Carbon storage? Dutch town says not here

Shell wants to pump it into depleted underground natural gas fields

 

BARENDRECHT, Netherlands – The people of this small Dutch town are not against pumping tons of carbon dioxide into the ground to fight global warming.

They just wish it wasn’t right beneath their houses. “Who wants to live in Barendrecht if one of these CO2 things is built?” asked retiree Marianne van Heugten.

The carbon dioxide storage experiment by Royal Dutch Shell and the Dutch government is only one of a dozen such projects across Europe to test a technology that could potentially slash emissions of greenhouse gases such as carbon dioxide into the atmosphere by storing it underground.

That would allow countries that have lots of coal, such as China and the United States, to cut emissions while using the cheap but polluting fossil fuel. Carbon dioxide from the burning of such fuels is considered the chief cause of global warming.

But questions remain about the technology and its costs and risks even as the EU prepares to spend billions on it.

If it works, the technology would buy the world time in the fight against global warming by reducing emissions until cleaner energy sources can be developed — and help the EU keep big promises. Three weeks before global talks on a new climate change pact in Copenhagen, the EU says it is ready to reduce greenhouse gas emissions by up to 95 percent by 2050. The EU thinks carbon storage could shave up to 10 percent off global emissions by 2030 and 20 percent by 2050.

The European Union has pledged some $1.5 billion in initial financing and will raise extra funding — likely some $6.7 billion — from selling permits to emit greenhouse gases under a cap-and-trade system where companies need to pay to pollute more.

It is also calling for all new coal-fired power stations built after 2020 to be capable of capturing carbon — even if the technology isn’t ready to be rolled out by then.

The Dutch government must decide whether to overrule Barendrecht residents objections or push forward with the unknown risks of storage under one of the most densely populated parts of Europe. Most current storage sites are in isolated areas.

The project would pump 10 million tons of carbon dioxide starting from 2011 into two depleted gas fields more than a mile under the town. The gas fields are considered by some a safer choice than current experiments under the the North Sea and the Sahara Desert where a water-bearing rock layer, or aquifer, is being used.

It’s only a trial; Shell says the Netherlands might need to store 30 million tons a year by 2025 and the entire country could potentially store 1 billion tons.

Some 43,000 people live in Barendrecht, a suburb 12 miles from Rotterdam and its port, Europe’s busiest. Real estate agent Frits Markus says worries about the project could affect the average $420,000 house price. People “will be scared that CO2 will be stored under where they live, they will feel their houses will lose value, and will have trouble selling them.”

Carbon dioxide, which provides the fizz in soft drinks, is naturally present in the atmosphere although levels have soared since start of the industrial revolution. Plants take it in and people breathe it out. But a sudden release of large amounts can kill by asphyxiation. Some 1,700 people died when a cloud of carbon dioxide escaped from a volcanic lake in Cameroon in 1986.

A slow leak would simply negate the costly efforts to store the gas. Greenpeace says this could happen if stored carbon dioxide mixes with water underground to from a weak carbonic acid that could corrode pipelines and rocks.

In Barendrecht, town council member Simon Zuurbier says he doesn’t fear a blowout under his town, something he says is only likely to happen when carbon dioxide is being injected into the site. But he isn’t sure the government will always be able to monitor “eternal storage.”

Stuart Haszeldine, a geology professor at the University of Edinburgh, says “nothing like” a dramatic blowout would happen at a depleted gas field because the carbon dioxide would be injected with relatively little extra pressure and only the gas in the borehole — and not the entire site — would be likely to escape.

Such “confined space” oil and gas fields are far safer and easier to monitor, he says, because energy companies understand the geology better than storage at other possible sites like aquifers where the carbon dioxide can move sidewise into the rock with more potential to leak.

Shell’s plans to pipe the gas to Barendrecht would turn the town into a waste landfill, claim local campaign group CO2isNee. It’s being labeled a dump, of sorts, that seems to anger locals the most.

“The value of houses, that’s the real worry here,” said resident Herman Bakker.

The sad truth

Hurricanes growing fiercer with global warming

Hurricanes have grown significantly more powerful and destructive over the last three decades due in part to global warming, says an MIT professor who warns that this trend could continue.

“My results suggest that future warming may lead to an upward trend in [hurricanes'] destructive potential, and–taking into account an increasing coastal population–a substantial increase in hurricane-related losses in the 21st century,” reports Kerry Emanuel in a paper appearing in the July 31 online edition of the journal Nature.

Emanuel is a professor of meteorology in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

Theories and computer simulations of climate indicate that warming should generate an increase in storm intensity. In other words, they should hit harder, produce higher winds and last longer.

To explore that premise, Emanuel analyzed records of tropical cyclones–commonly called hurricanes or typhoons–since the middle of the 20th century. He found that the amount of energy released in these events in both the North Atlantic and the North Pacific oceans has increased markedly since the mid-1970s. Both the duration of the cyclones and the largest wind speeds they produce have increased by about 50 percent over the past 50 years.

He further reports that these increases in storm intensity are mirrored by increases in the average temperature at the surface of the tropical oceans, suggesting that this warming–some of which can be ascribed to global warming–is responsible for the greater power of the cyclones.

According to Jay Fein, director of the National Science Foundation’s climate dynamics program, which funded the research, Emanuel’s work “has resulted in an important measure of the potential impact of hurricanes on social, economic and ecological systems. It’s an innovative application of a theoretical concept, and has produced a new analysis of hurricanes’ strength and destructive potential.”

Global Warming

Global warming could do more than just melt polar ice. It could change our maps, and displace people from cities and tropical islands.

Recent successes in Global Warming

Federal Policy

The world’s scientists agree that the window to prevent the worst effects of global warming is closing. The United States must act quickly to reduce its carbon emissions at least 80 percent by 2050, but Congress has yet to act. In 2008, UCS worked with allies in Congress to craft such a policy, and bolstered these efforts by organizing and distributing a statement signed by more than 1,700 prominent U.S. scientists and economists calling for the needed reductions. We also kept the issue in the public eye by inviting aspiring writers and photographers to submit entries for an online book—Thoreau’s Legacy: American Stories about Global Warming—to be published in partnership with Penguin Classics.

Regional Policies

We used our 2007 report Confronting Climate Change in the Northeast to educate policy makers and mobilize activists in an effort to ensure successful implementation of the nation’s first program limiting carbon emissions from power plants (which is now in effect). Our 2008 follow-up, Climate Change in Pennsylvania, supported legislation to cut that state’s emissions and strengthened support for federal climate policy among Pennsylvania’s members of Congress.

In the Midwest, our participation in several state advisory groups helped secure strong climate policy recommendations, and we played a lead role in developing a regional cap-and-trade program. We also helped win legislation in Minnesota to fund a study of cap-and-trade auctions, thereby providing lessons for all such programs. In the West, we helped strengthen proposals for cap-and-trade programs in California and the Western Climate Initiative (a collaborative effort among seven states and Canadian provinces).

International Policy

Our report Out of the Woods supported international climate negotiations by describing the important role an agreement reducing tropical deforestation can play in curbing global warming. This research provides a realistic estimate of the climate benefits such an agreement can achieve

Things you can do today to reduce Global Warming

Source: www.stopglobalwarming.org

Take Action!

There are many things you can do in your daily life that can have an effect on your immediate surrounding, and on places as far away as Antarctica. Here is a list of things that you can do to make a difference.

There are many things you can do today to reduce your own adding to on this problem!

Tropical Tree Growth Slowed
Other big changes are being monitored in the tropics, too. Data on tree growth, tropical air temperatures and CO2 readings collected over 16 years indicate that a warming climate may cause the tropical forests to give off more carbon dioxide than they take up. This would upset the common belief that tropical forests are always a counterbalance to carbon, taking huge amounts out of the atmosphere. The study, by Deborah and David Clark of the La Selva Biological Station in Costa Rica, and Charles Keeling and Stephen Piper of the Scripps Institution, reports that rainforest trees grow much more slowly in warmer nighttime temperatures, which is a hallmark of climate change in the tropics.
Tropical Tree Charles Keeling

Landscaping Your Home for Energy Efficiency
In Winter, by maximizing solar heating while deflecting winds away from your home; and
in Summer by maximizing shading while funneling breezes toward your home.

Buy a Hybrid Car
The average driver could save 16,000 lbs. of carbon dioxide and $3,750 per year driving a hybrid.

Buy a Fuel Efficient Car
Getting a few extra miles per gallon makes a big difference. Save thousands of lbs. of carbon dioxide and a lot of money per year.

Carpool When You Can
Own a big vehicle? Carpooling with friends and co-workers saves fuel. Save 790 lbs. of carbon dioxide and hundreds of dollars per year.

Inflate Your Tires
Keep the tires on your car adequately inflated. Save 250 lbs. of carbon dioxide and $840 per year.

Change Your Air Filter
Check your car’s air filter monthly. Save 800 lbs. of carbon dioxide and $130 per year.

Reduce Garbage
Buy products with less packaging and recycle paper, plastic and glass. Save 2,000 lbs. of carbon dioxide per year.
Composting helps reduce greenhouse gas emissions by reducing the number of trips trucks must make to the landfill as well as the amount of methane released by our landfills.

Use Recycled Paper
Make sure your printer paper is 100% post consumer recycled paper. Save 5 lbs. of carbon dioxide per ream of paper.

Buy Minimally Packaged Goods
Less packaging could reduce your garbage by about 10%. Save 1,200 pounds of carbon dioxide and $1,000 per year.

Unplug Un-used Electronics
Even when electronic devices are turned off, they use energy. Save over 1,000 lbs of carbon dioxide and $150 per year.

Plant a Tree
Trees provide a microclimate and sustained moisture for you. Trees suck up carbon dioxide and make clean air for us to breath. Save 2,000 lbs. of carbon dioxide per year.

Use Compact Fluorescent Bulbs
Replace 3 frequently used light bulbs with compact fluorescent bulbs. Save 300 lbs. of carbon dioxide and $60 per year.

Fill the Dishwasher
Run your dishwasher only with a full load. Save 100 lbs. of carbon dioxide and $40 per year.

Adjust Your Thermostat
Move your heater thermostat down two degrees in winter and up two degrees in the summer. Save 2000 lbs of carbon dioxide and $98 per year.

Check Your Waterheater
Keep your water heater thermostat no higher than 120EF. Save 550 lbs. of carbon dioxide and $30 per year.

Change the AC Filter
Clean or replace dirty air conditioner filters as recommended. Save 350 lbs. of carbon dioxide and $150 per year.

Take Shorter Showers
Showers account for 2/3 of all water heating costs. Save 350 lbs. of carbon dioxide and $99 per year.

Install a Low-Flow Showerhead
Using less water in the shower means less energy to heat the water. Save 350 lbs. of carbon dioxide and $150.

Buy Products Locally
Buy locally and reduce the amount of energy required to drive your products to your store.

Buy Energy Certificates
Help spur the renewable energy market and cut global warming pollution by buying wind certificates and green tags.

Insulate Your Water Heater
Keep your water heater insulated could save 1,000 lbs. of carbon dioxide and $40 per year.

Replace Old Appliances
Inefficient appliances waste energy. Save hundreds of lbs. of carbon dioxide and hundreds of dollars per year.

Weatherize Your Home
Caulk and weather strip your doorways and windows. Save 1,700 lbs. of carbon dioxide and $274 per year.

Use a Push Mower
Use your muscles instead of fossil fuels and get some exercise. Save 80 lbs of carbon dioxide and x $ per year.

Put on a Sweater
Instead of turning up the heat in your home, wear more clothes Save 1,000 lbs. of carbon dioxide and $250 per year.

Insulate Your Home
Make sure your walls and ceilings are insulated. Save 2,000 lbs. of carbon dioxide and $245 per year.

Air Dry Your Clothes
Line-dry your clothes in the spring and summer instead of using the dryer. Save 700 lbs. of carbon dioxide and $75 per year.

Switch to a Tankless Water Heater
Your water will be heated as you use it rather than keeping a tank of hot water. Save 300 lbs. of carbon dioxide and $390 per year.

Switch to Double Pane Windows
Double pane windows keep more heat inside your home so you use less energy. Save 10,000 lbs. of carbon dioxide and $436 per year.

Buy Organic Food
The chemicals used in modern agriculture pollute the water supply, and require energy to produce.

Bring Cloth Bags to the Market
Using your own cloth bag instead of plastic or paper bags reduces waste and requires no additional energy.

US, Canada rank last in curbing warming

With only five months left before a summit on climate change – it’s intended to produce a new global pact – none of the Group of Eight nations is doing enough to curb global warming, says a study released yesterday. It ranks the United States and Canada at the bottom.
The G-8 Climate Scorecards, compiled by the environmental group WWF, said even the greenest members of the rich nations’ club – Germany, Britain, and France – are not on track to meet a “danger threshold” of limiting temperature rises to below 2 degrees Celsius.
G-8 leaders gather in Italy next week to discuss the world financial crisis and climate change. They hope to make progress toward a pact on global warming that’s due to be signed in Copenhagen in December. It would replace a 1997 Kyoto deal.
They will be joined by members of President Obama’s Major Economies Forum.
“While there might be a bailout possibility for the financial system, no amounts of money will save the planet once climate change crosses the danger threshold,” the WWF’s head, James Leape, wrote in the foreword to the report.
Yesterday’s annual G-8 scorecard singled out Canada, saying Prime Minister Stephen Harper’s conservative government has not implemented a plan to curb emissions, already among the highest in the world per capita and increasing. Canada was not even close to meeting its Kyoto agreements, the WWF said.
The report praised Obama for making clean energy a priority and promoting green legislation, but said US per capita emissions are among the highest in the world and are projected to rise.
“There has been more action in the US in the last four months than in the last three decades – a trend that will hopefully continue,” the report said.
Obama’s government has not embraced the 2 degree Celsius goal adopted by the European Union. Temperatures have already risen by 0.7 percent since the start of the industrial era.
“To avoid or reduce the risk of catastrophic climate change, G-8 leaders must agree to do everything they can to stay below 2 degrees,” said Kim Carstensen, leader of the WWF’s Global Climate Initiative.
At the top of the G-8 rankings was Germany, followed by Britain. The WWF praised Berlin for promoting renewable energy and having an ambitious target of cutting greenhouse gases by 40 percent by 2020.
Britain has achieved its Kyoto pact targets because of a transition from coal to gas-fired power stations in the 1990s, but there is room to cut emissions in transportation and power generation, the report said.
France has low emissions per capita for an industrialized nation because of its reliance on nuclear power. The WWF does not support nuclear power concerns over radioactive waste.
Italy has low emissions compared with G-8 partners, mainly because of the structure of its economy, the WWF said, but emissions are rising and the government is not making headway on meeting Kyoto obligations.

Gordon Brown and Ed Miliband’s blueprint for global warming deal

Gordon Brown will tomorrow outline Britain’s blueprint for a new international deal on global warming, which world leaders are pushing to be agreed at December’s critical UN talks in Copenhagen. In a speech at London Zoo, the prime minister is expected to call on all developed countries, including Britain and the US, to show greater ambition in the fight against climate change.
The new agreement is intended to replace the Kyoto protocol in setting national limits on carbon pollution, and is billed by green campaigners as the last chance to save the planet from severe and dangerous levels of warming.
Brown and Ed Miliband, the energy and climate change secretary, will publish details in the government’s Road to Copenhagen document, which Miliband said was aimed at revitalising public interest in the issue.
Speaking ahead of the launch, Miliband said: “People are still not sufficiently aware of the scale of the problem this could create for them and future generations in Britain.
“People believe climate change is happening in the UK, most people don’t think it’s a plot or something made up, but most people don’t seem to think it will happen in their area.”
He said Britain, which will negotiate the new treaty as part of the EU bloc, was pushing for the new deal to force emissions from developed nations to reach a peak by 2015.
Global greenhouse gas output should peak and begin to decline by 2020, to “irreversibly break” the trend of rising emissions.
Scientists have warned that global emissions need to peak in the next few years, and then significantly shrink, to avoid dangerous rises in temperature and changes to the climate.
Miliband said: “We’re talking about reversing 150 to 200 years of the growth of carbon emissions. It’s difficult, there are many obstacles in the way, but it’s ­doable with the right political will.”
The UK wants the deal to include ­commitments in three areas – emissions cuts by developed countries, reductions by developing countries compared with what they would emit without an ­agreement, and finance for climate change measures.
He said various countries, including the US, Japan and the EU, had already made offers of commitments they would sign up to, while China and other developing countries wanted a deal. But he said there needed to be “greater ambition from all countries” since the world could not afford to fail on the issue.
Miliband said his department has established a “Copenhagen war room” and ministers from across Whitehall are being instructed to raise the issue on all overseas visits.
A pamphlet explaining the risks posed by climate change and the importance of a Copenhagen deal is being sent to nearly 20,000 organisations across the UK – including libraries, schools, health centres and GP surgeries, as well as Citizens Advice centres and local authorities.
Miliband said: “There’s a real danger of defeatism in this debate, a danger people think ‘nothing can be done, it’s inevitable, let’s just hide under the bedclothes’.”
He said leaders needed to be in the “business of optimism” and that he was genuinely optimistic about the efforts to tackle climate change.
The announcement comes the day after new data showed the growth of global ­carbon dioxide emissions fell by half in 2008 as a result of the recession, high oil prices and an increase in renewable energy. In addition, the figures show that, for the first time, carbon dioxide emissions from the developing world account for more than half of the global total.
The analysis, by the Netherlands Environmental Assessment Agency, shows that the rise in the world’s emissions from fossil fuel burning and cement production in 2008 was just 1.7%, compared with 3.3% in 2007.
The slowdown in emissions growth was caused primarily by a 0.6% fall in the consumption of oil – the first decline in global oil use since 1992. This trend was uneven around the world. In China, oil use continued to rise, but at only 3%, down from an average of 8% since 2001. In the US, oil consumption fell by a massive 7%.
By contrast, global coal use continued to creep up and the rise in the consumption of natural gas remained unchanged.
Increasing renewable energy capacity and improving energy efficiency in many countries also contributed to the reduced rise in carbon dioxide emissions. NEAA’s Jos Olivier said: “The impact of energy and climate policy is hard to distinguish from those of fuel prices and the recession, but policies encouraging renewable electricity generation will have helped avoid around 500m tonnes of carbon dioxide from fossil fuel power stations.”
It remains to be seen how the rate of emissions will change in 2009. If the recession continues to bite through the year, global emissions could flatten off entirely.
Meanwhile, policymakers are likely to be particularly struck by the revelation that, in 2008, the developing world accounted for 50.3% of carbon dioxide emissions, exceeding developed nations and international travel combined for the first time. This fact will provide ammunition for those arguing in favour of binding emissions ­targets for all nations, not just industrialised ones.
Furthermore, the data does not take into account the carbon dioxide released by deforestation, which accounts for almost 20% of all greenhouse gas emissions and takes place overwhelmingly in the developing world.

Projections of Climate Change

Because we can’t know the future for certain, scientists use computer-based climate models to project plausible scenarios for the coming century and beyond.
Recently, the IPCC developed a series of 24 future climate change projections, a much broader set than previously considered. This elaboration was intended to convey a broader range of possibilities while accounting for the important uncertainties still outstanding. The scenarios are based on a range of estimations of heat-trapping-gas and aerosol emissions and assumptions about future population, energy use, economic growth, land use changes, and so on.
The IPCC grouped these 24 scenarios into 6 “families” and showed each represented in a line graph together with an earlier reference scenario (IS92a). In the charts below, you see the projections for each of these scenarios regarding changes in CO2 emissions, the resulting atmospheric carbon dioxide concentrations, SO2 emissions, temperature change and sea-level rise between 1990 and 2100. Take the red dashed line — the A1T scenario — for example( - – -).

Chart (a) This red line basically says that CO2 emissions will be radically reduced after about 2040.

Chart (b) tells us that only those kinds of radical emission reductions will lead to a stabilized CO2 concentration in the atmosphere.

Chart (c) says that this reduction would be accompanied by a strong reduction in SO2 – probably due to a reduction in burning coal and other CO2- and SO2-rich fossil fuels.

Chart (d) then indicates that with such strong reductions we would still see a temperature increase, but a more modest one than under some of the other scenarios, and that the warming trend would level off late in the 21st century.

Chart (e), finally, shows how this degree of warming would produce a mid-range scenario of sea-level rise. Because of the slow response of the oceans to atmospheric warming, that upward trend is still continuing and will continue for many more years after heat-trapping gases are stabilized and the upward temperature trend levels off.

The growing empirical evidence of climate change that is consistent with model projections, and other recent advances in the understanding of climate science have led to increased confidence in the use of global circulation models to project future climate change, but predicting the future remains inherently risky.

The current estimate of the IPCC is that an unmitigated rise in atmospheric greenhouse gas concentrations will cause temperatures to rise between 2.4 and 10.5 degrees Fahrenheit over the 21st century. This projection is significantly larger than what the panel predicted in 1996 at the time of its second assessment report, primarily based on improved models and the assumed reduction of aerosol emissions (most of which have a cooling effect).

As a result of this warming, scientists predict:

Sea level could rise by 3.5 to 34.6 inches between 1990 and 2100, making coastal groundwater saltier, endangering wetlands, and inundating valuable land and coastal communities;

Changes in precipitation patterns could have a significant impact, especially in already water-scarce regions that are likely to suffer from further decreasing rainfall;

The ranges and abundance of plants and animals could change dramatically under changing climate conditions, and some of them are likely to be unable to adapt or migrate to new locations;

Future adverse impacts from projected global warming also include possible increases in forest productivity for very modest temperature increases but likely severe stress on forests for rapid and greater warming;

There could also be serious human health impacts, such as from increasing heat stress, worsening air pollution, declining water quality, and the spread of infectious diseases into regions previously free from them.

The impacts of global warming will vary by country and region. In some higher latitudes, agricultural productivity could actually increase while farmers in many subtropical and tropical regions could experience significant declines in their yields. Small island states and countries close to sea level — such as Bangladesh, with extensive low-lying coastal areas — are especially vulnerable to sea-level rise. Many high-mountain regions could experience significant changes in ecosystems and water resources.

IPCC Working Group II — which addresses the impacts of climate change, as well as vulnerability and adaptation issues — found in its 2001 report that “adaptation has the potential to reduce adverse impacts of climate change and enhance beneficial impacts, but will incur costs and will not prevent all damages.” In particular, “those with the least resources have the least capacity to adapt and are the most vulnerable.” In fact, Working Group II co-chair, Dr. James McCarthy (Harvard University), concluded, “most of the earth’s people will be on the losing side.”

Air Pollution, Aerosols, and Global Warming

Air pollution occurs when the air contains gases, dust, fumes or odor in harmful amounts—aerosols are a subset of air pollution that refers to the tiny particles suspended everywhere in our atmosphere. These particles can be both solid and liquid and are collectively referred to as ‘atmospheric aerosol particles.’ Most are produced by natural processes such as erupting volcanoes, and some are from human industrial and agricultural activities. Those particles in the lowest layer of the atmosphere, where our weather occurs, usually stay relatively close to the source of emissions and remain in the atmosphere only a few days to a week before they fall to the ground or are rained out; those higher up in the atmosphere travel farther and may linger in the atmosphere for a few years.

Light-colored aerosol particles can reflect incoming energy from the sun (heat) in cloud-free air and dark particles can absorb it. Aerosols can modify how much energy clouds reflect and they can change atmospheric circulation patterns—in short, aerosols can modify our climate.

Several climate engineering (so-called ‘geoengineering’) strategies for reducing global warming propose using atmospheric aerosol particles to reflect the sun’s energy away from Earth. Because aerosol particles do not stay in the atmosphere for very long—and global warming gases stay in the atmosphere for decades to centuries—accumulated heat-trapping gases will overpower any temporary cooling due to short-lived aerosol particles.

Aerosol sources, composition, and removal processes

Worldwide, most atmospheric aerosol particles are produced by ‘natural’ processes such as grinding and erosion of land surfaces resulting in dust, salt-spray formation in oceanic breaking waves, biological decay, forest fires, chemical reactions of atmospheric gases, and volcanic injection. Some particles, on the other hand, have human origins—industry, agriculture, transport (including aviation), and construction. The composition of atmospheric aerosol particles varies widely depending on their source—they may contain salts (predominantly sulfates), minerals (such as silicon), organic materials, and, in most cases, water.

The particles grow by absorbing water vapor and other gases. If the relative humidity is sufficiently high (usually about 80 percent or more), tiny water drops can form on some of the particles. A subset of these, called ‘cloud condensation nuclei,’ then grow into cloud drops, which eventually fall to the surface as rain or snow, depositing the particles on land or in the ocean. At higher altitudes, cloud ice particles form on some insoluble particles, such as dust.

Although dust plumes from the Sahara and Gobi deserts can be seen circling most of the globe in satellite pictures, aerosol particles in the lower troposphere (the lowest layer of the atmosphere where weather occurs) are usually removed from the atmosphere by settling and precipitation within several days to weeks after they were produced. Their impacts, then, are fairly localized. In the stratosphere (the atmosphere layer above the troposphere), chemical reactions of gases from volcanoes produce sulfate particles that can remain for one or more years, spreading over much of the globe.

Aerosol particles and climate

Although we are familiar with local particulate ‘air pollution’ due to human activities, the fact that atmospheric particles of both natural and human origin have substantial influence on our climate is less widely understood. The particles can play important climatic roles both outside and inside clouds.

In clear air, particles of sizes of approximately 0.1 to 1 micron (comparable to the dominant wavelengths in the solar spectrum) interact with the solar beam. Particles containing little carbon are effectively ‘white.’ They reflect solar radiation, making the air and Earth surface below them a bit cooler than they would otherwise be. Sulfate particles in the stratosphere from the Pinatubo volcanic eruption in 1991, for example, produced measurable cooling for two years over much of the globe (see global temperature figure in the human role FAQ). In contrast, particles containing substantial amounts of black carbon (e. g., soot, which is typically produced from combustion of fossil fuels, biofuels, and biomass burning) warm their surroundings by absorbing solar radiation before it reaches the ground.

When water vapor clings to water soluble particles in the same size range (~0.1 to 1 micron) it creates cloud droplets in the lower troposphere. In clean air, the concentrations of these droplets range from 10 to several 100 per cubic centimeter. At lower temperatures certain aerosol particles facilitate the formation of cloud ice. In and near urban areas, where the concentration of aerosol particles is high, the concentration of droplets can be as high as several thousand per centimeter cubed. The increased number of little drops causes the reflectivity of clouds to increase, so that, seen from above, clouds near polluted areas are often brighter than those above cleaner regions. Water droplets and ice particles are basically white, so they reflect solar radiation; on the other hand, the condensed water also traps and emits long wave radiation, producing heat. Thus clouds can have either cooling or warming effects on a local area, depending on whether the reflecting or trapping effect is strongest.

Because of many unknowns relating to aerosol particles, and in particular, to the possible effects of particles on cloud stability, the magnitude of aerosol impacts on climate remains among the most uncertain factors in climate projections.

How is human-caused air pollution changing our climate?

Human-caused particulate air pollution has a relatively minor—and likely decreasing—impact on our climate. Since aerosol particles of human origin both reflect and absorb solar energy as the solar beam travels down through the atmosphere, these particles can diminish the energy that arrives at the Earth’s surface as heat. Scientists estimate that particles produced by human activities have led to a net loss of solar energy (heat) at the ground (by as much as 8 percent in densely populated areas)[5] over the past few decades. This effect, sometimes referred to as ‘solar dimming,’ may have masked some of the late 20th century global warming due to heat-trapping gases.

Human activities that result in production of both reflecting and absorbing aerosol particle have been curtailed by legislation and modern technology in many places. The ‘pea soup fogs’ that so bedeviled London in Sherlock Holmes’ day, for example, were caused by particles produced by incomplete combustion of coal. These ‘fogs’ are now a thing of the past, thanks to mandatory scrubbers and other advanced combustion techniques. Clean air regulations in the United States have also decreased particle concentrations considerably. Even today, though, haze clouds seen over urban regions give dramatic proof of the effects of human-induced particles in the United States, while atmospheric soot production is still very high in many parts of Asia.

Global warming is primarily caused by emissions of too much carbon dioxide (CO2) and other heat-trapping gases into the atmosphere when we burn fossil fuels to generate electricity, drive our cars, and power our lives. These heat-trapping gases spread worldwide and remain in the atmosphere for decades to centuries. Thus, as we continue to emit these gases, their atmospheric concentrations build up over time. In contrast, atmospheric aerosol particles are largely localized near their sources, and do not linger in the atmosphere for long so that, even if we continue to emit them at current rates, their atmospheric concentrations will not build up markedly over time. Thus the effect of long-lived global warming emissions will far outweigh the cooling effect of short-lived particles.

Can climate engineering with aerosols save us from global warming?

Because global warming is such a serious threat, some scientists and engineers have explored the idea of harnessing the reflective power of some aerosol particles to temporarily combat global warming while non fossil fuel energy sources are being more fully developed. The idea is to artificially increase the concentrations of ‘white’ atmospheric aerosol particles above the surface of the ocean and/or in the lower stratosphere in order to reflect more of the sun’s energy away from Earth. The field of climate engineering (so-called ‘geoengineering’), still in its infancy, has the potential to buy us some time in the attempt to maintain relatively slow warming rates. However, experimentation with our very complex climate system by dramatically increasing reflecting aerosols carries with it the potential for large unintended, and potentially dangerous side effects on ecosystems, agriculture, and human health. In particular, the human health consequences associated with further increases in particulate pollution are a grave concern. For example, efforts are underway to reduce harmful black carbon emissions in developing countries through improved cook stoves to improve human health as well as curb global warming.