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In a study published online by the journal Science, Harvard University scientists reported that some storms send water vapor miles into the stratosphere — which is normally drier than a desert — and showed how such events could rapidly set off ozone-destroying reactions with chemicals that remain in the atmosphere from CFCs, refrigerant gases that are now banned.
The risk of ozone damage, scientists said, could increase if global warming leads to more such storms.
“It’s the union between ozone loss and climate change that is really at the heart of this,” said James G. Anderson, an atmospheric scientist and the lead author of the study.
For years, Dr. Anderson said, he and other atmospheric scientists were careful to keep the two concepts separate. “Now, they’re intimately connected,” he said.
Ozone helps shield people, animals and crops from damaging ultraviolet rays from the sun. Much of the concern about the ozone layer has focused on Antarctica, where a seasonal hole, or thinning, has been seen for two decades, and the Arctic, where a hole was observed last year. But those regions have almost no population.
A thinning of the ozone layer over the United States during summers could mean an increase in ultraviolet exposure for millions of people and a rise in the incidence of skin cancer, the researchers said.
The findings were based on sound science, Dr. Anderson and other experts said, but much more research is needed, including direct measurements in the stratosphere in areas where water vapor was present after storms.
“This problem now is of deep concern to me,” Dr. Anderson said. “I never would have suspected this.”
While there is conclusive evidence that strong warm-weather storms have sent water vapor as high as 12 miles — through a process called convective injection — and while climate scientists say one effect of global warming is an increase in the intensity and frequency of storms, it is not yet clear whether the number of such injection events will rise.
“Nobody understands why this convection can penetrate as deeply as it does,” said Dr. Anderson, who has studied the atmosphere for four decades.
Mario J. Molina, a co-recipient of a Nobel Prize for research in the 1970s that uncovered the link between CFCs and damage to the ozone layer, said the study added “one more worry to the changes that society’s making to the chemical composition of the atmosphere.” Dr. Molina, who was not involved in the work, said the concern was “significant ozone depletion at latitudes where there is a lot of population, in contrast to over the poles.”
The study, which was financed by the National Aeronautics and Space Administration, focused on the United States because that is where the data was collected. But the researchers pointed out that similar conditions could exist at other midlatitude regions.
Ralph J. Cicerone, an atmospheric scientist and the president of the National Academy of Sciences, who reviewed the study for Science, also called for more research. “One of the really solid parts of this paper is that they’ve taken the chemistry that we know from other atmospheric experiments and lab experiments and put that in the picture,” he said. “The thing to do is do field work now — measure moisture amounts and whether there is any impact around it.”
“The connection with future climate is the most important issue,” Dr. Cicerone said.
Large thunderstorms of the type that occur from the Rockies to the East Coast and over the Atlantic Ocean produce updrafts, as warm moist air accelerates upward and condenses, releasing more heat. In most cases, the updrafts stop at a boundary layer between the lower atmosphere and the stratosphere called the tropopause, often producing flat-topped clouds that resemble anvils. But if there is enough energy in a storm, the updraft can continue on its own momentum, punching through the tropopause and entering the stratosphere, said Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology.
When Dr. Anderson produced data about five years ago clearly showing these strong injections of water vapor, “I didn’t believe it at first,” Dr. Emanuel said. “But we’ve come to see that the evidence is pretty strong that we do get them.”
At the same time, he added, “we don’t really understand what determines the potential for convection in the atmosphere,” so it is difficult to say what the effect of climate change will be.
“We’re much further along on understanding how hurricanes respond to climate change than normal storms,” Dr. Emanuel said.
The use of CFCs, or chlorofluorocarbons, was phased out beginning in the late 1980s with the signing of an international treaty called the Montreal Protocol, but it will take decades for them to be cleansed fully from the atmosphere. It is chlorine from the CFCs that ultimately destroys ozone, upsetting what is normally a balanced system of ozone creation and decay. The chlorine has to undergo a chemical shift in the presence of sunlight that makes it more reactive, and this shift is sensitive to temperature.
Dr. Anderson and his colleagues found that a significant concentration of water vapor raises the air temperature enough in the immediate vicinity to allow the chemical shift, and the ozone-destroying process, to proceed rapidly.
“The rate of these reactions was shocking to us,” Dr. Anderson said. “It’s chemistry that was sitting there, waiting to be revealed.”
Dr. Anderson said that if climate change related to emissions of greenhouse gases like carbon dioxide and methane led to more events in which water was injected well into the stratosphere, the effect on ozone could not be halted because the chemistry would continue. “It’s irreversible,” he said.
If CFCs had not been banned, the ozone layer would be in far worse shape than it is. But by showing that CFC-related ozone destruction can occur in conditions other than the cold ones at the poles, the study suggests that the full recovery of the ozone layer may be further off than previously considered.
“The world said, ‘Oh, we’ve controlled the source of CFCs; we can move on to something else,’ ” Dr. Anderson said. “But the destruction of ozone is far more sensitive to water vapor and temperature.”
The inescapable importance of China to global energy and climate efforts has compelled the Joint Program—in collaboration with Tsinghua University—to launch a special research effort called the China Energy and Climate Project.
A growing population and rapid development will put a strain on land used to grow food over this century. But if reforestation is used to avoid climate change it will create further strain, says a new MIT study.
It’s no surprise that the United States and China are the world’s top 
greenhouse-gas emitters. What may be surprising is the country that ranks third in the lineup: Indonesia. Indonesia is a major culprit not because of its traffic or power plants, but because of its massive deforestation.
Deforestation accounts for almost 20 percent of global emissions—more than the world’s entire transportation sector. But saving the trees—as beneficial as it would be to the changing climate — comes at a significant cost as a growing, wealthier population competes for food, says a new MIT study.
“With a larger and wealthier population, both energy and food demand will grow,” says John Reilly, the lead author of the study and the co-director of the MIT Joint Program on the Science and Policy of Global Change. “Absent controls on greenhouse gases, we will see more emissions from fossil-fuel use and from land-use change. The resulting environmental change can reduce crop yields, and require even more land for crops. So this could become a vicious circle.”
The Reilly et al. study, recently published in Environmental Science & Technology, compares the effects of slashing emissions from energy sources alone to a strategy that also incorporates emissions associated with land use.
The report finds that, with a growing global population, fast-developing nations, and increasing agricultural productivity and energy use, the world is on the path to seeing average temperatures rise by as much as 6 degrees Celsius by the end of the century. Even with an aggressive global tax on energy emissions, the planet will not be able to limit this warming to 2 degrees Celsius—the target world leaders have agreed is needed to avoid dangerous climate change. But when the tax is applied to land-use emissions, the world community could come much closer, with temperatures by the year 2100 rising 2.4 degrees Celsius above pre-industrial levels.
To go one step further in reducing emissions the study incorporates biofuels production, which could increase carbon storage on land and be a cleaner source of energy, lessening the use of fossil fuels. The researchers find that increased biofuels production could cut fossil-fuel use in half by the end of the century—from 80 percent of energy without a tax to 40 percent with a tax—and further limit warming to bring the world just shy of the target.
The world could get even closer to the target, the study shows, by creating economic incentives for storing carbon on land—such as through reforestation. In combination with the global carbon tax, this could “bring the world closer to keeping warming below the 2 degree Celsius temperature,” Reilly says.
But there are always drawbacks.
“The environmental change avoided by reducing greenhouse-gas emissions is substantial and actually means less land used for crops,” Reilly says. “The big tradeoff is that diverting this amount of land to carbon storage, and using land to produce biofuels, leads to substantial rises in food and forestry prices.”
Food prices could rise more than 80 percent, the study shows. Along with this, nations could become wealthier, with global GDP increasing fivefold. On average, the share of a household’s budget for food, even with higher prices, might fall from 15 percent to 7 percent. But for poorer regions of the world, the food budget share could increase, meaning these food price impacts could have disproportionate effects on poorer regions.
Food shortages and higher food prices are becoming a major challenge, according to Jonathan Foley, director of the University of Minnesota’s Institute on the Environment, who spoke at a recent MIT event.
“In the last 20 years we’ve produced 28 percent more crops. But in the next 38 years, we need to double that growth,” Foley said. “We’re not going to grow our way out of the problem … we must look at other possibilities.”
An advocate of ending deforestation, Foley said we need to grow food more efficiently.
Reilly agrees, and says his study puts an emphasis on more effective use of land to produce food. Part of this means more efficient (intensive) use of pasture and grazing land. But, he says, the carbon tax scenarios he tests make the problem that much more difficult—with biofuels and carbon sequestration using up more land.
“And with all three of these demands for land—food, biofuels and carbon storage—the competition is intense, and as a result, food prices rise. So this is an important tradeoff the world needs to consider.”
By Eric Niiler
As world leaders gather to assess the planet's health, most reports are gloomy, save for a couple bits of good news.
The world's political and environmental leaders gather in Rio de Janeiro tomorrow to assess the state of the planet's health 20 years after the first such gathering in 1992. But if science is any guide, Earth still needs some help.
Several new climate studies reveal various aspects of the same foreboding problem: the atmosphere continues to warm, glaciers continue melting and seas keep rising.
But there is a tiny bit of good news -- the United States and Europe have been able to cut their heat-trapping industrial emissions by switching to less-polluting natural gas, driving fewer miles and of course, sinking into an economic recession where fewer factories are working across much of the globe.
And while North America's mild winter, warm spring and, in some areas, hot June can't be blamed on global climate change, extreme weather events do grab the public's attention. Even though it's not entirely accurate to link climate and weather, perhaps that's not a bad thing, says Gavin Schmidt, a climate researcher at NASA's Goddard Space Science Center in New York.
"People spend a lot of time talking about the weather and love to do so," Schmidt said. "It's an odd thing because as scientists we are using people's interest in weather and weather extremes to talk about something that is connected, but isn't quite the same."
Schmidt said that rather than focusing on extreme blips in weather, it's instead important to look at changes in temperature over the long term. Scientists at the National Oceanic and Atmospheric Administration are doing just that, and reported that the past 12 months from June 2011 to May 2012 were the hottest since record-keeping began in the 1880s. The month of May 2012 was the second-hottest on record (2010 was first). And it looks like 2012 will barge into the top three hottest calendar years on record as well.
At the same time, there is occasional "noise" in the Earth's climate system, explained Ronald Prinn, professor of atmospheric sciences at the Massachusetts Institute of Technology. That means that the linear warming trend could stagger a bit from year-to-year, or decade-to-decade depending on the cooling effects of cloud cover or the ocean's ability to soak up heat.
"If you take a 10-year running average," Prinn told Discovery News. "It's clear that world has been warming for a hundred-plus years."
Some climate skeptics have pointed to the world's forests as a likely carbon "sink" that could suck up heat-trapping carbon dioxide, methane and other such gasses from burning fossil fuels. But a new study by researchers in California found that scenario might not be so simple.
As soil warms up, they found, it releases carbon dioxide made from microbes that decompose dead leaves and fallen trees. About one-third of that release comes from older soil, more than 10 years old.
"While that older material is not going to decompose really fast, there's an awful lot of it," Susan Trumbore, a University of California, Irvine, scientist who led the study, told The Washington Post.
That means that at some point in the future, the world's temperate forests could switch from a carbon sink to a carbon faucet, increasing the vicious cycle of rising CO2 causing even more CO2 to be released.
Another new study finds that Chinese officials may be cooking the books when it comes to carbon emissions.
United Kingdom-based researchers found the gap between what Chinese state authorities report as the nation's industrial emissions and the aggregate of provincial reporting has widened to 1.4 gigatons, that's about 5 percent of the world's entire CO2 emissions budget. Local officials may be padding the books to show more industrial output, while national authorities want to appear more environmentally-friendly to the West.
Either way, the new figures wipe out any gains elsewhere.
"The trends are pretty bad," Schmidt said. "All of the flattening in Europe and the U.S. are being more than matched by increases in China and India."
Despite the recent gloomy news, experts say there are solutions: replacing individual dung-burning stoves in Chinese homes with more efficient centralized power plants; developing more efficient cars, homes and light bulbs in the West; and continuing to shift away from coal as a prime energy source in both the United States and China.
"Nobody wants (another recession) as a solution to the climate issue," Prinn said. "We don't want to be hurting our economies. We need to develop new energy sources."
Unless the world gets a handle on its fossil fuel habit, experts say there's likely to be more extreme events like floods, droughts, heat waves and tropical storms.
"Without climate change we would be seeing extreme heat waves once every 100 years, now it's more on the order of 10 times in 100 years," Schmidt said. "That's going to increase. The dice are loaded, and we're loading them even more."
NREL-MIT study shows an 80 percent renewable energy standard cuts water use in half.
In his first State of the Union address, President Barack Obama set a goal for 80 percent of America's electricity to come from clean energy. Last week, the release of the Renewable Electricity Future study by the U.S. National Renewable Energy Laboratory (NREL) confirms that reaching this goal by 2050 is very possible. But what impact would clean energy have on another key ingredient to daily life: clean water? Researchers at MIT helped answer that question in NREL's report.
The MIT research—Modeling Water Withdrawal and Consumption for Electricity Generation in the United States—is a compilation of the water segment of the Renewable Electricity Future study. In it, the researchers find that as solar panels, wind turbines and other sources of non-thermal renewable energy replace coal, gas and similar thermal powerplants, the use of water to cool those powerplants will decrease by about half.
"The most important use of water for electricity production is for cooling," says Adam Schlosser, an author of the study and the assistant director for science research at MIT's Joint Program on the Science and Policy of Global Change. "The benefit of renewables like wind or solar is that you don't need to boil water for steam to spin the turbines, and then you don't need water to cool the steam. That cooling process is removed, saving a lot of water."
This is good news for water-stressed regions, including much of the western United States, as production of electrical power results in one of the largest uses of water in the nation. A 2005 report by the U.S. Geological Survey found that about 201,000 million gallons of water each day were used to produce electricity, with much of this water going toward keeping powerplants cool.
While most Americans will use less water when powering their homes with renewable energy, the MIT researchers did find that areas that switch to thermal renewable technologies might end up using more water. Biomass energy, being produced mostly in the northwestern United States, is one strong example, the study finds.
"Biomass is obviously contributing to the carbon aspect of the overall problem," Schlosser says, "But it's actually exacerbating an already water-stressed situation because you not only need water to grow it, you also need water to cool the thermal electricity generation process."
Schlosser compares this to concentrated solar technology being used in the southwest, which typically relies on a dry cooling system where fans are used instead of water.
"Solar technology really benefits the southwest because it uses a resource that's so plentiful in that region—the sun—and doesn't use a resource that there is very little of—water," Schlosser says.
But Schlosser explains that the dry cooling technology—while an obvious choice for the drought-stricken southwestern United States because it uses 90 percent less water—is less efficient and more expensive because the electric plant would need to use electricity to run large fans that force air through the heat-exchange process. This explains why areas where water scarcity is more subtle would choose to stick to water cooling technologies in thermal electricity generation.
Along with using less water, the Renewable Electricity Future study finds that greenhouse gas emissions would be reduced by about 80 percent, potentially offering significant public health benefits. The National Research Council estimated that in 2005, air pollution emissions from coal powerplants cost $32 per megawatt of energy in public health damages, the report notes, suggesting that the health cost benefits could counterbalance the costs to build clean energy infrastructure.
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Three Questions with Research Scientist Sebastian Rausch
MIT Joint Program on the Science and Policy of Global Change co-director and TEPCO professor of atmospheric science Ron Prinn was recently interviewed on his latest publication released today in the Proceedings of the National Academy of Sciences. The report, “Development and Application of Earth System Models,” focuses on the importance of Earth System Models in studying climate change. It is based on a lecture Prinn gave at the National Academy of Sciences Sackler Colloquium last year (watch the speech here).
Below is a transcript of the interview:
Q: Why do we need Earth System Models?
A: In laboratory science, we have the luxury of running “control” experiments in which selected conditions that would otherwise influence the “main” experiment are omitted. In the case of our environment, the influencing conditions come from humans. Because we do not have another earth without human influence to serve as a “control,” we often cannot directly measure the impacts of human development on the environment. So we form computer models of the combined natural and human systems, compare the models with observations, and then apply the models as “numerical control” experiments. Our specific earth system model – MIT’s Integrated Global System Model (IGSM) – is so unique because it combines the human system with the natural system to see how the two systems impact each other for the purpose of improving our understanding of both systems and informing policy decisions. The IGSM is in fact a “framework” of linked sub-models of varying complexity with the choice of the sub-models being governed by the issues being addressed; uncertainty studies dictate use of the most computationally efficient models, whereas studies of specific scenarios allow use of the more complex but computationally demanding sub-models.
Q: What is the value of integrated Earth System Models like the IGSM, as opposed to other approaches, for those making decisions about climate mitigation and adaptation?
A: Applied, for example, to the climate issue, the IGSM framework allows us to determine, in a self-consistent way, the probabilities of various amounts of climate change, the relationship between greenhouse gas reduction targets and temperature changes, and the uncertainty in the costs of various proposed policies. The IGSM framework also enables integrated assessments of the economic and environmental implications of proposed new low emission energy technologies. In making these analyses, we are able to help decision-makers compare the value of various mitigation policies, energy technologies, and adaptation strategies in lowering the risks to society. We can also assess the costs for stabilization of greenhouse gases at various levels, and how these costs can be justified by the expected benefits from the avoided damages.
Q: What can the MIT IGSM tell us about our climate and energy future?
A: In this paper, I outline just some of the ways we’ve used the full IGSM framework, or the relevant parts of it, in the past. These uses include the examination of the effect of different greenhouse gas stabilization targets on forecasts of the odds of various amounts of temperature, precipitation, sea-level, and sea-ice change, and of the costs of these stabilization policies. Also, the relationship between stabilization targets and the future loss of the ability of the oceans to slow warming by absorbing heat and carbon dioxide has been examined. The Kyoto Protocol uses a CO2-only strategy to reduce emissions, and our work with the IGSM shows that a multi-gas control strategy greatly reduces the costs of fulfilling the Kyoto Protocol with little difference between the two strategies in mitigating climate and ecosystem impacts. Assessments of the substantial impact of air pollution on human health costs and carbon uptake by land vegetation have been investigated. Another example stems from our work in examining the consequences of renewable energy at large scales – like wind power and bio-fuels. Our studies of wind power show that offshore wind turbines can cause a surface cooling over the installed regions due to an increase in turbulent mixing caused by the turbines. Additionally, while wind power is an important renewable resource for our future, it suffers from significant intermittency caused by large seasonal wind variations over most major offshore sites. We’re expanding on this research to measure wind power intermittency over land in the U.S. Stay tuned for that study. Learn more about our offshore study here.
To read "Development and Application of Earth System Models," please click here.
Learn more about Dr. Ron Prinn here.
IMF-MIT study shows immediate – but realistic – actions are needed to confront climate change.
As global leaders prepare to gather for the Rio+20 sustainable development summit in Brazil next week, the International Monetary Fund (IMF) and a collection of economists from MIT and other organizations has released a report to help leaders confront the price tag associated with climate change. The publication— Fiscal Policy to Mitigate Climate Change: A Guide for Policymakers—details the most effective methods to reduce emissions and contain costs, namely through carbon pricing.
Until now, leaders have focused on slowing warming to 2 degrees Celsius to prevent catastrophic changes associated with climate change. Because this would mean taking drastic measures to hold emissions at about today's levels, researchers at MIT argue that leaders should be realistic and start smaller because the time to act is quickly running out. Their research—Emissions Pricing to Stabilize Global Climate—is a chapter within the IMF guide.
“Negotiations on the exact emission reduction target have been going on for a long time without much substantial progress,” says Sergey Paltsev, lead author of the MIT study and associate director for economic research at the Joint Program on the Science and Policy of Global Change. “But it is better to start with some policy that reduces emissions because even a small initial step is important as it sets the process on track.”
IMF’s Managing Director Christine Lagarde points to a tax or trade system.
“Perhaps we can help with a simple concept that everybody can understand—getting the prices right,” Lagarde said in a speech at the Center for Global Development. “Getting the prices right means using fiscal policy to make sure that the harm we do is reflected in the prices we pay. I am thinking about environmental taxes or emissions trading systems under which governments issue—and preferably sell—pollution rights.”
The MIT research suggests an emissions price—organized through either a tax or cap-and-trade system—of about $20 to $40 per ton by 2020 to help the world community reach less stringent targets that would keep warming to 2.9 or 3.6 degrees Celsius.
“These less stringent targets are more realistic and reachable, and they still reduce the risk of more severe climate impacts,” Paltsev says. But, he warns, “we have never experienced such changes and do not know exactly how the Earth will respond, so the smaller the changes we make, the greater the risk of something unexpected and bad happening.”
Still, making small changes is better than not acting at all, Paltsev says, and we shouldn’t wait for technology to fix the problem for us.
“We can wait for a miracle technology, like biofuels with carbon capture and storage, to appear and become economical— allowing us to reach more stringent target—but then we place our bets on something which may or may not materialize,” Paltsev says.
The longer the global community waits to take action, the higher the price tag could be and the less likely the world will be able to meet even less stringent targets. This could mean “unprecedented levels of damage and degradation” if current trends in production and consumption continue, United Nations Undersecretary General Achim Steiner said in a recent statement. He added, “The moment has come to put away the paralysis of indecision, acknowledge the facts and face up to the common humanity that unites all peoples.”
Andrew Steer, special envoy for climate change for the World Bank, agrees.
“We will turn the tide against climate change only when core economic policymakers wake up to the urgency of the issue and factor it into their fiscal and economic policies,” he said.
Making progress one step at a time
Even if all countries were able to agree on a uniform path forward, slowing emissions would require a complex burden-sharing system including incentives and compensation for emerging and developing countries—continuing an ongoing struggle about who pays what to confront the challenge.
While such an international effort may take time, the Green Climate Fund—formed in Cancun, Mexico, in 2010—could help developing countries. Meanwhile, major emitters like the United States, European Union and China could establish a relatively small carbon tax, the revenue from which could be returned to citizens to balance out the higher energy prices and increase public support. The idea is similar to parts of a proposal by U.S. Sen. Maria Cantwell (D-Wash.).
Still, cap-and-trade—a system invented by American economists—is far from being implemented in the United States, as countries around the world take steps to implement the system—like China.
“Just as many of our best innovations are produced in China, they may beat us in implementing such a system,” John Reilly, a co-director of the MIT Joint Program on the Science and Policy of Global Change and an author of the IMF chapter, said recently. "We're really being left behind.”
China is not the only country that has an edge on the United States. The EU, Australia, New Zealand and South Korea have already begun to set hard emission limits, and cap-and-trade programs are gaining traction in Brazil and Mexico as well.
Joëlle Chassard, manager of the Carbon Finance Unit of the World Bank, said in a statement that it was heartening to “see increasing interest in, and support for, new market-based mechanisms to mitigate climate change.”
Paltsev agrees that these systems are encouraging and useful, even at the local level. But, he says, “It is also important to harmonize the efforts” and “all major emitters, including the U.S., need to participate.”
Quito, Ecuador, is not considered a global leader by most measures. But there is one way in which Quito is at the forefront of metropolises worldwide: in planning for climate change.
By: Katherine Bagley
While the national climate debate is fixed on whether Earth is warming, climate scientists are focused on understanding how bad it will be.
The global warming debate in Congress, the states and on the campaign trail centers on two issues: Is Earth warming, and if so are humans to blame?
But ask most climate scientists, and they'll tell you that these are the only questions not in dispute. Climate change is a matter of how bad and by when, they'll say—not whether.
"Scientists are inherently skeptical," says Lonnie Thompson, a paleoclimatologist at Ohio State University, who has led studies of glaciers and ice sheets in 16 countries. "After enough evidence and observation, though, you have to start to accept findings. That is what happened with climate change. This wasn't a rash conclusion."
"There is not any serious debate about whether anthropogenic climate change is happening," says Daniel Sarewitz, co-director of the Consortium for Science, Policy and Outcomes at Arizona State University and a professor of science and society. "Scientists are certain about that, and it is unfortunate that the national debate is lagging so far behind."
The public and political discourse on global warming was framed by the 2007 report of the UN Intergovernmental Panel on Climate Change (IPCC), which concluded that climate change is occurring and human activity is the cause. That seminal report, and the subsequent coverage and debate, split the country into two partisan camps, with Democrats generally accepting the scientific consensus and Republicans questioning or flat-out denying it.
Missing from the discussion is the perhaps surprising, and rising, view of many scientists—that the UN climate panel gravely underestimated the immediacy and danger of global warming.
The IPCC process itself is partly, though not entirely, to blame. "It takes seven years to produce an IPCC report," says Thompson, who is also an IPCC author. "By the time it is published, the science is already dated ... and the models being used aren't accurately assessing how rapidly these changes are taking place."
There are real-world implications at stake, Thompson says. "We are in for tougher scenarios than what are being relayed in the reports."
A Flawed IPCC Assumption
The IPCC, the world's leading scientific body on global warming, is charged by the UN with assessing research and releasing periodic reviews of climate risks, which governments often use to set targets for cutting carbon emissions. In 2007, the panel shared the Nobel Peace Prize with Vice President Al Gore.
At the core of its assessments are IPCC "scenarios"—summaries of coming climatic conditions like global temperature and sea-level rise, which are based on a number of assumptions about future greenhouse gas emissions. One of those assumptions is that the world will make good on its carbon-cutting pledges.
Therein lies a key flaw, says John Reilly, co-director of the Massachusetts Institute of Technology's (MIT) Joint Program on the Science and Policy of Global Change and an expert on climate economic models. Many nations have failed to take promised steps to slash global warming emissions, particularly China and the United States, the world's biggest polluters. Even in the European Union greenhouse gases are on the rise. Yet the IPCC doesn't account for this.
The result, says Reilly, is that emissions today are higher than what the IPCC predicted in 2007. The panel's middle-of-the-road scenarios, for example, estimate that the world would emit between 27 and 28 billion metric tons of carbon dioxide in 2010. In reality, 30.6 billion metric tons of CO2 were released that year, the latest figures available, says data from the International Energy Agency. While that may seem like a small difference to a lay person, climate experts say that small increases can steamroll into something much bigger.
What Newer Climate Models Show
In 2009, Reilly and his colleagues at MIT, along with researchers from Penn State, the Marine Biological Institute in Massachusetts and the U.S. Environmental Protection Agency, decided to model forecasts for climate that assumed the world would continue with business as usual.
Their results, published in the June 2012 issue of Climatic Change and online last year, found that without major greenhouse gas cuts the median global temperature would increase by 5 degrees Celsius (9 degrees Fahrenheit) by 2100, compared to the IPCC's worst-case prediction of a 3.5 degree Celsius rise (6.3 degrees Fahrenheit).
The study found that the Arctic would warm up to three times as much as was foreseen by the IPCC. There would also be more severe extreme weather events and greater ocean warming, sea-level rise and ocean acidification.
"The IPCC suite of scenarios provide ... a bit too rosy of a picture," says Reilly. "Our study shows that without action, there is virtually no chance that we won't enter very dangerous territory."
Even moderate action isn't likely to help. Follow-up work by these same researchers published this year in MIT's annual Energy and Climate Outlook found that if countries achieve the emission cuts they promised at international climate negotiations, the global temperature would still increase by over 4 degrees Celsius (7.2 degrees Fahrenheit), with a significant chance of a 5 degree Celsius rise by century's end
For some scientists, however, the IPCC's findings are extreme.
"I'm surprised there are those who think the IPCC is too conservative," says John Christy, atmospheric scientist at the University of Alabama in Huntsville, IPCC author in 2001 and a well-known skeptic of human-caused climate change. "I think the simple evidence is very clear—the IPCC models overestimate the warming of the climate system." The IPCC declined to comment on the record.
Missing Ice Sheets and Slow Timing
Perhaps the biggest controversy surrounding the IPCC scenarios is that they omit the rapid melting of the Greenland and Antarctic ice sheets in sea-level rise projections.
Several researchers, including Thompson, the polar ice expert from Ohio State University, and James Hansen, head of the NASA Goddard Institute for Space Studies, have been vocal critics of that omission, which they say dramatically skews the IPCC scenarios. If the Greenland and Antarctic ice sheets, the only two in the world, continue to melt at their current pace, Thompson and other scientists believe sea levels could rise several feet and swamp coastlines this century, not the 8 to 17 inches projected in the IPCC mid-range scenarios.
"Those [ice sheets] are the big elephants in the room," says Thompson. "They are going to play a big role, yet they aren't taken into account." (The IPCC left them out because of uncertainty about how to predict effects of ice-sheet meltdowns in climate models.)
Some scientists say the very nature of the IPCC process means its reports can never be truly up to date. Research must be published at least two years before the release of an IPCC assessment to be considered. That lag time also means the projections will be on the conservative side, Thompson says. He argues that as scientific understanding of climate change improves, and as CO2 emissions continue to rise, the predictions grow more dire.
Reilly, the MIT scientist, says most scientists studying climate change today are viewing "the seemingly unstoppable rise in global greenhouse emissions" with "increasing alarm."
Why Aren't Scientists More Vocal?
So, if climate scientists are convinced that the Earth is warming faster than expected, then why aren't more speaking out?
The researchers interviewed for this story said many have retreated into silence to avoid the small but vocal band of climate skeptics. "Researchers find it hard to raise significant questions even within the climate science community for fear that it will be exploited by the skeptics," says Sarewitz, the science and society professor from Arizona State University.
"Climate science is a huge, sprawling area of discussion," explains Sarewitz, and skeptics are known to seize on arguments as proof that the science linking human activity to global warming is dubious.
Indeed, there are still many points not understood in climate science. Long-term changes in solar activity and their effects on the climate system are not well known. The effect of aerosols on global temperature is still uncertain, because they all react differently to atmospheric heat. Sulfates, for example, block sunlight, which in turn can cool the climate, while black carbon absorbs sunlight and can accelerate warming. Few doubt that sea levels will rise, but how fast and by how much is hotly contested.
There are also major limitations with climate models. They can predict whole-Earth scenarios better than localized scenarios, meaning regional trends still can't be predicted with much accuracy. They also don't reflect the physics of cloud formation well, an issue the IPCC has made a research priority.
While none of these undermine the consensus that climate change is human-caused, Sarewitz says, any dissension helps skeptics chisel away at the perception of scientific agreement. "It all makes it hard for the disinterested citizen ... to actually know how to untangle the conversation and who to trust."
Is silence the answer? Not according to Thompson of Ohio State, who admits to being "frustrated' by skeptic tactics and scientists' lack of response to them. "If they want to be more than just a historian documenting the change—if they want to make a difference—[scientists] have to speak out about these issues." Thompson himself regularly speaks about climate change, even allowing TV and print journalists to join his polar ice expeditions.
Reilly agrees. "Without interaction [with the public], it becomes too easy for people to vilify or defy those who disagree or agree with them, and there is little chance for real understanding."
