Thursday, September 10, 2020

 

Gather Moon rocks for us, NASA urges private companies

The US wants to become a leader in the exploitation of resources found in the soil or subsoil of asteroids and the Moon
The US wants to become a leader in the exploitation of resources found in the soil or subsoil of asteroids and the Moon

NASA on Thursday announced it was in the market for Moon rocks, and wants to pay companies to scoop out the dirt, take a photo, and then have it ready for collection by a future mission.

The contract doesn't actually involve getting to the Moon itself—a feat only achieved by the national space agencies of three countries—but instead envisages companies designing a robot that NASA or major private sector players can then launch.

"NASA is buying  from a commercial provider! It's time to establish the regulatory certainty to extract and trade space resources," tweeted administrator Jim Bridenstine.

The US wants to become a leader in the exploitation of resources found in the soil or subsoil of asteroids and the Moon, a policy outlined in an executive order by President Donald Trump last year, despite an absence of international or legal consensus on the best way to manage extraterrestrial mining.

The major space treaties are vague on the question.

For the current tender, it has asked companies from around the world to present proposals to collect 50 to 500 grams of Moon rock, or regolith, from anywhere on the surface, provide imagery to prove it, then transfer sole ownership to NASA.




Companies would set their own bids, and be paid 20 percent up front with the remainder upon successful completion of their mission.

NASA anticipates that the contracts will be worth some tens of thousands of dollars, according to the tender documents.

In a blog post, Bridenstine wrote that NASA would determine collection methods at a later date, but it wasn't clear whether that meant the rocks would be collected by future astronauts and stay on the Moon or be brought back to Earth.

The mission represents a proof of concept as NASA looks to return humans to the  by 2024 and then set its sights on Mars, harnessing the resources of the Moon and using it as a waypoint.

NASA hopes to excavate lunar ice from the  to supply both  and to split the molecules apart to make  for the onward journey.

The space agency is increasingly relying on a public-private model, where it no longer assumes the entire cost of developing and operating missions, but instead contracts out services to private space companies.

SpaceX, for instance, carries cargo for NASA to the International Space Station and recently completed a successful test flight to take astronauts too

NASA goes private for 1st astronaut lunar landers in decades


© 2020 AFP




BRASIL

Deforestation, Invasions and Mining Spread in Indigenous Lands near the Xingu River

In 2019, the Apyterewa and Trincheira Bacajá protected areas experienced their highest levels of deforestation since their ratifications


Sep.9.2020 2:20PM
Fabiano MaisonnaveLalo de Almeida
MANAUS and SÃO PAULO

In the Amazon, makeshift cities populate the mouth of the forest, close to mining or deforestation. Established in 2016, Vila Renascer continues to grow. Every day, houses, evangelical churches, bars, restaurants, auto repair shops, gas stations, markets, electricity poles, and even small hotels appear. By law, however, none of this should exist: the village exists in the Apyterewa Indigenous Land (TI) of the Parakanã people, approved in 2007.

The presence of non-indigenous people in Apyterewa began in the early 1980s. Their withdrawal was one of the environmental license conditions for constructing the Belo Monte hydroelectric plant on the Xingu River, which crosses the region. Instead, their numbers increased. In the Michel Temer government (MDB), the Ministry of Justice ignored the STF's determination and paralyzed the removal of squatters and invaders of bad faith, that is, who entered the area aware that it was an indigenous land.
  
Vila Renascer, in Apyterewa's land. ( Foto: Lalo de Almeida/ Folhapress ) - Folhapress

After the government's retreat, there were new invasions and the opening of new mining sites. This movement exploded in late 2018 and early 2019, with the promise of Jair Bolsonaro to revise land demarcations. Deforestation spread to the Bacajá Trench, of the Xikrin people, while the illegal market for lots within indigenous lands gained strength.

The result is that, in 2019, Apyterewa lost 8,420 hectares of forest, the highest rate of deforestation since its approval, 13 years ago. Bacajá Trench had 5,600 hectares deforested, also the biggest loss of vegetation cover since the approval, in 1996. The numbers are from the Prodes system, from Inpe (National Institute of Special Research), which measures from August to July of the following year.

Translated by Kiratiana Freelon


Amazon survey finds more than half of US workers say coronavirus has left them underemployed









More than half of the U.S. workers seeking work say their job hunt is due to the coronavirus pandemic.

That's a key finding of a new survey by  giant Amazon, which found that a quarter of U.S. workers are looking for new employment, while 27% say that at least some of their skills won't be of use in the job market in the next five years.

The survey, conducted by Morning Consult between Aug. 21 and 28, comes at a time when the nation's unemployment rate hovers at 8.4% as the economy haltingly returns from a shutdown sparked in the spring to slow the spread of the coronavirus.

Among workers, 36% say they are not working as many hours as they want to or are taking on tasks that don't tap their primary skills. And of that group, 53% say they are underemployed or underutilized because of the pandemic.

Amazon released the  on the eve of a career fair it is hosting on September 16 to fill tens of thousands of positions.

What slowdown? Amazon seeks to hire 33,000 people

©2020 USA Today
Distributed by Tribune Content Agency, LLC.

North Korean hackers steal billions in cryptocurrency. How do they turn it into real cash?

For Pyongyang’s hackers, the heist is the easy part. Actually getting their hands on the money is a different story.

by Patrick Howell O'Neill September 10, 2020
North Korean leader Kim Jong-un waves to photographers.GETTY | CARL COURT/STAFF

For years, North Korea’s Kim dynasty has made money through criminal schemes like drug trafficking and counterfeiting cash. In the last decade, Pyongyang has increasingly turned to cybercrime—using armies of hackers to conduct billion-dollar heists against banks and cryptocurrency exchanges, such as an attack in 2018 that netted $250 million in one fell swoop. The United Nations says these actions bring in vast sums which the regime uses to develop nuclear weapons that can guarantee its long-term survival.

But there is a big difference between hacking a cryptocurrency exchange and actually getting your hands on all the cash. Doing that requires moving the stolen cryptocurrency, laundering it so no one can trace it, and then exchanging it for dollars, euros, or yuan that can buy the weapons, luxuries, and necessities even bitcoins cannot.

“I’d say the laundering is more sophisticated than the hacks themselves,” says Christopher Janczewski, a lead case agent at the IRS who specializes in cryptocurrency cases.

Janczewski sees a lot of action these days. He led investigations into the recent hack that affected verified Twitter users, and into the Bitcoin-funded activities of the darknet’s largest site for images of child sexual abuse. Janczewski was most recently the lead investigator in a case to trace and seize $250 million in cryptocurrency from an unprecedented streak of multimillion-dollar hacks allegedly carried out by the North Korean hacking team known as Lazarus Group.

And, he says, Lazarus’s tactics are continuously evolving.

Washing dirty money clean

Once Lazarus has successfully hacked a target and taken control of the money, the group attempts to cover up its trail to throw off investigators. These tactics typically involve moving coins to different wallets and currencies—for example, switching from ether to Bitcoin.

Related Story

How the North Korean hackers behind WannaCry got away with a stunning crypto-heist

The so-called Lazarus group has used elaborate phishing schemes and cutting-edge money-laundering tools to steal money for Kim Jong-un’s regime.


But the North Korean playbook has evolved in the last few years. One tactic, known as a “peel chain,” moves money in rapid and automated transactions from one Bitcoin wallet to new addresses through hundreds or thousands of transactions in a way that both hides the source of the money and lessens the risk of setting off red flags. Another approach, called “chain hopping,” moves the money through different cryptocurrencies and blockchains to get it away from Bitcoin—where every transaction is posted to a public ledger—and into other, more private currencies. The idea is to make the trail go cold or, better yet, raise false alarms for investigators.

The Lazarus laundering operation, says Janczewski, involves creating and maintaining hundreds of false accounts and identities, a consistent level of sophistication and effort that underlines just how important the operation is for Pyongyang. It’s extremely difficult to name a precise amount, but experts have estimated that North Korea relies on criminal activity for up to 15% of its income, with a significant portion of that driven by cyberattacks.
A quiet arms race
  


Stealing cryptocurrency is far from the perfect crime, however. Police and regulators were once almost clueless, but they now have years of cryptocurrency investigation experience under their belts. In addition, they are gaining increasing levels of cooperation from exchanges, which face government pressure and want greater legitimacy. Investigators have moved from being perpetually on the back foot to being more proactive, with the result that many exchanges have responded with new rules and controls that simply did not exist before. Blockchain surveillance tools are powerful and increasingly widespread, proving that cryptocurrency is not as anonymous as popular myth might have it. It turns out the state still has plenty of power even in this cypherpunk world.

No matter how many peels and hops a hacker might throw the stolen cryptocurrency through, the effort usually comes up against an undeniable fact: if you’re trying to exchange a huge amount of cryptocurrency for US dollars, you’ll almost inevitably have to bring it all back to Bitcoin. No other cryptocurrency is so widely accepted or so easily converted to cash. Though new coins and privacy technologies have been emerging for years, Bitcoin and its public ledger remain “the backbone of the cryptocurrency economy,” says Janczewski.

That means the ultimate destination of the coin is often an over-the-counter trader—a bespoke operation in a country like China that can turn coin into cash, sometimes with no strings attached. These traders often ignore legal requirements, like the know-your-customer laws that make many bigger cryptocurrency exchanges risky places to launder stolen billions.

“What we used to see was just Bitcoin transactions between a theft and the movement toward over-the-counter traders that enable Lazarus to get out of Bitcoin. That’s relatively straightforward,” says Jonathan Levin, the founder of the cryptocurrency investigation firm Chainalysis. “Now there are a lot more currencies involved. They are able to move through obscure currencies, but eventually they end in the same spot, which is moving it back to Bitcoin and through the over-the-counter market.”


Over-the-counter operations are the preferred way for Lazarus to move millions in Bitcoin into cash.

And the business is enormous: the top 100 over-the-counter traders engaging in money laundering receive hundreds of millions of dollars in Bitcoin every month, accounting for around 1% of all Bitcoin activity.

Bitcoin-fueled illegal activity does not account for most use of blockchains, but it does remain significant and continues to grow, according to Chainalysis. Ransomware, for example, is a billion-dollar business made possible by cryptocurrency, while anonymous darknet markets moved over $600 million in Bitcoin in 2019.

“There is a sophistication higher than we’ve seen in the past,” Levin says. “Some of that has been successful, but with the US increasingly taking action and exchanges responding to requests to freeze funds and seize assets, these techniques may not be that effective moving forward.”



When will we see ordinary people going into space?

Space is more accessible than ever. But we're still a long ways from seeing the average person taking a trip into orbit and beyond.

by Neel V. Patel  September 9, 2020
Astronaut Bruce McCandless II on a spacewalk in 1984.NASA


Every week, the readers of our space newsletter, The Airlock, send in their questions for space reporter Neel V. Patel to answer. This week: How the average person can go to space.

What are the opportunities for ordinary citizens to go into space? If there is so much being done to help make space more accessible, why aren’t we seeing a bigger push to see the average person go into space? —Corey


This question reminds me of an episode of The Simpsons. Frustrated by the dearth of public enthusiasm for the US space program, NASA decides to drum up support by sending “the average person”—Homer—into space. The stunt ends in near disaster when Homer’s antics (beginning with smuggling a bag of potato chips into the capsule) destroy the navigation equipment, almost killing himself and the crew.


The average person is more intelligent than Homer, but the episode (which first aired in 1994, and features Buzz Aldrin as a guest star) actually raises some issues that still resonate today. Spaceflight still isn’t an endeavor the average person could be expected to handle without rigorous training. It’s not like taking a flight across the globe. There are intense physical rigors involved in riding a rocket into orbit and living in microgravity for more than a few days. There’s the psychological toll of living and working in such a small space for so long. Emergencies can prop up at any moment, requiring a very calm disposition even when your life and your crewmates’ lives are at stake. That’s why astronauts train for years before they actually fly into space.

The other issue is money. It’s still really, really, really expensive to send people into space, and those who are not bankrolled by a government or a wealthy company have to pay their own way. When SpaceX launches its mission around the moon in 2023, the six to eight passengers scheduled to go will include Japanese billionaire Yusaku Maezawa. It’s not clear how much he’s paying for the trip, but one has to assume it’s more than most of us could ever dream of making in our lifetimes. NASA wants to offer opportunities for tourists and private citizens to visit the International Space Station, and it would only charge $35,000 a night to pay for food and life support. But that’s not taking into account launch costs for a seat aboard the capsule that actually goes to the ISS (which could be up to $52 million).

That doesn’t mean space will always be closed off to the average person. Virgin Galactic and Blue Origin are looking to offer suborbital flights that will take people into space for a few minutes and allow them to experience weightlessness and get a view of Earth from high above. The training for these missions is far from intense, and anyone who’s healthy should be able to go. Virgin Galactic flight reservations are $250,000. Elon Musk has said his eventual goal is for a one-way ticket to Mars aboard Starship to cost about the same, but that’s decades down the road. Space will never be cheap, but it will get cheaper.

EXCERPT

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

Abstract

Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California's diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.

Plain Language Summary

Since the early 1970s, California's annual wildfire extent increased fivefold, punctuated by extremely large and destructive wildfires in 2017 and 2018. This trend was mainly due to an eightfold increase in summertime forest‐fire area and was very likely driven by drying of fuels promoted by human‐induced warming. Warming effects were also apparent in the fall by enhancing the odds that fuels are dry when strong fall wind events occur. The ability of dry fuels to promote large fires is nonlinear, which has allowed warming to become increasingly impactful. Human‐caused warming has already significantly enhanced wildfire activity in California, particularly in the forests of the Sierra Nevada and North Coast, and will likely continue to do so in the coming decades.

1 Introduction

In the western United States, annual area burned increased substantially in recent decades due to increased frequency and size of large wildfires (Abatzoglou & Williams, 2016; Balch et al., 2018; Dennison et al., 2014; Westerling, 2016). It is well established that this observed increase in wildfire activity was promoted in many areas by reduced fuel moisture due to warming‐induced increases in evaporative demand, reduced snowpack, and reduced warm‐season precipitation frequency (Abatzoglou & Williams, 2016; Holden et al., 2018; Kitzberger et al., 2017; Westerling, 2016). These recent climate trends are broadly consistent with those expected from anthropogenic climate change (Abatzoglou & Williams, 2016), but anthropogenic climate effects on wildfire can vary greatly across space and time due to confounding factors such as natural climate variations, land and fire management practices, ignitions from humans, spatial diversity in vegetation type, and the complex ways in which these processes interact (Williams & Abatzoglou, 2016). Therefore, location‐specific adaptation responses to wildfire require understanding how climate affects wildfire locally, how the key climate variables have changed over the past several decades, and whether these climate changes are likely to continue.

Perhaps nowhere on Earth has received more attention regarding recent wildfire trends and their causes than California. One reason for the attention is that increases in statewide burned area over the last several decades were dramatically punctuated in 2017 and 2018 by particularly extreme wildfire activity with substantial loss of life and property. In 2017, modern state records were set for the largest individual wildfire (Thomas Fire: 114,078 ha) and the most structures destroyed by an individual wildfire (Tubbs Fire: 5,636 structures), which led to 22 fatalities (CalFire, 2018). The total area burned in 2017 was also nearly a state record at the time (505,293 ha), behind 2007. In 2018, state records were set for total area burned (676,312 ha), largest individual wildfire (Mendocino Complex Fire: 185,800 ha), and most destructive wildfire (Camp Fire: 18,804 structures destroyed, 85 fatalities). In these 2 years, California spent over $1.5 billion on fire suppression, far more than any previous 2‐year period (CalFire, 2018).

California is a particularly difficult place to disentangle the drivers of changing wildfire activity. California's climate, vegetation cover, and human settlement patterns are highly diverse, causing the influences of these factors on fire activity to be spatially heterogeneous and complex (Jin et al., 2014; Jin et al., 2015; Keeley & Syphard, 2017; Swetnam & Baisan, 2003; Westerling & Bryant, 2008). Humans dominate the wildfire regime across much of the state by altering land cover (Sleeter et al., 2011; Syphard et al., 2018), supplying the vast majority of ignitions (Balch et al., 2017; Nagy et al., 2018), and attempting to suppress essentially all fires. Fire suppression over the past century allowed for artificial buildup of fuels in many regions that historically experienced frequent low‐intensity fires, reducing fuel limitation as a constraint on fire activity and putting many areas into a so‐called fire deficit (Higuera et al., 2015; Marlon et al., 2012; Minnich et al., 1995; Parks et al., 2015). Even under constant climate conditions, changes in California's fire activity over the past century would be expected as populations increased and cities expanded into surrounding wildlands (Radeloff et al., 2018), fire suppression strategies evolved (Stephens & Ruth, 2005), and frequency and type of human‐ignited wildfires changed (Balch et al., 2017; Keeley & Syphard, 2018). Changes in these nonclimatic factors may also promote nonstationarity in fire‐climate relationships, confounding efforts to isolate the influence of climate change on fire activity (Higuera et al., 2015; Hurteau et al., 2019; Littell, 2018; Mann et al., 2016; Marlon et al., 2012; Taylor et al., 2016).

The effect of climate on wildfire in California is highly seasonal and variable across vegetation gradients. In summer, when fires are most frequent in California, large burned areas are promoted by the cumulative drying effects of atmospheric aridity and precipitation deficits mainly in forest ecosystems where fuel availability is not a limiting factor (Abatzoglou & Kolden, 2013; Jin et al., 2014; Keeley & Syphard, 2016; Swetnam, 1993; Swetnam & Betancourt, 1998; Westerling et al., 2003; Williams et al., 2018). In fall, many of California's most destructive fires occur in coastal shrublands and are driven by often extreme offshore downslope wind events, where synoptic conditions advect dry air masses often originating from the continental interior high desert westward and southward across topographic barriers such as the Transverse, Peninsular, and Coastal Ranges (Conil & Hall, 2006; Guzman‐Morales et al., 2016; Hughes & Hall, 2010; Moritz et al., 2010; Nauslar et al., 2018). The most widely studied offshore wind events, termed Santa Ana winds in southern California, increase in frequency in the fall and peak in winter (Abatzoglou et al., 2013; Raphael, 2003). Strong offshore winds with very low relative humidity can quickly dry fuels and spread large wildfires when they occur prior to the onset of the winter precipitation season in California's Mediterranean climate (Billmire et al., 2014; Keeley, 2004; Moritz et al., 2010; Westerling et al., 2004).

The effects of anthropogenic climate change on California's fire regimes are likely to be diverse and complex, varying by region and season (Liang et al., 2017; Pierce et al., 2018; Syphard et al., 2019; Westerling, 2018). Climate model projections of warming and increased atmospheric aridity in California are strong and robust across models (Pierce et al., 2013). It is well established that warming promotes wildfire throughout the western United States, particularly in forested regions, by enhancing atmospheric moisture demand and reducing summer soil moisture as snowpack declines (Abatzoglou & Williams, 2016; Westerling et al., 2006). By contrast, model projections of precipitation in California are highly uncertain but with a tendency toward increased precipitation annual totals, particularly in northern California during winter (Maloney et al., 2013). However, many climate models have systematic biases in North Pacific storm tracks and tropical Pacific sea surface temperatures that should lead to strong skepticism regarding model simulations of future precipitation in California (Seager et al., 2019; Simpson et al., 2016). Climate models also project precipitation frequency declines in spring through fall that would partly offset winter increases, resulting in increased precipitation variability (AghaKouchak et al., 2018; Pierce et al., 2018; Polade et al., 2014; Polade et al., 2017; Swain et al., 2018). In fall, models project reduced frequency and intensity of Santa Ana wind events (Guzman‐Morales & Gershunov, 2019; Hughes et al., 2011). However, concurrent warming and decreased fall precipitation may, to some degree, counteract the effects of reduced offshore winds on fall fire risk in southwestern California (Hughes et al., 2011; Pierce et al., 2018), possibly extending the fire season towards the winter peak of the downslope wind season (Guzman‐Morales & Gershunov, 2019; Syphard et al., 2018).

While much has been published on projected changes in wildfire activity due to climate change (e.g., Barbero et al., 2015; Hurteau et al., 2019; Krawchuk & Moritz, 2012; Littell et al., 2018; Westerling, 2018; Westerling et al., 2011; Westerling & Bryant, 2008), less has been done to evaluate observed seasonal trends in fire‐relevant climate variables and whether these trends are consistent with those expected to arise from anthropogenic climate change. Here we provide a comprehensive empirical assessment of the observed effects of climate variability and change on California wildfire by season, region, and land cover. We first use wildfire and climate data within California to evaluate trends in seasonal burned area by region during 1972–2018, resolve the distinct seasonal and regional influences of climate and weather factors, and assess the stationarity of the dominant fire‐climate relationships over the past five decades. We then use climate model simulations to determine whether observed trends in the climate variables most pertinent to regional wildfire activity are consistent with expectations of anthropogenic climate change. A thorough and nuanced understanding of how, when, and where anthropogenic climate change has or has not affected wildfire in California over the past several decades is critical to guide sustainable societal decisions ranging from where to develop housing to how limited resources can be optimized for landscape management.

4 Conclusions

California has been the geographic focus of extensive speculation among scientists, politicians, and media as to the biophysical and societal factors that have contributed to recent exceptional wildfires and large increases in wildfire activity in recent decades (e.g., Krieger, 2018; Pierre‐Louis, 2018; Vore, 2018). Anthropogenic climate change is commonly debated as a driver of these recent wildfire changes, but there are many ways in which anthropogenic climate change could conceivably affect wildfire and many variables that wildfire in California is sensitive to. A nuanced understanding of how, when, where, and why California wildfire activity has increased in recent decades is critical for sustainable environmental and development decisions that specifically take into account how anthropogenic climate change is likely to proceed and affect wildfire across California's diverse landscapes. Our methods should be increasingly applicable to other regions globally, as governmental and satellite‐based records of wildfire activity are steadily alleviating observational duration as a major limiting factor for empirical studies of wildfire.

In this study we evaluated the various possible links between anthropogenic climate change and observed changes in California wildfire activity across seasons, regions, and land cover types since the early 1970s. The clearest link between California wildfire and anthropogenic climate change thus far has been via warming‐driven increases in atmospheric aridity, which works to dry fuels and promote summer forest fire, particularly in the North Coast and Sierra Nevada regions. Warming has been far less influential on summer wildfire in nonforest areas. In fall, the drivers of wildfire are particularly complex, but warming does appear to enhance the probability of large fall wildfires such as those in 2017 and 2018, and this effect is likely to grow in the coming decades.

Importantly, the effects of anthropogenic warming on California wildfire thus far have arisen from what may someday be viewed as a relatively small amount of warming. According to climate models, anthropogenic warming since the late 1800s has increased the atmospheric vapor‐pressure deficit by approximately 10%, and this increase is projected to double by the 2060s. Given the exponential response of California burned area to aridity, the influence of anthropogenic warming on wildfire activity over the next few decades will likely be larger than the observed influence thus far where fuel abundance is not limiting.

Below, we conclude with executive summaries of our primary findings for summer wildfire in forests, summer wildfire in nonforests, and fall wildfire.

4.1 Summer, Forest

Annual statewide burned area increased significantly during 1972–2018, largely due to an eightfold increase in annual summer forest‐fire extent, most of which occurred in the heavily forested North Coast and Sierra Nevada regions. Summer forest‐fire extent is strongly dictated by heat and atmospheric aridity, which reduce snowpack and dry out fuels. Warm‐season atmospheric aridity (vapor‐pressure deficit) increased significantly across California since the late 1800s, driven largely by daytime warming of approximately 1.8 °C (1.4 °C since the early 1970s). Based on a regression analysis, the vast majority of the observed increase in summer forest‐fire extent since 1972 is accounted for by observed significant increases in warm‐season vapor‐pressure deficit (caused by warming). Importantly, the sensitivity of burned area to aridity is modulated by background conditions such as fuel abundance and connectivity, ignition frequency, and resources dedicated toward suppression, all of which changed over the past century. However, the statistical relationship between vapor‐pressure deficit and forest fire area remained stable during 1972–2018, supporting the interpretation that increased aridity was the primary driver of the increase in summer forest‐fire area during this time. The observed rates of warming and increasing vapor‐pressure deficit are consistent with those simulated by climate models when forced by anthropogenic emissions, indicating that these trends are extremely likely to continue for decades to come. The large increase in California's annual forest‐fire area over the past several decades is very likely linked to anthropogenic warming.

4.2 Summer, Nonforest

Annual summer burned area did not increase in nonforest lands in the Central and South Coast regions, and increases in nonforest burned area were weak in the North Coast and Sierra Nevada. Summer nonforested burned area is most strongly promoted by high precipitation total in the year or two prior to the fire year, reflecting the necessity of precipitation for growth of fine fuels that can facilitate fire spread in the subsequent year. Fire‐year precipitation deficit and atmospheric aridity also appear to promote summer wildfire in these regions, but this effect is relatively weak. Over the past century, the frequency of wet years followed by dry years increased, which should have promoted nonforest summer wildfire. The lack of large increases in nonforest summer burned area may reflect the counteracting effects of the other factors such as human fire suppression, reduced ignitions, and reduced vegetation cover due to drought. Climate models do not represent the observed increase in interannual swings from wet to dry years as a robust result of anthropogenic climate change thus far. The link between anthropogenic climate change and summer wildfire in nonforest appears weak thus far.

4.3 Fall

Large fall wildfires became more frequent in California over the past several decades, mainly due to increases in the North Coast and Sierra Nevada regions. In all regions, large fall wildfires often occur when strong offshore wind events coincide with dry fuels. These conditions were extreme throughout California in 2017 and 2018, driving very large fall wildfires in all regions in one or both years. The character of offshore wind events did not change since records began in the mid‐1900s. Climate models project these wind events to decrease in frequency and intensity in the future. Fall fuel moisture is dictated largely by fall precipitation, but nonetheless is calculated to have declined significantly since the mid‐1900s due to warming. This warming‐induced drying was likely caused by a combination of anthropogenic forcing and natural multidecade variability and caused an 8‐day increase in the number of days per October–December with a high probability of large wildfires. This exemplifies an important secondary effect of background warming, which is projected to continue, on fall wildfires. In the South Coast, fall drying was also promoted by a small reduction in the frequency of fall precipitation, consistent with climate model projections. The link between anthropogenic climate change and fall wildfire appears weaker than in summer thus far but is likely to strengthen if continued warming and possibly delayed onset of winter precipitation counteract projected decreases in the intensity and frequency of offshore wind events.

Acknowledgments

All data sets used are publicly available, and the sources are listed in Table S1. A.P.W. was funded by Columbia University's Center for Climate and Life and the Zegar Family Foundation. We also acknowledge support from University of California Office of the President MRPI grant MRP‐17‐446315 (D.L., A.G., and J.G.M.), from NOAA via the CNAP RISA (D.L. and A.G.), from DOI via the Southwest Climate Adaptation Science Center grant G18AC00320 (A.G. and J.G.M.), the Visiting Scholar Program and Fire Centre Research Hub at the University of Tasmania (J.T.A.), Earth Lab through CIRES and the University of Colorado, Boulder's Grand Challenge Initiative (J.K.B.), and the USGS North Central Climate Adaptation Science Center (J.K.B.). LDEO publication 8332.