The group of UC Berkeley researchers woke up early each morning around 2 o’clock and piled into a truck to make their rounds. Stationed at a ranch in San Luis Obispo County, they visited dozens of oak and pine trees each day and took branch samples of each.
While one crew member inserted samples into a pressure chamber to test for signs of drought-related water stress, two others scurried up the hill with clippers and headlamps and took samples of outlying trees. Watching for rattlesnakes, they sprinted back to the vehicle and ran the same water tests on each sample. The researchers had to complete the tests within minutes of cutting the samples to produce a valid result.
Back at camp, they napped by day, resampled each tree after lunch, and got to bed around ten.
“Then we’d get up again at 2,” said Andrew Weitz, a UC Berkeley grad student who helped lead the project.
After nearly two years of studying 109 trees at the height of California’s historic drought, Weitz, his professor David Ackerly, and the rest of their team saw something remarkable: Some of the oldest oaks in California were dying.
At study sites near Kenwood, Sonoma County, Weitz said, valley and blue oaks wilted and turned brown. At the more southerly site in San Luis Obispo, hillsides of trees — most of them old enough to have stood over foraging grizzly bears in the 18th and 19th centuries and lived through many long dry spells — simply perished.
“The death of these old oak trees serves as an early warning of the effects of a changing climate,” said Ackerly, an ecologist in Cal’s Department of Integrative Biology.
Weitz added that warming and extreme droughts pose “very serious threats to the future of oak woodlands” in California.
The abrupt deaths of ancient oaks during the recent five-year drought is just one of many pieces of evidence that climatic baselines are shifting as the planet warms. All told, at least 100 million trees — mostly sugar pines — died in California during the drought. In the Sierra Nevada, scientists also saw a sudden, if small, spike in deaths of giant sequoias — ancient trees that had lived through their share of megadroughts.
In the same mountain range, scientists have discovered that bristlecone pines, the world’s oldest individual organisms, are being overwhelmed by faster growing species advancing upslope as temperatures rise in the high country. Giant sequoias have also shown signs of drought-induced stress, and researchers with UC Merced and the U.S. National Park Service recently published a study warning that the ancient trees could be imperiled by warming. Plus, the winter snowpack is melting more rapidly each year, a major threat to the state’s native salmon and trout.
For many scientists, the recent drought offered a valuable preview of what Californians can expect as greenhouse gases continue to accumulate and trap the sun’s energy in the atmosphere.
“In Mediterranean climates throughout the world, it’s going to get hotter and drier,” said Anthony Ambrose, a postdoctoral researcher at UC Berkeley who has been studying coastal redwoods and giant sequoias and their responses to extreme weather. Such extreme climate events will drive “range shifts and local extinctions,” Ambrose said.
Already in Southern California, higher-elevation conifer forests are being slowly replaced by oak woodlands and savannah. In the San Francisco Bay Area, climatic changes seem to be affecting distribution of vegetation and native birds, according to Josiah Clark, an ecologist and native bird expert in San Francisco. Clark, who conducts annual bird surveys throughout the Bay Area, said birds that have adapted to drier climates are becoming more prevalent in San Francisco, while ones that are dependent on more moisture are increasingly flying elsewhere.
Some scientists predict that in the coming decades, Northern California’s flora and fauna will increasingly resemble that of Southern California, which, in turn, will look more like Northern Mexico does today. In Northern California, as oak trees die off, they’ll likely be replaced by shrubs and grasslands. At higher elevations, oaks may replace conifer forests. And with fewer trees and forests, some animal species in Northern California will disappear.
In addition, intense wildfires like the recent blazes that tore through the North Bay could hasten the changing environment, scientists say. Forests that burned down might not come back as before, instead taken over by species that like hotter conditions and longer droughts.
Humans will hardly be immune to the devastating impacts of global warming. Searing heat waves that kill thousands have become recurring events and are expected to be routine by the end of the century. And hurricanes are getting a boost from warmer ocean water, which adds devastating energy to the storms.
Seas are rising, and so is the human death toll. Scientists say global warming fueled the drought that helped spark the conflict in Syria, where hundreds of thousands have been killed over six years.
Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, said the evidence of climate change is now so prominent that even laypeople can see and feel it happening, as hurricanes, droughts, and wildfires worsen.
Ackerly warns of an increasingly unstable future. “The new normal is rapid change,” he said.
The year 2016 was bad for trees around the world. That year, the world’s forests lost 73 million acres of canopy to drought, fires, and deforestation, according to a recent assessment by the organization Global Forest Watch. That’s 50 percent more than the canopy cover lost in 2015. Portugal was particularly hard hit last year, losing 4 percent of its tree cover. Much of it will grow back, certainly. Much probably won’t, however.
In California, an estimated 62 million trees died in 2016, bringing the state’s total tree mortality from the five-year drought — which modeling has shown was made worse by climate change — to more than 100 million.
Drought didn’t directly kill most of the trees, but it weakened them to the point that they succumbed to beetle infestation. Still, the die-off was massive, and it could prompt a landscape-scale change in the Sierra Nevada’s ecosystems, especially if another comparable drought occurs before seedling trees have a chance to become adults.
“This is how plants move — they die off in one place and regrow in others,” explained Nate Stephenson, a forest ecologist with the U.S. Geological Survey. “To me, the drought was a preview of what could happen if it continues to warm.”
The majority of California’s drought-induced tree deaths occurred in the Sierra Nevada’s conifer forests, where many species are physiologically adapted to living in soils kept moist through the summer by high mountain snowmelt. It’s in these mountains and their foothills where impacts from warming will materialize first, said UC Berkeley’s Ambrose. That’s because the ecosystems there depend on snowmelt that originates in the highest summits.
“As temperatures keep increasing, the loss of snowpack will mean less recharge of the groundwater they depend on,” he explained.
Droughts are natural and frequent events in California. So are fires, which in October killed countless more trees throughout the state. “But when they occur, their intensity is increasing,” noted Ackerly. “The low rainfall of a drought is one thing, but to have higher temperatures on top of that means greater intensity.”
This means dry spells that California’s native vegetation could once withstand will, in a warmer future, push many species past their thresholds for survival. Oaks will die off in low valleys — as Ackerly and his students have seen happen — and conifers will retreat up the mountains. “We’re already seeing a pine-to-oak transition as oaks basically move uphill,” Ackerly said. “It’s a signature of climate change that we see in the fossil record through the ages.”
Bill Stewart, a forestry specialist at UC Berkeley’s Department of Environmental, Science and Policy Management, said that, during this century, Northern California’s landscape will begin, if it hasn’t already, to resemble that of Southern California. “It’s like we’re moving one or two counties south every decade,” Stewart said.
Ackerly said the North Bay fires, along with the Sierra Nevada tree mortality and the forest clearing effects of sudden oak death, could also result in new plant communities. “We don’t know what recovery will look like,” he said. “Some systems might rebound as the same species grow up underneath the dead adult trees. Others might transition into new habitat types.”
Williams, at Columbia University, said that, in some areas of the Sierra Nevada, the gaps left by fires and drought-related mortality “are so large that natural reseeding may not be possible. These gaps could take centuries or even thousands of years to naturally recolonize.”
Just what recolonization will look like is unclear, he said, because of how quickly climatic conditions are changing. “Temperatures are rising so rapidly that it’s likely the same places will burn over and over again in the next few decades,” said Williams, who is a California native. “These forests might not have time to recover.”
In northern New Mexico, destructive wildfires have transformed conifer-dominated landscapes into ecosystems dominated by shrubs. A drought in the 1950s similarly allowed pinyon pine and juniper to recolonize an area previously home mostly to ponderosa pine.
LeRoy Westerling, professor of Management of Complex Systems and co-director of the Center for Climate Communication at UC Merced, also believes California’s burned woodlands could see a dramatic shift in biodiversity. “When the ecosystem begins to recover after these disturbances, they’re recovering in a new climate regime, and so they may not go back and reset to what they looked like before,” he said.
The loss of moisture also seems to be affecting biomes in the Bay Area. Clark, the ecologist in San Francisco, said “creeping, perennial vegetation” — like California blackberry, honeysuckle and woodland strawberry — has retreated and become less prevalent in Golden Gate Park, the Presidio, and the Marin Headlands. The Labor Day heatwave, he noted, caused an abrupt, widespread die-off.
“There’s less moisture in the ground, and it gets used by the trees first,” he explained. Such conditions exert “a selective force that directly selects for species that can tolerate drier conditions.”
Animal communities are also responding to the changing environment. For example, in San Francisco, the Nuttall’s woodpecker — a species well suited to drier conditions — has largely replaced the Downy woodpecker — a species that favors environments more frequently dampened by fog and rain, Clark said.
Other native animals will decline as brush thins and the land grows drier, he explained. “Ecological productivity declines the drier it is,” he said. “There is less food, less forage, and less shelter. Animals have fewer places to hide in a simplified environment.”
But how dry will California be in 50 or 100 years? Williams said essentially that all climate models agree that the bands of desert that circle the planet at about 30 degrees of latitude will shift poleward with global warming (the East Bay’s latitude is about 38 degrees). This could push landscape conditions that we see in northern Mexico into California, where forests would likely dry out, burn up in huge wildfires, and fail to grow back.
However, because California sits on the transition zone between the subtropical deserts and the wet latitudes watered by the global westerly winds, the state’s climatic future is not a sure thing. Williams explained that the poleward shift of the subtropical deserts will probably occur in an uneven, wobbly line, making it difficult to predict how the change will specifically affect California.
“The one thing we can all bet on is it’s going to get hotter,” Williams said.
He has personally helped construct models that predict the state — already 2 degrees Fahrenheit warmer on average than it was in preindustrial times — could be another 5 degrees warmer by the century’s end if no significant progress is made in reducing greenhouse gas emissions.
The warmer temperatures will mean that less precipitation falls as snow. Mountain snowpack is currently the state’s largest water storage source, and as it retreats, water security will be compromised for millions of people. Farmers may have insufficient water to irrigate their land. Losing snowmelt will also increase the seasonality of streams, which will gush with water during rainy spells and quickly disappear as spring rains taper off and the mountains drain dry. This could doom the state’s native salmon and trout, according to scientists with UC Davis and the group California Trout. They released a report in May warning of likely extinction for dozens of genetically distinct species and populations by 2100.
It may be possible to stop global warming — but definitely not on a dime, Williams said. He said that no matter how swiftly humans curb emissions of greenhouse gases, the Earth’s temperatures will continue rising for decades.
“We’re locked in for warming over the next 30 years,” he said.
For theoretical purposes, scientists frequently discuss what would happen if the entire global community halted greenhouse gas emissions overnight. It’s an impossible scenario, but it helps set a baseline for how real the effects of global warming are going to be.
That’s because, even if emissions of greenhouse gases stopped tomorrow, positive feedback cycles that are already happening will drive warming for many years. The disappearance of sea ice cover, for instance, means that less sunlight is deflected back into space. Instead, the oceans absorb the sun’s energy, causing temperatures to increase globally as currents transfer the heat around the planet.
Another positive feedback cycle relates to Arctic permafrost, which is thawing as record heatwaves — with temperatures into the 80s — strike the Arctic. The softening of this frozen soil releases methane, a powerful greenhouse gas that has been locked in the ground for millennia, further driving the planet’s greenhouse effect. Similarly, as droughts worsen, large areas of forest will die and release vast amounts of carbon into the atmosphere.
Conversely, Williams noted that some areas around the globe will get greener. Plants, after all, consume CO2, and more of the gas in the air allows plants to grow faster.
Yet even if emissions stopped tomorrow, the sea would continue rising, said Zack Wasserman, chair of the Bay Conservation and Development Commission and a lawyer at the Oakland law firm Wendel Rosen. “For rising sea level, we’ve passed the tipping point,” Wasserman said. “If greenhouse gas emissions went to zero tomorrow, the sea would continue to rise through this century and into the next.”
The ocean’s surface, on average around the globe, is now 6 to 8 inches higher than it was in 1900, according to the Smithsonian Institution. The change is due mainly to the melting of the continental polar ice caps of Antarctica and Greenland (and less so to the thermal expansion of the now-warmer oceans). Projections vary for what we can expect in the next 80 years, from 3 feet of rise to as high as 20. Familiar landmarks will disappear under the surf. Maps will need to be updated every few decades. Seawalls might be needed to prevent Alameda and downtown Oakland and San Francisco from looking and functioning like Venice, Italy.
Amplified hurricanes and the low-pressure cells that come with them will periodically accentuate rising average sea levels with storm surges that swamp coastal cities. Climate Central has warned that an average global temperature increase of 7.2 degrees Fahrenheit will cause the ocean to swell enough to directly displace as many as 760 million people. Stopping warming at 3.6 degrees Fahrenheit, the organization reports, would mean just 130 million people displaced.
But stopping warming at 3.6 degrees from preindustrial times is starting to look futile. In all likelihood, the planet will be 6.1 degrees Fahrenheit warmer by 2100, according to a United Nations panel that convened during the 2015 Paris climate talks. The authors of a paper published in the journal Nature in early 2016 predicted a global average of 10 degrees of warming by century’s end.
Since water warms less rapidly than land, warming will occur disproportionately over the continents. This will mean countless deadly heatwaves — already a materializing threat. In the summer of 2003, tropical winds shifted north and smothered the European continent for weeks in 100-degree air. Heat, trapped in thick stone walls, essentially baked people in their homes, killing between 35,000 and possibly 70,000 people. Seven years later, a similar weather event snuffed the life out of 55,000 people in Russia. Five years later, a May 2015 spell of hot weather killed more than 2,000 people in India and Pakistan.
In early September, a record heatwave hit California. San Francisco set an all-time high of 106. Farther south, the temperature in San Luis Obispo hit 114 degrees, another all-time record. The event lasted several days, and six people died in the Bay Area. It was an indicator of what many believe is likely to come for California — even in coastal cities that usually serve as refuges from heat spells.
“Heatwaves like that will become worse and more frequent,” said Veerabhadran Ramanathan, a professor of atmospheric and climate sciences at UC San Diego’s Scripps Institution of Oceanography. “It will keep getting warmer and warmer.”
Of the 17 warmest years recorded, 16 have occurred this century: 2014, 2015, and 2016 each succeeded the previous year as the planet’s hottest on record. Globally, 2017 is on its way to being the second hottest year; 2016 was slightly warmer but had the thermal influence of El Niño behind it. In California, the summer of 2017 was the state’s warmest ever. The mercury registered triple digits a record 72 times in Redding, and Death Valley recorded 127 degrees one day in June.
Ramanathan recently published a paper in the journal Proceedings of the National Academy of Sciences in which he calculated that the planet faces a one-in-20 chance of “catastrophic” warming by 2100 — that is, a climate so much hotter than today’s that humanity will be unable to adapt.
In fact, scientists have warned that lethal heatwaves like those seen recently in Eurasia could become almost routine in most nations of the world. In an analysis of heatwaves published in 2014 in the journal Geophysical Research Letters, a team of European scientists concluded that by 2100, extreme hot spells that kill thousands of people could occur in almost any tropical or temperate region as often as every other year.
And the Natural Resources Defense Council released a report in June warning that extreme heat will kill almost 30,000 Americans every year by the 2090s — up from an annual average of 1,360 heat-related deaths from 1975 to 2010.
Some states seem to be listening to the dire warnings. California, for one, has set formal goals for curbing greenhouse gas emissions to 1990s levels by 2020 and a further 40 percent by 2030. So far, California is on track to meet the first goal, but it doesn’t actually mark tremendous progress.
Air emissions peaked in 2004 at 489 million metric tons. Over the next 13 years, emissions declined only 10 percent, making the 2030 target of 250 million metric tons seem like a long shot. In fact, the state’s emissions actually increased significantly between 2011 and 2012, ending a short period of rapid decline. Through 2015, California’s annual emissions have remained relatively stable.
In fact, California would do well to follow other nations. France and the United Kingdom, for example, plan to ban diesel cars by 2040. China, so often lambasted as a polluter, is working on installing a carbon trading market. Its leaders also have ambitious plans for an electric vehicle fleet and have imposed aggressive targets for reducing conventional cars emissions.
By comparison, wheels of change in America are spinning as leaders remain stalled in backward dialogue that questions the significance of the planet’s changing climate.
“I don’t think CO2 is a pollutant,” U.S. Rep. Joe Barton, R-Texas, recently told a Vox reporter.
Sen. Ted Cruz, R-Texas, has claimed in formal hearings that there has been “no significant warming whatsoever” in most of the past two decades. He used data he cherry-picked from flawed temperature recording methods that scientists have since readjusted.
President Donald Trump famously declared via Twitter that climate change is a hoax invented by the Chinese. At a news conference on June 1, he told the American public he “cares deeply about the environment” but announced the country would withdraw from the 2015 Paris climate accord to avoid disrupting economic status quos.
The American fossil fuel industry couldn’t be more thrilled with the current U.S. political climate, as well as the country’s disinterest in the planet’s future. Catherine Reheis-Boyd, president of the Western States Petroleum Association, an industry group, recently boasted that hers is “an industry that drives economic growth and sustains our way of life in the West.”
Americans represent 5 percent of the global population but emit 15 percent of the planet’s greenhouse gas emissions, and Reheis-Boyd’s words exhibit precisely the sort of defiance and self-endowed privileges of a wealthy society that Peter Kalmus hopes to help reverse. Kalmus, an atmospheric scientist at NASA’s Jet Propulsion Laboratory who spoke on his own behalf in interviews, said he is discouraged by Americans’ general complacence with current industrial and political trajectories.
“It’s the tragedy of our times that climate change has become so politicized,” he said. “We’re talking about physics, chemistry, quantum mechanics, radiative processes.”
Scientists, he noted, “aren’t being listened to, and some of us are being attacked because we’re trying to get the word out. We’re doing our jobs and sounding an alarm, and we get called alarmists.”
Even in California, where the general public and state leaders generally support progressive climate change policy, action at the individual level is often weak. For one thing, Californians may be driving more than ever before. Gridlock is at all-time highs in major urban centers — and this is not a trivial matter. Transportation accounts for almost 40 percent of the state’s greenhouse gas emissions, making driving less one of the single most important actions an individual can take.
“But, in general, I don’t see a lot of people willing to change their own lives,” Kalmus said. “I see a lot of people wanting to have their cake and eat it, too. They want to be carbon neutral but they don’t want to change their lifestyles, so they buy carbon offsets and buy electric cars or install solar panels, instead of making lifestyle changes, like living closer to work or flying less.”
Kalmus, a father of two, has written a book called Being the Change: Live Well and Spark a Climate Revolution. The book describes the five-year transformation of his own lifestyle. He has estimated that his personal annual greenhouse gas footprint is now 2 metric tons — about one-tenth that of the average American.
He’s given up flying and eating meat and he walks and rides a bicycle most places, which provides exercise and engages him with neighbors and his community. He shops at local businesses and he grows some of his own food, including avocados and tomatoes.
With his book, Kalmus hopes “to shift the conventional wisdom that using less fossil fuel will make your life worse.”
“Your life actually becomes more fulfilling,” he said. “It also becomes a powerful thing to advocate for lifestyle changes that you’ve made yourself.” In his book, he characterizes global warming as the product of “a consumerist lifestyle that doesn’t even make us happy.”
Kalmus argues in Being the Change that there is ultimately little difference between physically attacking a person and burning fossil fuels, and he anticipates the day when the latter will be as socially shunned as the former.
“Burning fossil fuels should be unacceptable socially, the way physical assault is unacceptable,” he wrote.
“The connection is clear,” he told me. “Burning fossil fuels hurts people and causes harm.”
Kalmus said he also objects to the popular catchphrase “the new normal,” often used to characterize climate change.
“To say this is the new normal creates a sense of complacency, like, ‘Oh, this is it — we just have to adapt to a slightly warmer world,'” he said. “This isn’t the new normal. It’s still changing. Until we stop burning fossil fuel, it’s going to get worse and worse and worse.”
On Oct. 24, the same day that the NRDC issued a report about extreme heat days, another asphalt-softening heatwave baked California. Temperatures hit 108 in San Luis Obispo, while Long Beach and Los Angeles saw the mercury peak at 105 and 104, respectively. In many locations, it hadn’t been so hot in late October for almost 60 years.
The science may never be enough to convince Americans to take action and reduce their emissions: Plant communities sometimes respond so slowly to warming trends that only trained botanists can detect most of the changes; the numbers — 1 degree here, another there — aren’t always convincing to laypeople; warnings that hundreds of millions of people will be impacted seem almost abstract and distantly futuristic; and scientists armed with models and wielding data are portrayed as “biased” by industry-friendly politicians.
But Kalmus believes even diehard climate denialists will be hard-pressed to ignore rising temperatures much longer. As more people each summer and fall swelter under an atmosphere of accumulating greenhouse gases, global warming, he thinks, will push people to action.
“My hope is that people are starting to sense that it’s getting hotter, that these heatwaves are getting worse and worse,” Kalmus said.
Williams, at Columbia University, feels that politicians who continue to dismiss scientific evidence of climate change will begin to lose the confidence of their voter base. “Because increasingly we don’t need a temperature record to show us that warming is happening,” he said. “We can see it happening now in the West, where the rate and intensity of forest fires have been exploding.”
Warming has strengthened deadly hurricanes and worsened droughts, and it’s killing California’s ancient oaks. Williams noted that warming trends have become evident in the global die-off of coral reefs, and that carbon emissions, while heating the atmosphere, are simultaneously acidifying the ocean.
“We can see the fingerprint of climate change now almost everywhere we look,” he said.