Green Tech

Google for the first time showed off its server design. (Click to enlarge)

(Credit: Stephen Shankland/CNET)

Updated at 4:08 p.m. PDT April 1 with further details about Google's data center efficiency and shipping containers modules and 6:30 a.m. April 2 to correct the time frame of efficiency statistics.

MOUNTAIN VIEW, Calif.--Google is tight-lipped about its computing operations, but the company for the first time on Wednesday revealed the hardware at the core of its Internet might at a conference here about the increasingly prominent issue of data center efficiency.

Most companies buy servers from the likes of Dell, Hewlett-Packard, IBM, or Sun Microsystems. But Google, which has hundreds of thousands of servers and considers running them part of its core expertise, designs and builds its own. Ben Jai, who designed many of Google's servers, unveiled a modern Google server before the hungry eyes of a technically sophisticated audience.

Google server designer Ben Jai

(Credit: Stephen Shankland/CNET)

Google's big surprise: each server has its own 12-volt battery to supply power if there's a problem with the main source of electricity. The company also revealed for the first time that since 2005, its data centers have been composed of standard shipping containers--each with 1,160 servers and a power consumption that can reach 250 kilowatts.

It may sound geeky, but a number of attendees--the kind of folks who run data centers packed with thousands of servers for a living--were surprised not only by Google's built-in battery approach, but by the fact that the company has kept it secret for years. Jai said in an interview that Google has been using the design since 2005 and now is in its sixth or seventh generation of design.

"It was our Manhattan Project," Jai said of the design.

Google has an obsessive focus on energy efficiency and now is sharing more of its experience with the world. With the recession pressuring operations budgets, environmental concerns waxing, and energy prices and constraints increasing, the time is ripe for Google to do more efficiency evangelism, said Urs Hoelzle, Google's vice president of operations.

"There wasn't much benefit in trying to preach if people weren't interested in it," said Hoelzle, but now attitudes have changed.

The company also focuses on data center issues such as power distribution, cooling, and ensuring hot and cool air don't intermingle, said Chris Malone, who's involved in the data center design and efficiency measurement. Google's data centers now have reached efficiency levels that the Environmental Protection Agency hopes will be attainable in 2011 using advanced technology.

"We've achieved this now by application of best practices and some innovations--nothing really inaccessible to the rest of the market," Malone said.

The rear side of Google's server.

(Credit: Stephen Shankland/CNET)

Why built-in batteries?
Why is the battery approach significant? Money.

Typical data centers rely on large, centralized machines called uninterruptible power supplies (UPS)--essentially giant batteries that kick in when the main supply fails and before generators have time to kick in. Building the power supply into the server is cheaper and means costs are matched directly to the number of servers, Jai said.

"This is much cheaper than huge centralized UPS," he said. "Therefore no wasted capacity."

Efficiency is another financial factor. Large UPSs can reach 92 to 95 percent efficiency, meaning that a large amount of power is squandered. The server-mounted batteries do better, Jai said: "We were able to measure our actual usage to greater than 99.9 percent efficiency."

Urs Hoelzle, Google's vice president of operations

(Credit: Stephen Shankland/CNET)

The Google server was 3.5 inches thick--2U, or 2 rack units, in data center parlance. It had two processors, two hard drives, and eight memory slots mounted on a motherboard built by Gigabyte. Google uses x86 processors from both AMD and Intel, Jai said, and Google uses the battery design on its network equipment, too.

Efficiency is important not just because improving it cuts power consumption costs, but also because inefficiencies typically produce waste heat that requires yet more expense in cooling.

Costs add up
Google operates servers at a tremendous scale, and these costs add up quickly.

Jai has borne a lot of the burden himself. He was the only electrical engineer on the server design job from 2003 to 2005, he said. "I worked 14-hour days for two and a half years," he said, before more employees were hired to share the work.

Google has patents on the built-in battery design, "but I think we'd be willing to license them to vendors," Hoelzle said.

Another illustration of Google's obsession with efficiency comes through power supply design. Power supplies convert conventional AC (alternating current--what you get from a wall socket) electricity into the DC (direct current--what you get from a battery) electricity, and typical power supplies provide computers with both 5-volt and 12-volt DC power. Google's designs supply only 12-volt power, with the necessary conversions taking place on the motherboard.

Google's data center efficiency has been improving gradually.

(Credit: Stephen Shankland/CNET)

That adds $1 or $2 to the cost of the motherboard, but it's worth it not just because the power supply is cheaper, but because the power supply can be run closer to its peak capacity, which means it runs much more efficiently. Google even pays attention to the greater efficiency of transmitting power over copper wires at 12 volts compared to 5 volts.

Google also revealed new performance results for data center energy efficiency measured by a standard called power usage effectiveness. PUE, developed by a consortium called the Green Grid, measures how much power goes directly to computing compared to ancillary services such as lighting and cooling. A perfect score of 1 means no power goes to the extra costs; 1.5 means that ancillary services consume half the power devoted to computing.

Google's PUE scores are enviably low, but the company is working to lower them further. In the third quarter of 2008, Google's PUE was 1.21, but it dropped to 1.20 for the fourth quarter and to 1.19 for the first quarter of 2009 through March 15, Malone said.

Older Google facilities generally have higher PUEs, he said; the best has a score of 1.12. When the weather gets warmer, Google notices is that it's harder to keep servers cool.

An excerpt from a video tour Google presented of its data center containers. Like conventional data centers, Google's shipping containers have raised floors.

(Credit: Stephen Shankland/CNET)

Shipping containers
Most people buy computers one at a time, but Google thinks on a very different scale. Jimmy Clidaras revealed that the core of the company's data centers are composed of standard 1AAA shipping containers packed with 1,160 servers each, with many containers in each data center.

Modular data centers are not unique to Google; Sun Microsystems and Rackable Systems both sell them. But Google started using them in 2005.

Google's first experiments had some rough patches, though, Clidaras said--for example when they found the first crane they used wasn't big enough to actually lift one.

Overall, Google's choices have been driven by a broad analysis on cost that encompasses software, hardware, and facilities.

"Early on, there was an emphasis on the dollar per (search) query," Hoelzle said. "We were forced to focus. Revenue per query is very low."

Mainstream servers with x86 processors were the only option, he added. "Ten years ago...it was clear the only way to make (search) work as free product was to run on relatively cheap hardware. You can't run it on a mainframe. The margins just don't work out," he said.

Operating at Google's scale has its challenges, but it also has its silver linings. For example, a given investment on research can be applied to a larger amount of infrastructure, yielding return faster, Hoelzle said.

A diagram of a Google modular data center

(Credit: Stephen Shankland/CNET)

Google is using the mighty power of its home page to promote a site where people can calculate the financial benefits of various ways to save energy.

The Halloween-theme energy savings calculator is one of a long list of Google's moves to tackle the country's energy problems. The site also includes a link to some advanced energy-saving tips.

However, Google Blogoscoped pointed out, the link doesn't work in some countries outside the United States.

Google counts every word on its home page in an effort to maximize page-loading speed and present an uncluttered user interface, but it often uses the few words below its search box to promote different efforts. The text for the energy savings plan reads, "Haunted by high energy costs? Here are some easy ways to save."

Google promoted this energy savings calculator from its front page. (Click to enlarge.)

(Credit: CNET News)

SAN FRANCISCO--The United States government has been unable to fix the country's energy problems, Google Chief Executive Eric Schmidt said, but the Internet giant on Wednesday proposed its own 22-year solution.

"We have seen a total and complete failure of leadership in the political parties of the United States," Schmidt said in a speech at the Commonwealth Club here. "We've been working on a plan to help solve this problem."

Google CEO Eric Schmidt describes the company's energy plan.

(Credit: Stephen Shankland/CNET News)

Earlier in the day, Google unveiled that plan, which doesn't lack for chutzpah: Clean Energy 2030 aims to wean the United States from its dependence on fossil fuels within 22 years.

Schmidt said the plan requires $4.5 trillion in spending to pull it off, but it'll pay for itself with $5.5 trillion in savings. "With this plan, it's cheaper to fix global warming than it is to ignore it," Schmidt said.

The general plan consists of various efforts to save energy; a shift to renewable wind, geothermal, and solar energy; and a complete cessation of energy from coal and oil and halving of natural gas. Those changes would cut energy production-related carbon dioxide emissions from about 6 billion metric tons per year today to 4 billion per year in 2030.

Energy efficiency is at the forefront of Google's thoughts: the company operates hundreds of thousands of servers, and the company has warned that energy costs could outpace server hardware costs. So a decline in energy costs makes practical sense, Schmidt said.

"We save a lot of money when prices go down. It's good for shareholders, good for earnings," he said.

However, he made clear in a meeting with reporters later that the effort is also driven by the moral beliefs of Google's co-founders, Larry Page and Sergey Brin.

Also on Wednesday, Google announced the fruits of its effort to increase the energy efficiency of its data centers.

Google's Clean Energy 2030 plan would completely eliminate coal and oil use for energy production in 22 years.

(Credit: Google)

Economic stimulus
The present financial crisis, with an expected bailout that will cost $700 billion, likely will be followed by further economic stimulus spending that likely will reach $100 million, Schmidt predicted.

"Why not use that money to solve once and for all the things we debate: energy security, rising oil prices, a lack of jobs--especially in rural areas--(and) a lack of technology investment?" Schmidt said. "If you follow my reasoning and take advantage of the technological opportunities--and the apparent willingness of the government to write large checks during a crisis--we can do this."

He acknowledged that the problem will require sustained attention to solve, but said that's the job of governments. "The government spends lots of money on many things that are strategic. It seems to me that energy independence, given the history of the last 10 years, should be at the top of the list," Schmidt said.

Google predicts energy-related carbon dioxide emissions will drop by about a third with its plan.

(Credit: Google)

Energy plan details
How does Google propose to transform the country's energy usage? Here's Google's description:

• Deploying aggressive end-use electrical energy efficiency measures (about 1.4 percent per year savings) to reduce demand 33 percent.

• Replacing all coal and oil electricity generation, and about half of that from natural gas, with renewable electricity: 380 gigawatts (GW) wind: 300 GW onshore + 80 GW offshore; 250 GW solar: 170 GW photovoltaic + 80 GW concentrating solar power; 80 GW geothermal: 15 GW conventional + 65 GW enhanced geothermal systems

• Increasing plug-in vehicles (hybrids & pure electrics) to 90 percent of new car sales in 2030, reaching 42 percent of the total U.S. fleet that year

• Increasing new conventional vehicle fuel efficiency from 31 mpg to 45 mpg in 2030

• Accelerating the turnover of the vehicle fleet from 19 to 13 years (resulting in 25 million new vehicle sales per year in 2030, a 31 percent increase over the baseline)

Advising Obama
Schmidt, who said he's an adviser to Sen. Barack Obama's presidential campaign, said he prefers that candidate's energy plans. "The Obama program is more in line with the one I'm describing," Schmidt said.

He also dinged Republicans for using the term "clean coal," which he called an oxymoron not unlike "limited nuclear war," and said that offshore oil drilling, although a lively topic of debate, will satisfy only a tiny fraction of the nation's needs and only five years from now at that.

Now is the time to offer the plan, according to author Jeffery Greenblatt, climate and energy technology manager for the company's philanthropic Google.org arm.

"With a new administration and Congress--and multiple energy-related imperatives--this is an opportune, perhaps unprecedented, moment to move from plan to action," Greenblatt said.

BURLINGAME, Calif.--Chipmakers have been applying lessons learned in mobile computing to servers in an effort to increase efficiency by lowering power consumption. But a noted Google engineer threw some cold water on the approach on Monday, arguing the two styles of computing are too different.

"The data center is a different device than the key targets for mobile electronics, laptops, and mobile devices," said Luis Barroso, a Google engineer who closely studies the company's power consumption, speaking at the O'Reilly Velocity conference here.

And naturally, with at least hundreds of thousands of servers in operation and its data centers placed near power plants to cut electricity costs, Google is trying to get computing equipment makers more excited about efficiency.

"Maybe if you call this a land-held computer, perhaps they'll help us," he quipped, showing an aerial view of a sprawling Google data center.

The basic problem is that mobile devices and servers have different modes of activity.

Mobile devices have been improving through better exploitation of the fact that they spend a lot of time dormant with occasional bursts of activity. That lets processors and other electronics save power by spending most time in low-power sleep modes, then snapping awake for peak-power high-performance modes when necessary.

Google's servers, though, have the opposite type of activity: they spend most of their time doing modest amounts of work, with frenzied moments of peak activity and complete lulls a rarity, Barroso said. The measurements are based on measurements of about 5,000 servers performing four different Google applications, he added.

The company's servers simply can't go to sleep, he said. Each machine is "rarely fully idle," he said. "The fraction of time the servers are actually doing exactly nothing is very small."

Thus, Google is urging electronics designers to create products that more gracefully reduce power demands as activity diminishes. Servers naturally consume peak power at peak activity, but what's bad is that they still consume about half peak power when at zero activity.

Processors have gotten a bad rap for squandering ever more energy--indeed, Barroso himself, once a chip designer for Digital Equipment, has expressed such concerns. But chips actually are better than hard drives, memory, and network adapters at reducing power consumption during periods of moderate activity.

Some sophisticated hard drives, for example, can slow down their rotational speed to save power during periods of lower activity. However, "They need to bump to higher RPM to do something useful," to read and write, he said, unlike processors, which can actually still process data when in low-activity modes.

Correction at 3:30 p.m. PST Thursday: Blame my Rust Belt ignorance. The Ohio river that burned is the Cuyahoga.

The retreat of the Jakobshavn Glacier on western Greenland is accelerating, Thompson said. Shown here are lines indicating the location of the end of the glacier starting in 1850 at the far left. The furthest yellow line on the right is 2000, and the two red lines are 2003 and, at far right, 2005.

(Credit: Lonnie Thompson/Ohio State University)

SAN FRANCISCO--I've been spending some time at the the American Geophysical Union conference here, and I've had a recurring thought: When it comes to apocalyptic predictions, geophysicists have the Book of Revelations beat, hands down.

Sometime in the last few years, the idea that global warming is a reality and that it's caused in large measure by people has finally started sinking in. But perhaps because of the remaining skepticism, and more likely because of the fascinating research involved, scientists just can't leave the issue alone.

Global warming has been a major theme among the 14,500 scientists who have converged here for the 40th AGU conference. Seemingly, they can't get enough of it: A year after former Vice President Al Gore addressed conference attendees during the height of hype around his Inconvenient Truth documentary, organizers again gave the stage to an articulate speaker on the issue. This time it was Lonnie Thompson, an Ohio State University scientist who has spent innumerable hours drilling into icecaps at the world's highest elevations.

Lonnie Thompson at AGU

(Credit: Stephen Shankland/CNET News.com)

Global warming, a decades-old idea that posits certain greenhouse gases will keep heat from escaping into space, has moved gradually from a prediction to a measurable phenomenon. But for those who are inclined to feel comfort that scientists got it right, Thompson had sobering words on Wednesday evening: the pace of glacial melting is accelerating, and scientists don't have a handle on the new patterns.

"We're in unfamiliar territory," Thompson said. "The observed rapid changes in Greenland and Antarctica are not predicted. What we're seeing is fast glacier flow."

Thompson uses yaks to carry back each one of hundreds of six-foot ice core samples retrieved from holes drilled in glaciers.

(Credit: Lonnie Thompson/Ohio State University)

Take the Jacobshavn Ice Stream, a glacier on the west side of Greenland that drains about 6.5 percent of the continent's massive ice sheet. Between 2000 and 2003, its rate of retreat nearly doubled. Scientists expected a slow and linear response to global warming, but instead the response has been fast and accelerating. Another example is the Qori Kalis Glacier in Peru, whose initial retreat rate around 1991 was about 6 meters per year but now is 60 meters per year.

"It's not just retreating. It's an exponential increase," he said.

Humanity has a lousy track record dealing with environmental crises before they become severe, he said, pointing as an example to Ohio's famously polluted Cuyahoga River.

"When did we do anything about that river? When it caught on fire," he said. "We've cleaned it up. Now there are walleye and pike in it. It wasn't that we couldn't do it; it was that we didn't have the political will to do it."

Compared to some crises, though, global warming poses long-term challenges because greenhouse gases stay in the atmosphere 70 to 120 years after being emitted, he said.

This year, melting split the Furtwangler Glacier on Africa's Mt. Kilamanjaro into two halves.

(Credit: Lonnie Thompson/Ohio State University)

Glaciers are only one reflection of overall climate trends, but Thompson believes they're an important one--especially the ones he's specialized in studying, those growing at the tops of high mountains in central latitudes rather than the vast expanses in the Arctic and Antarctic regions.

"Glaciers, especially tropical glaciers, are the canaries in the coal mine for our global climate system," he said.

In his research, Thompson has spent 840 days above 18,000 feet, setting up camps and drilling out cores of ice from the glaciers. The ice cores record in tiny air bubbles volcanic activity and greenhouse gas levels; each year has its own layer that can be dated by characteristic patterns of dust deposition and by wet and dry seasons.

The ice core records are disappearing along with the glaciers, though. Several he's examined, for example, show evidence of above-ground thermonuclear bomb tests from the Soviet Union in the 1960s and the United States in the 1950s. But there's no evidence of either on the Naimona'nyi Glacier on the Tibetan Plateau.

"These glaciers are wasting from the surface down," Thompson said.

This graphic shows in red the area of arctic ice that was present in the summer of 1980 but missing this summer. At lower right is the equivalent surface area in terms of the size of the United States.

(Credit: Credit: Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory)

SAN FRANCISCO--Warmth may not be an attribute you associate with a place where the sun doesn't shine in the winter and the sea freezes over, but all things are relative. And compared to earlier years, the Arctic was downright sweltering this year.

According to new research presented here at the the American Geophysical Union conference, the Arctic Ocean reached record high temperatures, arctic ice diminished to a record low, and ice melted on Greenland for a record number of days.

"In 2007, we had off-the-charts warming" of the Arctic Sea in the summer, said Mike Steele, an oceanographer with the Polar Science Center at the University of Washington.

Specifically, he said the Arctic Sea surface temperature was 3.5 degrees Celsius (6.3 degrees Fahrenheit) warmer than the 100-year historical average and 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer than the historical maximum. Two factors were at play in the heating: the sun and, to a lesser degree, warmer ocean currents, he said. In one area north of Russia, temperatures were 5 degrees Celsius (9 degrees Fahrenheit) above average.

This comparison shows the 'off-the-charts' relative warmth of the Arctic Ocean in the summer of 2007.

(Credit: Mike Steele, University of Washington)

There's a feedback loop that connects the ocean temperature and the melting of sea ice. "The ocean absorbs heat, which melts the ice, which means there's more open ocean, which means more heat is absorbed," said Don Perovich, an arctic ice scientist at the U.S. Army Cold Regions Research and Engineering Laboratory. "It's a classic positive feedback."

It's no surprise that the arctic ice is shrinking. But the new data gives a specific measurement for how much is gone.

Between September 1980 and September 2007, the Arctic Sea ice dropped from 7.8 million square kilometers to 4.2 million square kilometers, Perovich said. "You can see the Northwest Passage, the shortcut across the top of the world, was ice-free at the end of the summer."

For comparison, the area of ice is the same as all the states east of the Mississippi River and a broad swath of those to its west, he said.

The math behind the feedback loop involves a property called albedo, which measures the fraction of sunlight that's reflected. The albedo of ice is about 85 percent, compared to 7 percent for the ocean.

What got the feedback loop started is a subject of some debate. "The ice-albedo feedback needs a trigger," Perovich said.

Culprits include a surge of warm water from the Pacific Ocean and anomalous winds that may have pushed ice to create more open ocean. And global warming in general means warmer air, which means a later start to winter ice freezing and less freezing when it does begin, Steele said.

Steele estimates that 2007's warm summer will reduce ice thickness by about a meter, Steele added.

With thinner ice, it's easier to start the feedback loop again. "The ice is more vulnerable to a short-term wind event," Perovich said.

Greenland, too, is showing signs of warming.

Red areas here show areas of Greenland where ice melting in 2007 lasted unusually long--the darkest being 30 days more than the average of the years from 1988 through 2006.

(Credit: Credit Marco Tedesco, University of Maryland)

"2007 set a new record, with melting occurring for 25 to 30 days longer than the average of 1980 to 2006," said Marco Tedesco of the University of Maryland.

The rate of increase in melting since 1988 is about 19,000 additional square kilometers each year, about 1.5 times the size of Maryland, Tedesco said.

Greenland, too, has an albedo-related feedback loop. When less snow falls, older and darker snow is more exposed, and this older snow absorbs more heat, Tedesco said. That albedo effect, combined with unusually high temperatures, were responsible for the increased melting, Tedesco said.

Arctic Sea ice melting doesn't increase sea level, but Greenland is another matter: all its water is on land today, so thawing will increase oceans.

This image shows the alternating periods of stronger and weaker rainfall, called a Madden-Julian Oscillation. Blue and red represent high and low rainfall across the equatorial region of the Earth. The 1987-1988 season had particularly pronounced MJO activity, and MJOs are strongest in the Indian Ocean region.

(Credit: NASA)

SAN FRANCISCO--Scientists are trying to peer a bit further into the future than the typical five-day weather forecasts available today.

Forecasting weather is a notoriously tough challenge that combines physics modeling, data collection, and computer processing--and unlike many scientific problems, pretty much everyone on the planet cares how well it's done. But forecasts today peter out after a few days, leaving a cloud of uncertainty (forgive me) that only lifts when it comes to predicting seasonal weather phenomena such as El Nino.

Scientists are now getting a handle on intermediate-term forecasts by computer models of a particular type of large-scale weather phenomenon called a Madden-Julian Oscillation discovered in the early 1970s. These MJOs are linked to phenomena including Atlantic hurricane seasons and South Asian monsoons, and modeling them with a computer can "provide new predictions with lead times of one to three weeks," said Duane Waliser, principal scientist for water and carbon cycles at NASA's Jet Propulsion Laboratory, speaking today at the American Geophysical Union conference here.

When MJOs occur, rainfall alternates between periods of greater and lesser intensity, typically with each period lasting 40 to 50 days and the pattern gradually traveling east across the planet, Waliser said. Although they take place at equatorial latitudes, their effects extend farther north and south into the middle latitudes, Waliser said.

Only recently have MJO computer models become very good at predicting the actual phenomena, he said.

"Five to ten years ago, you would have been hard-pressed to find any models that represented it that well at all," Waliser said. Now, though, multiple institutions are working on the problem, and scientists actually have a choice of models.

One problem with using MJOs to predict medium-term weather, though, is that they are only intermittent phenomena that take place roughly two to six times per year. "If it's there, we have something to go on. If it's not, then we don't."

SAN FRANCISCO--A Stanford research team has concluded that the ocean not far off the Northern California coastline is the most promising spot for an offshore wind farm to generate power.

Specifically, the researchers concluded that the sea off Cape Mendocino, roughly 150 miles northwest of San Francisco, was their top pick. Wind turbines there could supply 5 percent of California's electrical power needs, they projected.

The researchers plan to present their findings Thursday at the American Geophysical Union conference here Thursday.

There are a number of offshore wind farms--one to the west of Denmark springs to mind--but most of the attention on wind power in the U.S. has focused on terrestrial installations. The Stanford team, though, evaluated several locations in the Pacific Ocean to the west of California.

The researchers compared three spots on the basis of sea depth as well as wind speed and consistency. Ocean winds are stiffer farther offshore, where seas are deeper, but it's prohibitively expensive to build there. Thus was the ocean off the San Francisco Bay Area ruled out.

Most of the Southern California coast isn't windy in the summer, so it, too, was scratched from the list. That left the sea off Cape Mendocino, north of San Francisco. Actually building such a farm would require environmental and other reviews and probably would take at least seven years, said Michael Dvorak, a doctoral student who worked on the study.

No doubt that wouldn't sit well with some folks who appreciate their pristine Pacific views today, the researchers acknowledged in a statement.

But even in the case of a controversial 130-turbine Cape Cod power project, opposition came from a vocal minority. An Opinion Research Corp. study earlier this year found 58 percent of those who live on or near Cape Cod support the wind farm project, the Stanford researchers said.

Other researchers involved in the study are Mark Jacobson, a professor, and Cristina Archer, an assistant professor.

Jacobson and Archer also are presenting separate research at AGU that found linking multiple regional wind farm projects together can even out supply gaps caused by inconstant winds.

SAN FRANCISCO--Researchers have linked global climate change to a tripling in the frequency of large fires in major forests of Alaska and Canada.

Black spruce forests cover about 2.7 million square kilometers in Canada and Alaska--about a third of the area of the lower 48 states of the U.S., and fire records date back to the 1950s. Beginning around 1987, the rate that large wildfires struck the forest jumped from about once every 10 years to once every 3 years, said Eric Kasischke of the University of Maryland at College Park, speaking at the American Geophysical Union conference here Monday.

"We've seen an increase in the number of very large arboreal fires," Kasischke said. (He defines a large fire as one that burns more than 1 percent of the land area in a particular region, such as Alaska's interior.)

There are two links to the gradually warming climate, he said. First, the fires increasingly show up in the fall, when soils are driest and fires therefore are more severe, he said.

Second, the fires are burning deeper into the soil, a significant change given that these northern forests have a thick layer of biological material, typically about 10 inches deep.

"The fires that change the ecosystem the most are occurring more frequently," he said. He predicted that the gradual warming will mean black spruce forests gradually will be replaced by aspen, birch, lodgepole pine, and jack pine forests. In addition, when the organic layer burns, permafrost below no longer is as well insulated.

The deep-burning fires are something of a vicious cycle, too, from a global warming perspective. With the thick layer of biomass, the black spruce forests typically have about 50 tons of carbon per hectare--or about 20 tons per acre--where ordinary U.S. forests have only about a fifth that. When burned, that carbon becomes carbon dioxide, the dominant greenhouse gas culprit in global warming.

The deep burn releases enough carbon dioxide that "you can detect the signal in trace gas emissions," Kasischke said.