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Sunday, November 30, 2008

Arctic Melt Unnerves the Experts

The Arctic ice cap shrank so much this summer that waves briefly lapped along two long-imagined Arctic shipping routes, the Northwest Passage over Canada and the Northern Sea Route over Russia.

Over all, the floating ice dwindled to an extent unparalleled in a century or more, by several estimates.

Now the six-month dark season has returned to the North Pole. In the deepening chill, new ice is already spreading over vast stretches of the Arctic Ocean. Astonished by the summer’s changes, scientists are studying the forces that exposed one million square miles of open water — six Californias — beyond the average since satellites started measurements in 1979.

At a recent gathering of sea-ice experts at the University of Alaska in Fairbanks, Hajo Eicken, a geophysicist, summarized it this way: “Our stock in trade seems to be going away.”

Scientists are also unnerved by the summer’s implications for the future, and their ability to predict it.

Complicating the picture, the striking Arctic change was as much a result of ice moving as melting, many say. A new study, led by Son Nghiem at NASA’s Jet Propulsion Laboratory and appearing this week in Geophysical Research Letters, used satellites and buoys to show that winds since 2000 had pushed huge amounts of thick old ice out of the Arctic basin past Greenland. The thin floes that formed on the resulting open water melted quicker or could be shuffled together by winds and similarly expelled, the authors said.

The pace of change has far exceeded what had been estimated by almost all the simulations used to envision how the Arctic will respond to rising concentrations of greenhouse gases linked to global warming. But that disconnect can cut two ways. Are the models overly conservative? Or are they missing natural influences that can cause wide swings in ice and temperature, thereby dwarfing the slow background warming?

The world is paying more attention than ever.

Russia, Canada and Denmark, prompted in part by years of warming and the ice retreat this year, ratcheted up rhetoric and actions aimed at securing sea routes and seabed resources.

Proponents of cuts in greenhouse gases cited the meltdown as proof that human activities are propelling a slide toward climate calamity.

Arctic experts say things are not that simple. More than a dozen experts said in interviews that the extreme summer ice retreat had revealed at least as much about what remains unknown in the Arctic as what is clear. Still, many of those scientists said they were becoming convinced that the system is heading toward a new, more watery state, and that human-caused global warming is playing a significant role.

For one thing, experts are having trouble finding any records from Russia, Alaska or elsewhere pointing to such a widespread Arctic ice retreat in recent times, adding credence to the idea that humans may have tipped the balance. Many scientists say the last substantial warming in the region, peaking in the 1930s, mainly affected areas near Greenland and Scandinavia.

Some scientists who have long doubted that a human influence could be clearly discerned in the Arctic’s changing climate now agree that the trend is hard to ascribe to anything else.

“We used to argue that a lot of the variability up to the late 1990s was induced by changes in the winds, natural changes not obviously related to global warming,” said John Michael Wallace, a scientist at the University of Washington. “But changes in the last few years make you have to question that. I’m much more open to the idea that we might have passed a point where it’s becoming essentially irreversible.”

Experts say the ice retreat is likely to be even bigger next summer because this winter’s freeze is starting from such a huge ice deficit. At least one researcher, Wieslaw Maslowski of the Naval Postgraduate School in Monterey, Calif., projects a blue Arctic Ocean in summers by 2013.

In essence, Arctic waters may be behaving more like those around Antarctica, where a broad fringe of sea ice builds each austral winter and nearly disappears in the summer. (Reflecting the different geography and dynamics at the two poles, there has been a slight increase in sea-ice area around Antarctica in recent decades.)

While open Arctic waters could be a boon for shipping, fishing and oil exploration, an annual seesawing between ice and no ice could be a particularly harsh jolt to polar bears.

Many Arctic researchers warned that it was still far too soon to start sending contai
ner ships over the top of the world. “Natural variations could turn around and counteract the greenhouse-gas-forced change, perhaps stabilizing the ice for a bit,” said Marika Holland, of the National Center for Atmospheric Research in Boulder, Colo.

But, she added, that will not last. “Eventually the natural variations would again reinforce the human-driven change, perhaps leading to even more rapid retreat,” Dr. Holland said. “So I wouldn’t sign any shipping contracts for the next 5 to 10 years, but maybe the next 20 to 30.”

While experts debate details, many agree that the vanishing act of the sea ice this year was probably caused by superimposed forces including heat-trapping clouds and water vapor in the air, as well as the ocean-heating influence of unusually sunny skies in June and July. Other important factors were warm winds flowing from Siberia around a high-pressure system parked over the ocean. The winds not only would have melted thin ice but also pushed floes offshore where currents and winds could push them out of the Arctic Ocean.

But another factor was probably involved, one with roots going back to about 1989. At that time, a periodic flip in winds and pressure patterns over the Arctic Ocean, called the Arctic Oscillation, settled into a phase that tended to stop ice from drifting in a gyre for years, so it could thicken, and instead carried it out to the North Atlantic.

The new NASA study of expelled old ice builds on previous measurements showing that the proportion of thick, durable floes that were at least 10 years old dropped to 2 percent this spring from 80 percent in the spring of 1987, said Ignatius G. Rigor, an ice expert at the University of Washington and an author of the new NASA-led study.

Without the thick ice, which can endure months of nonstop summer sunshine, more dark open water and thin ice absorbed solar energy, adding to melting and delaying the winter freeze.

The thinner fresh-formed ice was also more vulnerable to melting from heat held near the ocean surface by clouds and water vapor. This may be where the rising influence of humans on the global climate system could be exerting the biggest regional influence, said Jennifer A. Francis of Rutgers University.

Other Arctic experts, including Dr. Maslowski in Monterey and Igor V. Polyakov at the University of Alaska, Fairbanks, also see a role in rising flows of warm water entering the Arctic Ocean through the Bering Strait between Alaska and Russia, and in deep currents running north from the Atlantic Ocean near Scandinavia.

A host of Arctic scientists say it is too soon to know if the global greenhouse effect has already tipped the system to a condition in which sea ice in summers will be routinely limited to a few clotted passageways in northern Canada.

But at the university in Fairbanks — where signs of northern warming include sinkholes from thawing permafrost around its Arctic research center — Dr. Eicken and other experts are having a hard time conceiving a situation that could reverse the trends.

“The Arctic may have another ace up her sleeve to help the ice grow back,” Dr. Eicken said. “But from all we can tell right now, the means for that are quite limited.”

Boreal North America

A mature spruce stand near
Delta Junction, Alaska

The North American boreal forest is an integral part of our global ecosystem and an important influence on the global cycling of energy, carbon and water. Over the past 30 years, global boreal forests have experienced a significant amount of warming and drying which, if trends continue as predicted, are likely to induce feedbacks that may further influence global climate. The goal of our North American Boreal Carbon program is to quantify the magnitude and variability of carbon exchange, and to assess the mechanisms by which fire disturbance influences these processes. By synthesizing results from direct field measurements, satellite remote sensing and ecosystem modeling, we study the processes driving changes in the boreal forest in order to inform assessments and predictions of how those changes will be expressed under a future climate regime.

Why Study Boreal Forests?

  • Coverage - Boreal forests cover approximately 14.5% of the earth's land surface. Learn More »
  • Carbon Storage - The great expanse and large quantity of carbon contained in vegetation and soils (particularly peat) make the boreal biome the world's largest terrestrial carbon reservoir. Learn More »
  • Changing Climate - At high latitudes in North America, substantial warming and drying has occurred, and this trend is predicted to continue. Increased temperatures in the boreal region release large quantities of carbon previously immobilized in the cold and frozen soils. The large quantity of carbon contained in the cold and frozen soils of the boreal biome is susceptible to mobilization under a changing climate system. Learn More »
  • Fire and Regrowth - Warming and drying associated with climate change increase the frequency and intensity of the boreal fire regime, and lead to changes in vegetation composition and the carbon cycle. Learn More »

Coverage of Boreal Forests

MODIS Tree Cover data displaying the forests of North America and Eurasia. Percent tree cover increases as colors become darker.

It is estimated that boreal forests and woodlands cover approximately 14.5% of the earth's land surface, comprising an area of nearly 16 million square kilometers (5.7 million square miles) – or about the size of the conterminous United States. The boreal region forms a circumpolar band throughout the northern hemisphere, extending through Russia, Northern Europe, Canada, and Alaska (see image, right). The southern limit of the boreal forest biome is not a distinctly defined boundary, but generally varies between 50° and 60°N latitude, although in Siberia it dips as far south as 45°N. The North American boreal region makes up approximately one third of the global boreal biome, and thus constitutes a significant component of the boreal carbon pool.

Carbon Storage in Boreal Forests

The boreal region covers just under 15% of the global land surface, but contains over 30% of all carbon contained in the terrestrial biome. This is largely due to the disproportionate amount of carbon held in boreal soils compared to other forest biomes. In general, the amount of carbon stored in forest soils is controlled by the rate of supply and release of carbon. Carbon is supplied to the soil through litterfall, fallen woody debris, and root mortality. This detritus is subsequently decomposed through various microbial pathways and the carbon is released to the atmosphere.

Comparison of Carbon Storage in Boreal, Temperate, and Tropical Forests

Biome Area (x 106 ha) Soil Carbon (Pg) Plant Biomass Carbon (Pg) Total Carbon (Pg)
Boreal Forest 1,509 625 78 703
Tropical forest 1,756 216 159 375
Temperate forest 1,040 100 21 121
Based on Kasischke, 2000

(One Pg [petagram]=one billion metric tonnes or one trillion kg)

In boreal regions, extremely low temperatures promote the formation of cold and frozen soils called permafrost. The cold temperatures within these soils reduce decomposition rates, thereby leading to the development of deep organic soils that may be hundreds of years old. These cold, often saturated or frozen organic soils release relatively little CO2 to the atmosphere through microbial respiration, although large amounts may be rapidly released by increasingly frequent forest fires, which also generate deep soil thawing once the insulating blanket of moss and peat is removed.

New England: Land Cover and Forest Ecology

New England map

At the Woods Hole Research Center, we are studying how the forests and land cover of New England are changing.

In southeastern Massachusetts and on Cape Cod, we quantify rates of forest clearing and other changes in land use with satellite data and GIS data. We also look at the expansion of impervious surfaces, and their impact on water flow and water quality.

In Massachusetts and Maine, we study how climate and disturbance (e.g. nitrogen deposition and forest management) influence the exchange of carbon dioxide between the atmosphere and the forest. This research helps quantify the contribution of New Englands’ forests to the global carbon budget, and how this contribution might change in the future.

The Greenhouse Effect

Solar radiation interacts with the surface of the earth in several ways. Some portion of this energy is reflected back into space by the earth's atmosphere, another portion is dispersed and scattered by the molecules in the atmosphere and a large portion penetrates through the earth's atmosphere to reach the surface of the earth. The radiation reaching the earth's surface is largely absorbed resulting in surface warming (Figure 1).

The Greenhouse Effect

Figure 1. The greenhouse effect. Select image for larger version (77KB, opens in new window).

Much of this absorbed energy is eventually re-radiated in longer infrared wavelengths. As it leaves the earth, it once again interacts with the atmosphere. Some of this re-radiated energy escapes to space, but much of this re-radiated energy is reflected back to the earth's surface by molecules in the earth's atmosphere. This phenomenon is similar to the warming that occurs in an automobile parked outside on a sunny day (Figure 2).

The Greenhouse Effect

Figure 2. A parked car in the sun creates a localized greenhouse effect. Select image for larger version (81KB, opens in new window).

The molecules responsible for this phenomenon are called greenhouse gases, i.e. water (H2O), nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) because they act like the glass in a greenhouse, trapping re-radiated energy. Without these gases most life on earth would not be possible, as the surface temperature of the earth would likely be about 60°F colder.

In essence, greenhouse gases act like an insulator or blanket above the earth, keeping the heat in. Increasing the concentration of these gases in the atmosphere increases the atmosphere's ability to block the escape of infrared radiation. In other words, the earth's insulator gets thicker. Therefore too great a concentration of greenhouse gases can have dramatic effects on climate and significant repercussions upon the world around us. Climates suitable for human existence do not exist simply above some minimum threshold level of greenhouse gas concentration, rather they exist within a finite window - a limited range of greenhouse gas concentrations that makes life as we know it possible.

Is Global Warming Causing Bigger Hurricanes?

Does global warming cause bigger and/or more frequent hurricanes? This was an intriguing hypothetical question several years ago. Since 2005, which not only brought us Hurricane Katrina but set new records (28 named storms, four of which reached Category 5 strength), it has become a grippingly real one. Al Gore treats the idea that warming spawns worse storms as gospel in An Inconvenient Truth, the poster of which depicts the swirl of a hurricane rising out of a smokestack. "Temperature increases are taking place all over the world, and that's causing stronger storms," Gore declares. At one point in the film, the soundtrack turns ominous and Gore's profile is silhouetted against the glowing screen of his PowerBook. It shows a CNN feed of broken levees, flooded New Orleans streets, and Mayor Ray Nagin making his famous rant a few days after Katrina struck. It's a clear and powerful message: Global warming is not just a looming disaster we can palm off on future generations. It's here now, and people are dying because of it.

The latest big global-warming study has buttressed the link between global warming and hurricanes. The study, published in the Proceedings of the National Academy of Sciences, makes the case that man-made climate change is probably responsible for heating up tropical oceans—specifically, the two bands on either side of the equator where hurricanes form. The researchers used 22 computer models to demonstrate what many scientists already believed: that the atmosphere, warmed up by mankind's relentless pumping of carbon dioxide into the air, is also warming up the world's prime hurricane breeding grounds. (Tropical sea surface temperatures have risen by about 1 degree Fahrenheit since 1970, but a direct link to the warming atmosphere had not been so clearly established.) A media firm working for one of the study's sponsoring institutions turned the hype up a notch, billing the revelation as "the final piece of the puzzle" connecting an upsurge in powerful hurricanes to global warming.

But that, like the alarmist certainty of An Inconvenient Truth, is a more troubling claim. The hurricane-warming link isn't settled at all. Rather, it's a very contentious debate between two groups of scientists—computer-modeling atmospheric scientists versus meteorologists—who have very different methods, ideas, and priorities. The debate has been raging for months, with attacks and counterattacks—albeit very polite ones—appearing regularly in top scientific journals. Because the issue has massive policy implications and the particulars are difficult to understand and explain, the competing groups have also resorted to dueling press releases and other forms of media outreach. Their disagreement over hurricanes isn't just an academic dispute, but a conflict that has very real consequences for how America addresses climate change.

Over the past year, four scientific papers have appeared in prominent journals suggesting that global warming is the major factor in a worldwide rise in hurricane activity. The drumbeat of studies comes from a group of atmospheric scientists whose principal tools are large-scale computer models. Their point man is Kerry Emanuel, a professor at the Massachusetts Institute of Technology who was among the first to suggest a possible warming-hurricane link in a 1987 paper. The idea makes sense intuitively—hurricanes are, in effect, enormous heat engines. In thermodynamics, a heat engine moves warmth around, releasing "work"—physical energy—in the process. A steam engine converts heat to spin gears or wheels. As hurricanes vent heat upward into the cooler reaches of the atmosphere, they convert some of it into high winds, tornadoes, and condensing falling rain. If the air and ocean temperature go up, it's logical to theorize that more and/or bigger storms will form to dissipate the extra heat and moisture. "When you can evaporate water faster into the atmosphere, you are essentially pumping heat into the engine at a great rate," Emanuel says.

In 1987, Emanuel could only theorize. But starting in 1995, hurricane activity in the Atlantic spiked upward alarmingly at the same time as global temperatures were steadily rising—and with them, ocean temperatures. In a field that trades in century-long projections and grand abstractions, Emanuel was handed a rare opportunity: The atmosphere, oceans, and storm activity were all changing before his eyes, fast enough, perhaps, to tease out connections as they happened. One question was how to measure hurricane activity. There are many ways to do it—numbers of storms, their relative strengths (a function of wind speed), atmospheric pressure in the eye, et al. Emanuel came up with something he dubbed the Power Dissipation Index, the annual sum, in a given region, of all storms' cumulative energy output. When he crunched the numbers, Emanuel found that around the world the power of hurricanes was spiking upward at rates that far exceeded anything that had come before. He also found a strong correlation between those increases and rising sea-surface temperatures. He published those results in a paper last fall, which was followed quickly by a related study led by scientists at the Georgia Institute of Technology. Their analysis of global data showed that the proportion of big storms—Category 4 and 5 on the Saffir-Simpson hurricane scale—had more than doubled since 1995. That suggests that global warming may not lead to greater numbers of hurricanes, but that it indeed may be pumping weak ones up into monster storms.

Enter the skeptics, led by Chris Landsea (yes, that's his real name), one of the National Oceanic and Atmospheric Association's top hurricane researchers. The group is made up of meteorologists—scientists who make their living forecasting the annual shifts in hurricane activity and the paths of individual storms. It includes Max Mayfield, the outgoing director of the National Hurricane Center, who famously warned President Bush that Katrina was likely to overwhelm the New Orleans levees. Most aren't global-warming skeptics, but they have attacked Emanuel's research, the Georgia Tech study, and others that suggest a hurricane-warming tie. Their favored technique is to comb the data—which, for meteorologists, is a stock in trade—and expose inconsistencies. They point out that the quality of hurricane measurements varies depending on where and when they were compiled. The technology and standards employed by developing nations in the Pacific basin have historically lagged behind the United States and other nations around the Atlantic basin. Infrared satellite photography of hurricanes—which allows easier assessment of size and strength—didn't begin in earnest until the 1980s. All of these problems, argue the skeptics, fatally compromise the global trend lines that show we're in an emerging era of souped-up megastorms. In a paper published in May, Philip Klotzbach of the University of Colorado—who issues well-known annual hurricane forecasts with William Gray—curtly dismissed the Georgia Tech study's conclusions about more big hurricanes: "Most of this increase is likely due to improved observational technology. These findings indicate that other important factors govern intensity and frequency of tropical cyclones besides SSTs (sea surface temperatures)."

Instead, Landsea and his colleagues have placed their chits—at least as far as the western Atlantic and neighboring eastern Pacific, the main focus of their own research—on a phenomenon called the Atlantic Multidecadal Oscillation. The AMO consists of decades-long ups and downs in sea-surface temperatures. Landsea and his colleagues say it is principally responsible for the sharp rise in hurricane activity since 1995. While a significant leap, they say, it doesn't diverge from dramatic shifts measured over the past century. (One reason storms seem more severe, they correctly note, is that there is simply more human settlement along the coastlines than in the previous up-cycle during the 1920s to the 1960s—ergo, more stuff gets destroyed now than used to.)

Landsea argues that if ocean temperatures are going up, and the worldwide trends toward bigger hurricanes are overstated or nonexistent (he and his allies tie the rise in the Atlantic basin to the AMO and dispute studies that say the same thing is happening elsewhere around the globe), then global warming can't be having much effect. Plus, many other things affect hurricane strength—for example, the shifting pattern in the prevailing winds in the upper atmosphere. Close to the tops of hurricanes, the vertical wind shear—varying wind speed at different altitudes—can make or break a storm. If wind shear is high, it can literally lop off the tops of thunderstorms, stifling nascent hurricanes. And if wind shear is low or nonexistent, hurricanes will flourish unimpeded. No one has yet tied changes in wind shear to global warming.

As it happens, vertical wind shear is particularly hard to incorporate into the global computer models used by scientists chasing the global warming link. And therein lies the chief difference between the two camps. It's not a difference of opinion, but of basic perspective, how different cliques of scientists view the world quite differently. The groups represent two distinct nerd archetypes. The meteorologists of the Landsea group are saying, we know better than anyone how the weather works, and you're oversimplifying it. They're more detail- and history-oriented, involved in short-term forecasting—workaday nerds, in other words, and temperamentally more conservative. "Hurricane forecasters are focused on what is the hurricane out there going to be doing in the next 24 hours," Emanuel says, "and that's not going to have much to do with global warming." And, indeed, their main objections are not a direct rebuttal of the theory on global warming and hurricanes, but a chipping away at the foundations, the data. They have kept their opponents busy rebutting their critiques, but have not really presented a clear argument why global warming should not be disrupting whatever natural cycles exist out there.

Emanuel and the climate scientists, by contrast, are more like prima donnas, looking for the big breakthrough, more willing to go out on a limb in their theories and speculations.

The hurricane war is also, naturally, about political turf. The skeptics occupy some of the most valued scientific ground out there—many, including Landsea and Mayfield, work for NOAA and are involved in the federal government's annual efforts to forecast and track hurricanes. That gives them automatic authority in the public eye and ready pulpits in the media and on Capitol Hill. "The other side has arguably had a certain advantage in communicating its ideas on this subject to the public," says Judith Curry, one of the authors of the Georgia Tech study. NOAA, the nation's premier scientific agency, hasn't even acknowledged there is a debate about one of the most urgent and disputed global-warming topics. Nature magazine recently reported that when a panel of NOAA scientists drafted a consensus statement on the issue suggesting that warming might be affecting hurricanes, administrators quashed it.

Whichever side you're on, there's no reason to relax: Everybody agrees that the Atlantic is due for several decades of bigger, more powerful storms. Practically speaking, the key difference of opinion is what will happen after that—whether the cycle will turn mercifully quiet again or whether the hurricane trend line will simply continue to climb. If the latter scenario comes to pass, our current levees-and-a-prayer approach won't be of much use.

Is Global Warming Making Hurricanes Worse?

Hurricanes bring winds and slashing rains that flood streets, flatten homes, and leave survivors struggling to pick up the pieces. But has global warming given the storms an added punch, making the aftereffects more dreadful?

According to hurricane historian Jay Barnes of Pine Knoll Shores, North Carolina, ocean heat is the key ingredient for hurricane formation. More heat could "generate more storms and more intense hurricanes," he said.

Numerous studies in recent years have found no evidence that the number of hurricanes and their northwest Pacific Ocean cousins, typhoons, is increasing because of the rise in global temperatures.

But a new study in the journal Nature found that hurricanes and typhoons have become stronger and longer-lasting over the past 30 years. These upswings correlate with a rise in sea surface temperatures.

The duration and strength of hurricanes have increased by about 50 percent over the last three decades, according to study author Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology in Cambridge.

Emanuel's finding defies existing models for measuring storm strength. Current models suggest that the intensity of hurricanes and typhoons should increase by 5 percent for every 1ºC (1.8ºF) rise in sea surface temperature.

"We've had half a degree [Celsius] of warming, so that should have led to a 2.5 percent increase [in intensity], which is probably not detectable," Emanuel said. "What we've seen is somewhat bigger than that, and we don't really know why."

One possibility, Emanuel said, is that ocean temperatures may be increasing more quickly than atmospheric temperatures.

"When that happens we've shown theoretically you get an increase in the intensity of hurricanes," he said.

Anatomy of a Hurricane

According to Barnes, who has authored several books on U.S. hurricane history, the physics of hurricanes are complex and full of variables. "But the sun beating down on Earth is the primary thing that gets it going," he said.

Barnes explains in his book North Carolina's Hurricane History that the summer heat warms the ocean's surface and spurs evaporation. As heat and moisture rise into the atmosphere, billowing clouds, scattered showers, and thunderstorms form.

As the thunderstorms multiply, they can get picked up by low-pressure systems drifting through equatorial waters, forming a tropical depression. The spin of the Earth causes the winds within the storm to whirl around the center of the low pressure. This spinning can form an eye of a storm.

The strongest part of a hurricane is the eye wall, on the edge of the calm center. "The size of the eye wall can vary, and the intensity of the storm can vary depending on how much heat is available" and other factors such as high altitude winds, Barnes said.

According to Emanuel, if global temperatures continue to rise, it is reasonable to assume that hurricane activity will increase, as there is more heat to drive the storms.

Global Observation

Previous studies have tried to measure whether typhoons and hurricanes were becoming more frequent. Emanuel's research, however, focused on the total energy generated by the storms over their duration.

"They can have the same frequency, but if they get stronger or last longer this metric will show an increase," he said.

When Emanuel looked at the hurricane record in the North Atlantic, where the storms of most interest to U.S. residents form, he found that intensity fluctuated from decade to decade.

This fluctuation roughly corresponded with factors such as the El Niño weather phenomenon, which has been shown to influence hurricane formation.

However, North Atlantic hurricanes account for only 12 percent of the total number of hurricanes and typhoons that form globally each year, Emanuel said.

"If you look at a more global measure of this metric, you don't see these strong interdecadal swings. They cancel each other out between one ocean and the other," he said. "You see instead a large upward trend."

According to Emanuel, on a global scale, the strength of storms corresponds with ocean temperatures: It goes up when temperatures go up, down when temperatures goes down.

Most scientists say the rise in sea surface temperature in the last 30 to 50 years is a signal of global warming.

"That's their conclusion, not mine," Emanuel said. "[But] it would follow reasonably well from this metric that the upswing [in intensity] … is a result of global warming."

Saturday, November 29, 2008

The Impact Global Warming Has On The Environment

Global warming is currently the world's biggest issue. The increase in greenhouse gases is rapidly changing the face of the Earth. Greenhouse gases come from the burning of fossil fuels. These gases have been on the rise since the industrial revolution in the mid 17th century. This is when people began to make machines to help them work. Carbon dioxide (CO²) is the gas given off from the burning of fossil fuels. Carbon dioxide only makes up a small part of the atmosphere but is the main heat absorbing component. Most infra-red radiation from the sun was once bounced back into space. Now carbon dioxide absorbs a lot more of the sun's energy. There is an estimated 150 000 deaths each year from global warming.

Global warming is on the rise and needs to be halted. We have to cut greenhouse gas emissions and use renewable energy sources

like solar or wind. The burning of fossil fuels makes up to 40% of greenhouse gases. An average of 16 million tonnes of carbon dioxide is emitted into the atmosphere every 24 hours or approximately 11000 tonnes per second by humans worldwide.

Global warming is caused by greenhouse gases trapping in more of the sun's heat. In the mid 17th century people began to invent machines to help them work. Most of the machines were steam powered and burned coal to produce the heat. When coal or any other fossil fuel is burnt it produces carbon dioxide. Fossil fuels are a non-renewable energy source. There is currently 10% more CO² in the atmosphere than there was 30 years ago. There are over 600 million motor vehicles in the world. In the next 30 years this figure is expected to double. Global warming is caused by the increasing amount of CO² in Earth's atmosphere. Earth's climate is being directly affected by human activity. CO² is released when fossil fuels are burnt. Records show that 11 of the last 12 years have been some of the hottest on earth. Carbon dioxide is a great conductor of heat, because of the increasing amount the earth is getting hotter.

Global warming is the average temperature on Earth increasing. The increasing temperature on Earth has lead to some of the polar ice melting. If polar ice continues to melt the sea level will rise and many coastal towns and cities will be flooded. According to NASA the polar ice caps are now melting at the rate of 9% per decade. Artic ice thickness has decreased 40% since the 1960's. The number of category 4 and 5 cyclones and hurricanes has almost doubled in the last 30 years. There are also stronger and more frequent storms.

Global warming also changes weather patterns. This causes droughts in places that once had plenty of rain and floods in other countries. The lack of water in some countries will lead to famines and in places that are flooded many will become homeless. Many glaciers around the world are slowly melting. Up to 100 million people will become refugees if polar ice continues to melt. Many pacific islands and low lying countries like Bangladesh will be flooded.

The rise in temperature has also affected animals and insects. The warmer climate has lead to animals having to shift and change where they live. Warmer weather has also lead to diseases becoming wider spread. Mosquitoes that carry diseases like the Ross River Virus and Malaria are able to travel to places that were once cold.

Many coral reefs are being devastated by global warming. With increasing water temperatures, coral can't survive. Many fish that live off coral or live in coral reefs will also be affected. Many animals that live on ice will also suffer from the effects of global warming. Polar bears have to travel further to find ice that is thick enough to support them. In recent years many polar bears have failed to reach thick ice and have drowned.

Global warming needs to be stopped if humans want to live on Earth any longer. Global warming will have to be halted soon if we want to stop sea levels rising. If sea levels continue to rise many people will be left homeless. A great deal of resources will have to be used to relocate people that have suffered from rising sea levels.

Many pacific islands will be flooded and there will be millions of refugees. If the world can work together in halting global warming, future generations will be better off than if we leave gas levels to continue rising. If gas levels continue to rise many ocean animals will die. Many fish will die and many people will die also from no food. Other people will loose jobs because there will be no fish and other marine animals to catch. In Africa large lakes are drying up.

Many people are also loosing their jobs. Most fishermen from Lake Chad have turned to farming to support their families. Lake Chad was once Africa's third largest inland lake. If global warming isn't halted now we will have to use more power to keep cool in summer. We will also have to use lots of resources to build new places for people to live because rising sea levels will cover many low lying countries. Fresh water lakes will dry up and we will have to use desalination plants.

Australians will also be affected by global warming. Since the middle of the 20th century Australian temperatures have risen by about 1° Celsius. The southern half of Australia will become drier and the north will become wetter. Australia has the largest coral reef in the world. The Great Barrier Reef will die if greenhouse gas emissions aren't stopped. Australians are also the worst polluters of greenhouse gases per person. Australians spend $37 billion each year on energy. Most of this energy is wasted. Australians should spend this money on reducing greenhouse gases and to make use of renewable energy sources.

Many things are being done already to try and slow global warming. There have been agreements to cut greenhouse gases. One of these agreements was signed at Kyoto in Japan. All countries except Australia and America have signed the Kyoto agreement to cut greenhouse gas emissions. The world's worst country for pollution is America. Many people are taking it upon themselves to cut greenhouse gases. People are buying hybrid cars while others are planting trees. Trees use carbon dioxide for photosynthesis and exhale oxygen but there aren't enough trees in the world to lower CO² levels.

Global warming is changing the world. The increasing temperature affects everything that is on the Earth. Rising greenhouse gas levels are changing the Earth in many ways. Diseases are wider spread, the sea level is rising and the average temperature on Earth is increasing. Weather patterns are also changing and many countries are being affected. Countries are suffering from severe drought, while others are experiencing stronger and more frequent storms and cyclones. If something is to be done about global warming the cost will be great, but it will be far greater if we don't do anything now. Everyone has to work together to cut greenhouse gas emissions and halt global warming.

The Top 10 Global-Warming Facts

1. It's more than 90% sure; humans cause global warming
That was the unanimous conclusion in a recent report by the Intergovernmental Panel on Climate Change (IPCC). The IPCC authors includes scientists and official government participants from 40 countries, including the US. Predictive models agree with observed temperatures only when anthropogenic effects are included.

2. Eleven of last 12 years were the hottest ever recorded
That's since 1850. And the high temperatures of the last 50 years are unusual for at least the last 1300 years. Global Warming is real!


Pounds of CO2 since 1750
3. We are dumping about 1000 tons of CO2 per second into the atmosphere Current rates of greenhouse gas emissions into the atmosphere are unprecedented. Carbon dioxide emissions are mostly from burning fossil fuels.

4. Current greenhouse gas levels are far higher than for the previous 650,000 years
The current atmospheric concentrations of carbon dioxide is 35% greater than pre-industrial levels. Methane concentrations have increased by 250%. These dramatic increases in greenhouse gases are human-caused.

5. Global warming produces severe weather and rising seas.
Warming oceans and melting ice have caused the sea level to rise at a rate unprecedented in the last 3000 years. Other changes associated with warming include increased incidences of drought, flooding, heat waves, and intense cyclones.

6. Global warming effects are predicted to get much worse
By 2100, global temperatures will increase another 2 to 11 °F. Increases are predicted in heat waves, drought, intense cyclones, and loss of coastal and low areas.

7. Global warming will affect millions of people by 2100
Loss of habitable land is predicted to result from flooding and droughts. Increases are predicted in heat-caused deaths, famines, drinking water scarcity, disease, and forest fires.

8. 25% of the world's species could be lost from global warming effects
More than 1 million plant and animal species will vanish if global temperatures continue to rise as predicted in the next 50 years.

9. China plans to build about one coal-fired electrical power plant per week over a period of a decade
The US currently emits more greenhouse gases than any other nation, but China will soon pass the US as the worst greenhouse gas emitter.

10. It's too late to stop global warming, but we can limit it
Models show that limiting greenhouse gas emissions can prevent the most extreme scenarios for global warming.

Definitions and Debate

Definition of Global Warming: Gradual increase in the earth's surface temperature.
Popular usage definition: Warming caused by human activity.
Technical term for this: Anthropogenic global warming.
Definition of Greenhouse Gas: A gas, like CO2, which traps the sun's heat.

The debate:
Is the observed global warming natural or man made?

Human causes: Carbon dioxide (CO2), e.g. exhaust from cars and power plants.
Natural causes: Some claim the sun is getting hotter.

U.S. Government Position: The Energy Act of 2005 states: "the President shall establish a Committee on Climate Change Technology [which] shall submit to the Secretary and the President a national strategy to promote the deployment and commercialization of greenhouse gas intensity reducing technologies and practices."

History: In 1896 Svante Arrhenius (1903 Nobel Prize in Chemistry) pre dicted the decrease in CO2 need ed to cause past ice ages. He wasn't far off, and it is not a large decrease. This helped confirm the 1859 prediction that human-produced increases in CO2 would cause just the reverse: global warming.

What Causes Global Warming, human activity or the sun? The final answer is not in, but you can see the results so far. (1) Exhaust is clearly the source of CO2. (2) Everyone now agrees the earth is warming. (3) Decide for yourself if warming is better explained by CO2, or the sun's heat.

Stoft  2005 09 hurricane global warming-S

The Effects of Global Warming. We can see the long-term effects coming in the melting of polar ice and glaciers. But a powerful trend in Atlantic hurricane data indicates we can already see the impact. Katrina was partly the result of a normal weather cycle, but that cannot explain away stronger hurricanes world wide.


Can we Stop Global Warming?
It's too late for that, but we can slow it down and lessen its effects. CO2 does not last as long in the air as was once thought, so the big problem is slowing human use of fossil energy, especially coal. (Especially since CO2 goes into the ocean and destroys coral reefs.)

Friday, November 28, 2008

Global Warming is Hot Stuff !!

Global warming is a hot topic (no pun intended). Some scientists believe the Earth is warming up. While that may be hard to believe in the middle of a Wisconsin winter, if it's true it could mean big changes for our planet.

How do you keep a whole planet warm?

Light from the sun warms land, water, and air. In turn, the warmed-up land, water, and air give off heat, which rises up toward the sky. Gases in the Earth's atmosphere capture some of that heat and prevent it from escaping into space. This heat trap keeps the ground, oceans and air at fairly stable, predictable temperatures -- warm enough to allow thousands of plant and animal species (including humans, like us) to thrive.

Without heat trapping, the earth's surface would be about 60 degrees Fahrenheit colder than it is now. If you’re living in a place like Wisconsin, that means you’d have to wear boots and a heavy coat in July. BRRRRR! (We won’t even talk about January!) The earth’s overall temperature has changed often across the eras -- the long periods of time we use to measure the Earth’s age. We know this because paleontologists have studied the fossils of plants and animals, and because geologists can read the earth’s history in rocks and soil. In hotter eras, dinosaurs clomped across warm green landscapes filled with plants. In colder eras, the wooly mammoth survived in rugged terrain of ice and snow.

For the past 10,000 years, the earth has had relatively stable temperatures. But, for the past 100 years or so, scientists have noticed the Earth seems to be warming up more than usual. This phenomenon is called global warming.

What is the greenhouse effect?

You now know the Earth’s surface and atmosphere stay warm when gases in the air trap heat from the sun. Have you ever been inside a greenhouse, the all-glass buildings where plants are grown? They’re very warm, because the glass walls allow the sun’s rays in but prevent the heat from getting out.

Think of the earth as being inside a giant greenhouse. The gases act like a greenhouse’s glass walls -- they keep heat from escaping into space, and the earth stays warm.

Try this easy experiment: Take two jars and put a teaspoon of water in each jar. Put a lid on just one jar. Place both jars in a sunny spot. After a few hours, check on the jars. You’ll see that the open jar hasn’t changed, but the closed jar will be steamy and hot inside. What happened? The heat from the sun could not escape from the closed jar.

The greenhouse gases

The main gases that cause the greenhouse effect are:

* water vapor
* carbon dioxide, or CO2
* methane
* nitrous oxide

Some "greenhouse gases" occur naturally in the Earth’s atmosphere. But scientists measuring the gases say the amount of gases in the atmosphere has increased in the past few decades. For instance, the amount of CO2 in the atmosphere is 30% greater than what it was 150 years ago. Scientists believe CO2 levels will rise another 30% during the next 50 years.

The increase in greenhouse gases is expected to raise the average global temperature of the planet by 2 to 9 degrees Fahrenheit over the next 50 to 100 years.

Most of the increase is due to human activities, like:

* burning gasoline to drive cars and trucks
* burning oil, coal or wood to produce electricity
* for heating, cooling, and other purposes burning forests to clear land

All these activities, and many others, release greenhouse gases into the atmosphere. With greater amounts of greenhouse gases in the air, more heat will be trapped, and the Earth will get warmer...and warmer...and warmer.

What might happen if Earth heats up?

If Earth gets hotter, some of the following things might occur:

* New coastlines would have to be drawn on maps! Because water expands as it is heated, and because oceans absorb more heat than land, sea levels around the world would rise. Cities on coasts would flood.* Temperate places that now receive frequent rain and snowfall (like Wisconsin) might become hotter and drier. Inland lakes and rivers would shrink. Forest fires could occur more often. Frequent periods of drought would make it hard to raise crops for food. There would be less water available for drinking, showers, irrigation, even swimming pools!

* Plants and animals unable to take the heat may go extinct, and be replaced by heat-tolerant species.

* Hurricanes, tornadoes and other storms caused by changes in heat and water evaporation might occur more frequently and be more intense.

Global warming: It is more than just a game of up-and-down on a thermometer.

There’s a lot of debate going on about global warming. Some scientists say it’s nature’s way -- something that has happened in the past and will likely occur again. Other say global warming is occuring faster because of human beings and that human beings can stop it, or slow it, if they so choose.

One thing is certain: We do not yet know enough about how Earth works to accurately predict what the increase in greenhouse gases caused by humans will do to the planet. The relationships among land, water, air, plants and animals do not follow a simple pattern, where one action automatically leads to the same result.

For instance, an increase in carbon dioxide (the main greenhouse gas) may warm the Earth, and with the greater warmth more trees might grow. Trees absorb carbon dioxide to make wood and grow larger. With more CO2 captured in trees and less CO2 in the atmosphere to hold in heat, the Earth would cool down. Right? On the other hand, trees are also very good at trapping the sun’s heat. So with more trees, the Earth would get warmer. Right?

We really don’t know for sure. After all, the Earth is a big place -- a place that’s worthy of your attention and study. Perhaps someday you’ll unlock yet another of Earth’s secrets.

YOU can help slow global warming!

Just because we’re not absolutely certain of how more greenhouse gases will affect the Earth doesn’t mean we should sit back and do nothing.

Besides increasing greenhouse gases, burning too much gasoline and other fossil fuels creates air pollution and wastes energy. Who wants to breathe bad air, or always look up at a dirty sky?

You can help slow global warming by:

* Walking, riding your bicycle, or taking the bus instead of always going by car.
* Not wasting electricity (turn off the lights, the radio, the TV and the computer when you’re not using them).
* Reducing, reusing or recycling all kinds of items, from soda pop cans to clothes, to save energy and raw materials.
* Planting trees to help absorb excess CO2, and to provide shade and windbreaks to keep buildings at more even temperatures so they will require less energy for heating or cooling.


* Era: The longest division of geologic time, measured in millions of years.
* Fossil fuels: A fuel such as oil, which comes from decomposed living matter from another geologic era.
* Geologist: Someone who studies the origin and structure of the Earth.
* Greenhouse: A glass-enclosed building used to raise plants that need controlled temperatures and humidity.
* Greenhouse gases: Gases that trap heat in the atmosphere. They include water vapor, carbon dioxide (CO2), methane and nitrous oxide.
* Paleontologist: Someone who studies fossils, such as skeletons or leaf imprints.

Wednesday, November 26, 2008

Tragedy of the Commons

When doing what's good for you isn't good for you.


Picture yourself in a rural setting with villages surrounded by grassland open to herdsmen to graze their animals. This “commons” is available to all without restriction.

Imagine that the common pasture is supporting the maximum number of sheep that it can. There is just enough grass to keep all the sheep well fed, but no more. Adding sheep would mean less food for each.

However, for each herdsman it appears to be an advantage to increase the size of his herd. More sheep means more wool and more income. There is also a disadvantage in doing this: there will be slightly less food for each of his sheep. But this disadvantage appears small since it is spread among all the sheep, including those of the other herdsmen. So from the point of view of each herdsman, the gain is great and the loss is small.

The tragedy is that when all herdsmen act this way, the small losses add up to a disaster for everyone.

The Tragedy of the Traffic Jam

Traffic jam
Photo courtesy of U.S. Census Bureau.

A modern example of a “tragedy of the commons” is traffic jams in major cities. A public good gets overused and lessened in value for everyone. Each individual trying to get to work quickly uses the freeway because it is the fastest route. In the beginning, each additional person on the highway does not slow down traffic because there is enough "slack" in the system to absorb the extra users. At some critical level, however, each additional driver brings about a decrease in the average speed. Eventually, there are so many drivers that traffic crawls at a snail's pace. Each person seeking to minimize driving time has in fact conspired to guarantee a long drive for everyone.

Failing Fisheries

Photo courtesy of NOAA.

Can you be a successful fisherman while preserving the common fishing grounds for everyone? Give it a try with the Fishing Game.

We see this same pattern in fisheries around the world. The oceans are not owned by individual fishermen or controlled by countries. They provide a common resource of fish. As the number of fishing boats increases year after year, the total catch increases. Sounds good, right? However, as the total catch increases, it reduces the fish population's ability to restore itself.

Eventually the total individual and collective catch drops. This puts more financial pressure on fishermen to try to catch even more fish. Catching more fish only erodes the restoration capacity of the fish population even more. What would you do if you were a fishing boat captain faced with these issues? You can find out for yourself by playing the Fishing Game.

Waste in Our Waterways


In some cases the problem is not one of taking too much from a common resource. Instead the problem is putting too much in. With a small population it is not a problem to dump waste into a river. Waterways cleanse themselves with time. As long as the load of waste is not too great, the river can maintain its clean state. But if there is too much waste the river becomes polluted. People can no longer drink the water. They may not even be able to safely swim or go boating in it.

Greenhouse Gases

This is the way it is with the atmosphere. Carbon dioxide (CO2) is constantly going into the atmosphere and out of it in the carbon cycle. The oceans and forests absorb CO2. With industrialization, factories, cars, and power plants pump CO2 into the atmosphere faster than it can be absorbed. The commons is being overwhelmed.

Think of the Earth’s atmosphere as a tremendous bathtub. Imagine the concentration of greenhouse gases as the water in the bathtub. Water flows into the tub like CO2 goes into the atmosphere. Like the water running down the drain, CO2 is removed from the atmosphere. If the rate of flow from the faucet into the tub is equal to what is going down the drain, the water level remains the same. If you turn up the faucet, the level rises and the tub may overflow. Right now our atmospheric bathtub is filling twice as fast as it is draining.

What Can Be Done?

The term Tragedy of the Commons was coined by Garrett Hardin in an article he wrote in 1968. He says that problems that fall into this category have no technical solutions. They require changes in human attitudes and behavior.

In the case of climate change, the solutions are both behavioral and technical. We can use energy more efficiently, increase the use of alternative energy sources that do not produce CO2, and capture and store the CO2 that we do produce. So what’s the problem?

The problem is that individuals acting in their own interests feel immediate gain from their actions. But the losses from the impact of global warming are not felt immediately. So I may drive a large car because I feel more comfortable in it. The discomfort I will feel when sea levels rise or storms intensify may be decades away. And, I don’t see any immediate connection between my actions and those consequences. In fact, if I were the only one driving a big car, there would be no negative consequences. Like the herdsman who adds a sheep to his flock, the benefit is clear and immediate while the loss is diluted and delayed. But when many herdsmen act this way they all suffer.

A solution requires people to collectively make a decision to alter the behavior of everyone, including themselves. One way to do this is to cause climate-friendly actions to have immediate positive results. For example, in the Sleipner gas field in the North Sea, the tax policy of the Norwegian government makes it economically advantageous to capture and store CO2 rather than release it into the atmosphere. The mechanism is simple: there is a tax on CO2 that is released. Sure, it costs money to capture and store CO2. But in this situation it costs more not to.

The Impact of Global Warming

Over the past 425,000 years the earth has gone through four ice ages punctuated by brief warm periods. We are currently in such a warm period. The trend over the past century has been one of generally rising global temperature. The consensus among climatologists is that there will be a continued increase during the rest of this century. OK. But is this a problem? Yes it is. Even though there might be a few benefits of warming, such as longer growing seasons in some cooler agricultural areas, the consequences for most people in most parts of the world will be negative. Here are some of the problems.

Sea Level Changes

At the height of the last ice age 18,000 years ago, the oceans were about 120 m (400 ft) lower than they are today. Large amounts of water were sitting on land in the form of glaciers that covered a good portion of North America, Europe, and Asia.

The North Sea and the Baltic Sea were mostly land. The Bering Strait that now separates Siberia from Alaska was also above sea level. It is believed that people walked across this land bridge and populated the Americas for the first time in human history.

As the ice age ended, the glaciers mostly melted and their water returned to the oceans. Sea levels rose. Another factor affecting sea level is the temperature of the water. Water, like most substances, expands as it is warmed. The expanded seawater has a larger volume, which contributes to rising seas.

Image based on data from the Intergovernmental Panel on Climate Change (IPCC).

If we look at the recent past, we see a continuing rise in sea levels. The chart shows sea levels at three locations in Europe over the past 300 years. During this period sea level has risen 100 mm (3.9 in) or more. But the rise in sea level is not the same in all parts of the world. In some places, sea level is actually falling, as shown in the map World Sea Level Rise and Fall.

This may sound strange. If all the oceans are connected, how can the level be different from one place to another? Actually it can. Sea level is locally affected by currents, winds, rate of flow of water from land into the oceans, air pressure, and tides. But mostly, it is because of our definition of sea level. We are measuring “relative sea level,” that is, the level of the sea relative to nearby land. Land may be rising or falling. For example, the area around the Mississippi Delta, where the river empties into the Gulf of Mexico, is subsiding. The land is made of recently deposited sediments that are settling. Many areas that were covered by the glaciers of the last ice age are rising since the weight of the ice has been lifted. Places on the southern coast of Alaska are experiencing a falling sea level. This is also true of many ports in Scandinavia.

More than 100 million people live on land within 1 m (3 ft) of sea level. Some island countries such as the Seychelles off the east coast of Africa are mostly less than 1 m above sea level. It is estimated that a rise of 1 m would put half of the land of Bangladesh under water. Although there are local variations in sea level, the key question is what is happening to the volume of ocean water worldwide. The major determining factor is the amount of water in glaciers on land, especially in Greenland and Antarctica.

What Will Happen Next?

While the ice-age glaciers have mostly retreated, Greenland and Antarctica remain covered with ice that is 2,000 to 4,000 m (6,550 to 13,000 ft) thick. The fate of these ice packs will have a significant impact on future sea levels. The Intergovernmental Panel on Climate Change (IPCC) reported in 2001 that it expects a rise in sea level by 2100 of up to 66 cm (26 in) due to glacier melting. In a 2002 report researchers at the University of Colorado, USA, analyzed the rate of melting of glaciers around the world. They calculated that glaciers are melting faster than previously thought and that by 2100 the sea level could rise by as much as 89 cm (35 in). But more recent studies raise questions about these predictions. Two studies reported in 2005 show that during the period from 1992 to 2003, snowfall increased over large portions of the interiors of Antarctica and Greenland. The glaciers are melting at the edges, but they are thickening in the interior. The question is how these contradictory tendencies will balance out.

Greenland's ice thickness changes

Antarctic ice
Photo by Ben Holt, Sr.
courtesy o

A special report in the March 24, 2006, issue of Science includes several studies that point to an increasingly rapid loss of the world's ice sheets. In particular, it has been found that the movement of Antarctic and Greenland glaciers toward the sea is accelerating. This will certainly result in quicker loss of these ice caps and consequently more rapidly rising sea levels.

Precipitation Changes

Over the last 100 years many dry areas have become even drier and wet areas have become wetter. Many long-standing weather records have been broken in recent years. In 1992, the Danube and Elbe rivers burst their banks in central Europe. The southern section of the Sahara desert suffered a serious, long-lasting drought in the 1990s. Droughts affect different parts of the western United States each year. In some locations the drought may last more than a year.

Image based on data from the Intergovernmental Panel on Climate Change (IPCC).

Tropical Storms

Tropical storms form over warm ocean waters near the equator. Warmer water results in more storms and more intense storms. In recent years there has been an increase in both the number and severity of tropical storms. The 2005 Atlantic hurricane season was particularly devastating, with three major storms—Katrina, Rita, and Wilma—causing extensive damage in the United States and Mexico.

The season for Atlantic tropical storms is considered to be from June through November. But in 2005, Tropical Storm Zeta, the final storm of the season, formed in late December and lasted into January 2006. It is tempting to attribute the increase in storm activity to rising global temperatures. This may be the case, but the situation is more complicated. There have been cycles of storm intensity and frequency in the past. The 1930s through the1950s were a period of greater storm activity. This was followed by several decades of relative calm and then the period of increased activity that we are currently experiencing. These cycles are due to changes in rainfall, ocean currents, and salinity. So there are two tendencies, one cyclical and the other long-term. Even if storm activity ebbs and flows as it has in the past, warmer oceans are likely to result in more storms and more intense storms. The quiet parts of the cycle will not be as calm as in the past. The active periods are likely to be worse. People in some parts of the world are in particular danger from storms in combination with rising sea levels. The Gulf of Mexico and the Bay of Bengal are places where relative sea level is rising most rapidly. They are also subject to frequent tropical storms.

Can Global Warming Cause Cooling?

While many parts of the world can expect warmer weather, global warming might have the opposite effect in some places. Western Europe is quite warm for its latitude. This is because the Gulf Stream, a warm ocean current, reaches into the North Atlantic. Winds passing over the warm water and onto land have a moderating effect on the climate. For example, the average winter temperature in London, England, is about 4°C (39°F). Calgary, in western Canada, is at about the same latitude but has an average winter temperature of -9°C (16°F). The Norwegian port of Tromso and the Russian port city of Murmansk are ice-free year round even though they are in the Arctic. The Gulf Stream is part of a worldwide circulation of ocean water known as the thermohaline circulation. Thermo refers to temperature and haline to salinity. Temperature and salinity both affect the density of water.

Thermohaline circulation

Thermohaline circulation

Click for animation.

This is a simplified diagram of the global thermohaline circulation. Surface currents carry warm water, while deep currents are cold. The warm current that reaches into the North Atlantic is called the Gulf Stream. It is responsible for keeping western Europe relatively warm.

Image courtesy of NOAA.

As the Gulf Stream waters flow northward, water evaporates. This causes an increase in salinity because the same amount of salt is now held by less water. At the same time, the waters cool.

Increased salinity and decreased temperature both result in the water becoming denser. The denser water sinks and flows south. What does this have to do with global warming? The melting of Arctic ice is adding fresh water to the North Atlantic. This means that the waters at northern latitudes are becoming less dense and therefore less prone to sinking. The result could be a decrease in the rate of flow of the currents. A reduced Gulf Stream flow would have less of a warming effect on western Europe. There have been some predictions that the thermohaline circulation could shut down suddenly, causing a temperature drop of about 8°C (14°F) in western Europe in a matter of a few decades. Most climatologists think this is very unlikely. However, there could be a slowing of the circulation resulting in some cooling effect. But since global temperature is rising, the net effect may be that western Europe stays the same, or gets just a bit warmer. Since climate is very complicated, it is difficult to make accurate predictions. Specific tendencies are known, but how they interact with each other is less certain.

What Can We Expect?

The world's climate system is complicated. It is difficult to make precise predictions. But the future trends are becoming increasingly clear: rising sea levels, more frequent and more intense storms, and increased drought in many already dry parts of the world.

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