moisture leads to another problem, known as agricultural drought. The average soil moisture levels in the western U.S. in April were at or near their lowest levels in over 120 years of observations.

Four US maps showing drought levels of precipitation, vapor pressure deficit, evapotranspiration and streamflow
Four signs of drought. Climate Toolbox

These factors can all drive ecosystems beyond their thresholds – into a condition called ecological drought – and the results can be dangerous and costly. Fish hatcheries in Northern California have started trucking their salmon to the Pacific Ocean, rather than releasing them into rivers, because the river water is expected to be at historic low levels and too warm for young salmon to tolerate.

Snow drought

One of the West’s biggest water problems this year is the low snowpack.

The western U.S. is critically dependent on winter snow slowly melting in the mountains and providing a steady supply of water during the dry summer months. But the amount of water in snowpack is on the decline here and across much of the world as global temperatures rise.

Several states are already seeing how that can play out. Federal scientists in Utah warned in early May that more water from the snowpack is sinking into the dry ground where it fell this year, rather than running off to supply streams and rivers. With the state’s snowpack at 52% of normal, streamflows are expected to be well below normal through the summer, with some places at less than 20%.

Map of western U.S. showing many areas with low snowpack
Snowpack is typically measured by the amount of water it holds, known as snow water equivalent. National Resource Conservation Service

Anthropogenic drought

It’s important to understand that drought today isn’t only about nature.

More people are moving into the U.S. West, increasing demand for water and irrigated farmland. And global warming – driven by human activities like the burning of fossil fuels – is now fueling more widespread and intense droughts in the region. These two factors act as additional straws pulling water from an already scarce resource.

As demand for water has increased, the West is pumping out more groundwater for irrigation and other needs. Centuries-old groundwater reserves in aquifers can provide resilience against droughts if they are used sustainably. But groundwater reserves recharge slowly, and the West is seeing a decline in those resources, mostly because water use for agriculture outpaces their recharge. Water levels in some wells have dropped at a rate of 6.5 feet (2 meters) per year.

The result is that these regions are less able to manage droughts when nature does bring hot, dry conditions.

Fish pour out of a pipe into a bay.
California fish hatcheries have started trucking their salmon to the Pacific Ocean because the rivers they are usually released into are too low and warm. AP Photo/Rich Podroncelli

Rising global temperatures also play several roles in drought. They influence whether precipitation falls as snow or rain, how quickly snow melts and, importantly, how quickly the land, trees and vegetation dry out.

Extreme heat and droughts can intensify one another. Solar radiation causes water to evaporate, drying the soil and air. With less moisture, the soil and air then heat up, which dries the soil even more. The result is extremely dry trees and grasses that can quickly burn when fires break out, and also thirstier soils that demand more irrigation.

Alarmingly, the trigger for the drying and warming cycle has been changing. In the 1930s, lack of precipitation used to trigger this cycle, but excess heat has initiated the process in recent decades. As global warming increases temperatures, soil moisture evaporates earlier and at larger rates, drying out soils and triggering the warming and drying cycle.

Fire warnings ahead

Hot, dry conditions in the West last year fueled a record-breaking wildfire season that included the largest fires on record in Colorado and California.

As drought persists, the chance of large, disastrous fires increases. The seasonal outlook of warmer and drier-than-normal conditions for summer and fire season outlooks by federal agencies suggest another tough, long fire year is ahead.

This article was updated with a statement from Secretaries Deb Haaland and Tom Vilsack.

Mojtaba Sadegh, Assistant Professor of Civil Engineering, Boise State University; Amir AghaKouchak, Associate Professor of Civil & Environmental Engineering, University of California, Irvine, and John Abatzoglou, Associate Professor of Engineering, University of California, Merced

This article is republished from The Conversation under a Creative Commons license. Read the original article.

High Plaines Climate Center develops tool to accompany release of new Climate Normals

When a meteorologist says that a chilly day in May was 12 degrees lower than normal, the normal being referenced is typically from the official 30-year U.S. Climate Normals. Updated every decade, the Normals are based on 30-year averages of climate observations recorded at thousands of weather stations across the country.

On May 4, the 1991-2020 U.S. Climate Normals are being released by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NCEI). In conjunction, the University of Nebraska–Lincoln’s High Plains Regional Climate Center is publishing a new tool that allows users to examine what normal looks like relative to longer or shorter timeframes than the most recent 30 years.

The new U.S. Climate Normals are here. What do they tell us about climate change?

Annual U.S. temperature compared to the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right).
Annual U.S. temperature compared to the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right). (NOAA NCEI)

Read the full story from NOAA. See also the story in the Washington Post.

Every 10 years, NOAA releases an analysis of U.S. weather of the past three decades that calculates average values for temperature, rainfall and other conditions.  

That time has come again.

Known as the U.S. Climate Normals, these 30-year averages — now spanning 1991-2020 — represent the new “normals” of our changing climate. They are calculated using climate observations collected at local weather stations across the country and are corrected for bad or missing values and any changes to the weather station over time before becoming part of the climate record.

Simply stated: The Normals are the basis for judging how daily, monthly and annual climate conditions compare to what’s normal for a specific location in today’s climate. 

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