Cutting carbon emissions could have indirect effects on hunger

 

Thu, 06/11/2015 - 9:05am American Chemical Society As many of the world’s nations prepare and implement plans to cut greenhouse gas emissions, researchers say another critical factor needs to be considered. A new study has found for the first time that efforts to keep global temperatures in check will likely lead to more people going hungry. That risk, they say in Environmental Science & Technology, doesn’t negate the need for mitigation but highlights the importance of comprehensive policies. Previous studies have shown that climate change reduces how much food farms can produce, which could lead to more people suffering from hunger. Curbing the greenhouse gas emissions that lead to climate change can help maintain the yields of existing crops. But there might be indirect ways in which cutting emissions could actually put more people at risk of going hungry. For example, some grasses and other vegetation used for biofuels require agricultural land that might otherwise be used for food production. So, increased biofuel consumption could negatively affect the food supply. Also, the high cost of low-emissions technologies such as carbon capture and storage will be borne by consumers, who will then have less money to spend on food. Tomoko Hasegawa and colleagues wanted to get a better idea of how these pieces fit together. The researchers used multiple models to determine the effects of strict emissions cuts and found that many more people would be at risk of hunger than if those cuts weren’t in place. The team concludes that governments will have to take measures, such as increasing food aid, as they address climate change. Source: American Chemical Society

CO2 warming effects felt just a decade after emitted

 

Wed, 12/03/2014 - 10:54am Institute of Physics It takes just 10 years for a single emission of carbon dioxide to have its maximum warming effects on the Earth. This is according to researchers at the Carnegie Institute for Science who have dispelled a common misconception that the main warming effects from a carbon dioxide emission will not be felt for several decades. The results, which have been published in Environmental Research Letters, also confirm that warming can persist for more than a century and suggest that the benefits from emission reductions will be felt by those who have worked to curb the emissions and not just future generations. Some of these benefits would be the avoidance of extreme weather events, such as droughts, heat waves and flooding, which are expected to increase concurrently with the change in temperature. However, some of the bigger climate impacts from warming, such as sea-level rise, melting ice sheets and long-lasting damage to ecosystems, will have a much bigger time lag and may not occur for hundreds or thousands of years later, according to the researchers. Lead author of the study Dr. Katharine Ricke said: “Amazingly, despite many decades of climate science, there has never been a study focused on how long it takes to feel the warming from a particular emission of carbon dioxide, taking carbon-climate uncertainties into consideration. “A lot of climate scientists may have an intuition about how long it takes to feel the warming from a particular emission of carbon dioxide, but that intuition might be a little bit out of sync with our best estimates from today's climate and carbon cycle models. To calculate this timeframe, Dr. Ricke, alongside Prof. Ken Caldeira, combined results from two climate modeling projects. The researchers combined information about the Earth’s carbon cycle—specifically how quickly the ocean and biosphere took up a large pulse of carbon dioxide into the atmosphere—with information about the Earth’s climate system taken from a group of climate models used in the latest IPCC assessment. The results showed that the median time between a single carbon dioxide emission and maximum warming was 10.1 years, and reaffirmed that most of the warming persists for more than a century. The reason for this time lag is because the upper layers of the oceans take longer to heat up than the atmosphere. As the oceans take up more and more heat which causes the overall climate to warm up, the warming effects of carbon dioxide emissions actually begin to diminish as carbon dioxide is eventually removed from the atmosphere. It takes around 10 years for these two competing factors to cancel each other out and for warming to be at a maximum. “Our results show that people alive today are very likely to benefit from emissions avoided today and that these will not accrue solely to impact future generations,” Dr. Ricke continued. "Our findings should dislodge previous misconceptions about this timeframe that have played a key part in the failure to reach policy consensus.” Source: Institute of Physics

Six vital steps world leaders must agree to take to protect Earth

 

International talks in Paris in 2015 could see the world’s nations agree to limit global warming to a rise of 2C. Actually achieving that target will require huge commitments – not least by developed nations

A power station in Pennsylvania, USA: most of the CO2 in the atmosphere has come from developed nations. Photograph: Alamy

 

1 Global warming must be limited to 2C

Every year, carbon emissions from cars, factories and power plants across the planet rise inexorably. The resulting elevation in carbon dioxide levels in the atmosphere mean that in 30 years temperatures on Earth will be 2C hotter than they were in pre-industrial times, scientists say. This is the maximum temperature that they believe the world can tolerate without there being devastating environmental consequences: spreading deserts, worsening storms and widespread flooding. Therefore, the first and most important decision that world leaders need to take at the Paris climate talks next year is to agree, through a binding commitment, that 2C is the upper, acceptable limit of global warming on Earth. All other decisions taken in Paris will follow as a consequence of that agreement.

 

2 Nations must make real commitments

Delegates to the Paris talks will then have to establish a network of creditable commitments from individual countries, as well as power blocks such as the EU, that will achieve carbon emissions cuts to ensure the 2C limit is achieved. The devil will be in the detail when it comes to making these agreements.

 

3 Emissions must be monitored

Once nations have agreed to make a particular cut in their carbon output, it will be necessary to set up a commission or group whose job will be to monitor nations’ emissions to check that they are keeping to their commitments.

 

4 Developed nations must pledge billions

Most of the carbon dioxide that has been added to the atmosphere is the handiwork of the industries of developed nations. Developing countries, which have produced relatively little carbon dioxide, will demand a clear commitment from these rich nations to provide financial support to help them adapt to a hotter planet and to mitigate against the worst effects of global warming. Last week a total of $9.3bn was pledged by the west to setting up such a green climate fund. However, by 2020, the amount of money needed for this purpose is expected to be around $100bn a year. If this sort of money is not pledged by the developed world, developing nations will refuse to sign any deals in Paris.

Many Pacific islands and other areas are in danger of being swamped by rising seas as a result of global warming. Photograph: Giff Johnson/AFP/Getty Images

 

5 The most vulnerable places must be compensated

Even if nations can come up with a binding agreement that will keep the global temperature rise to 2C, there will be environmental impacts that, for some nations, will be not just damaging but utterly devastating. For example, islands such as the Maldives and archipelagos in the Pacific already face inundation, as do large tracts of coastline in Bangladesh. Levels of carbon dioxide currently in the atmosphere make the future of these look increasingly untenable. Compensation for loss and damage to populations who could lose their homelands will need special attention and a mechanism will have to be agreed in Paris to ensure these people are properly recompensed for many generations to come.

 

6 Green technologies must be shared

Technology will be a key factor in holding temperatures to a modest level. New forms of tide, wave and wind power plants will have to be developed to replace generators that rely on fossil fuels. Other engineering solutions will need to include systems for preventing carbon dioxide from being emitted by power plants, a process known as carbon capture and sequestration. Some of these systems will be funded by governments, some will be developed by private companies. A method to allow systems created in one country to be shared with other countries in an equitable manner will have to be agreed to ensure the rapid take-up of technologies that will be crucial to efforts to keep global warming within bearable limits.

The United States Is Far and Away the Leader in Carbon Dioxide Emissions

 

The effects of atmospheric carbon linger for centuries, so historical emissions totals are relevant context for the global climate policy debate.

• By Mike Orcutt on November 12, 2014

Why It Matters

Nations will need to cooperate on climate policy if global emissions reduction targets are to be met.

The newly published synthesis of the Fifth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) is yet another reminder that to maintain a legitimate shot at avoiding warming of greater than 2 °C, greenhouse-gas emissions must be cut 40 to 70 percent by midcentury and reduced to zero by 2100.

How exactly to achieve this is the subject of ongoing geopolitical debate. The United States points to its annual emissions, which have been gradually trending downward, and argues that China, now the world’s leading annual emitter, bears equal responsibility, along with other high-emitting nations like India. China, meanwhile, argues that because the U.S. and other wealthy nations have contributed a disproportionate share of the greenhouse gases already accumulated in the atmosphere, they should be held more accountable for emissions cuts over the next several decades.

Since the effects of atmospheric carbon dioxide linger for centuries (See “Climate Change: The Moral Choices”), that’s a fair point. In the fifth assessment report, the IPCC has for the first time embraced the concept of a carbon budget. According to the panel, ensuring that warming remains below 2 °C will require keeping the total of human-caused emissions, from the beginning of the industrial era through the end of this century, below about a trillion tons of carbon. Over half of that total had already been emitted into the atmosphere by 2011.

At the very least, an accounting of cumulative historical emissions by individual countries is relevant context for today’s geopolitical gridlock. For example, according to the World Resources Institute, the United States has emitted some 10 times as much as India, whose population is nearly four times larger.

 

source – www.technologyreview.com

Global shift away from cars would save US$100 trillion, eliminate 1,700 megatons of carbon dioxide pollution

 

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The "High Shift" scenario for global transportation: slashing CO2 pollution, saving money, improving lives.

More than $100 trillion in cumulative public and private spending, and 1,700 megatons of annual carbon dioxide (CO₂) -- a 40 percent reduction of urban passenger transport emissions -- could be eliminated by 2050 if the world expands public transportation, walking and cycling in cities, according to a new report released by the University of California, Davis, and the Institute for Transportation and Development Policy (ITDP).

Further, an estimated 1.4 million early deaths could be avoided annually by 2050 if governments require the strongest vehicle pollution controls and ultralow-sulfur fuels, according to a related analysis of these urban vehicle activity pathways by the International Council on Clean Transportation (ICCT) included in the report.

"Transportation, driven by rapid growth in car use, has been the fastest growing source of CO₂ in the world, said Michael Replogle, ITDP's managing director for policy and co-author of the report. "An affordable but largely overlooked way to cut that pollution is to give people clean options to use public transportation, walking and cycling, expanding mobility options especially for the poor and curbing air pollution from traffic."

"The analysis shows that getting away from car-centric development will cut urban CO₂ dramatically and also reduce costs, especially in rapidly expanding economies," said report co-author Lew Fulton, co-director of NextSTEPS Program at the Institute of Transportation Studies at UC Davis. "It is also critical to reduce the energy use and carbon emissions of all vehicles."

The report, A Global High Shift Scenario, is the first study to examine how major changes in transport investments worldwide would affect urban passenger transport emissions as well as the mobility of different income groups. The authors calculated CO₂ emissions in 2050 under two scenarios, a business-as-usual scenario and a "High Shift" scenario where governments significantly increased rail and clean bus transport, especially Bus Rapid Transit (BRT), and helped urban areas provide infrastructure to ensure safe walking, bicycling and other active forms of transportation. The projections also include moving investments away from road construction, parking garages and other ways that encourage car ownership.

Under this High Shift, not only would CO₂ emissions plummet, but the net financial impact of this shift would be an enormous savings over the next 35 years, covering construction, operating, vehicle and fuel-related costs.

The report was released at the United Nations Habitat III Preparatory Meeting in New York on September 17th, in advance of the September 23rd United Nations Secretary-General's Climate Summit, where many nations and corporations will announce voluntary commitments to reduce greenhouse gas emissions, including new efforts focused on sustainable transportation.

"This timely study is a significant contribution to the evidence base showing that public transport should play central role in visions for the city of tomorrow" says Alain Flausch, Secretary General of the International Association of Public Transport, and member of UN Secretary General's Advisory Group on Sustainable Transport.

Better Mobility Leads to Social Mobility

The new report also describes sustainable transportation as a key factor in economic development. Under the High Shift scenario, mass transit access is projected to more than triple for the lowest income groups and more than double for the second lowest groups. Notably, the overall mobility evens out between income groups, providing those more impoverished with better access to employment and services that can improve their family livelihoods.

"Today and out to 2050, lower income groups will have limited access to cars in most countries under almost any scenario; improving access to modern, clean, high-capacity public transport is crucial," said Fulton.

"Unmanaged growth in motor vehicle use threatens to exacerbate growing income inequality and environmental ills, while more sustainable transport delivers access for all, reducing these ills. This report's findings should help support wider agreement on climate policy, where costs and equity of the cleanup burden between rich and poor are key issues," noted Replogle.

Emission Standards Save Lives

Air pollution is a leading cause of early death, responsible for more than 3.2 million early deaths annually. Exposure to vehicle tailpipe emissions is associated with increased risk of early death from cardiopulmonary disease and lung cancer, as well as respiratory infections in children. Car and diesel exhaust also increases the risk of non-fatal health outcomes, including asthma and cardiovascular disease.

The International Council on Clean Transportation evaluated the impacts of urban travel by cars, motorcycles, trucks and buses on the number of early deaths from exposure to soot emitted directly from vehicle tailpipes. "Future growth in vehicle activity could produce a four-fold increase in associated early deaths by 2050, even with a global shift to mass transit," said ICCT's Joshua Miller, a contributor to the study. "We could avoid about 1.4 million early deaths annually if national leaders committed to a global policy roadmap that requires the strongest vehicle pollution controls and ultralow-sulfur fuels." Cleaner buses alone would account for 20 percent of these benefits.

Fuel Economy Standards Save Fuel and Cut CO₂ Emissions

While this study has not focused on further actions to boost motor vehicle fuel economy, it takes into account existing policies that, in the International Energy Agency's Baseline scenario, improve average new car fuel economy by 32 percent in countries that belong to the Organisation for Economic Co-operation and Development (OECD), a group of 34 of the world's most developed, democratic, market economies, and 23 percent in non-OECD countries.

The High Shift scenario increases this to 36 percent and 27 percent respectively, due to improved in-use driving conditions and a slight shift to smaller vehicles. However, the Global Fuel Economy Initiative (GFEI) calls for much more: a 50 percent reduction in fuel use per kilometer for light-duty vehicles worldwide by 2030. Achieving the GFEI 2030 goal could reduce 700 megatons of CO₂ annually beyond the 1,700 reduction possible from a High Shift scenario. Taken together, achieving this fuel economy goal with better public transport, walking and cycling could cut annual urban passenger transport CO₂ emissions in 2050 by 55 percent from what they might otherwise be in 2050 and 10 percent below 2010 levels.

Cutting Emissions with Sustainable Transportation Across the World's Cities

Transportation in urban areas accounted for about 2,300 megatons of CO₂ in 2010, almost one quarter of carbon emissions from all parts of the transportation sector. Rapid urbanization -- especially in fast developing countries like China and India -- will cause these emissions to double by 2050 in the baseline scenario.

Among the countries examined in the study, three stand out:

• United States: Currently the world leader in urban passenger transportation CO₂ emissions, with nearly 670 megatons annually, the US is projected to lower these emissions to 560 megatons by 2050 because of slower population growth, higher fuel efficiencies, and a decline in driving per person that has already started as people move back to cities. But this pace can be sharply accelerated with more sustainable transportation options, dropping to about 280 megatons, under the High Shift scenario.
• China: CO₂ emissions from transportation are expected to mushroom from 190 megatons annually to more than 1,100 megatons, due in large part to the explosive growth of China's urban areas, the growing wealth of Chinese consumers, and their dependence on automobiles. But this increase can be slashed to 650 megatons under the High Shift scenario, in which cities develop extensive BRT and metro systems. The latest data show China is already sharply increasing investments in public transport.
• India: CO₂ emissions are projected to leap from about 70 megatons today to 540 megatons by 2050, also because of growing wealth and urban populations. But this increase can be moderated to only 350 megatons, under the High Shift scenario, by addressing crucial deficiencies in India's public transport.

Carbon dioxide concentration surges: Record greenhouse gas levels impact atmosphere and oceans, WMO report finds

 

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Earth (stock image).

The amount of greenhouse gases in the atmosphere reached a new record high in 2013, propelled by a surge in levels of carbon dioxide. This is according to the World Meteorological Organization's annual Greenhouse Gas Bulletin, which injected even greater urgency into the need for concerted international action against accelerating and potentially devastating climate change.

The Greenhouse Gas Bulletin showed that between 1990 and 2013 there was a 34% increase in radiative forcing -- the warming effect on our climate -- because of long-lived greenhouse gases such as carbon dioxide (CO₂), methane and nitrous oxide.

In 2013, concentration of CO₂ in the atmosphere was 142% of the pre-industrial era (1750), and of methane and nitrous oxide 253% and 121% respectively.

The observations from WMO's Global Atmosphere Watch (GAW) network showed that CO₂ levels increased more between 2012 and 2013 than during any other year since 1984. Preliminary data indicated that this was possibly related to reduced CO₂ uptake by Earth's biosphere in addition to the steadily increasing CO₂ emissions.

The WMO Greenhouse Gas Bulletin reports on atmospheric concentrations -- and not emissions -- of greenhouse gases. Emissions represent what goes into the atmosphere. Concentrations represent what remains in the atmosphere after the complex system of interactions between the atmosphere, biosphere and the oceans. About a quarter of the total emissions are taken up by the oceans and another quarter by the biosphere, reducing in this way the amount of CO₂ in the atmosphere.

The ocean cushions the increase in CO₂ that would otherwise occur in the atmosphere, but with far-reaching impacts. The current rate of ocean acidification appears unprecedented at least over the last 300 million years, according to an analysis in the report.

"We know without any doubt that our climate is changing and our weather is becoming more extreme due to human activities such as the burning of fossil fuels," said WMO Secretary-General Michel Jarraud.

"The Greenhouse Gas Bulletin shows that, far from falling, the concentration of carbon dioxide in the atmosphere actually increased last year at the fastest rate for nearly 30 years. We must reverse this trend by cutting emissions of CO₂ and other greenhouse gases across the board," he said. "We are running out of time."

"Carbon dioxide remains in the atmosphere for many hundreds of years and in the ocean for even longer. Past, present and future CO₂ emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are non-negotiable," said Mr Jarraud.

"The Greenhouse Gas Bulletin provides a scientific base for decision-making. We have the knowledge and we have the tools for action to try keep temperature increases within 2°C to give our planet a chance and to give our children and grandchildren a future. Pleading ignorance can no longer be an excuse for not acting," said Mr Jarraud.

"The inclusion of a section on ocean acidification in this issue of WMO's Greenhouse Gas Bulletin is appropriate and needed. It is high time the ocean, as the primary driver of the planet's climate and attenuator of climate change, becomesa central part of climate change discussions," said Wendy Watson-Wright, Executive Secretary of the Intergovernmental Oceanographic Commission of UNESCO.

"If global warming is not a strong enough reason to cut CO₂ emissions, ocean acidification should be, since its effects are already being felt and will increase for many decades to come. I echo WMO Secretary General Jarraud's concern -- we ARE running out of time," she said.

Atmospheric Concentrations

Carbon dioxide accounted for 80% of the 34% increase in radiative forcing by long-lived greenhouse gases from 1990 to 2013, according to the U.S. National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index.

On the global scale, the amount of CO₂ in the atmosphere reached 396.0 parts per million in 2013. The atmospheric increase of CO₂ from 2012 to 2013 was 2.9 parts per million, which is the largest annual increase for the period 1984-2013. Concentrations of CO₂ are subject to seasonal and regional fluctuations. At the current rate of increase, the global annual average CO₂ concentration is set to cross the symbolic 400 parts per million threshold in 2015 or 2016.

Methane is the second most important long-lived greenhouse gas. Approximately 40% of methane is emitted into the atmosphere by natural sources (e.g., wetlands and termites), and about 60 % comes from human activities like cattle breeding, rice agriculture, fossil fuel exploitation, landfills and biomass burning. Atmospheric methane reached a new high of about 1824 parts per billion (ppb) in 2013, due to increased emissions from anthropogenic sources. Since 2007, atmospheric methane has been increasing again after a temporary period of leveling-off.

Nitrous oxide (N₂O)

Nitrous oxide is emitted into the atmosphere from both natural (about 60%) and anthropogenic sources (approximately 40%), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. Its atmospheric concentration in 2013 was about 325.9 parts per billion. Its impact on climate, over a 100-year period, is 298 times greater than equal emissions of carbon dioxide. It also plays an important role in the destruction of the stratospheric ozone layer which protects us from the harmful ultraviolet rays of the sun.

Ocean Acidification

For the first time, this Bulletin contains a section on ocean acidification prepared in collaboration with the International Ocean Carbon Coordination Project (IOCCP) of the Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO), the Scientific Committee on Oceanic Research (SCOR), and the Ocean Acidification International Coordination Centre (OA-ICC) of the International Atomic Energy Agency (IAEA).

The ocean currently absorbs one-fourth of anthropogenic CO₂ emissions, reducing the increase in atmospheric CO₂ that would otherwise occur because of fossil fuel combustion. Enhanced ocean CO₂ uptake alters the marine carbonate system and lead to increasing acidity. The ocean's acidity increase is already measurable as oceans take up about 4 kilogrammes of CO₂ per day per person.

The current rate of ocean acidification appears unprecedented at least over the last 300 million years, based on proxy-data from paleo archives. In the future, acidification will continue to accelerate at least until mid-century, based on projections from Earth system models.

The potential consequences of ocean acidification on marine organisms are complex. A major concern is the response of calcifying organisms, such as corals, algae, mollusks and some plankton, because their ability to build shell or skeletal material (via calcification) depends on the abundance of carbonate ion. For many organisms, calcification declines with increased acidification. Other impacts of acidification include reduced survival, development, and growth rates as well as changes in physiological functions and reduced biodiversity.

The WMO Global Atmosphere Watch Programme (www.wmo.int/gaw) coordinates systematic observations and analysis of greenhouse gases and other trace species. Fifty countries contributed data for the Greenhouse Gas Bulletin. Measurement data are reported by participating countries and archived and distributed by the World Data Centre for Greenhouse Gases (WDCGG) at the Japan Meteorological Agency. (http://ds.data.jma.go.jp/gmd/wdcgg)

The summary on ocean acidification was jointly produced by the International Ocean Carbon Coordination Project (IOCCP) of the Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO), the Scientific Committee on Oceanic Research (SCOR), and the Ocean Acidification International Coordination Centre (OA-ICC) of the International Atomic Energy Agency (IAEA).

To address climate change, nothing substitutes for reducing carbon dioxide emissions

 

The politically expedient way to mitigate climate change is essentially no way at all, according to a comprehensive new study by University of Chicago climatologist Raymond Pierrehumbert.

Among the climate pollutants humans put into the atmosphere in significant quantities, the effects of carbon dioxide (CO₂) are the longest-lived, with effects on climate that extend thousands of years after emissions cease. But finding the political consensus to act on reducing CO₂ emissions has been nearly impossible. So there has been a movement to make up for that inaction by reducing emissions of other, shorter-lived gasses, such as methane, hydrofluorocarbons, and nitrous oxide, and particulates such as soot and black carbon, all of which contribute to warming as well.

Pierrehumbert 's study shows that effort to be, as he puts it, a delusion. "Until we do something about CO₂, nothing we do about methane or these other things is going to matter much for climate," he said.

Pierrehumbert is the Louis Block Professor in Geophysical Sciences at UChicago, and holder of the King Carl XVI Gustaf Chair in Environmental Sciences at Stockholm University for 2014-2015. His study, published in Annual Review of Earth and Planetary Sciences, brings together findings from the scientific literature with new research and analysis. Its conclusions are clear.

"Ray convincingly shows the benefit and importance of doing everything we can to lower CO₂ emissions, and as soon as possible," said Katherine H. Freeman, professor of geosciences at Pennsylvania State University. "We should lower short-lived pollutants like methane too. But, as he makes clear, we should not let them distract us from the urgent need to stop burning fossil fuels."

The basic physics of climate pollutants has been well known for a long time. The warming effect of methane and other short-lived climate pollutants disappears quite quickly after the pollutants are removed from the atmosphere. When you remove them, you get a one-time-only, lump-sum benefit. CO₂, on the other hand, lingers in the atmosphere. And if you are still emitting CO₂ while you are reducing methane and its fellows, that additional CO₂ continues to affect the climate for thousands of years.

Perhaps as a result of wishful thinking, the policy implications of those facts had become confused, said Pierrehumbert. Part of the problem is that the statistical tool used to compare the climate effect of gasses is badly flawed. The measure, called Global Warming Potential (GWP), predicts the effect on climate by comparing the emission rate of carbon dioxide with the emission rate of methane. But a one-ton-per-year reduction in the amount of methane emitted translates into a single lowering of the global thermostat, while a one-ton-per-year reduction in CO₂ yields a climate benefit that increases over time. That's because each extra ton of CO₂ that would have been emitted would have irreversibly ratcheted up the global thermostat by an additional increment.

Despite its well-known defects, GWP has been used since 1990 and was incorporated into the Kyoto Protocols in the climate-trading schemes implemented by Europe. Pierrehumbert proposes a different metric, which looks at the climate effect of reducing CO₂ emission by a fixed number of tons and then finds the rate by which you have to reduce methane emissions to get the same effect.

Pierrehumbert's study doesn't propose a single "right" policy on climate change, said Richard Alley, Evan Pugh Professor of Geosciences at Penn State. "But it is a very useful analysis that will be viewed carefully by people who are interested in making good policies, and the main conclusions will help inform those policies."

Pierrehumbert himself hopes that his work will help lead policymakers to abandon Kyoto-style multi-gas trading schemes, which treat the gasses equivalently, and put the emphasis on CO₂ for the next 50 years or so. "I see puncturing the excessive enthusiasm about short-lived climate pollution control as a step in the right direction," he said, "because it takes away one of the grounds for procrastination on CO₂. If you're serious about protecting climate, it's the CO₂ you've got to deal with first."