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1 Twenty-four Frequently Asked Questions on Climate Change This short guide contains answers to twenty-four commonly asked questions about climate change. It is divided into three sections. The first fifteen questions address climate change science; the next seven, the potential impacts of a changed climate; and the last two, what scientific research is needed and how it should be organized. Climate Change Science 1. How does the climate system work? The sun provides the energy that drives the climate system. The intensity of solar energy reaching the earth and its interaction with the atmosphere and the earth’s surface are the key factors determining climate. The greenhouse effect, which traps thermal energy re-radiated by the earth in the atmosphere, is one of the important interactions. 2. What are greenhouse gases? Greenhouse gases are gases (water vapor, carbon dioxide, methane, nitrous oxide, and others) that can absorb the thermal energy emitted by the earth, creating the greenhouse effect, which warms the earth. 3. How has the concentration of greenhouse gases in the atmosphere changed since 1750? Atmospheric concentrations of carbon dioxide, methane and the other greenhouse gases have increased since 1750. 4. What other changes have affected the climate system since 1750? Since 1750, there have been increases in the amount of particulates in the atmosphere, changes in land cover, and the creation of contrails in the upper atmosphere, all of which can affect the climate system. The George C. Marshall Institute 1625 K Street, NW – Suite 1050 Washington, D.C. 20006 202-296-9655 – fax 202-296-9714 www.marshall.org email: [email protected] 2 5. How accurate are measurements of the earth’s temperature? Surface temperature records contain biases that could introduce errors 0.2-0.3° C (0.4-0.6o F), or one-third to one-half of the warming observed during the 20th century. 6. How accurate are satellite measurements of the temperature of the troposphere? Satellite measurements of the temperature of the troposphere, once corrected for known sources of error, appear to be very accurate. 7. Are there differences between measurements of surface tropospheric temperatures and if so, are the differences real? and Satellite temperature measurements show the troposphere warming at a slower rate than the surface. In 2000, the National Research Council concluded that the differences were real and could not be explained with our current scientific understanding. 8. What is the greenhouse “fingerprint”? Has it been found? The greenhouse “fingerprint” refers to predictions from current theory and climate model simulations that tropospheric temperatures should rise faster than surface temperatures. A comparison of satellite and surface temperature data shows just the opposite. 9. Has the earth’s temperature increased over the last 100 years in step with increasing atmospheric concentrations of greenhouse gases? No. Greenhouse gas concentrations have increased steadily, but global average surface temperature declined from 1940 to 1975. 10. What influence does the sun have on global climate? The sun provides the energy that drives the climate system. Long-term variations in the intensity of solar energy reaching the earth are believed to cause climate change on geological time-scales. New studies indicate that changes in the sun’s magnetic field may be responsible for shorter-term changes in climate, including th much of the climate of the 20 century. The George C. Marshall Institute 1625 K Street, NW – Suite 1050 Washington, D.C. 20006 202-296-9655 – fax 202-296-9714 www.marshall.org email: [email protected] 3 11. How much does the global climate vary naturally? Climate scientists do not know the answer to this question, but the available data suggest that natural climate can change very rapidly. 12. Are computer simulations of the earth’s climate accurate? No. Because knowledge of the detailed working of the climate system is incomplete, climate models can provide only poor simulations of the earth’s climate. For example, estimates of the temperature rise that would result from a doubling of atmospheric concentration of carbon dioxide vary by a factor of three. 13. Isn’t the temperature rise since 1975 proof that humans are changing the climate? No. The claim that the temperature rise since 1975 is the result of human emissions of greenhouse gases is based on climate model studies that suffer all of the shortcomings and limitations discussed in Question 12, and historical data on greenhouse gas and particulate emissions that can only be guessed at. 14. Can we predict future climate? Not now, and possibly not ever. Current climate models have not been validated, and even if climate models can be validated, the inputs required to determine future human emissions of greenhouse gases and aerosols are probably unknowable. 15. How will we know if climate has changed and whether the change was caused by human activities? Climate change is defined as a change in climate that is greater than natural climate variability. Natural climate variability is currently unknown, but should be knowable with further research. Validated climate models can be used to determine the cause of the change. If the change is large enough, it may be possible to determine its cause without using a model. Climate Change Impacts 16. How much will the earth’s temperature rise if the amount of human-made greenhouse gas in the atmosphere continues to rise for the next 100 years? The George C. Marshall Institute 1625 K Street, NW – Suite 1050 Washington, D.C. 20006 202-296-9655 – fax 202-296-9714 www.marshall.org email: [email protected] 4 Climate scientists do not know the answer to this question for two reasons. First, because the rates of human emissions of greenhouse gases and particulates decades from now are unknowable. Second, because our understanding of the climate system is incomplete the impacts of human emissions on climate are highly uncertain. These two sources of uncertainty are about equal in magnitude. 17. Will the earth’s climate change in other ways? Increased precipitation and increases in flood and droughts are a common prediction about future climate. However, climate model projections, even if one is willing to accept them, do not show consistent changes in precipitation. Floods and droughts are affected by so many other factors that determining the affect of climate change is very difficult. 18. Will climate change produce a major rise in sea level and cause flooding? Not for the next century. Projections for longer time-scales are too uncertain to be credible. 19. Will climate change produce more violent storms? Unlikely, since the warming of the 20th century did not produce any significant change in storm frequency or intensity. Future trends cannot be accurately predicted because climate models do an even poorer job of simulating small events like hurricanes than they do in simulating global average climate. 20. Will climate change cause the spread of infectious diseases? No. Climate is a relatively small factor in determining the rate of vector-borne infectious disease. Appropriate public health measures are the key to controlling both the current incidence of these diseases and any increase due to climate change. 21. Will climate change lead to massive species extinctions? th No. The warming of the 20 century was implicated in the extinction of only one species, indicating that species are more resilient to climate change than indicated in modeling studies. The George C. Marshall Institute 1625 K Street, NW – Suite 1050 Washington, D.C. 20006 202-296-9655 – fax 202-296-9714 www.marshall.org email: [email protected] 5 22. Could human emissions of greenhouse gases cause the next ice age? No. Human emissions of greenhouse gases causing an ice age do not agree with our scientific understanding of either ice ages or the climate system. Ice ages are believed to be caused by changes in the earth’s orbit and tilt that cause reductions in the amount of solar energy reaching the earth’s surface. Climate Science Research 23. What are the most important priorities for the U.S. Climate Change Science Program (CCSP)? The most important priorities for the CCSP are: (1) Achieving the theoretical understanding of important climate processes, including the roles of water vapor, clouds, particulates, and ocean currents, needed to understand better potential human influences on the climate system. (2) Building and maintaining an effective climate observation network. (3) Developing empirical knowledge and theoretical understanding of adaptation. 24. Aren’t most scientists in agreement on climate change? should we listen to those who disagree with the consensus? Why Scientific knowledge doesn’t move forward because there is a consensus. It moves forward because of new ideas that depart from the consensus. The George C. Marshall Institute 1625 K Street, NW – Suite 1050 Washington, D.C. 20006 202-296-9655 – fax 202-296-9714 www.marshall.org email: [email protected]