Climate Q&A

The ozone hole and global warming are not the same thing, and neither is the main cause of the other.

The ozone hole is an area in the stratosphere above Antarctica where chlorine and bromine gases from human-produced chlorofluorocarbons (CFCs) and halons have destroyed ozone molecules.

Global warming is the rise in average global surface temperature caused primarily by the build-up of human-produced greenhouses gases, mostly carbon dioxide and methane, which trap heat in the lower levels of the atmosphere.

There are some connections between the two phenomena.

For example, the CFCs that destroy ozone are also potent greenhouse gases, though they are present in such small concentrations in the atmosphere (several hundred parts per trillion, compared to several hundred parts per million for carbon dioxide) that they are considered a minor player in greenhouse warming. CFCs account for about 13% of the total energy absorbed by human-produced greenhouse gases.

The ozone hole itself has a minor cooling effect (about 2 percent of the warming effect of greenhouses gases) because ozone in the stratosphere absorbs heat radiated to space by gases in a lower layer of Earth’s atmosphere (the upper troposphere). The loss of ozone means slightly more heat can escape into space from that region.

Global warming is also predicted to have a modest impact on the Antarctic ozone hole. The chlorine gases in the lower stratosphere interact with tiny cloud particles that form at extremely cold temperatures — below -80 degrees Celsius (-112 degrees Fahrenheit). While greenhouse gases absorb heat at a relatively low altitudes and warm the surface, they actually cool the stratosphere. Near the South Pole, this cooling of the stratosphere results in an increase in polar stratospheric clouds, increasing the efficiency of chlorine release into reactive forms that can rapidly deplete ozone.

  1. References:

  2. Allen, Jeannie. (2004, February 10). Tango in the Atmosphere: Ozone and Climate Change. Earth Observatory. Accessed: September 14, 2010.
  3. Baldwin, M.P., Dameris, M., Shepherd, T.G. (2007, June 15). How will the stratosphere affect climate change? Science, 316 (5831), 1576-1577.
  4. Intergovernmental Panel on Climate Change, (2007). Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge, United Kingdom, and New York, New York: Cambridge University Press.
  5. NASA. Ozone Hole Watch. Accessed: September 14, 2010.

Science suggests that to mitigate the human contribution to global warming, we should reduce carbon dioxide and other greenhouse gas emissions. Because some additional warming is inevitable—even if we achieve significant greenhouse gas reductions quickly—we should make plans to adapt to coming climate change. If we are unable to control emissions and/or adapt to unavoidable changes quickly enough, a carefully selected geoengineering strategy could conceivably provide an emergency stopgap to slow global warming. As yet, however, several of the strategies being discussed are very risky and unproven.

Controlling Emissions
Controlling emissions is a large, complex, and potentially expensive problem that no single strategy will solve. On the other hand, the costs of uncontrolled global warming will probably also be significant. Many economists have concluded that putting existing scientific and technological strategies into place and developing new ones may stimulate the economy, and would also generate significant near-term benefits in public health through air pollution reduction.

The Carbon Mitigation Initiative, a university and industry partnership based at Princeton University, has identified strategies—based solely on existing technologies—that used in combination over the next 50 years, would keep the amount of carbon dioxide in the atmosphere from more than doubling the pre-industrial level. (Many scientists believe doubled carbon dioxide levels will cause a dangerous interference with the climate.) These strategies are:

  1. Increase the energy efficiency of our cars, homes, and power plants while lowering our consumption by adjusting our thermostats and traveling fewer miles;
  2. Capture the carbon emitted by power plants and store it underground;
  3. Produce more energy from nuclear, natural gas, and renewable fuels—solar, wind, hydroelectric, and bio-fuels;
  4. Halt deforestation and soil degradation worldwide, while reforesting more areas.

Some of those strategies will have to be put into place by governments and industry, but individuals can also do a lot on their own. On average, individual Americans emit 19 tons of carbon dioxide annually while driving our cars and heating our homes—more than people in any other country. If we can reduce our personal emissions by just 5 percent, total U.S. emissions would drop by 300 million tons. That reduction could be easily achieved by replacing appliances and light bulbs with more efficient ones, planning our automobile trips more carefully, driving more fuel-efficient cars, taking fewer flights, and so on.

By learning about global warming, by communicating with elected officials about the problem, and by making energy-conscious decisions, individuals will play a meaningful role in what must be a global effort to respond to global warming.

Adapting to Climate Change
Climate has been fluctuating throughout Earth’s history, and recently, humans have become one of the factors contributing to climate change. Changes related to human activity are already being felt. Even if we were to stop greenhouse gas emissions today, additional climate change from emissions already in the atmosphere would be inevitable. For this reason, many governments and industries are beginning to adapt policies, disaster response plans, or infrastructure to prepare for anticipated changes. While some adaptations are difficult and expensive, many are relatively inexpensive and offer immediate benefits.

Adaptation strategies vary from region to region, depending on the greatest threat posed by climate change locally. For example, coastal regions facing rising sea levels and increased coastal erosion might eliminate incentives to develop high-risk coastlines and encourage a “living buffer” of sand dunes and forest between the ocean and infrastructure. New York City has already integrated climate change into the process it uses to plan future development, reducing the need for expensive retrofitting later.

Local governments may adjust disaster response plans to accommodate changes in weather patterns. The city of Philadelphia recently implemented an emergency response plan to limit the health impact of increasingly frequent heat waves on its population. Philadelphia officials estimate that their heat response plan has already reduced heat-related deaths.

More extreme and expensive adaptations may become necessary in some regions. Thawing permafrost and increased storms, windiness and coastal erosion are now putting at least 166 communities at risk in Alaska. Moving each community to safer areas will cost an estimated 30 to 50 million dollars per village, estimates the U.S. Army Corps of Engineers. Six communities have already decided to relocate.

For individuals, governments, and businesses, adapting to climate change requires understanding and accepting the risks of regional climate change, assessing the immediate and long-term costs and benefits of adaptation strategies, and implementing adaptations that bring the most benefits relative to the cost and risk.

Though risky and unproven, geoengineering could provide another near-term strategy for slowing global warming until carbon emissions can be reduced enough to prevent catastrophic climate change. In this context, geoengineering means deliberately altering the atmosphere, land, or ocean to counter the effects of global warming.

Many geoengineering schemes have been proposed, but all can be reduced to two main strategies: reduce the amount of greenhouse gases in the atmosphere (increase the amount of infrared radiation escaping to space) or reduce the amount of solar energy the Earth system absorbs. Two of the most common examples of these geoengineering strategies involve removing carbon from the atmosphere by adding fertilizer to selected regions of the ocean to increase phytoplankton growth and reflecting more sunlight by injecting tiny, non-absorbing particles (aerosols) into the upper atmosphere (stratosphere).

While both of these geoengineering examples might counter global warming for a time, they could also have significant drawbacks. Increased fertilizers and/or phytoplankton growth could have unintended consequences on ocean ecosystems, including increased ocean dead zones and toxic blooms. Adding aerosols to the upper atmosphere could modify the chemistry of the upper atmosphere, affecting ozone and thereby having possible unintended impacts on the lower atmosphere.

Because the impact of geoengineering on the complex global climate system hasn’t been extensively studied, any large-scale geoengineering strategy could have serious unexpected consequences. As a result, most scientists consider geoengineering only as a last-resort, emergency measure.

  1. References

  2. America’s Climate Choices. (2010, May). Adapting to the impacts of climate change. National Research Council of the National Academies. Accessed July 16, 2010.
  3. Intergovernmental Panel on Climate Change. (2007). Summary for Policymakers. In: Climate Change 2007: Mitigation of Climate Change
    Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.
    Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  4. Pacala, S., and Socolow, R. (2004) Solving the Climate Problem for the Next 50 Years with Current Technologies. Science, 305 (5686), 968-972.
  5. Parkinson, C. L. (2010). Coming Climate Crisis? Consider the Past, Beware the Big Fix. Lanham, Maryland: Rowman & Littlefield Publishers.
  6. Robock, A., Marquardt, A., Kravitz, B, and Stenchikov, G. (2009, October 2). Benefits, risks, and costs of stratospheric geoengineering. Geophysical Research Letters, 36, L19703.
  7. Further Reading

  8. The Carbon Mitigation Initiative, is a collaboration between Princeton University, BP, and Ford to find solutions to the global warming problem.
  9. The Energy Star Website, published by the U.S. Department of Energy and the U.S. Environmental Protection Agency provides information for individuals and businesses on making energy-conscious choices.

The Intergovernmental Panel on Climate Change stated in their most recent report that global surface temperature at the end of this century will probably be between 1.8 and 4 degrees Celsius warmer than it was at the end of the last century.

It’s natural to question whether we and future generations will regret our efforts to reduce greenhouse gas emissions if it turns out global warming isn’t as bad as predicted. But the best science we have to guide us at this time indicates that the chance that warming will be much larger than the best estimate is greater than the chance that it will be much smaller.

Climate scientists know that there is plenty they don’t know about the way the Earth system works. Some of the physical processes that models describe are thoroughly well-established—the melting point of ice, for example, and the law of gravity.

Other physical processes are less perfectly known: when the air temperature is not far below 0 Celsius, for example, will water vapor condense into liquid or ice? Either is possible, depending on atmospheric conditions.

To understand how uncertainty about the underlying physics of the climate system affects climate predictions, scientists have a common test: they have a model predict what the average surface temperature would be if carbon dioxide concentrations were to double pre-industrial levels.

They run this simulation thousands of times, each time changing the starting assumptions of one or more processes. When they put all the predictions from these thousands of simulations onto a single graph, what they get is a picture of the most likely outcomes and the least likely outcomes.

The pattern that emerges from these types of tests is interesting. Few of the simulations result in less than 2 degrees of warming—near the low end of the IPCC estimates—but some result in significantly more than the 4 degrees at the high end of the IPCC estimates.

This pattern (statisticians call it a “right-skewed distribution”) suggests that if carbon dioxide concentrations double, the probability of very large increases in temperature is greater than the probability of very small increases.

Our ability to predict the future climate is far from certain, but this type of research suggests that the question of whether global warming will turn out to be less severe than scientists think may be less relevant than whether it may be far worse.

  1. References:

  2. Intergovernmental Panel on Climate Change, Core Writing Team. (2007). Chapter 3: Climate change and its impacts in the near and long term under different scenarios. In Pachauri, R. & Reisinger, A. (Eds.), Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva, Switzerland: IPCC.
  3. Ramanathan, V., & Xu, Y. (2010). The Copenhagen Accord for limiting global warming: Criteria, constraints, and available avenues. Proceedings of the National Academy of Sciences, 107(18), 8055.
  4. (2007, October 26). The certainty of uncertainty. Accessed June 21, 2010.
  5. Roe, G. H., & Baker, M. B. (2007). Why Is Climate Sensitivity So Unpredictable? Science, 318(5850), 629-632.
  6. Stainforth, D. A., Aina, T., Christensen, C., Collins, M., Faull, N., Frame, D. J., Kettleborough, J. A., et al. (2005). Uncertainty in predictions of the climate response to rising levels of greenhouse gases.

NASA employs the world’s largest concentration of climate scientists. NASA’s mission to study Earth involves monitoring atmospheric conditions, global temperatures, land cover and vegetation, ice extent, ocean productivity, and a number of other planetary vital signs with a fleet of space-based sensors. This information is critical in understanding how Earth’s climate works and how it is responding to change.

In addition to collecting information about the Earth, NASA also builds global and regional climate models to understand the causes and effects of climate change, including global warming. NASA shares its climate data and information with the public and policy leaders freely and in a timely manner. As part of the U.S. Climate Change Science Program, NASA works with other agencies—including the National Oceanic and Atmospheric Administration, the U.S. Geological Survey, the Environmental Protection Agency, the Department of Energy, and many others—to conduct research and to ensure climate science results are available to all users to address a broad range of societal needs.